ieee-recommended-practice-for-monitoring-electric-power-quality
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IEEE Std 1159-1995 IEEE Recommended Practice for Monitoring Electric Power Quality Sponsor IEEE Standards Coordinating Committee 22 on Power Quality Approved June 14, 1995 IEEE Standards Board Abstract: The monitoring of electric power quality of ac power systems, definitions of power quality terminology, impact of poor power quality on utility and customer equipment, and the measurement of electromagnetic phenomena are covered. Keywords: data interpretation, electric power quality, electromagnetic phenomena, monitoring, power quality definitions The Institute of Electrical and Electronics Engineers, Inc. 345 East 47th Street, New York, NY 10017-2394, USA Copyright © 1995 by the Institute of Electrical and Electronics Engineers, Inc. All rights reserved. Published 1995. Printed in the United States of America. ISBN 1-55937-549-3 No part of this publication may be reproduced in any form, in an electronic retrieval system or otherwise, without the prior written permission of the publisher. Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Standards documen1s are developed wi1hin 1he Technical Commi11ees of 1he IEEE Socie1ies and 1he S1andards Coordina1ing Commi11ees of 1he IEEE S1andards Board. Members of 1he commi11ees serve volun1arily and wi1hou1 compensa1ion. They are no1 necessarily members of 1he Ins1i1u1e. The s1andards developed wi1hin IEEE represen1 a consensus of 1he broad exper1ise on 1he subjec1 wi1hin 1he Ins1i1u1e as well as 1hose ac1ivi1ies ou1side of IEEE 1ha1 have expressed an in1eres1 in par1icipa1ing in 1he developmen1 of 1he s1andard. Use of an IEEE S1andard is wholly volun1ary. The exis1ence of an IEEE S1andard does no1 imply 1ha1 1here are no o1her ways 1o produce, 1es1, measure, purchase, marke1, or provide o1her goods and services rela1ed 1o 1he scope of 1he IEEE S1andard. Fur1hermore, 1he viewpoin1 expressed a1 1he 1ime a s1andard is approved and issued is subjec1 1o change brough1 abou1 1hrough developmen1s in 1he s1a1e of 1he ar1 and commen1s received from users of 1he s1andard. Every IEEE S1andard is subjec1ed 1o review a1 leas1 every five years for revision or reaffirma1ion. When a documen1 is more 1han five years old and has no1 been reaffirmed, i1 is reasonable 1o conclude 1ha1 i1s con1en1s, al1hough s1ill of some value, do no1 wholly reflec1 1he presen1 s1a1e of 1he ar1. Users are cau1ioned 1o check 1o de1ermine 1ha1 1hey have 1he la1es1 edi1ion of any IEEE S1andard. Commen1s for revision of IEEE S1andards are welcome from any in1eres1ed par1y, regardless of membership affilia1ion wi1h IEEE. Sugges1ions for changes in documen1s should be in 1he form of a proposed change of 1ex1, 1oge1her wi1h appropria1e suppor1ing commen1s. In1erpre1a1ions: Occasionally ques1ions may arise regarding 1he meaning of por1ions of s1andards as 1hey rela1e 1o specific applica1ions. When 1he need for in1erpre1a1ions is brough1 1o 1he a11en1ion of IEEE, 1he Ins1i1u1e will ini1ia1e ac1ion 1o prepare appropria1e responses. Since IEEE S1andards represen1 a consensus of all concerned in1eres1s, i1 is impor1an1 1o ensure 1ha1 any in1erpre1a1ion has also received 1he concurrence of a balance of in1eres1s. For 1his reason IEEE and 1he members of i1s 1echnical commi11ees are no1 able 1o provide an ins1an1 response 1o in1erpre1a1ion reques1s excep1 in 1hose cases where 1he ma11er has previously received formal considera1ion. Commen1s on s1andards and reques1s for in1erpre1a1ions should be addressed 1o: Secre1ary, IEEE S1andards Board 445 Hoes Lane P.O. Box 1331 Pisca1away, NJ 08855-1331 USA IEEE S1andards documen1s may involve 1he use of pa1en1ed 1echnology. Their approval by 1he Ins1i1u1e of Elec1rical and Elec1ronics Engineers does no1 mean 1ha1 using such 1echnology for 1he purpose of conforming 1o such s1andards is au1horized by 1he pa1en1 owner. I1 is 1he obliga1ion of 1he user of such 1echnology 1o ob1ain all necessary permissions. Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. Introduction (This in1roduc1ion is no1 par1 of IEEE S1d 1159-1995, IEEE Recommended Prac1ice for Moni1oring Elec1ric Power Quali1y.) This recommended prac1ice was developed ou1 of an increasing awareness of 1he difficul1y in comparing resul1s ob1ained by researchers using differen1 ins1rumen1s when seeking 1o charac1erize 1he quali1y of lowvol1age power sys1ems. One of 1he ini1ial goals was 1o promo1e more uniformi1y in 1he basic algori1hms and da1a reduc1ion me1hods applied by differen1 ins1rumen1 manufac1urers. This proved difficul1 and was no1 achieved, given 1he free marke1 principles under which manufac1urers design and marke1 1heir produc1s. However, consensus was achieved on 1he con1en1s of 1his recommended prac1ice, which provides guidance 1o users of moni1oring ins1rumen1s so 1ha1 some degree of comparisons migh1 be possible. An impor1an1 firs1 s1ep was 1o compile a lis1 of power quali1y rela1ed defini1ions 1o ensure 1ha1 con1ribu1ing par1ies would a1 leas1 speak 1he same language, and 1o provide ins1rumen1 manufac1urers wi1h a common base for iden1ifying power quali1y phenomena. From 1ha1 s1ar1ing poin1, a review of 1he objec1ives of moni1oring provides 1he necessary perspec1ive, leading 1o a be11er unders1anding of 1he means of moni1oring—1he ins1rumen1s. The opera1ing principles and 1he applica1ion 1echniques of 1he moni1oring ins1rumen1s are described, 1oge1her wi1h 1he concerns abou1 in1erpre1a1ion of 1he moni1oring resul1s. Suppor1ing informa1ion is provided in a bibliography, and informa1ive annexes address calibra1ion issues. The Working Group on Moni1oring Elec1ric Power Quali1y, which under1ook 1he developmen1 of 1his recommended prac1ice, had 1he following membership: J. Charles Smith, Chair Gil Hensley, Secretary Larry Ray, Technical Kditor Mark Andresen Vladi Basch Roger Bergeron John Burne11 John Dal1on Andrew De11loff Dave Griffi1h Thomas Gruzs Erich Gun1her Mark Kempker Thomas Key Jack King David Kreiss François Mar1zloff Alex McEachern Bill Moncrief Allen Morinec Ram Mukherji Richard Nailen David Pileggi Harry Rauwor1h John Rober1s An1hony S1. John Marek Samo1yj Ron Smi1h Bill S1un1z John Sullivan David Vannoy Marek Waclawlak Daniel Ward S1eve Whisenan1 In addi1ion 1o 1he working group members, 1he following people con1ribu1ed 1heir knowledge and experience 1o 1his documen1: Ed Can1well John Curle11 Chris1y Herig Allan Ludbrook Harshad Meh1a Tejindar Singh Maurice Te1reaul1 iii Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. The following persons were on 1he ballo1ing commi11ee: James J. Burke David A. Dini W. Mack Grady David P. Har1mann Michael Higgins Thomas S. Key Joseph L. Koepfinger David Kreiss Michael Z. Lowens1ein François D. Mar1zloff S1ephen McCluer A. McEachern W. A. Moncrief P. Richman John M. Rober1s Jacob A. Roiz Marek Samo1yj Ralph M. Showers J. C. Smi1h Rober1 L. Smi1h Daniel J. Ward Charles H. Williams When 1he IEEE S1andards Board approved 1his s1andard on June 14, 1995, i1 had 1he following membership: E. G. “Al” Kiener, Chair Gilles A. Baril Clyde R. Camp Joseph A. Canna1elli S1ephen L. Diamond Harold E. Eps1ein Donald C. Fleckens1ein Jay Fors1er* Donald N. Heirman Donald C. Loughry, Vice Chair Andrew G. Salem, Secretary Richard J. Holleman Jim Isaak Ben C. Johnson Sonny Kas1uri Lorraine C. Kevra Ivor N. Knigh1 Joseph L. Koepfinger* D. N. “Jim” Logo1he1is L. Bruce McClung Marco W. Migliaro Mary Lou Padge11 John W. Pope Ar1hur K. Reilly Gary S. Robinson Ingo Rusch Chee Kiow Tan Leonard L. Tripp *Member Emeri1us Also included are 1he following nonvo1ing IEEE S1andards Board liaisons: Sa1ish K. Aggarwal Richard B. Engelman Rober1 E. Hebner Ches1er C. Taylor Rochelle L. S1ern IKKK Standards Project Kditor iv Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. Contents CLAUSE 1. PAGE Overview ...................................................................................................................................................................1 1.1 Scope .................................................................................................................................................................1 1.2 Purpose .............................................................................................................................................................2 2. References ................................................................................................................................................................2 3. Defini1ions. ..............................................................................................................................................................2 3.1 Terms used in 1his recommended prac1ice ....................................................................................................................... 2 3.2 Avoided 1erms ...............................................................................................................................................7 3.3 Abbrevia1ions and acronyms..................................................................................................................8 4. Power quali1y phenomena ................................................................................................................................9 4.1 4.2 4.3 4.4 5. Moni1oring objec1ives ...................................................................................................................................... 24 5.1 5.2 5.3 5.4 5.5 6. In1roduc1ion ......................................................................................................................................................... 29 AC vol1age measuremen1s .................................................................................................................. 29 AC curren1 measuremen1s ................................................................................................................... 30 Vol1age and curren1 considera1ions .................................................................................................................................. 30 Moni1oring ins1rumen1s........................................................................................................................ 31 Ins1rumen1 power.............................................................................................................................................. 34 Applica1ion 1echniques. .................................................................................................................................. 35 7.1 7.2 7.3 7.4 7.5 8. In1roduc1ion ......................................................................................................................................................... 24 Need for moni1oring power quali1y. .................................................................................................................................. 25 Equipmen1 1olerances and effec1s of dis1urbances on equipmen1 ................................................................... 25 Equipmen1 1ypes. .............................................................................................................................................. 25 Effec1 on equipmen1 by phenomena 1ype...................................................................................................................... 26 Measuremen1 ins1rumen1s ..................................................................................................................................... 29 6.1 6.2 6.3 6.4 6.5 6.6 7. In1roduc1ion ............................................................................................................................................................ 9 Elec1romagne1ic compa1ibili1y ...................................................................................................................... 9 General classifica1ion of phenomena .................................................................................................................................... 9 De1ailed descrip1ions of phenomena ................................................................................................................................. 11 Safe1y ...................................................................................................................................................................... 35 Moni1oring loca1ion ................................................................................................................................. 38 Equipmen1 connec1ion ........................................................................................................................... 41 Moni1oring 1hresholds ............................................................................................................................ 43 Moni1oring period ..................................................................................................................................... 46 In1erpre1ing power moni1oring resul1s ...................................................................................................................................... 47 8.1 8.2 8.3 8.4 8.5 In1roduc1ion ......................................................................................................................................................... 47 In1erpre1ing da1a summaries ...................................................................................................................... 48 Cri1ical da1a ex1rac1ion .................................................................................................................................. 49 In1erpre1ing cri1ical even1s .......................................................................................................................... 51 Verifying da1a in1erpre1a1ion ...................................................................................................................... 59 v ANNEXES PAGE Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. 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Annex A Calibra1ion and self 1es1ing (informa1ive) ........................................................................................................................ 60 A.1 In1roduc1ion........................................................................................................................................................... 60 A.2 Calibra1ion issues ........................................................................................................................................................... 61 Annex B Bibliography (informa1ive) .............................................................................................................................................. 63 B.1 Defini1ions and general ................................................................................................................................................ 63 B.2 Suscep1ibili1y and symp1oms—vol1age dis1urbances and harmonics ................................................ 65 B.3 Solu1ions ........................................................................................................................................................65 B.4 Exis1ing power quali1y s1andards ........................................................................................................................... 67 vi Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Recommended Practice for Monitoring Electric Power Quality 1. Overview 1.1 Scope This recommended prac1ice encompasses 1he moni1oring of elec1ric power quali1y of single-phase and polyphase ac power sys1ems. As such, i1 includes consis1en1 descrip1ions of elec1romagne1ic phenomena occurring on power sys1ems. The documen1 also presen1s defini1ions of nominal condi1ions and of devia1ions from 1hese nominal condi1ions, which may origina1e wi1hin 1he source of supply or load equipmen1, or from in1erac1ions be1ween 1he source and 1he load. Brief, generic descrip1ions of load suscep1ibili1y 1o devia1ions from nominal condi1ions are presen1ed 1o iden1ify which devia1ions may be of in1eres1. Also, 1his documen1 presen1s recommenda1ions for measuremen1 1echniques, applica1ion 1echniques, and in1erpre1a1ion of moni1oring resul1s so 1ha1 comparable resul1s from moni1oring surveys performed wi1h differen1 ins1rumen1s can be correla1ed. While 1here is no implied limi1a1ion on 1he vol1age ra1ing of 1he power sys1em being moni1ored, signal inpu1s 1o 1he ins1rumen1s are limi1ed 1o 1000 Vac rms or less. The frequency ra1ings of 1he ac power sys1ems being moni1ored are in 1he range of 45–450 Hz. Al1hough i1 is recognized 1ha1 1he ins1rumen1s may also be used for moni1oring dc supply sys1ems or da1a 1ransmission sys1ems, de1ails of applica1ion 1o 1hese special cases are under considera1ion and are no1 included in 1he scope. I1 is also recognized 1ha1 1he ins1rumen1s may perform moni1oring func1ions for environmen1al condi1ions (1empera1ure, humidi1y, high frequency elec1romagne1ic radia1ion); however, 1he scope of 1his documen1 is limi1ed 1o conduc1ed elec1rical parame1ers derived from vol1age or curren1 measuremen1s, or bo1h. Finally, 1he defini1ions are solely in1ended 1o charac1erize common elec1romagne1ic phenomena 1o facili1a1e communica1ion be1ween various sec1ors of 1he power quali1y communi1y. The defini1ions of elec1romagne1ic phenomena summarized in 1able 2 are no1 in1ended 1o represen1 performance s1andards or equipmen1 1olerances. Suppliers of elec1rici1y may u1ilize differen1 1hresholds for vol1age supply, for example, 1han 1he ± 10% 1ha1 defines condi1ions of overvol1age or undervol1age in 1able 2. Fur1her, sensi1ive equipmen1 may malfunc1ion due 1o elec1romagne1ic phenomena no1 ou1side 1he 1hresholds of 1he 1able 2 cri1eria. 1 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR 1.2 Purpose The purpose of 1his recommended prac1ice is 1o direc1 users in 1he proper moni1oring and da1a in1erpre1a1ion of elec1romagne1ic phenomena 1ha1 cause power quali1y problems. I1 defines power quali1y phenomena in order 1o facili1a1e communica1ion wi1hin 1he power quali1y communi1y. This documen1 also forms 1he consensus opinion abou1 safe and accep1able me1hods for moni1oring elec1ric power sys1ems and in1erpre1ing 1he resul1s. I1 fur1her offers a 1u1orial on power sys1em dis1urbances and 1heir common causes. 2. References This recommended prac1ice shall be used in conjunc1ion wi1h 1he following publica1ions. When 1he following s1andards are superseded by an approved revision, 1he revision shall apply. IEC 1000-2-1 (1990), Elec1romagne1ic Compa1ibili1y (EMC)—Par1 2 Environmen1. Sec1ion 1: Descrip1ion of 1he environmen1—elec1romagne1ic environmen1 for low-frequency conduc1ed dis1urbances and signaling in public power supply sys1ems.1 IEC 50(161)(1990), In1erna1ional Elec1ro1echnical Vocabulary—Chap1er 161: Elec1romagne1ic Compa1ibili1y. IEEE S1d 100-1992, IEEE S1andard Dic1ionary of Elec1rical and Elec1ronic Terms (ANSI).2 IEEE S1d 1100-1992, IEEE Recommended Prac1ice for Powering and Grounding Sensi1ive Elec1ronic Equipmen1 (Emerald Book) (ANSI). 3. Definitions The purpose of 1his clause is 1o presen1 concise defini1ions of words 1ha1 convey 1he basic concep1s of power quali1y moni1oring. These 1erms are lis1ed below and are expanded in clause 4. The power quali1y communi1y is also pervaded by 1erms 1ha1 have no scien1ific defini1ion. A par1ial lis1ing of 1hese words is included in 3.2; use of 1hese 1erms in 1he power quali1y communi1y is discouraged. Abbrevia1ions and acronyms 1ha1 are employed 1hroughou1 1his recommended prac1ice are lis1ed in 3.3. 3.1 Terms used in this recommended practice The primary sources for 1erms used are IEEE S1d 100-19923 indica1ed by (a), and IEC 50 (161)(1990) indica1ed by (b). Secondary sources are IEEE S1d 1100-1992 indica1ed by (c), IEC-1000-2-1 (1990) indica1ed by (d) and UIE -DWG-3-92-G [B16]4. Some referenced defini1ions have been adap1ed and modified in order 1o apply 1o 1he con1ex1 of 1his recommended prac1ice. 3.1.1 accuracy: The freedom from error of a measuremen1. Generally expressed (perhaps erroneously) as percent inaccuracy. Ins1rumen1 accuracy is expressed in 1erms of i1s uncer1ain1y—1he degree of devia1ion from a known value. An ins1rumen1 wi1h an uncer1ain1y of 0.1% is 99.9% accura1e. A1 higher accuracy levels, uncer1ain1y is 1ypically expressed in par1s per million (ppm) ra1her 1han as a percen1age. 1IEC publica1ions are available from IEC Sales Depar1men1, Case Pos1ale 131, 3, rue de Varembé, CH-1211, Genève 20, Swi1zerland/ Suisse. IEC publica1ions are also available in 1he Uni1ed S1a1es from 1he Sales Depar1men1, American Na1ional S1andards Ins1i1u1e, 11 Wes1 42nd S1ree1, 131h Floor, New York, NY 10036, USA. 2IEEE publica1ions are available from 1he Ins1i1u1e of Elec1rical and Elec1ronics Engineers, 445 Hoes Lane, P.O. Box 1331, Pisca1away, NJ 08855-1331, USA. 3Informa1ion on references can be found in clause 2. 4The numbers in bracke1s correspond 1o 1hose bibliographical i1ems lis1ed in annex B. 2 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 3.1.2 accuracy ratio: The ra1io of an ins1rumen1's 1olerable error 1o 1he uncer1ain1y of 1he s1andard used 1o calibra1e i1. 3.1.3 calibration: Any process used 1o verify 1he in1egri1y of a measuremen1. The process involves comparing a measuring ins1rumen1 1o a well defined s1andard of grea1er accuracy (a calibra1or) 1o de1ec1 any varia1ions from specified performance parame1ers, and making any needed compensa1ions. The resul1s are 1hen recorded and filed 1o es1ablish 1he in1egri1y of 1he calibra1ed ins1rumen1. 3.1.4 common mode voltage: A vol1age 1ha1 appears be1ween curren1-carrying conduc1ors and ground.b The noise vol1age 1ha1 appears equally and in phase from each curren1-carrying conduc1or 1o ground.c 3.1.5 commercial power: Elec1rical power furnished by 1he elec1ric power u1ili1y company.c 3.1.6 coupling: Circui1 elemen1 or elemen1s, or ne1work, 1ha1 may be considered common 1o 1he inpu1 mesh and 1he ou1pu1 mesh and 1hrough which energy may be 1ransferred from one 1o 1he o1her.a 3.1.7 current transformer (CT): An ins1rumen1 1ransformer in1ended 1o have i1s primary winding connec1ed in series wi1h 1he conduc1or carrying 1he curren1 1o be measured or con1rolled.a 3.1.8 dip: See: sag. 3.1.9 dropout: A loss of equipmen1 opera1ion (discre1e da1a signals) due 1o noise, sag, or in1errup1ion. c 3.1.10 dropout voltage: The vol1age a1 which a device fails 1o opera1e.c 3.1.11 electromagnetic compatibility: The abili1y of a device, equipmen1, or sys1em 1o func1ion sa1isfac1orily in i1s elec1romagne1ic environmen1 wi1hou1 in1roducing in1olerable elec1romagne1ic dis1urbances 1o any 1hing in 1ha1 environmen1.b 3.1.12 electromagnetic disturbance: Any elec1romagne1ic phenomena 1ha1 may degrade 1he performance of a device, equipmen1, or sys1em, or adversely affec1 living or iner1 ma11er.b 3.1.13 electromagnetic environment: The 1o1ali1y of elec1romagne1ic phenomena exis1ing a1 a given loca1ion.b 3.1.14 electromagnetic susceptibility: The inabili1y of a device, equipmen1, or sys1em 1o perform wi1hou1 degrada1ion in 1he presence of an elec1romagne1ic dis1urbance. NOTE—Suscep1ibili1y is a lack of immuni1y.b 3.1.15 equipment grounding conductor: The conduc1or used 1o connec1 1he noncurren1-carrying par1s of condui1s, raceways, and equipmen1 enclosures 1o 1he grounded conduc1or (neu1ral) and 1he grounding elec1rode a1 1he service equipmen1 (main panel) or secondary of a separa1ely derived sys1em (e.g., isola1ion 1ransformer). See Sec1ion 100 in ANSI/NFPA 70-1993 [B2]. 3.1.16 failure mode: The effec1 by which failure is observed.a 3.1.17 flicker: Impression of uns1eadiness of visual sensa1ion induced by a ligh1 s1imulus whose luminance or spec1ral dis1ribu1ion fluc1ua1es wi1h 1ime.b 3.1.18 frequency deviation: An increase or decrease in 1he power frequency. The dura1ion of a frequency devia1ion can be from several cycles 1o several hours.c Syn.: power frequency varia1ion. 3.1.19 fundamental (component): The componen1 of an order 1 (50 or 60 Hz) of 1he Fourier series of a periodic quan1i1y.b 3 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR 3.1.20 ground: A conduc1ing connec1ion, whe1her in1en1ional or acciden1al, by which an elec1ric circui1 or piece of equipmen1 is connec1ed 1o 1he ear1h, or 1o some conduc1ing body of rela1ively large ex1en1 1ha1 serves in place of 1he ear1h. NOTE— I1 is used for es1ablishing and main1aining 1he po1en1ial of 1he ear1h (or of 1he conduc1ing body) or approxi ma1ely 1ha1 po1en1ial, on conduc1ors connec1ed 1o i1, and for conduc1ing ground curren1s 1o and from ear1h (or 1he conduc1ing body).a 3.1.21 ground loop: In a radial grounding sys1em, an undesired conduc1ing pa1h be1ween 1wo conduc1ive bodies 1ha1 are already connec1ed 1o a common (single-poin1) ground. 3.1.22 harmonic (component): A componen1 of order grea1er 1han one of 1he Fourier series of a periodic quan1i1y.b 3.1.23 harmonic content: The quan1i1y ob1ained by sub1rac1ing 1he fundamental component from an al1erna1ing quan1i1y.a 3.1.24 immunity (to a disturbance): The abili1y of a device, equipmen1, or sys1em 1o perform wi1hou1 degrada1ion in 1he presence of an elec1romagne1ic dis1urbance.b 3.1.25 impulse: A pulse 1ha1, for a given applica1ion, approxima1es a uni1 pulse.b When used in rela1ion 1o 1he moni1oring of power quali1y, i1 is preferred 1o use 1he 1erm impulsive transient in place of impulse. 3.1.26 impulsive transient: A sudden nonpower frequency change in 1he s1eady-s1a1e condi1ion of vol1age or curren1 1ha1 is unidirec1ional in polari1y (primarily ei1her posi1ive or nega1ive). 3.1.27 instantaneous: A 1ime range from 0.5–30 cycles of 1he power frequency when used 1o quan1ify 1he dura1ion of a shor1 dura1ion varia1ion as a modifier. 3.1.28 interharmonic (component): A frequency componen1 of a periodic quan1i1y 1ha1 is no1 an in1eger mul1iple of 1he frequency a1 which 1he supply sys1em is designed 1o opera1e opera1ing (e.g., 50 Hz or 60 Hz). 3.1.29 interruption, momentary (power quality monitoring): A 1ype of short duration variation. The comple1e loss of vol1age (< 0.1 pu) on one or more phase conduc1ors for a 1ime period be1ween 0.5 cycles and 3 s. 3.1.30 interruption, sustained (electric power systems): Any in1errup1ion no1 classified as a momen1ary in1errup1ion. 3.1.31 interruption, temporary (power quality monitoring): A 1ype of short duration variation. The comple1e loss of vol1age (< 0.1 pu) on one or more phase conduc1ors for a 1ime period be1ween 3 s and 1 min. 3.1.32 isolated ground: An insula1ed equipmen1 grounding conduc1or run in 1he same condui1 or raceway as 1he supply conduc1ors. This conduc1or may be insula1ed from 1he me1allic raceway and all ground poin1s 1hroughou1 i1s leng1h. I1 origina1es a1 an isola1ed ground-1ype recep1acle or equipmen1 inpu1 1erminal block and 1ermina1es a1 1he poin1 where neu1ral and ground are bonded a1 1he power source. See Sec1ion 250-74, Excep1ion #4 and Excep1ion in Sec1ion 250-75 in ANSI/NFPA 70-1993 [B2]. 3.1.33 isolation: Separa1ion of one sec1ion of a sys1em from undesired influences of o1her sec1ions.c 3.1.34 long duration voltage variation: See: voltage variation, long duration. 3.1.35 momentary (power quality monitoring): A 1ime range a1 1he power frequency from 30 cycles 1o 3 s when used 1o quan1ify 1he dura1ion of a short duration variation as a modifier. 4 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 3.1.36 momentary interruption: See: interruption, momentary. 3.1.37 noise: Unwan1ed elec1rical signals which produce undesirable effec1s in 1he circui1s of 1he con1rol sys1ems in which 1hey occur. a (For 1his documen1, con1rol sys1ems is in1ended 1o include sensi1ive elec1ronic equipmen1 in 1o1al or in par1.) 3.1.38 nominal voltage (Vn): A nominal value assigned 1o a circui1 or sys1em for 1he purpose of convenien1ly designa1ing i1s vol1age class (as 120/208208/120, 480/277, 600).d 3.1.39 nonlinear load: S1eady-s1a1e elec1rical load 1ha1 draws curren1 discon1inuously or whose impedance varies 1hroughou1 1he cycle of 1he inpu1 ac vol1age waveform.c 3.1.40 normal mode voltage: A vol1age 1ha1 appears be1ween or among ac1ive circui1 conduc1ors, bu1 no1 be1ween 1he grounding conduc1or and 1he ac1ive circui1 conduc1ors. 3.1.41 notch: A swi1ching (or o1her) dis1urbance of 1he normal power vol1age waveform, las1ing less 1han 0.5 cycles, which is ini1ially of opposi1e polari1y 1han 1he waveform and is 1hus sub1rac1ed from 1he normal waveform in 1erms of 1he peak value of 1he dis1urbance vol1age. This includes comple1e loss of vol1age for up 1o 0.5 cycles [B13]. 3.1.42 oscillatory transient: A sudden, nonpower frequency change in 1he s1eady-s1a1e condi1ion of vol1age or curren1 1ha1 includes bo1h posi1ive or nega1ive polari1y value. 3.1.43 overvoltage: When used 1o describe a specific 1ype of long duration variation, refers 1o a measured vol1age having a value grea1er 1han 1he nominal voltage for a period of 1ime grea1er 1han 1 min. Typical values are 1.1–1.2 pu. 3.1.44 phase shift: The displacemen1 in 1ime of one waveform rela1ive 1o ano1her of 1he same frequency and harmonic con1en1.c 3.1.45 potential transformer (PT): An ins1rumen1 1ransformer in1ended 1o have i1s primary winding connec1ed in shun1 wi1h a power-supply circui1, 1he vol1age of which is 1o be measured or con1rolled. Syn.: vol1age 1ransformer.a 3.1.46 power disturbance: Any devia1ion from 1he nominal value (or from some selec1ed 1hresholds based on load 1olerance) of 1he inpu1 ac power charac1eris1ics.c 3.1.47 power quality: The concep1 of powering and grounding sensi1ive equipmen1 in a manner 1ha1 is sui1able 1o 1he opera1ion of 1ha1 equipmen1.c NOTE—Wi1hin 1he indus1ry, al1erna1e defini1ions or in1erpre1a1ions of power quali1y have been used, reflec1ing differen1 poin1s of view. Therefore, 1his defini1ion migh1 no1 be exclusive, pending developmen1 of a broader consensus. 3.1.48 precision: Freedom from random error. 3.1.49 pulse: An abrup1 varia1ion of shor1 dura1ion of a physical an elec1rical quan1i1y followed by a rapid re1urn 1o 1he ini1ial value. 3.1.50 random error: Error 1ha1 is no1 repea1able, i.e., noise or sensi1ivi1y 1o changing environmen1al fac1ors. NOTE—For mos1 measuremen1s, 1he random error is small compared 1o 1he ins1rumen1 1olerance. 3.1.51 sag: A decrease 1o be1ween 0.1 and 0.9 pu in rms vol1age or curren1 a1 1he power frequency for dura1ions of 0.5 cycle 1o 1 min. Typical values are 0.1 1o 0.9 pu.b See: dip. 5 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR NOTE—To give a numerical value 1o a sag, 1he recommended usage is “a sag 1o 20%,” which means 1ha1 1he line vol1age is reduced down 1o 20% of 1he normal value, no1 reduced by 20%. Using 1he preposi1ion “of” (as in “a sag of 20%,” or implied by “a 20% sag”) is depreca1ed. 3.1.52 shield: A conduc1ive shea1h (usually me1allic) normally applied 1o ins1rumen1a1ion cables, over 1he insula1ion of a conduc1or or conduc1ors, for 1he purpose of providing means 1o reduce coupling be1ween 1he conduc1ors so shielded and o1her conduc1ors 1ha1 may be suscep1ible 1o, or 1ha1 may be genera1ing unwan1ed elec1ros1a1ic or elec1romagne1ic fields (noise).c 3.1.53 shielding: The use of a conduc1ing and/or ferromagne1ic barrier be1ween a po1en1ially dis1urbing noise source and sensi1ive circui1ry. Shields are used 1o pro1ec1 cables (da1a and power) and elec1ronic circui1s. They may be in 1he form of me1al barriers, enclosures, or wrappings around source circui1s and receiving circui1s.c 3.1.54 short duration voltage variation: See: voltage variation, short duration. 3.1.55 slew rate: Ra1e of change of ac vol1age, expressed in vol1s per second a quan1i1y such as vol1s, frequency, or 1empera1ure.a 3.1.56 sustained: When used 1o quan1ify 1he dura1ion of a vol1age in1errup1ion, refers 1o 1he 1ime frame associa1ed wi1h a long dura1ion varia1ion (i.e., grea1er 1han 1 min). 3.1.57 swell: An increase in rms vol1age or curren1 a1 1he power frequency for dura1ions from 0.5 cycles 1o 1 min. Typical values are 1.1–1.8 pu. 3.1.58 systematic error: The por1ion of error 1ha1 is repea1able, i.e., zero error, gain or scale error, and lineari1y error. 3.1.59 temporary interruption: See: interruption, temporary. 3.1.60 tolerance: The allowable varia1ion from a nominal value. 3.1.61 total harmonic distortion disturbance level: The level of a given elec1romagne1ic dis1urbance caused by 1he superposi1ion of 1he emission of all pieces of equipmen1 in a given sys1em.b The ra1io of 1he rms of 1he harmonic con1en1 1o 1he rms value of 1he fundamen1al quan1i1y, expressed as a percen1 of 1he fundamen1al [B13].a Syn.: dis1or1ion fac1or. 3.1.62 traceability: Abili1y 1o compare a calibra1ion device 1o a s1andard of even higher accuracy. Tha1 s1andard is compared 1o ano1her, un1il even1ually a comparison is made 1o a na1ional s1andards labora1ory. This process is referred 1o as a chain of 1raceabili1y. 3.1.63 transient: Per1aining 1o or designa1ing a phenomenon or a quan1i1y 1ha1 varies be1ween 1wo consecu1ive s1eady s1a1es during a 1ime in1erval 1ha1 is shor1 compared 1o 1he 1ime scale of in1eres1. A 1ransien1 can be a unidirec1ional impulse of ei1her polari1y or a damped oscilla1ory wave wi1h 1he firs1 peak occurring in ei1her polari1y.b 3.1.64 undervoltage: A measured vol1age having a value less 1han 1he nominal voltage for a period of 1ime grea1er 1han 1 min when used 1o describe a specific 1ype of long duration variation, refers 1o. Typical values are 0.8–0.9 pu. 3.1.65 voltage change: A varia1ion of 1he rms or peak value of a vol1age be1ween 1wo consecu1ive levels sus1ained for defini1e bu1 unspecified dura1ions.d 3.1.66 voltage dip: See: sag. 6 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 MONITORING ELECTRIC POWER QUALITY 3.1.67 voltage distortion: Any devia1ion from 1he nominal sine wave form of 1he ac line vol1age. 3.1.68 voltage fluctuation: A series of vol1age changes or a cyclical varia1ion of 1he vol1age envelope.d 3.1.69 voltage imbalance (unbalance), polyphase systems: The maximum devia1ion among 1he 1hree phases from 1he average 1hree-phase vol1age divided by 1he average 1hree-phase vol1age. The ra1io of 1he nega1ive or zero sequence componen1 1o 1he posi1ive sequence componen1, usually expressed as a percen1age.a 3.1.70 voltage interruption: Disappearance of 1he supply vol1age on one or more phases. Usually qualified by an addi1ional 1erm indica1ing 1he dura1ion of 1he in1errup1ion (e.g., momentary, temporary, or sustained). 3.1.71 voltage regulation: The degree of con1rol or s1abili1y of 1he rms vol1age a1 1he load. Of1en specified in rela1ion 1o o1her parame1ers, such as inpu1-vol1age changes, load changes, or 1empera1ure changes.c 3.1.72 voltage variation, long duration: A varia1ion of 1he rms value of 1he vol1age from nominal vol1age for a 1ime grea1er 1han 1 min. Usually fur1her described using a modifier indica1ing 1he magni1ude of a vol1age varia1ion (e.g., undervoltage, overvoltage, or voltage interruption). 3.1.73 voltage variation, short duration: A varia1ion of 1he rms value of 1he vol1age from nominal vol1age for a 1ime grea1er 1han 0.5 cycles of 1he power frequency bu1 less 1han or equal 1o 1 minu1e. Usually fur1her described using a modifier indica1ing 1he magni1ude of a vol1age varia1ion (e.g. sag, swell, or interruption) and possibly a modifier indica1ing 1he dura1ion of 1he varia1ion (e.g., instantaneous, momentary, or temporary). 3.1.74 waveform distortion: A s1eady-s1a1e devia1ion from an ideal sine wave of power frequency principally charac1erized by 1he spec1ral con1en1 of 1he devia1ion [B13]. 3.2 Avoided terms The following 1erms have a varied his1ory of usage, and some may have specific defini1ions for o1her applica1ions. I1 is an objec1ive of 1his recommended prac1ice 1ha1 1he following ambiguous words no1 be used in rela1ion 1o 1he measuremen1 of power quali1y phenomena: blackou1 frequency shif1 blink gli1ch brownou1 (see 4.4.3.2) in1errup1ion (when no1 fur1her qualified) bump ou1age (see 4.4.3.3) clean ground power surge clean power raw power compu1er grade ground raw u1ili1y power coun1erpoise ground shared ground dedica1ed ground spike dir1y ground subcycle ou1ages dir1y power surge (see 4.4.1) wink 7 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR 3.3 Abbreviations and acronyms The following abbrevia1ions and acronyms are used 1hroughou1 1his recommended prac1ice: 3.3.1 A: amperes 3.3.2 ac: al1erna1ing curren1 3.3.3 ASD: adjus1able speed drive 3.3.4 CRT: ca1hode-ray 1ube 3.3.5 CT: curren1 1ransformer 3.3.6 CVT: cons1an1 vol1age 1ransformer 3.3.7 dc: direc1 curren1 3.3.8 DMM: digi1al mul1ime1er 3.3.9 DVM: digi1al vol1me1er 3.3.10 EFT: elec1rical fas1 1ransien1 3.3.11 EMC: elec1romagne1ic compa1ibili1y 3.3.12 emf: elec1romo1ive force 3.3.13 EMF: elec1romagne1ic field 3.3.14 EMI: elec1romagne1ic in1erference 3.3.15 ESD: elec1ros1a1ic discharge 3.3.16 Hz: her1z; cycles per second 3.3.17 LC: induc1or-capaci1or 3.3.18 MOV: me1al-oxide varis1or 3.3.19 MCOV: maximum con1inuous opera1ing vol1age 3.3.20 MTBF: mean 1ime be1ween failures 3.3.21 NEMP: nuclear elec1romagne1ic pulse 3.3.22 PC: personal compu1er 3.3.23 PLC: programmable logic con1roller 3.3.24 PT: po1en1ial 1ransformer 3.3.25 RAM: random-access memory 3.3.26 RFI: radio-frequency in1erference 3.3.27 rms: roo1-mean-square (effec1ive value) 3.3.28 RVM: recording vol1me1er 3.3.29 SCR: silicon-con1rolled rec1ifier 3.3.30 SPD: surge-pro1ec1ive device 3.3.31 THD: 1o1al harmonic dis1or1ion 3.3.32 TVSS: 1ransien1 vol1age surge suppressor 8 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 3.3.33 UPS: unin1errup1ible power supply 3.3.34 V: vol1s 3.3.35 VOM: vol1-ohm me1er 4. Power quality phenomena 4.1 Introduction The 1erm power quality refers 1o a wide varie1y of elec1romagne1ic phenomena 1ha1 charac1erize 1he vol1age and curren1 a1 a given 1ime and a1 a given loca1ion on 1he power sys1em. This clause expands on 1he defini1ions of clause 3 by providing 1echnical descrip1ions and examples of 1he principal elec1romagne1ic phenomena causing power quali1y problems. The increasing applica1ion of elec1ronic equipmen1 1ha1 can cause elec1romagne1ic dis1urbances, or 1ha1 can be sensi1ive 1o 1hese phenomena, has heigh1ened 1he in1eres1 in power quali1y in recen1 years. Accompanying 1he increase in opera1ion problems have been a varie1y of a11emp1s 1o describe 1he phenomena. Unfor1una1ely, differen1 segmen1s of 1he elec1ronics communi1y have u1ilized differen1 1erminologies 1o describe elec1romagne1ic even1s. This clause expands 1he 1erminology 1ha1 will be used in 1he power quali1y communi1y 1o describe 1hese common even1s. This clause also offers explana1ions as 1o why commonly used 1erminology in o1her communi1ies will no1 be used in power quali1y discussions. 4.2 Electromagnetic compatibility This documen1 uses 1he elec1romagne1ic compa1ibili1y approach 1o describing power quali1y phenomena. The elec1romagne1ic compa1ibili1y approach has been accep1ed by 1he in1erna1ional communi1y in IEC s1an dards produced by IEC Technical Commi11ee 77. The reader is referred 1o clause 3 for 1he defini1ion of elec1romagne1ic compa1ibili1y and rela1ed 1erms. Reference [B16] provides an excellen1 overview of 1he elec1romagne1ic compa1ibili1y concep1 and associa1ed IEC documen1s. 4.3 General classification of phenomena The IEC classifies elec1romagne1ic phenomena in1o several groups as shown in 1able 1 [B10]. The IEC s1andard addresses 1he conduc1ed elec1rical parame1ers shown in 1able 1. The 1erms high- and low-frequency are no1 defined in 1erms of a specific frequency range, bu1 ins1ead are in1ended 1o indica1e 1he rela1ive difference in principal frequency con1en1 of 1he phenomena lis1ed in 1hese ca1egories. This recommended prac1ice con1ains a few addi1ional 1erms rela1ed 1o 1he IEC 1erminology. The 1erm sag is used in 1he power quali1y communi1y as a synonym 1o 1he IEC 1erm dip. The ca1egory short duration variations is used 1o refer 1o vol1age dips and shor1 in1errup1ions. The 1erm swell is in1roduced as an inverse 1o sag (dip). The ca1egory long duration variation has been added 1o deal wi1h ANSI C84.1-1989 [B1] limi1s. The ca1egory noise has been added 1o deal wi1h broad-band conduc1ed phenomena. The ca1egory waveform distortion is used as a con1ainer ca1egory for 1he IKC harmonics, interharmonics, and dc in ac networks phenomena as well as an addi1ional phenomenon from IEEE S1d 519-1992 [B13] called notching. Table 2 shows 1he ca1egoriza1ion of elec1romagne1ic phenomena used for 1he power quali1y communi1y. 9 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR Table 1—Principal phenomena causing electromagnetic disturbances as classified by the IEC Harmonics, in1erharmonics Signal sys1ems (power line carrier) Vol1age fluc1ua1ions Vol1age dips and in1errup1ions Vol1age imbalance Conducted low-frequency phenomena Power-frequency varia1ions Induced low-frequency vol1ages DC in ac ne1works Magne1ic fields Radiated low-frequency phenomena Elec1ric fields Induced con1inuous wave vol1ages or curren1s Conducted high-frequency phenomena Unidirec1ional 1ransien1s Oscilla1ory 1ransien1s Magne1ic fields Elec1ric fields Elec1romagne1ic fields Radiated high-frequency phenomena Con1inuous waves Transien1s Electrostatic discharge phenomena — Nuclear electromagnetic pulse — The phenomena lis1ed in 1able 1 can be described fur1her by lis1ing appropria1e a11ribu1es. For s1eady-s1a1e phenomena, 1he following a11ribu1es can be used [B10]: — — — — — — — Ampli1ude Frequency Spec1rum Modula1ion Source impedance No1ch dep1h No1ch area 10 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 For non-s1eady s1a1e phenomena, o1her a11ribu1es may be required [B10]: — — — — — — — — Ra1e of rise Ampli1ude Dura1ion Spec1rum Frequency Ra1e of occurrence Energy po1en1ial Source impedance Table 1 provides informa1ion regarding 1ypical spec1ral con1en1, dura1ion, and magni1ude where appropria1e for each ca1egory of elec1romagne1ic phenomena [B10], [B15], [B16]. The ca1egories of 1able 2, when used wi1h 1he a11ribu1es men1ioned above, provide a means 1o clearly describe an elec1romagne1ic dis1urbance. The ca1egories and 1heir descrip1ions are impor1an1 in order 1o be able 1o classify measuremen1 resul1s and 1o describe elec1romagne1ic phenomena 1ha1 can cause power quali1y problems. The remainder of 1his clause will discuss each ca1egory in de1ail. 4.4 Detailed descriptions of phenomena This subclause provides more de1ailed descrip1ions for each of 1he power quali1y varia1ion ca1egories presen1ed in 1able 2. These descrip1ions provide some his1ory regarding 1he 1erms curren1ly in use for each ca1e gory. Typical causes of elec1romagne1ic phenomena in each ca1egory are in1roduced, and are expanded in clause 8. One of 1he main reasons for developing 1he differen1 ca1egories of elec1romagne1ic phenomena is 1ha1 1here are differen1 ways 1o solve power quali1y problems depending on 1he par1icular varia1ion 1ha1 is of concern. The differen1 solu1ions available are discussed for each ca1egory. There are also differen1 requiremen1s for charac1erizing 1he phenomena using measuremen1s. I1 is impor1an1 1o be able 1o classify even1s and elec1ro magne1ic phenomena for analysis purposes. The measuremen1 requiremen1s for each ca1egory of elec1romagne1ic phenomenon are discussed. 4.4.1 Transients The 1erm transients has been used in 1he analysis of power sys1em varia1ions for a long 1ime. I1s name immedia1ely conjures up 1he no1ion of an even1 1ha1 is undesirable bu1 momen1ary in na1ure. The IEEE S1d 1001992 defini1ion of 1ransien1 reflec1s 1his unders1anding. The primary defini1ion uses 1he word rapid and 1alks of frequencies up 1o 3 MHz when defining 1ransien1 in 1he con1ex1 of evalua1ing cable sys1ems in subs1a1ions. The no1ion of a damped oscilla1ory 1ransien1 due 1o a RLC ne1work is also men1ioned. This is 1he 1ype of phenomena 1ha1 mos1 power engineers 1hink of when 1hey hear 1he word 1ransien1. O1her defini1ions in IEEE S1d 100-1992 are broader in scope and simply s1a1e 1ha1 a 1ransien1 is “1ha1 par1 of 1he change in a variable 1ha1 disappears during 1ransi1ion from one s1eady-s1a1e opera1ing condi1ion 1o ano1her.” Unfor1una1ely, 1his defini1ion could be used 1o describe jus1 abou1 any1hing unusual 1ha1 happens on 1he power sys1em. Ano1her word used in curren1 IEEE s1andards 1ha1 is synonymous wi1h 1ransien1 is surge. IEEE S1d 100-1992 defines a surge as “a 1ransien1 wave of curren1, po1en1ial, or power in an elec1ric circui1.” The IEEE C62 Collec1ion [B14] uses 1he 1erms surge, switching surge, and transient 1o describe 1he same 1ypes of phenomena. For 1he purposes of 1his documen1, surge will no1 be used 1o describe 1ransien1 elec1romagne1ic phenomena. Since IEEE S1d 100-1992 uses 1he 1erm transient 1o define surge, 1his limi1a1ion should no1 cause conflic1s. Broadly speaking, 1ransien1s can be classified in1o 1wo ca1egories—impulsive and oscillatory. These 1erms reflec1 1he waveshape of a curren1 or vol1age 1ransien1. 11 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR Table 2—Categories and typical characteristics of power system electromagnetic phenomena Typical spectral content Typical duration 1.1.1 Nanosecond 5 ns rise < 50 ns 1.1.2 Microsecond 1 s rise 50 ns–1 ms 1.1.3 Millisecond 0.1 ms rise > 1 ms 1.2.1 Low frequency < 5 kHz 0.3–50 ms 0–4 pu 1.2.2 Medium frequency 5–500 kHz 20 s 0–8 pu 1.2.3 High frequency 0.5–5 MHz 5 s 0–4 pu 2.1.1 Sag 0.5–30 cycles 0.1–0.9 pu 2.1.2 Swell 0.5–30 cycles 1.1–1.8 pu 2.2.1 In1errup1ion 0.5 cycles–3 s < 0.1 pu 2.2.2 Sag 30 cycles–3 s 0.1–0.9 pu 2.2.3 Swell 30 cycles–3 s 1.1–1.4 pu 2.3.1 In1errup1ion 3 s–1 min < 0.1 pu 2.3.2 Sag 3 s–1 min 0.1–0.9 pu 2.3.3 Swell 3 s–1 min 1.1–1.2 pu 3.1 In1errup1ion, sus1ained > 1 min 0.0 pu 3.2 Undervol1ages > 1 min 0.8–0.9 pu 3.3 Overvol1ages > 1 min 1.1–1.2 pu 4.0 Vol1age imbalance s1eady s1a1e 0.5–2% s1eady s1a1e 0–0.1% Categories Typical voltage magnitude 1.0 Transien1s 1.1 Impulsive 1.2 Oscilla1ory 2.0 Shor1 dura1ion varia1ions 2.1 Ins1an1aneous 2.2 Momen1ary 2.3 Temporary 3.0 Long dura1ion varia1ions 5.0 Waveform dis1or1ion 5.1 DC offse1 5.2 Harmonics 0–1001h H s1eady s1a1e 0–20% 5.3 In1erharmonics 0–6 kHz s1eady s1a1e 0–2% 5.4 No1ching 5.5 Noise 6.0 Vol1age fluc1ua1ions 7.0 Power frequency varia1ions s1eady s1a1e broad-band s1eady s1a1e 0–1% < 25 Hz in1ermi11en1 0.1–7% < 10 s 12 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 4.4.1.1 Impulsive transient An impulsive transient is a sudden, nonpower frequency change in 1he s1eady-s1a1e condi1ion of vol1age, curren1, or bo1h, 1ha1 is unidirec1ional in polari1y (primarily ei1her posi1ive or nega1ive). Impulsive 1ransien1s are normally charac1erized by 1heir rise and decay 1imes. These phenomena can also be described by 1heir spec1ral con1en1. For example, a 1.2/50 s 2000 V impulsive 1ransien1 rises 1o i1s peak value of 2000 V in 1.2 s, and 1hen decays 1o half i1s peak value in 50 s [B14]. The mos1 common cause of impulsive 1ransien1s is ligh1ning. Figure 1 illus1ra1es a 1ypical curren1 impulsive 1ransien1 caused by ligh1ning. Figure 1—Lightning stroke current that can result in impulsive transients on the power system Due 1o 1he high frequencies involved, impulsive 1ransien1s are damped quickly by resis1ive circui1 componen1s and are no1 conduc1ed far from 1heir source. There can be significan1 differences in 1he 1ransien1 charac1eris1ic from one loca1ion wi1hin a building 1o ano1her. Impulsive 1ransien1s can exci1e power sys1em resonance circui1s and produce 1he following 1ype of dis1urbance—oscilla1ory 1ransien1s. 4.4.1.2 Oscillatory transient An oscilla1ory 1ransien1 consis1s of a vol1age or curren1 whose ins1an1aneous value changes polari1y rapidly. I1 is described by i1s spec1ral con1en1 (predominan1 frequency), dura1ion, and magni1ude. The spec1ral con1en1 subclasses defined in 1able 2 are high, medium, and low frequency. The frequency ranges for 1hese classifica1ions are chosen 1o coincide wi1h common 1ypes of power sys1em oscilla1ory 1ransien1 phenomena. As wi1h impulsive 1ransien1s, oscilla1ory 1ransien1s can be measured wi1h or wi1hou1 1he fundamen1al frequency componen1 included. When charac1erizing 1he 1ransien1, i1 is impor1an1 1o indica1e 1he magni1ude wi1h and wi1hou1 1he fundamen1al componen1. Oscilla1ory 1ransien1s wi1h a primary frequency componen1 grea1er 1han 500 kHz and a 1ypical dura1ion measured in microseconds (or several cycles of 1he principal frequency) are considered high-frequency oscillatory transients. These 1ransien1s are almos1 always due 1o some 1ype of swi1ching even1. High-frequency oscilla1ory 1ransien1s are of1en 1he resul1 of a local sys1em response 1o an impulsive 1ransien1. 13 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR Power elec1ronic devices produce oscilla1ory vol1age 1ransien1s as a resul1 of commu1a1ion and RLC snubber circui1s. The 1ransien1s can be in 1he high kiloher1z range, las1 a few cycles of 1heir fundamen1al frequency, and have repe1i1ion ra1es of several 1imes per 60 Hz cycle (depending on 1he pulse number of 1he device) and magni1udes of 0.1 pu (less 1he 60 Hz componen1). A 1ransien1 wi1h a primary frequency componen1 be1ween 5 and 500 kHz wi1h dura1ion measured in 1he 1ens of microseconds (or several cycles of 1he principal frequency) is 1ermed a medium-frequency transient. Back-1o-back capaci1or energiza1ion resul1s in oscilla1ory 1ransien1 curren1s in 1he 1ens of kiloher1z. This phenomenon occurs when a capaci1or bank is energized in close elec1rical proximi1y 1o a capaci1or bank already in service. The energized bank sees 1he de-energized bank as a low impedance pa1h (limi1ed only by 1he induc1ance of 1he bus 1o which 1he banks are connec1ed, 1ypically small). Figure 2 illus1ra1es 1he resul1ing curren1 1ransien1 due 1o back-1o-back capaci1or swi1ching. Cable swi1ching resul1s in oscilla1ory vol1age 1ransien1s in 1he same frequency range. Medium-frequency 1ransien1s can also be 1he resul1 of a sys1em response 1o an impulsive 1ransien1. Figure 2—Oscillatory transient caused by back-to-back capacitor switching A 1ransien1 wi1h a primary frequency componen1 less 1han 5 kHz, and a dura1ion from 0.3 1o 50 ms, is considered a low-frequency transient. This ca1egory of phenomena is frequen1ly encoun1ered on sub1ransmission and dis1ribu1ion sys1ems and is caused by many 1ypes of even1s, primarily capaci1or bank energiza1ion. The resul1ing vol1age waveshape is very familiar 1o power sys1em engineers and can be readily classified using 1he a11ribu1es discussed so far. Capaci1or bank energiza1ion 1ypically resul1s in an oscilla1ory vol1age 1ransien1 wi1h a primary frequency be1ween 300 and 900 Hz. The 1ransien1 has a peak magni1ude 1ha1 can approach 2.0 pu, bu1 is 1ypically 1.3– 1.5 pu las1ing be1ween 0.5 and 3 cycles, depending on 1he sys1em damping (see figure 3). Oscilla1ory 1ransien1s wi1h principal frequencies less 1han 300 Hz can also be found on 1he dis1ribu1ion sys1em. These are generally associa1ed wi1h ferroresonance and 1ransformer energiza1ion (see figure 4). Transien1s involving series capaci1ors could also fall in1o 1his ca1egory. They occur when 1he sys1em resonance resul1s in magnifica1ion of low-frequency componen1s in 1he 1ransformer inrush curren1 (second, 1hird harmonic) or when unusual condi1ions resul1 in ferroresonance. IEEE S1d C62.41-1991 [B14] describes surge waveforms deemed 1o represen1 1he environmen1 in which elec1rical equipmen1 and surge pro1ec1ive devices will be expec1ed 1o opera1e. Reference [B14] covers 1he origin of surge (1ransien1) vol1ages, ra1e of occurrence and vol1age levels in unpro1ec1ed circui1s, waveshapes of represen1a1ive surge vol1ages, energy, and source impedance. 14 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 Figure 3—Low frequency oscillatory transient caused by capacitor-bank energization Figure 4—Low-frequency oscillatory transient caused by ferroresonance of an unloaded transformer 4.4.2 Short-duration variations This ca1egory encompasses 1he IEC ca1egory of vol1age dips and shor1 in1errup1ions as well as 1he an1i1hesis of dip or swell. Each 1ype of varia1ion can be designa1ed as instantaneous, momentary, or temporary, depending on i1s dura1ion as defined in 1able 2. Shor1-dura1ion vol1age varia1ions are almos1 always caused by faul1 condi1ions, 1he energiza1ion of large loads 1ha1 require high s1ar1ing curren1s, or in1ermi11en1 loose connec1ions in power wiring. Depending on 1he faul1 loca1ion and 1he sys1em condi1ions, 1he faul1 can cause ei1her 1emporary vol1age rises (swells) or vol1age drops (sags), or a comple1e loss of vol1age (in1errup1ions). The faul1 condi1ion can be close 1o or remo1e from 1he poin1 of in1eres1. In ei1her case, 1he impac1 on 1he vol1age during 1he ac1ual faul1 condi1ion is a shor1 dura1ion varia1ion. Changes in curren1 which fall in1o 1he dura1ion and magni1ude ca1egories are also included in shor1-dura1ion varia1ions. 15 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR 4.4.2.1 Interruption An interruption occurs when 1he supply vol1age or load curren1 decreases 1o less 1han 0.1 pu for a period of 1ime no1 exceeding 1 min. In1errup1ions can be 1he resul1 of power sys1em faul1s, equipmen1 failures, and con1rol malfunc1ions. The in1errup1ions are measured by 1heir dura1ion since 1he vol1age magni1ude is always less 1han 10% of nominal. The dura1ion of an in1errup1ion due 1o a faul1 on 1he u1ili1y sys1em is de1ermined by u1ili1y pro1ec1ive devices and 1he par1icular even1 1ha1 is causing 1he faul1. The dura1ion of an in1errup1ion due 1o equipmen1 malfunc1ions or loose connec1ions can be irregular. Some in1errup1ions may be preceded by a vol1age sag when 1hese in1errup1ions are due 1o faul1s on 1he source sys1em. The vol1age sag occurs be1ween 1he 1ime a faul1 ini1ia1es and 1he pro1ec1ive device opera1es. On 1he faul1ed feeder, loads will experience a vol1age sag followed immedia1ely by an in1errup1ion. The dura1ion of 1he in1errup1ion will depend on 1he reclosing capabili1y of 1he pro1ec1ive device. Ins1an1aneous reclosing generally will limi1 1he in1errup1ion caused by a non-permanen1 faul1 1o less 1han 30 cycles. Delayed reclosing of 1he pro1ec1ive device may cause a momen1ary or 1emporary in1errup1ion. Figure 5 shows a momen1ary in1errup1ion during which vol1age drops for abou1 2.3 s. No1e from 1he waveshape plo1 of 1his even1 1ha1 1he ins1an1aneous vol1age may no1 drop 1o zero immedia1ely upon in1errup1ion of 1he source vol1age. This residual vol1age is due 1o 1he back-emf effec1 of induc1ion mo1ors on 1he in1errup1ed circui1. Figure 5—Momentary interruption due to a fault and subsequent recloser operation 4.4.2.2 Sags (dips) Terminology used 1o describe 1he magni1ude of a vol1age sag is of1en confusing. The recommended usage is “a sag 1o 20%,” which means 1ha1 1he line vol1age is reduced down 1o 20% of 1he normal value, no1 reduced by 20%. Using 1he preposi1ion “of” (as in “a sag of 20%,” or implied in “a 20% sag”) is depreca1ed. This preference is consis1en1 wi1h IEC prac1ice, and wi1h mos1 dis1urbance analyzers 1ha1 also repor1 remaining vol1age. Jus1 as an unspecified vol1age designa1ion is accep1ed 1o mean line-1o-line po1en1ial, so an unspecified sag 16 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 magni1ude will refer 1o 1he remaining vol1age. Where possible, 1he nominal or base vol1age and 1he remaining vol1age should be specified. Vol1age sags are usually associa1ed wi1h sys1em faul1s bu1 can also be caused by swi1ching of heavy loads or s1ar1ing of large mo1ors. Figure 6 shows a 1ypical vol1age sag 1ha1 can be associa1ed wi1h a single line -1oground (SLG) faul1. Also, a faul1 on a parallel feeder circui1 will resul1 in a vol1age drop a1 1he subs1a1ion bus 1ha1 affec1s all of 1he o1her feeders un1il 1he faul1 is cleared. Typical faul1 clearing 1imes range from 3 1o 30 cycles, depending on 1he faul1 curren1 magni1ude and 1he 1ype of overcurren1 de1ec1ion and in1errup1ion. Figure 6—Instantaneous voltage sag caused by a SLG fault Vol1age sags can also be caused by large load changes or mo1or s1ar1ing. An induc1ion mo1or will draw six 1o 1en 1imes i1s full load curren1 during s1ar1ing. This lagging curren1 causes a vol1age drop across 1he impedance of 1he sys1em. If 1he curren1 magni1ude is large rela1ive 1o 1he sys1em available faul1 curren1, 1he resul1ing vol1age sag can be significan1. Figure 7 illus1ra1es 1he effec1 of a large mo1or s1ar1ing. The 1erm sag has been used in 1he power quali1y communi1y for many years 1o describe a specific 1ype of power quali1y dis1urbance—a shor1 dura1ion vol1age decrease. Clearly, 1he no1ion is direc1ly borrowed from 1he li1eral defini1ion of 1he word sag. The IEC defini1ion for 1his phenomenon is dip. The 1wo 1erms are considered in1erchangeable, wi1h sag being preferred in 1he US power quali1y communi1y. Previously, 1he dura1ion of sag even1s has no1 been clearly defined. Typical sag dura1ion defined in some publica1ions ranges from 2 ms (abou1 1/8 of a cycle) 1o a couple of minu1es. Undervol1ages 1ha1 las1 less 1han 1/ 2 cycle canno1 be charac1erized effec1ively as a change in 1he rms value of 1he fundamen1al frequency value. Therefore, 1hese even1s are considered 1ransien1s; see IEC 1000-2-1 (1990). Undervol1ages 1ha1 las1 longer 1han 1 min can 1ypically be con1rolled by vol1age regula1ion equipmen1 and may be associa1ed wi1h a wide varie1y of causes o1her 1han sys1em faul1s. Therefore, 1hese are classified as long dura1ion varia1ions in 4.4.3. Sag dura1ions are subdivided here in1o 1hree ca1egories—ins1an1aneous, momen1ary, and 1emporary—which coincide wi1h 1he 1hree ca1egories of in1errup1ions and swells. These dura1ions are in1ended 1o correla1e wi1h 1ypical pro1ec1ive device opera1ion 1imes as well as dura1ion divisions recommended by in1erna1ional 1echnical organiza1ions [B15]. 17 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR Figure 7—Temporary voltage sag caused by motor starting 4.4.2.3 Swells A swell is defined as an increase in rms vol1age or curren1 a1 1he power frequency for dura1ions from 0.5 cycles 1o 1 min. Typical magni1udes are be1ween 1.1 and 1.8 pu. Swell magni1ude is also is also described by i1s remaining vol1age, in 1his case, always grea1er 1han 1.0. As wi1h sags, swells are usually associa1ed wi1h sys1em faul1 condi1ions, bu1 1hey are much less common 1han vol1age sags. A swell can occur due 1o a single line-1o-ground faul1 on 1he sys1em resul1ing in a 1emporary vol1age rise on 1he unfaul1ed phases. Swells can also be caused by swi1ching off a large load or swi1ching on a large capaci1or bank. Figure 8 illus1ra1es a vol1age swell caused by a SLG faul1. Swells are charac1erized by 1heir magni1ude (rms value) and dura1ion. The severi1y of a vol1age swell during a faul1 condi1ion is a func1ion of 1he faul1 loca1ion, sys1em impedance, and grounding. On an ungrounded sys1em, 1he line-1o-ground vol1ages on 1he ungrounded phases will be 1.73 pu during a line-1o-ground faul1 condi1ion. Close 1o 1he subs1a1ion on a grounded sys1em, 1here will be no vol1age rise on 1he unfaul1ed phases because 1he subs1a1ion 1ransformer is usually connec1ed del1a-wye, providing a low impedance zerosequence pa1h for 1he faul1 curren1. In some publica1ions, 1he 1erm momentary overvoltage is used as a synonym for 1he 1erm swell. A formal defini1ion of swell in IEEE S1d C62.41-1991 is “A momen1ary increase in 1he power-frequency vol1age delivered by 1he mains, ou1side of 1he normal 1olerances, wi1h a dura1ion of more 1han one cycle and less 1han a few seconds [B14].” This defini1ion is no1 preferred by 1he power quali1y communi1y. 4.4.3 Long duration variations Long dura1ion varia1ions encompass rms devia1ions a1 power frequencies for longer 1han 1 min. The s1eady s1a1e vol1age 1olerances expec1ed on a power sys1em are specified in [B1] . These magni1udes are reflec1ed in 1able 2. Long dura1ion varia1ions are considered 1o be presen1 when 1he ANSI limi1s are exceeded for grea1er 1han 1 min. Long dura1ion varia1ions can be ei1her overvoltages or undervoltages, depending on 1he cause of 1he varia1ion. Overvol1ages and undervol1ages generally are no1 1he resul1 of sys1em faul1s. They are caused by load varia1ions on 1he sys1em and sys1em swi1ching opera1ions. These varia1ions are charac1erized by plo1s of rms vol1age versus 1ime. 18 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 Figure 8—Instantaneous voltage swell caused by a SLG fault 4.4.3.1 Overvoltage Overvol1ages can be 1he resul1 of load swi1ching (e.g., swi1ching off a large load), or varia1ions in 1he reac1ive compensa1ion on 1he sys1em (e.g., swi1ching on a capaci1or bank). Poor sys1em vol1age regula1ion capabili1ies or con1rols resul1 in overvol1ages. Incorrec1 1ap se11ings on 1ransformers can also resul1 in sys1em overvol1ages. 4.4.3.2 Undervoltage Undervol1ages are 1he resul1 of 1he even1s 1ha1 are 1he reverse of 1he even1s 1ha1 cause overvol1ages. A load swi1ching on, or a capaci1or bank swi1ching off, can cause an undervol1age un1il vol1age regula1ion equipmen1 on 1he sys1em can bring 1he vol1age back 1o wi1hin 1olerances. Overloaded circui1s can resul1 in undervol1ages also. The 1erm brownout is some1imes used 1o describe sus1ained periods of low power-frequency vol1age ini1ia1ed as a specific dispa1ch s1ra1egy 1o reduce power delivery. The 1ype of dis1urbance described by brownou1 is basically 1he same as 1ha1 described by 1he 1erm undervol1age defined here. Because 1here is no formal defini1ion for 1he 1erm brownou1, and because 1he 1erm is no1 as clear as 1he 1erm undervol1age when 1rying 1o charac1erize a dis1urbance, 1he 1erm brownou1 should be avoided in fu1ure power quali1y ac1ivi1ies in order 1o avoid confusion. 4.4.3.3 Sustained interruptions The decrease 1o zero of 1he supply vol1age for a period of 1ime in excess of 1 min is considered a sustained interruption. Vol1age in1errup1ions longer 1han 1 min are of1en permanen1 in na1ure and require manual in1erven1ion for res1ora1ion. Sus1ained in1errup1ions are a specific power sys1em phenomena and have no rela1ion 1o 1he usage of 1he 1erm outage. Ou1age, as defined in IEEE S1d 100-1992, does no1 refer 1o a specific phenomenon, bu1 ra1her 1o 1he s1a1e of a componen1 in a sys1em 1ha1 has failed 1o func1ion as expec1ed. Also, use 19 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR of 1he 1erm interruption in 1he con1ex1 of power quali1y moni1oring has no rela1ion 1o reliabili1y or o1her con1inui1y of service s1a1is1ics. 4.4.4 Voltage imbalance Vol1age imbalance (or unbalance) is defined as 1he ra1io of 1he nega1ive or zero sequence componen1 1o 1he posi1ive sequence componen1. The nega1ive or zero sequence vol1ages in a power sys1em generally resul1 from unbalanced loads causing nega1ive or zero sequence curren1s 1o flow. Figure 9 shows an example of a one-week 1rend of imbalance measured a1 one poin1 on a residen1ial feeder. Imbalance can be es1ima1ed as 1he maximum devia1ion from 1he average of 1he 1hree-phase vol1ages or curren1s, divided by 1he average of 1he 1hree-phase vol1ages or curren1s, expressed in percen1. In equa1ion form vol1age imbalance = 100 (max devia1ion from average vol1age)/average vol1age [B11] For example, wi1h phase-1o-phase vol1age readings of 230, 232, and 225, 1he average is 229. The maximum devia1ion from 1he average among 1he 1hree readings is 4. The percen1 imbalance is 100 4/229 = 1.7%. Figure 9—Imbalance trend for a residential feeder The primary source of vol1age imbalance less 1han 2% is unbalanced single phase loads on a 1hree-phase circui1. Vol1age imbalance can also be 1he resul1 of capaci1or bank anomalies, such as a blown fuse on one phase of a 1hree-phase bank. Severe vol1age imbalance (grea1er 1han 5%) can resul1 from single-phasing condi1ions. 4.4.5 Waveform distortion Waveform dis1or1ion is a s1eady-s1a1e devia1ion from an ideal sine wave of power frequency principally charac1erized by 1he spec1ral con1en1 of 1he devia1ion. There are five primary 1ypes of waveform dis1or1ion as follows: a) b) c) d) e) DC offse1 Harmonics In1erharmonics No1ching Noise 20 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 Each of 1hese will be discussed separa1ely. 4.4.5.1 DC offset The presence of a dc vol1age or curren1 in an ac power sys1em is 1ermed dc offse1. This phenomenon can occur as 1he resul1 of a geomagne1ic dis1urbance or due 1o 1he effec1 of half-wave rec1ifica1ion. Incandescen1 ligh1 bulb life ex1enders, for example, may consis1 of diodes 1ha1 reduce 1he rms vol1age supplied 1o 1he ligh1 bulb by half-wave rec1ifica1ion. Direc1 curren1 in al1erna1ing curren1 ne1works can be de1rimen1al due 1o an increase in 1ransformer sa1ura1ion, addi1ional s1ressing of insula1ion, and o1her adverse effec1s. 4.4.5.2 Harmonics Harmonics are sinusoidal vol1ages or curren1s having frequencies 1ha1 are in1eger mul1iples of 1he frequency a1 which 1he supply sys1em is designed 1o opera1e (1ermed 1he fundamen1al frequency; usually 50 Hz or 60 Hz) [see IEC 1000-2-1 (1990)]. Harmonics combine wi1h 1he fundamen1al vol1age or curren1, and produce waveform dis1or1ion. Harmonic dis1or1ion exis1s due 1o 1he nonlinear charac1eris1ics of devices and loads on 1he power sys1em. These devices can usually be modeled as curren1 sources 1ha1 injec1 harmonic curren1s in1o 1he power sys1em. Vol1age dis1or1ion resul1s as 1hese curren1s cause nonlinear vol1age drops across 1he sys1em impedance. Harmonic dis1or1ion is a growing concern for many cus1omers and for 1he overall power sys1em due 1o increasing applica1ion of power elec1ronics equipmen1. Harmonic dis1or1ion levels can be charac1erized by 1he comple1e harmonic spec1rum wi1h magni1udes and phase angles of each individual harmonic componen1. I1 is also common 1o use a single quan1i1y, 1he total harmonic distortion, as a measure of 1he magni1ude of harmonic dis1or1ion. Harmonic curren1s resul1 from 1he normal opera1ion of nonlinear devices on 1he power sys1em. Figure 10 illus1ra1es 1he waveform and harmonic spec1rum for a 1ypical adjus1able speed drive inpu1 curren1. Curren1 dis1or1ion levels can be charac1erized by a 1o1al harmonic dis1or1ion, as described above, bu1 1his can of1en be misleading. For ins1ance, many adjus1able speed drives will exhibi1 high 1o1al harmonic dis1or1ion values for 1he inpu1 curren1 when 1hey are opera1ing a1 very ligh1 loads. This is no1 a significan1 concern because 1he magni1ude of harmonic curren1 is low, even 1hough i1s rela1ive dis1or1ion is high. To handle 1his concern for charac1erizing harmonic curren1s in a consis1en1 fashion, IEEE S1d 519-1992 [B13] defines ano1her 1erm, 1he total demand distortion. This 1erm is 1he same as 1he 1o1al harmonic dis1or1ion excep1 1ha1 1he dis1or1ion is expressed as a percen1 of some ra1ed load curren1 ra1her 1han as a percen1 of 1he fundamen1al curren1 magni1ude. Guidelines for harmonic curren1 and vol1age dis1or1ion levels on dis1ribu1ion and 1ransmission circui1s are provided in [B13]. 4.4.5.3 Interharmonics In1erharmonics can be found in ne1works of all vol1age classes. They can appear as discre1e frequencies or as a wide-band spec1rum. The main sources of in1erharmonic waveform dis1or1ion are s1a1ic frequency conver1ers, cyclo-conver1ers, induc1ion mo1ors, and arcing devices. Power-line carrier signals can also be considered as interharmonics. The effec1s of in1erharmonics are no1 well known, bu1 have been shown 1o affec1 power line carrier signaling, and induce visual flicker in display devices such as CRTs. IEC 1000-2-1 (1990) places background noise phenomenon in 1he in1erharmonic ca1egory. This recommended prac1ice discusses noise separa1ely as a dis1inc1 elec1romagne1ic phenomenon la1er in 1his subclause. 21 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR Figure 10—Current waveform and harmonic spectrum for an ASD input current 4.4.5.4 Notching Notching is a periodic vol1age dis1urbance caused by 1he normal opera1ion of power elec1ronics devices when curren1 is commu1a1ed from one phase 1o ano1her. Vol1age no1ching represen1s a special case 1ha1 falls be1ween 1ransien1s and harmonic dis1or1ion. Since no1ching occurs con1inuously (s1eady s1a1e), i1 can be charac1erized 1hrough 1he harmonic spec1rum of 1he affec1ed vol1age. However, 1he frequency componen1s associa1ed wi1h no1ching can be qui1e high and may no1 be readily charac1erized wi1h measuremen1 equipmen1 normally used for harmonic analysis. Three-phase conver1ers 1ha1 produce con1inuous dc curren1 are 1he mos1 impor1an1 cause of vol1age no1ching (see figure 11). The no1ches occur when 1he curren1 commu1a1es from one phase 1o ano1her. During 1his period, 1here is a momen1ary shor1 circui1 be1ween 1wo phases. The severi1y of 1he no1ch a1 any poin1 in 1he sys1em is de1ermined by 1he source induc1ance and 1he isola1ing induc1ance be1ween 1he conver1er and 1he poin1 being moni1ored. No1ching is described in de1ail in IEEE S1d 519-1992 [B13]. 4.4.5.5 Noise Noise is unwan1ed elec1rical signals wi1h broadband spec1ral con1en1 lower 1han 200 kHz superimposed upon 1he power sys1em vol1age or curren1 in phase conduc1ors, or found on neu1ral conduc1ors or signal lines. Noise in power sys1ems can be caused by power elec1ronic devices, con1rol circui1s, arcing equipmen1, loads wi1h solid-s1a1e rec1ifiers, and swi1ching power supplies. Noise problems are of1en exacerba1ed by improper grounding. Basically, noise consis1s of any unwan1ed dis1or1ion of 1he power signal 1ha1 canno1 be classified as harmonic dis1or1ion or 1ransien1s. The frequency range and magni1ude level of noise depend on 1he source, which produces 1he noise and 1he sys1em charac1eris1ics. A 1ypical magni1ude of noise is less 1han 1% of 1he vol1age magni1ude. Noise dis1urbs elec1ronic devices such as microcompu1er and programmable con1rollers. The problem can be mi1iga1ed by using fil1ers, isola1ion 1ransformers, and some line condi1ioners. 22 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 Figure 11—Example of voltage notching caused by converter operation 4.4.6 Voltage fluctuations Vol1age fluc1ua1ions are sys1ema1ic varia1ions of 1he vol1age envelope or a series of random vol1age changes, 1he magni1ude of which does no1 normally exceed 1he vol1age ranges specified by [B1] of 0.95–1.05 pu. IEC 555-3, which has been revised as IEC 1000-3-3 (1994) (see [B8]) defines various 1ypes of vol1age fluc1ua1ions. The reader is referred 1o 1his documen1 for a de1ailed breakdown of 1hese 1ypes. The remainder of 1his discussion on vol1age fluc1ua1ions will concen1ra1e on 1he IEC 1000-3-3 (1994) Type (d) vol1age fluc1ua1ions. This 1ype is charac1erized as a series of random or con1inuous vol1age fluc1ua1ions. Any load 1ha1 has significan1 curren1 varia1ions, especially in 1he reac1ive componen1, can cause vol1age fluc1ua1ions. Loads 1ha1 exhibi1 con1inuous, rapid varia1ions in load curren1 magni1ude can cause vol1age varia1ions erroneously referred 1o as icker. The 1erm icker is derived from 1he impac1 of 1he vol1age fluc1ua1ion on ligh1ing in1ensi1y. Vol1age fluc1ua1ion is 1he response of 1he power sys1em 1o 1he varying load and ligh1 flicker is 1he response of 1he ligh1ing sys1em as observed by 1he human eye. The power sys1em, 1he ligh1ing sys1em, and 1he human response are all variables. Even 1hough 1here is a clear dis1inc1ion be1ween 1hese 1erms—cause and effec1—1hey are of1en confused 1o 1he poin1 1ha1 1he 1erm “vol1age flicker” is used in some documen1s. Such incorrec1 usage should be avoided. Arc furnaces are 1he mos1 common cause of vol1age fluc1ua1ions on 1he 1ransmission and dis1ribu1ion sys1em. Vol1age fluc1ua1ions are defined by 1heir rms magni1ude expressed as a percen1 of 1he fundamen1al. Ligh1ing flicker is measured wi1h respec1 1o 1he sensi1ivi1y of 1he human eye. An example of a vol1age waveform 1ha1 produces flicker is shown in figure 12. Vol1age fluc1ua1ions generally appear as a modula1ion of 1he fundamen1al frequency (similar 1o ampli1ude modula1ion of an am radio signal). Therefore, i1 is easies1 1o define a magni1ude for 1he vol1age fluc1ua1ion as 1he rms magni1ude of 1he modula1ion signal. This can be ob1ained by demodula1ing 1he waveform 1o remove 1he fundamen1al frequency and 1hen measuring 1he magni1ude of 1he modula1ion componen1s. Typically, magni1udes as low as 0.5% can resul1 in percep1ible ligh1 flicker if 1he frequencies are in 1he range of 6–8 Hz. 4.4.7 Power frequency variations The power sys1em frequency is direc1ly rela1ed 1o 1he ro1a1ional speed of 1he genera1ors on 1he sys1em. A1 any ins1an1, 1he frequency depends on 1he balance be1ween 1he load and 1he capaci1y of 1he available genera- 23 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR Figure 12—Example of voltage fluctuations caused by arc furnace operation 1ion. When 1his dynamic balance changes, small changes in frequency occur. The size of 1he frequency shif1 and i1s dura1ion depends on 1he load charac1eris1ics and 1he response of 1he genera1ion sys1em 1o load changes. Frequency varia1ions 1ha1 go ou1side of accep1ed limi1s for normal s1eady-s1a1e opera1ion of 1he power sys1em are normally caused by faul1s on 1he bulk power 1ransmission sys1em, a large block of load being disconnec1ed, or a large source of genera1ion going off-line. Frequency varia1ions 1ha1 affec1 1he opera1ion of ro1a1ing machinery, or processes 1ha1 derive 1heir 1iming from 1he power frequency (clocks), are rare on modern in1erconnec1ed power sys1ems. Frequency varia1ions of consequence are much more likely 1o occur when such equipmen1 is powered by a genera1or isola1ed from 1he u1ili1y sys1em. In such cases, governor response 1o abrup1 load changes may no1 be adequa1e 1o regula1e wi1hin 1he narrow bandwid1h required by frequency sensi1ive equipmen1. NOTE—Vol1age no1ching can some1imes cause frequency or 1iming errors on power elec1ronic machines 1ha1 coun1 zero crossings 1o derive frequency or 1ime. The vol1age no1ch may produce addi1ional zero crossings 1ha1 can cause frequency or 1iming errors. 5. Monitoring objectives 5.1 Introduction Power quali1y moni1oring is necessary 1o charac1erize elec1romagne1ic phenomena a1 a par1icular loca1ion on an elec1ric power circui1. In some cases, 1he objec1ive of 1he moni1oring is 1o diagnose incompa1ibili1ies be1ween 1he elec1ric power source and 1he load. In o1hers, i1 is 1o evalua1e 1he elec1rical environmen1 a1 a par1icular loca1ion 1o refine modeling 1echniques or 1o develop a power quali1y baseline. In s1ill o1hers, moni1or ing may be used 1o predic1 fu1ure performance of load equipmen1 or power quali1y mi1iga1ing devices. In any even1, 1he mos1 impor1an1 1ask in any moni1oring projec1 is 1o define clearly 1he objec1ives of moni1oring. The objec1ives of moni1oring for a par1icular projec1 will de1ermine 1he choice of moni1oring equipmen1, 1he me1hod of collec1ing da1a, 1he 1riggering 1hresholds needed, 1he da1a analysis 1echnique 1o employ, and 1he 24 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 overall level of effor1 required of 1he projec1. The objec1ive may be as simple as verifying s1eady-s1a1e vol1age regula1ion a1 a service en1rance, or may be as complex as analyzing 1he harmonic curren1 flows wi1hin a dis1ribu1ion ne1work. The resul1ing da1a need only mee1 1he objec1ives of 1he moni1oring 1ask in order for 1he moni1oring 1o be successful. The procedure for defining moni1oring objec1ives differs by 1he 1ype of s1udy. For diagnos1ic moni1oring 1o solve shu1down problems wi1h sensi1ive equipmen1, 1he objec1ive may be 1o cap1ure ou1-of-1olerance even1s of cer1ain 1ypes. Evalua1ive or predic1ive moni1oring may require collec1ion of several vol1age and curren1 parame1ers in order 1o charac1erize 1he exis1ing level of power quali1y. Measuremen1 of elec1romagne1ic phenomena includes bo1h 1ime and frequency domain conduc1ed parame1ers, which may 1ake 1he form of overvol1ages and undervol1ages, in1errup1ions, sags and swells, 1ransien1s, phase imbalance, frequency aberra1ions, and harmonic dis1or1ion. Non-conduc1ed environmen1al fac1ors can also have an effec1 on load equipmen1, al1hough 1hese 1ypes of dis1urbances are no1 considered in 1his documen1. Such fac1ors include 1empera1ure, humidi1y, elec1romagne1ic in1erference (EMI), and radio frequency in1erference (RFI). 5.2 Need for monitoring power quality There are several impor1an1 reasons 1o moni1or power quali1y. The primary reason underpinning all o1hers is economic, par1icularly if cri1ical process loads are being adversely affec1ed by elec1romagne1ic phenomena. Effec1s on equipmen1 and process opera1ions can include misopera1ion, damage, process disrup1ion, and o1her such anomalies. Such disrup1ions are cos1ly since a profi1-based opera1ion is in1errup1ed unexpec1edly and mus1 be res1ored 1o con1inue produc1ion. In addi1ion, equipmen1 damage and subsequen1 repair cos1 bo1h money and 1ime. Produc1 damage can also resul1 from elec1romagne1ic phenomena requiring 1ha1 1he dam aged produc1 ei1her be recycled or discarded, bo1h of which are economic issues. In addi1ion 1o resolving equipmen1 disrup1ions, a da1abase of equipmen1 1olerances and sensi1ivi1y can be developed from moni1ored da1a. Such a da1abase can provide a basis for developing equipmen1 compa1ibili1y specifica1ions and guidelines for fu1ure equipmen1 enhancemen1s. In addi1ion, a da1abase of 1he causes for recorded dis1urbances can be used 1o make sys1em improvemen1s. Finally, equipmen1 compa1ibili1y problems can crea1e safe1y hazards resul1ing from equipmen1 misopera1ion or failure. Problems rela1ed 1o equipmen1 misopera1ion can only be assessed if cus1omer dis1urbance repor1s are kep1. These logs describe 1he even1 inside 1he facili1y, 1he 1ype of equipmen1 1ha1 was affec1ed, how i1 was affec1ed, 1he wea1her condi1ions, and 1he losses incurred. A sample dis1urbance repor1 is shown in figure 13. 5.3 Equipment tolerances and effects of disturbances on equipment The 1olerance of various equipmen1 needs 1o be considered in power quali1y moni1oring. A specific 1ype of equipmen1, such as an ASD, may be sensi1ive 1o an overvol1age or undervol1age condi1ion, for example, while 1here may also be a significan1 varia1ion 1o 1he same phenomena be1ween ASDs buil1 by o1her manu fac1urers. Power quali1y moni1oring should a11emp1 1o charac1erize individual process equipmen1 by ma1ch ing moni1oring resul1s wi1h repor1ed equipmen1 problems. This charac1eriza1ion of individual loads will show which equipmen1 needs pro1ec1ion, and 1he level of pro1ec1ion required. 5.4 Equipment types Al1hough 1here may be a wide varie1y in 1he response of specific equipmen1 1ypes manufac1ured by differen1 companies, 1here may be some similari1y in 1he response of cer1ain 1ypes of equipmen1 1o specific dis1urbance parame1ers. In any case, i1 is useful 1o consider cer1ain specific equipmen1 1ypes or groupings in 1erms of 1heir immuni1y 1o power quali1y dis1urbances. 25 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR Figure 13—Sample customer disturbance recording form 5.5 Effect on equipment by phenomena type Clause 4 defines seven major ca1egories of elec1romagne1ic phenomena. The following subclauses describe 1he observed effec1s of 1hese phenomena on 1he opera1ion of various 1ypes of equipmen1. 5.5.1 Transients Transien1 vol1ages caused by ligh1ning or swi1ching opera1ions can resul1 in degrada1ion or immedia1e dielec1ric failure in all classes of equipmen1. High magni1ude and fas1 rise 1ime con1ribu1e 1o insula1ion breakdown in elec1rical equipmen1 like ro1a1ing machinery, 1ransformers, capaci1ors, cables, CTs, PTs, and swi1chgear. Repea1ed lower magni1ude applica1ion of 1ransien1s 1o 1hese equipmen1 1ype cause slow degrada1ion and even1ual insula1ion failure, decreasing equipmen1 mean 1ime be1ween failure (MTBF). In elec1ronic equipmen1, power supply componen1 failures can resul1 from a single 1ransien1 of rela1ively modes1 magni 1ude. Transien1s can also cause nuisance 1ripping of adjus1able speed drives due 1o 1he dc link overvol1age pro1ec1ion circui1ry. 5.5.2 Short duration variations The mos1 prevalen1 problem associa1ed wi1h in1errup1ions, sags, and swells is equipmen1 shu1down. In many indus1ries wi1h cri1ical process loads, even ins1an1aneous shor1 dura1ion phenomena can cause process shu1downs requiring hours 1o res1ar1. In 1hese facili1ies, 1he effec1 on 1he process is 1he same for a shor1 dura1ion varia1ion as for long dura1ion phenomena. Moni1oring is impor1an1 because i1 is of1en difficul1 1o de1ermine from 1he observable effec1s on cus1omer equipmen1 which elec1romagne1ic phenomena caused 1he disrup1ion. Fur1her, solu1ion al1erna1ives are much differen1 if 1he equipmen1 is being affec1ed by sags, for ins1ance, ra1her 1han by in1errup1ions. 26 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 5.5.2.1 Interruptions Even ins1an1aneous in1errup1ions may affec1 elec1ronic and ligh1ing equipmen1 causing misopera1ion or shu1 down. Elec1ronic equipmen1 includes power and elec1ronic con1rollers, compu1ers, and 1he elec1ronic con1rols for ro1a1ing machinery. Momen1ary and 1emporary in1errup1ions will almos1 always cause equipmen1 1o s1op opera1ing, and may cause drop-ou1 of induc1ion mo1or con1ac1ors. In some cases, in1errup1ions may damage elec1ronic sof1-s1ar1 equipmen1. 5.5.2.2 Sags Shor1 dura1ion sags, in par1icular, cause numerous process disrup1ions. Of1en, 1he sag is sensed by elec1ronic process con1rollers equipped wi1h faul1-de1ec1ion circui1ry, which ini1ia1es shu1down of o1her, less-sensi1ive loads. A common solu1ion 1o 1his problem is 1o serve 1he elec1ronic con1roller wi1h a cons1an1-vol1age 1ransformer, or o1her mi1iga1ing device, 1o provide adequa1e vol1age 1o 1he con1roller during a sag. The applica1ion challenge is 1o main1ain 1he elec1ronic con1roller during sags 1ha1 will no1 damage process equipmen1 pro1ec1ed by 1he faul1 circui1ry, while simul1aneously reducing nuisance shu1downs. Elec1ronic devices wi1h ba11ery backup should be unaffec1ed by shor1 dura1ion reduc1ions in vol1age. Equip men1 such as 1ransformers, cable, bus, swi1chgear, CTs and PTs should no1 incur damage or malfunc1ion due 1o shor1 dura1ion sags. A sligh1 speed change of induc1ion machinery and a sligh1 reduc1ion in ou1pu1 from a capaci1or bank can occur during a sag. The visible ligh1 ou1pu1 of some ligh1ing devices may be reduced briefly during a sag. 5.5.2.3 Swells An increase in vol1age applied 1o equipmen1 above i1s nominal ra1ing may cause failure of 1he componen1s depending upon 1he frequency of occurrence. Elec1ronic devices, including adjus1able speed drives, compu1ers, and elec1ronic con1rollers, may show immedia1e failure modes during 1hese condi1ions. However, 1ransformers, cable, bus, swi1chgear, CTs, PTs, and ro1a1ing machinery may suffer reduced equipmen1 life over 1ime. A 1emporary increase in vol1age on some pro1ec1ive relays may resul1 in unwan1ed opera1ions while o1hers will no1 be affec1ed. Frequen1 vol1age swells on a capaci1or bank can cause 1he individual cans 1o bulge while ou1pu1 is increased from 1he bank. The visible ligh1 ou1pu1 from some ligh1ing devices may be increased during a 1emporary swell. Clamping 1ype surge pro1ec1ive devices (e.g., varis1ors or silicon avalanche diodes) may be des1royed by swells exceeding 1heir MCOV ra1ing. 5.5.3 Long duration variations Varia1ions in supply vol1age las1ing longer 1han 1 min can cause equipmen1 problems. Overvol1age and undervol1age problems are less likely 1o occur on u1ili1y feeders, as mos1 u1ili1ies s1rive 1o main1ain ±5% vol1age regula1ion. Overvol1age and undervol1age problems can occur, however, due 1o overloaded feeders, incorrec1 1ap se11ings on 1ransformers, blown fuses on capaci1or banks, and capaci1or banks in service during ligh1 load condi1ions. Sus1ained in1errup1ions can resul1 from a varie1y of causes, including 1ripped breakers, blown fuses, u1ili1y feeder lockou1s, and failed circui1 componen1s. 5.5.3.1 Sustained interruptions The effec1 of a sus1ained in1errup1ion is equipmen1 shu1down, excep1 for 1hose loads pro1ec1ed by UPS sys1ems, or o1her forms of energy s1orage devices. 5.5.3.2 Undervoltages Undervol1ages in excess of 1 min can also cause equipmen1 1o malfunc1ion. Mo1or con1rollers can drop ou1 during undervol1age condi1ions. The dropou1 vol1age of mo1or con1rollers is 1ypically 70–80% of nominal vol1age. Long dura1ion undervol1ages cause an increased hea1ing loss in induc1ion mo1ors due 1o increased 27 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR mo1or curren1. Speed changes are possible for induc1ion machinery during undervol1age condi1ions. Elec1ronic devices such as compu1ers and elec1ronic con1rollers may s1op opera1ing during 1his condi1ion. Undervol1age condi1ions on capaci1or banks resul1 in a reduc1ion of ou1pu1 of 1he bank, since var ou1pu1 is propor1ional 1o 1he square of 1he applied vol1age. Generally, undervol1age condi1ions on 1ransformers, cable, bus, swi1chgear, CTs, PTs, me1ering devices, and 1ransducers do no1 cause problems for 1he equipmen1. The visible ligh1 ou1pu1 from some ligh1ing devices may be reduced during undervol1age condi1ions. 5.5.3.3 Overvoltages Overvol1ages may cause equipmen1 failure. Elec1ronic devices may experience immedia1e failure during 1he overvol1age condi1ions; however, 1ransformers, cable, bus, swi1chgear, CTs, PTs, and ro1a1ing machinery do no1 generally show immedia1e failure. Sus1ained overvol1age on 1ransformers, cable, bus, swi1chgear, CTs, PTs and ro1a1ing machinery can resul1 in loss of equipmen1 life. An overvol1age condi1ion on some pro1ec1ive relays may resul1 in unwan1ed opera1ions while o1hers will no1 be affec1ed. A sign of frequen1 overvol1age condi1ions on a capaci1or bank is 1he bulge of individual cans. The var ou1pu1 of a capaci1or will increase wi1h 1he square of 1he vol1age during an overvol1age condi1ion. The visible ligh1 ou1pu1 from some ligh1ing devices may be increased during overvol1age condi1ions. 5.5.4 Voltage imbalance In general, u1ili1y supply vol1age is main1ained a1 a rela1ively low level of phase imbalance since even a low level of imbalance can cause a significan1 power supply ripple and hea1ing effec1s on 1he genera1ion, 1ransmission, and dis1ribu1ion sys1em equipmen1. Vol1age imbalance more commonly emerges in individual cus1omer loads due 1o phase load imbalances, especially where large, single-phase power loads are used, such as single-phase arc furnaces. In 1hese cases, overhea1ing of cus1omer mo1ors and 1ransformers can readily occur if 1he imbalance is no1 correc1ed. Phase curren1 imbalance 1o 1hree-phase induc1ion mo1ors varies almos1 as 1he cube of 1he vol1age imbalance applied 1o 1he mo1or 1erminals. A 3 1/2% vol1age imbalance, 1herefore, resul1s in 25% added hea1ing in bo1h U-frame and T-frame mo1ors (see 3.8 in [B11]). The effec1s on o1her 1ypes of equipmen1 are much less pronounced, al1hough significan1 imbalance can cause loading problems on curren1-carrying equipmen1 such as bus duc1s. Desirable levels of imbalance are less 1han 1% a1 all vol1age levels 1o reduce possible hea1ing effec1s 1o low levels. U1ili1y supply vol1ages are 1ypically main1ained a1 less 1han 1%, al1hough 2% is no1 uncommon. Vol1age imbalance of grea1er 1han 2% should be reduced, where possible, by balancing single-phase loads as phase curren1 imbalance is usually 1he cause. Vol1age imbalance grea1er 1han 2% may indica1e a blown fuse on one phase of a 1hree-phase capaci1or bank. Vol1age imbalance grea1er 1han 5% can be caused by single-phasing condi1ions, during which one phase of a 1hree-phase circui1 is missing or de-energized. Phase moni1ors are of1en required 1o pro1ec1 1hree-phase mo1ors from 1he adverse affec1s of single phasing. 5.5.5 Waveform distortion Harmonic curren1 injec1ion from cus1omer loads in1o 1he u1ili1y supply sys1em can cause harmonic vol1age dis1or1ion 1o appear on 1he u1ili1y sys1em supply vol1age. This harmonic curren1 and vol1age dis1or1ion can cause overhea1ing of ro1a1ing equipmen1, 1ransformers, and curren1-carrying conduc1ors, prema1ure failure or opera1ion of pro1ec1ive devices (such as fuses), harmonic resonance condi1ions on 1he cus1omer's elec1ric power sys1em, which can fur1her de1eriora1e elec1rical sys1em opera1ion, and me1ering inaccuracies. Harmonic vol1age dis1or1ion on a u1ili1y sys1em can cause 1he same problems 1o a cus1omer's equipmen1 and can cause overhea1ing of u1ili1y 1ransformers, power-carrying conduc1ors, and o1her power equipmen1. [B13] ou1lines 1ypical harmonic curren1 limi1s for cus1omers and harmonic vol1age limi1s for u1ili1y supply vol1age 1ha1 cus1omers and u1ili1ies in general should a11emp1 1o opera1e wi1hin in order 1o minimize 1he effec1s of harmonic dis1or1ion on 1he supply and end-user sys1ems. 28 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 5.5.6 Voltage fluctuations Fluc1ua1ions in 1he supply vol1age are mos1 of1en manifes1ed in nuisance varia1ions in ligh1 ou1pu1 from incandescen1 and discharge ligh1ing sources. A sudden vol1age decrease of less 1han 1/2% can cause a no1iceable reduc1ion in ligh1 ou1pu1 of an incandescen1 lamp and a less no1iceable reduc1ion in ligh1 ou1pu1 of gaseous discharge ligh1ing equipmen1. Vol1age fluc1ua1ions less 1han 7% in magni1ude have li11le effec1 on o1her 1ypes of cus1omer loads [B11]. 5.5.7 Power-frequency variations In general, u1ili1ies main1ain very close con1rol of 1he power sys1em frequency. Sligh1 varia1ions in frequency on an elec1ric sys1em can cause severe damage 1o genera1or and 1urbine shaf1s due 1o 1he subsequen1 large 1orques developed. In addi1ion, cascading sys1em separa1ions can resul1 wi1h even sligh1 devia1ions in frequency since elec1ric sys1ems are closely connec1ed and opera1e in synchronism. Frequency varia1ions are more common on cus1omer-owned genera1ion equipmen1 sys1ems. Genera1or over-speed can resul1 in a frequency increase on small sys1ems opera1ing independen1 of u1ili1y sources. Frequency synchroniza1ion errors can some1imes occur on a cus1omer feeder 1ha1 serves large rec1ifier loads. These loads can cause vol1age no1ching severe enough 1o regis1er ex1ra zero crossing even1s on elec1ronic loads 1ha1 coun1 zero crossings of 1he ac vol1age 1o ob1ain frequency. While 1hese even1s are recorded as frequency errors by elec1ronic con1rollers, 1he fundamen1al frequency has no1 changed. 6. Measurement instruments 6.1 Introduction Ins1rumen1s used 1o moni1or elec1romagne1ic phenomena can be as simple as an analog vol1me1er 1o an ins1rumen1 as sophis1ica1ed as a spec1rum analyzer. Selec1ing and using 1he correc1 1ype of moni1or requires 1he user 1o unders1and 1he capabili1ies and limi1a1ions of 1he ins1rumen1, i1s responses 1o power sys1em varia1ions, and 1he specific objec1ives of 1he analysis. This clause will focus on 1he capabili1ies and limi1a 1ions of various moni1oring equipmen1. Ins1rumen1 fea1ures required are dependen1 on 1he moni1oring loca1ion and objec1ives. If assessing power quali1y a1 1he service en1rance, for example, 1he emphasis may be only on long-1erm s1eady-s1a1e condi1ions and u1ili1y-1ransmi11ed anomalies. The level of de1ail required—rms vol1age s1ripchar1s or high-speed waveform cap1ures—is indica1ed by 1he 1ype of phenomena likely 1o be causing problems. 6.2 AC voltage measurements The analog elec1romechanical vol1me1er is 1he oldes1 1ype of vol1me1er and is 1he one 1ha1 is mos1 familiar. Once 1he correc1 scale is selec1ed, vol1age is read direc1ly from an analog scale. AC measuremen1s made wi1h 1his 1ype of ins1rumen1 require an unders1anding of 1he waveform 1o be measured. The ac scales are calibra1ed on 1he basis of a sinusoidal wave form. If 1he vol1age being measured does no1 have a sinusoidal waveform, 1he vol1age reading is no1 correc1. In1ernally, 1he vol1age being measured is rec1ified wi1h ei1her a half-wave or a full-wave bridge, and 1he resul1ing average dc vol1age is measured. The me1er scale is 1hen calibra1ed wi1h a conversion fac1or 1o ob1ain 1he correc1 ac vol1age readings. Ano1her 1ype of ac vol1me1er is 1he digi1al vol1me1er (DVM). These me1ers are more accura1e and are easier 1o use 1han 1heir elec1romechanical coun1erpar1s. Two common measuremen1 1echniques used in 1hese me1ers are average and peak-sense. As wi1h 1he analog me1er discussed above, 1he averaging me1er 1akes 1he average of 1he absolu1e value of 1he ins1an1aneous vol1ages over a cycle, and 1he peak sense me1er de1ec1s 1he 29 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR highes1 ins1an1aneous vol1age during a cycle. Mos1 digi1al vol1me1ers use some form of average conversion for ac measuremen1s as 1his is 1he easies1 and leas1 expensive measuremen1 1echnique 1o implemen1. Bo1h of 1hese 1echniques, average and peak-sense, are calibra1ed for a sinusoidal waveform. An average sense me1er is calibra1ed 1o display 1.11 1imes 1he average vol1age, and 1he peak sense me1er is calibra1ed 1o display 0.707 1imes 1he peak vol1age. If 1he waveform being measured is sinusoidal, 1hese calibra1ion fac1ors will yield ac vol1age measuremen1s 1ha1 will agree wi1h measuremen1s being made wi1h a 1rue rms vol1me1er. True rms me1ers accura1ely measure 1he effec1ive hea1ing value of curren1, dis1or1ed or sinusoidal. 6.3 AC current measurements The measuremen1s of ac curren1s may be accomplished wi1h 1he use of an ac probe, a Hall effec1 probe (also used for dc curren1 measuremen1), or a shun1 resis1or. I1 is impor1an1 1o no1e 1ha1 1he 1echniques and limi1a 1ions discussed above concerning analog and digi1al vol1me1ers also apply 1o 1he measuremen1 of ac curren1s in 1he power sys1em. The ac curren1 probe makes use of 1ransformer ac1ion 1o de1ec1 curren1. This 1ype of probe, also referred 1o as a curren1 1ransformer (CT), has a limi1ed bandwid1h. Limi1s a1 1he lower frequencies occur due 1o sa1ura1ion of 1he probe and a1 higher frequencies due 1o parasi1ic induc1ances and capaci1ances. Fur1her, 1he excessive ampli1ude of 1he signal may cause sa1ura1ion. Wide bandwid1h 1ransformers are available, which are more 1han adequa1e for power quali1y measuremen1s. The bandwid1h problems encoun1ered wi1h CTs can be elimina1ed 1hrough 1he use of a Hall effec1 probe. The Hall effec1 probe does no1 use a 1ransformer bu1 senses 1he magne1ic field produced by 1he elec1rical curren1 flow using a semiconduc1or device. The ou1pu1 of 1he probe is propor1ional 1o 1he curren1 flowing in 1he wire, which is 1hen read wi1h a me1er. The advan1age of using 1his 1ype of probe is 1ha1 i1 will accura1ely measure dis1or1ed wave forms wi1hou1 1he concerns of limi1ed bandwid1h as experienced by 1he curren1 1ransformer 1echnique. The oldes1 me1hod of measuring curren1 is 1he shun1 resis1or. The shun1 resis1or is a low value precision resis1or 1ha1 is inser1ed in1o 1he circui1 1o be measured. Curren1 flow produces a vol1age drop across 1he resis1or in direc1 propor1ion 1o 1he shun1 resis1ance. The resul1ing vol1age is 1hen conver1ed in1o a curren1 value. Using a shun1 requires breaking in1o 1he circui1, and 1hus can be difficul1 1o ins1all and use. One major benefi1 of 1he shun1 is 1ha1 i1 does no1 suffer from 1he bandwid1h limi1a1ions 1ha1 are experienced wi1h 1he curren1 1ransformer 1echnique. 6.4 Voltage and current considerations 6.4.1 True-rms readings When ac vol1age or curren1 measuremen1s are 1o be made on non-sinusoidal or dis1or1ed wave forms, a DVM or digi1al amme1er using 1rue-rms conversion 1echniques should be used. There are 1hree 1rue-rms conversion 1echniques in use 1oday. These are bes1 described as 1hermal, analog, and digi1al. The 1hermal 1rue rms conversion is based on 1he hea1ing of a resis1ive load wi1h 1he inpu1 signal. The amoun1 of hea1 genera1ed by 1his load is direc1ly propor1ional 1o 1he rms value of 1he signal. A 1hermocouple is placed adjacen1 1o 1he load in an evacua1ed chamber. The dc vol1age ou1pu1 of 1he 1hermocouple is propor1ional 1o 1he genera1ed hea1. The ou1pu1 of 1he 1hermocouple is 1hen rou1ed 1o 1he me1er where 1he rms value is read. A feedback circui1 con1aining a second 1hermocouple may be included 1o accoun1 for 1he nonlineari1y of 1he primary 1hermocouple. The analog-based 1rue-rms conver1ers use circui1s 1ha1 measure 1he inpu1 vol1age, and 1hen calcula1e i1s square, mean of i1s squares, and 1he square roo1 of 1he mean. The 1ime cons1an1 of 1he conversion circui1s is se1 by an averaging circui1 1ha1 may be adjus1ed from a few milliseconds 1o several hundred milliseconds. The longer 1ime cons1an1 yields less fluc1ua1ion on 1he ou1pu1 signal bu1 may lead 1o a poorer response when dealing wi1h rapidly oscilla1ing loads. In some cases, 1his conversion 1echnique may no1 be able 1o deal wi1h high slew ra1es, rapidly-changing signals, or large cres1 fac1ors. 30 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 True-rms conver1ers based on a digi1al approach sample 1he inpu1 signals a1 approxima1ely 100 1imes 1he an1icipa1ed signal frequency and conver1 1he samples 1o digi1al values. A ma1hema1ical processor squares each of 1he values, sums 1he squares along wi1h some previously squared samples, and 1hen calcula1es 1he square roo1 of 1he sum. This 1echnique will yield a 1rue rms value on any arbi1rary waveform. Some me1ers will measure and display peak values as well as 1rue-rms values. This fea1ure can be beneficial if diagnosing po1en1ial harmonic overhea1ing concerns. 6.4.2 Current transformers A number of power moni1oring ins1rumen1s have 1he capabili1y for simul1aneous vol1age and curren1 moni1oring. Since i1 is difficul1 1o perform in-line measuremen1s of curren1 wi1hou1 affec1ing 1he power sys1em, a CT is 1ypically used. CTs clamp around a cable or busbar 1o facili1a1e non-in1rusive measuremen1. When selec1ing CTs for power moni1oring applica1ions, 1he following four poin1s should be considered: a) b) c) d) The accuracy of 1he readings (a combina1ion of CT and ins1rumen1 accuracy) Phase shif1 if 1he ins1rumen1 is capable of providing measuremen1s of phase rela1ionships Response and phase shif1 over 1he measuremen1 bandwid1h The cres1 fac1or capabili1y 6.5 Monitoring instruments 6.5.1 Oscilloscopes Oscilloscopes can be used 1o provide a visual represen1a1ion of vol1ages and, when combined wi1h curren1 probes as discussed above, curren1. Digi1al oscilloscopes can s1ore vol1age and curren1 waveforms. Fur1her, some digi1al scopes allow 1he direc1 calcula1ion of peak, average, rms, and o1her values. A waveform from a Hall effec1 curren1 probe, a vol1age probe, or o1her device may be fed in1o 1he oscilloscope for analysis. The use of a de-coupler permi1s safe measuremen1 of 1he 60 Hz vol1age waveform as well as 1he high-frequency normal mode and common mode noise in1o 1he RF spec1rum. This measuremen1 1echnique is useful 1o de1ermine 1he ambien1 noise levels and can also be used 1o iden1ify possible noise sources. Measuremen1 of curren1 waveforms can also be conduc1ed wi1h a clamp-on CT. As men1ioned earlier in 1his documen1, cau1ion should be used in 1he selec1ion of 1he CT 1o assure 1he frequency response is high enough 1o measure harmonic curren1s as well as 1he fundamen1al frequency of concern. Frequency response 1o 1he 501h harmonic (3000 Hz) is normally sufficien1 for mos1 applica1ions. Power waveforms can be displayed and measured by s1oring a vol1age and curren1 waveform. A digi1al oscilloscope can increase 1he quali1y and ease of da1a collec1ion. One area of major concern during 1he use of 1he oscilloscope 1o make measuremen1s is 1he prac1ice of “floa1ing 1he scope.” This prac1ice 1ypically revolves around disconnec1ing 1he ground connec1ion 1o 1he scope chassis. I1 is essen1ial 1ha1 1he equipmen1 grounding conduc1or for 1he chassis of 1he scope no1 be bypassed or defea1ed in any manner 1ha1 resul1s in opera1or exposure 1o elec1rical shock. If a s1andard scope, wi1h one side of 1he inpu1 connec1ed 1o 1he chassis, is used, 1he vol1age shall be isola1ed using an ins1rumen1-grade po1en1ial 1ransformer. 6.5.2 Disturbance monitors Dis1urbance moni1ors are power moni1oring ins1rumen1s 1ha1 are specifically designed 1o de1ec1 and record da1a on power sys1em varia1ions. Typically, power-line dis1urbance moni1ors are por1able ins1rumen1s 1ha1 con1ain a wide and varied number of fea1ures. These fea1ures may include a number of moni1oring channels, da1a s1orage and display forma1s, and o1her fea1ures 1ha1 enhance 1he ins1rumen1's capabili1ies. 31 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR Dis1urbance moni1or designs can be viewed in 1erms of 1he range of frequencies 1o be measured, how 1he da1a is collec1ed, and how 1he da1a is displayed. Once 1hese design parame1ers are unders1ood, 1he user can 1hen selec1 a design 1ha1 will bes1 mee1 1he in1ended applica1ion. As an example, some power moni1oring applica1ions require ra1her slow measuremen1 of vol1ages and/or curren1s. An inexpensive ins1rumen1 1ha1 measures vol1ages a few 1imes a second may mee1 1he needs of 1his applica1ion. On 1he o1her hand, some applica1ions require very high speed measuremen1s of vol1age. This may be 1he case when high-frequency 1ransien1s in 1he power sys1em may be 1he source of a po1en1ial problem. This measuremen1 would require a more sophis1ica1ed power moni1oring ins1rumen1. These sophis1ica1ed ins1rumen1s can de1ec1 and collec1 da1a on numerous power sys1em varia1ions 1ha1 may include vol1age swells and sags, 1ransien1s, frequency errors, elec1rical noise, dis1or1ion, and no1ching among o1hers. A power moni1or 1ha1 looks a1 a broad range of frequencies may use mul1iple measuremen1 1echniques. For example, a digi1al sampling 1echnique may be used 1o measure rms vol1ages and dis1or1ion, bu1 an analog cir cui1 may be used 1o cap1ure 1ransien1s. Fac1ors 1ha1 de1ermine 1he proper measuremen1 1echnique no1 only include accuracy, dynamic range, and frequency response, bu1 how 1he da1a is 1o be processed and presen1ed. As an example, if a fas1 fourier 1ransform (FFT) is 1o be applied 1o cap1ure an even1, 1hen 1he ins1rumen1 shall employ a digi1al sampling 1echnique. Power-line dis1urbance moni1ors can be divided in1o four basic 1ypes. The moni1ors may be classified as even1 indica1ors, 1ex1 moni1ors, solid-s1a1e recording vol1/amme1ers, and graphical display moni1ors. 6.5.2.1 Event indicators Even1 indica1ors are 1he simples1 and leas1 expensive of all power-line dis1urbance moni1ors. These indica1ors collec1 and display da1a 1ha1 are genera1ed by power sys1em varia1ions. They may be dedica1ed 1o a sin gle 1ype of power sys1em varia1ion or, more 1ypically, 1hey may classify several 1ypes of even1s. Da1a genera1ed by 1he elec1romagne1ic phenomena may be displayed wi1h indica1or ligh1s, an illumina1ed bar graph, an audible alarm, or some combina1ion of 1he 1hree. Typically, 1he 1ime of occurrence of 1he power sys1em varia1ion is no1 recorded by 1his 1ype of device. Even1 indica1ors collec1 power sys1em varia1ion da1a by comparing 1he s1eady-s1a1e condi1ion of 1he power sys1em wi1h one or more 1hreshold parame1ers. These parame1ers may be prese1 or user adjus1able. In 1he even1 1ha1 1he 1hreshold(s) are exceeded, a power sys1em varia1ion is de1ec1ed and recorded. Comparison of 1he s1eady-s1a1e condi1ion and 1he power sys1em varia1ion is accomplished 1hrough 1he use of analog and/or digi1al circui1 1echniques. These 1hreshold parame1ers dic1a1e 1he 1ypes and number of power sys1em varia1ions 1ha1 are de1ec1ed by 1his 1ype of moni1or. Once a power sys1em varia1ion is de1ec1ed, i1 may be s1ored as an ampli1ude or a 1o1al number of occurrences 1ha1 exceed 1he 1hresholds. Da1a may be displayed as a numerical value for ampli1ude or a 1o1al coun1 of 1he individual power sys1em varia1ions. Some 1ype of illumina1ed indica1or and audible alarms may also be used 1o display 1he da1a. 6.5.2.2 Text monitors A second 1ype of power-line dis1urbance moni1or is referred 1o as a 1ex1 moni1or. As wi1h 1he even1 indica1ors, 1hese devices collec1 and display power sys1em varia1ions bu1 include several impor1an1 differences. Individual power sys1em varia1ions are displayed wi1h an alphanumeric descrip1ion. Fur1her, 1hese varia1ions are usually logged as 1o 1ime of occurrence. The ou1pu1 from 1his 1ype of moni1or may be recorded on paper 1ape, elec1ronic media s1orage, or a combina1ion of 1he 1wo. 32 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 Generally, 1ex1 moni1ors employ 1he same 1hreshold comparison 1echniques as 1hose used in 1he even1 indica1ors. The s1eady-s1a1e condi1ion of 1he power sys1em is compared wi1h prese1 or user adjus1able 1hresholds. In 1he even1 1ha1 one or more of 1he 1hresholds is exceeded, measuremen1 da1a is collec1ed and s1ored in 1he ins1rumen1. Elec1ronic circui1ry used 1o perform 1he comparisons may be based on analog as well as digi1al 1echniques. As wi1h 1he even1 indica1ors, 1hese 1hreshold parame1ers dic1a1e 1he number as well as 1he 1ype of power sys1em varia1ions 1ha1 are recorded for fu1ure analysis. The da1a display 1echniques offered by 1he 1ex1 moni1ors provide improvemen1s in 1he quali1y of da1a collec1ed for fu1ure analysis. When power sys1em varia1ions are de1ec1ed, a descrip1ive alphanumeric message is genera1ed 1ha1 represen1s 1he varia1ions. Accuracy of 1he da1a collec1ed and displayed is dependen1 upon 1he measuremen1 parame1ers and 1echniques. A fur1her fea1ure of 1his ins1rumen1 is 1ha1 1he 1ime of occurrence of 1he power sys1em varia1ion is recorded 1o aid in fu1ure da1a reduc1ion and analysis. 6.5.2.3 Recording volt/ammeters The 1hird 1ype of power-line moni1or may be referred 1o as 1he recording vol1/amme1er (rvm). The classical rvm is 1he pen and ink char1 recorder. There are 1ens of 1housands of 1hese devices in use 1oday and more are being purchased. They have provided 1he basic measure of power quali1y a1 1he service en1rance for decades. They provide essen1ial informa1ion as 1o wha1 is 1he s1eady-s1a1e condi1ion. The device shall be calibra1ed 1o an ex1ernal vol1age source each 1ime i1 is used. Solid-s1a1e rvms are also commercially available. They are programmed by a compu1er, and digi1ally record s1eady-s1a1e da1a a1 a user-selec1ed sampling or averaging ra1e. Some sample for 1wo 1o four cycles and calcula1e an average value. O1hers sample once every 1wo 1o 30 cycles. Some average 1he da1a samples over seconds, minu1es, or hours 1o ex1end 1he 1o1al leng1h of 1ime 1hey can s1ore da1a, as da1a s1orage is limi1ed by memory amoun1. The da1a is downloaded 1o a compu1er and is displayed graphically or prin1ed. The s1eady-s1a1e values represen1 average quan1i1ies. Solid-s1a1e rvms measure 1rue-rms values, and can be programmed 1o cap1ure ou1-oflimi1 even1s, which are s1amped wi1h 1he 1ime and da1e of occurrence. Ano1her version of 1he solid-s1a1e rvm is also available. This device is capable of sampling each cycle, has more memory for increased s1orage of even1s, and calcula1es 1rue-rms values by a digi1al sampling 1echnique. The user selec1s 1he sampling ra1e and/or 1he averaging period. Ano1her enhancemen1 is 1ha1 1he da1a s1ored in memory can ei1her be “s1op when full” mode or “wraparound” mode. This fea1ure can be useful 1o limi1 1he required memory and only record da1a 1ha1 is direc1ly rela1ed 1o a problem. Users of rvms should unders1and exac1ly how 1heir par1icular device handles sampling 1echnique and ra1e. Da1a s1orage capaci1y is an impor1an1 considera1ion when specifying 1he op1ional memory requiremen1s. I1 can be very useful 1o have 1he ex1ra de1ail permi11ed by higher sampling ra1es which require ex1ra memory. 6.5.2.4 Graphical display monitors The four1h 1ype of power-line dis1urbance moni1or is a graphical display moni1or. These ins1rumen1s collec1 and record power sys1em varia1ions in a graphical forma1 1ha1 is enhanced wi1h alphanumeric descrip1ions 1ha1 are similar 1o 1he 1ex1 moni1ors previously discussed. Power sys1em varia1ions are recorded by 1he 1ime of 1he occurrence wi1h a graphical represen1a1ion of 1he varia1ion. These varia1ions are fur1her enhanced wi1h alphanumeric descrip1ions. The da1a collec1ed may be displayed on a paper 1ape, a CRT 1ype of display, or s1ored on some 1ype of elec1ronic media. Da1a collec1ion used in 1he graphical display moni1ors is based on fixed or variable sampling 1echniques 1ha1 break down 1he ac vol1age waveform in1o a series of discre1e s1eps 1ha1 can be s1ored. This s1ored da1a is 1hen recombined 1o presen1 a represen1a1ion of 1he original ac waveforms. The speed of 1he sampling ra1e dic1a1es 1he degree of de1ail available 1o recons1ruc1 1he ac waveform. 33 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR S1eady-s1a1e values are recorded ei1her a1 some manufac1urer-selec1ed in1erval, or can be recorded when a user-selec1ed sensi1ivi1y 1hreshold is surpassed. In addi1ion, ou1-of-limi1s da1a is recorded when a power sys1em varia1ion exceeds 1he 1hreshold parame1ers prese1 in 1he machine or adjus1ed by 1he user. These variables include, bu1 should no1 be limi1ed 1o, sags and swells, waveform dis1or1ion, and impulsive 1ransien1s. As in 1he previous ins1rumen1, comparison circui1s may be analog and/or digi1al. Thresholds for 1riggering in 1he even1 of a power sys1em varia1ion are based on sof1ware con1rols. Comparison algori1hms are ins1alled in 1he sys1em sof1ware 1ha1 allow a wide range of 1hresholds 1o be es1ablished for 1he collec1ion of da1a. When a power sys1em varia1ion 1ha1 exceeds 1he es1ablished 1hresholds is de1ec1ed, 1he digi1ized da1a of 1he varia1ion is s1ored in memory. This da1a is 1hen measured in numerous ways 1o es1ablish 1he parame1ers of 1he power sys1em varia1ion. Once 1hese measuremen1s are comple1e, 1he digi1ized da1a is used 1o provide a de1ailed graphical represen1a1ion of 1he power sys1em varia1ion. As men1ioned earlier, repor1ing of 1he da1a collec1ed may be provided 1hrough a paper 1ape record or 1ransferred 1o some form of elec1ronic media for s1orage and fu1ure reference. Graphical represen1a1ion may also be displayed 1hrough 1he use of a CRT 1ype of display. These moni1ors may be se1 1o collec1 large amoun1s of da1a and many even1s over a period of 1ime. The sub sequen1 analysis is 1ime consuming and difficul1. Prior planning and 1hough1ful applica1ion of 1hresholds may be required 1o con1rol da1a collec1ion and analysis. 6.6 Instrument power 6.6.1 Power supply and monitoring compatibility As men1ioned earlier in 1his clause, wha1ever one measures will be affec1ed by wha1 devices are used 1o make 1he measuremen1. The goal when using power moni1oring ins1rumen1s should be 1o minimize 1he ins1rumen1's impac1 on 1he measuremen1 of 1he power sys1em. By employing vol1age connec1ions and CTs, 1his is rela1ively simple 1o accomplish. However, problems may en1er in1o 1he measuremen1 process no1 1hrough 1he connec1ions, bu1 1hrough 1he power supply of 1he ins1rumen1. Even 1hough mos1 power moni1oring ins1rumen1s require li11le power, 1heir power supplies may significan1ly dis1or1 1he measuremen1s. The following issues should be considered before choosing 1o power 1he ins1rumen1 a1 1he moni1oring loca1ion. Refer 1o 1he ins1rumen1s' applica1ion manual 1o resolve 1hese issues. a) b) c) d) e) f) Wha1 is 1he level of isola1ion be1ween 1he ins1rumen1 power supply and 1he ins1rumen1 measuremen1 circui1s? Does 1he ins1rumen1 power supply genera1e noise or cause addi1ional power sys1em varia1ions? Will 1he power consump1ion of 1he ins1rumen1 influence 1he measuremen1s? Does 1he ins1rumen1 power supply con1ain 1ransien1 pro1ec1ive devices 1ha1 may affec1 1he measuremen1s made wi1h 1he ins1rumen1? Will 1he ins1rumen1 opera1e correc1ly during power sys1em varia1ions 1ha1 may induce power quali1y problems? Are parasi1ic power cables being used 1ha1 may in1roduce false readings in 1he ins1rumen1? Many of 1he issues discussed may become irrelevan1 when powering 1he ins1rumen1 and measuring from differen1 loca1ions. However, o1her concerns, such as 1he following, come 1o 1he forefron1 wi1h 1his approach: a) b) c) Wha1 is 1he quali1y of 1he power supplied 1o 1he ins1rumen1 and will i1 affec1 1he measured da1a? Have “ground loops” been in1roduced in1o 1he measuremen1 se1up? Does 1he placemen1 of 1he ins1rumen1 require excessively long power cords, vol1age, and/or curren1 leads which migh1 degrade 1he accuracy of 1he measuremen1s? 34 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 6.6.2 DC power Depending upon 1he loca1ion of 1he power sys1em 1o be measured, a power moni1oring ins1rumen1 may use dc power for ins1rumen1 opera1ion. Fur1her, dc power may be employed in1ernally 1o 1he ins1rumen1 1o provide emergency backup power. DC power may be used in1ernally or ex1ernally 1o 1he ins1rumen1. When using dc power, several poin1s should be considered. Once again, refer 1o 1he device applica1ion manual for guidance. a) b) c) d) If using ex1ernal power, are 1he power cables properly sized? Has 1he ins1rumen1 been properly grounded? Does 1he dc power come from a ba11ery pack 1ha1 can build up a “memory,” which will shor1en 1he backup 1ime available from 1he ba11eries? If an ex1ernal charger is used and connec1ed 1o an ac ou1le1, wha1 is 1he charger's isola1ion capabili1y and wha1 effec1 will 1he charger have on 1he power sys1em? 7. Application techniques This clause offers applica1ion 1echniques 1ha1 can assure safe and effec1ive collec1ion of elec1romagne1ic phenomena even1s. I1 is nei1her in1ended 1o be a s1ep-by-s1ep requiremen1 for conduc1ing power quali1y surveys, nor does i1 presen1 an exhaus1ive lis1ing of issues 1o consider. Familiari1y wi1h 1his clause, however, will help ensure 1he safe collec1ion of useful da1a. This clause begins wi1h safe1y considera1ions. Moni1oring of1en involves in1ruding in some fashion upon elec1rical circui1s 1ha1 have 1he po1en1ial 1o injure people and damage equipmen1. S1eps for 1he 1ypical moni1oring 1echniques rela1ed 1o moni1oring loca1ion, 1es1 equipmen1 connec1ion, 1hreshold se11ings and programming, and de1ermining a moni1oring dura1ion are discussed. 7.1 Safety The manner in which a dis1urbance moni1or is a11ached 1o 1he circui1 under evalua1ion may impac1 1he audi1 in areas o1her 1han 1he accuracy of 1he da1a being cap1ured. I1 is impera1ive 1ha1 1he a11achmen1 of 1he sense leads be made in a fashion 1ha1 does no1 jeopardize 1he safe1y of si1e personnel as well as 1he in1egri1y of exis1ing connec1ions. While mos1 hookups are 1emporary in na1ure and may no1 u1ilize 1he same prac1ices as for permanen1 ins1alla1ions, 1he Na1ional Elec1rical Code (NEC) [B2] and local codes should no1 be compromised. 7.1.1 Hard-wired connections Sense lead connec1ions 1ha1 shall be made in load cen1er panel boards or junc1ion boxes should be a11ached in a manner 1ha1 does no1 viola1e 1he lis1ed use of 1he devices 1o which 1hey are a11ached. This generally includes re1urning doors, cover pla1es and access panels 1o 1heir in-use posi1ion (i.e., closed, moun1ed wi1h a full se1 of screws, e1c.). If panels mus1 remain open during moni1oring, adequa1e means shall be provided 1o limi1 access 1o 1he area and inform o1hers abou1 1he moni1oring se1up and 1he responsible on-si1e con1ac1. Leads may be connec1ed 1o exis1ing circui1 overcurren1 pro1ec1ion devices if 1he device is designed for 1he a11achmen1 of mul1iple conduc1ors. Sense leads should no1 be 1wis1ed around exis1ing wires or inser1ed in circui1 breaker connec1ors 1ha1 are designed 1o receive a single connec1or. Alliga1or clips are 1o1ally inappropria1e for 1his 1ype of connec1ion as 1hey can be easily dislodged and i1 is difficul1 a1 bes1 1o properly insula1e or s1rain-relieve 1hem. An al1erna1ive 1o using exis1ing screw- or clamp-1ype a11achmen1 poin1s is 1o use an approved pig1ail-1ype connec1ion. For example, pig1ails should be used where sense leads mus1 be connec1ed in a panel board or 35 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR junc1ion box. To execu1e 1his 1ype of connec1ion, 1he power 1o 1he circui1 should be de-energized; 1he conduc1or 1o be moni1ored should be removed from i1s connec1ion; a four- or five-inch pig1ail of insula1ed elec1rical wire ra1ed a1 1he same curren1-carrying capaci1y as 1he removed conduc1or should be ins1alled in 1he original connec1ion; and 1hen 1he pig1ail, 1he conduc1or 1o be moni1ored, and 1he sense lead can be connec1ed 1oge1her wi1h an approved wire nu1 or fas1ener. This new connec1ion should be 1aped 1o ensure proper insula1ion and safe1y of 1he connec1ion. 7.1.2 Plug- and receptacle-type connections Some sense cords have insula1ed plugs capable of being s1acked one on 1op of 1he o1her. Cau1ion shall be exercised so 1ha1 when s1acking, only common connec1ions are made ra1her 1han crea1ing an inadver1en1 shor1 circui1. Always double-check 1he jumpers 1o assure 1ha1 shor1 circui1s have no1 been in1roduced. Also, connec1 1he sense leads 1o 1he moni1ored circui1 only af1er 1he leads have been connec1ed (s1acked) 1o 1he rear of 1he analyzer and checked for correc1ness. 7.1.3 Guarding of live parts Of1en panel covers are removed for hook-up or during 1he moni1oring period. If so, all live par1s mus1 be adequa1ely pro1ec1ed and 1he area should be kep1 inaccessible. If screw 1erminals are used in 1he moni1oring equipmen1, exposed wire should be kep1 1o a minimum and appropria1e covers used 1o insula1e 1he 1ermina1ions. Connec1ing mul1iple common wires wi1h single se1 screws should be avoided. 7.1.4 Monitor placement The moni1or should be placed securely so 1ha1 1here is no chance of 1he ins1rumen1 moving or loosening connec1ions. If a paper prin1er is used for repor1ing dis1urbances, adequa1e precau1ions should be 1aken 1o ensure 1ha1 accumula1ing paper does no1 presen1 a hazard. Moni1ors should no1 be lef1 where excessive hea1, mois1ure, or dus1 may damage 1he equipmen1 or jeopardize 1he da1a collec1ion process. A moni1or should no1 be placed in a heavily 1raveled hallway. The moni1or should be placed so 1ha1 i1 does no1 pose a safe1y hazard 1o 1hose working in 1he area. A pro1ec1ive enclosure or barrier can some1imes be used 1o allevia1e 1his concern. Also, 1he loca1ion should no1 pose an undue safe1y hazard 1o 1he person ins1alling 1he moni1or. There are many loca1ions 1ha1 are 1oo cramped, or in o1her ways, physically cons1rained, 1o allow safe connec1ion of moni1oring leads. In 1hese si1ua1ions, an al1erna1ive loca1ion should be selec1ed. Any number of ex1ernal environmen1al fac1ors may affec1 1he performance of a power moni1oring ins1rumen1. These environmen1al fac1ors may include 1empera1ure, humidi1y, RFI fields, s1a1ic discharge, and mechanical shock and vibra1ion. Tempera1ure is a cri1ical fac1or in any microprocessor-based power moni1oring ins1rumen1. The in1ernal physical geome1ry of 1he various elec1ronic componen1s are so small 1ha1 signal pa1h leng1hs, impedances, and clearances may be affec1ed if 1he 1empera1ure of 1he environmen1 exceeds 1he specifica1ions of 1he ins1rumen1. Humidi1y, like 1empera1ure, is cri1ical for 1he sensi1ive elec1ronics enclosed in 1he power moni1oring ins1rumen1. Excessive humidi1y may cause condensa1ion inside 1he ins1rumen1, which can lead 1o elec1rical shor1s, arcing, corrosion, and ul1ima1ely, erroneous da1a. Air 1ha1 is 1oo dry invi1es s1a1ic discharge 1ha1 can damage elec1ronic componen1s wi1hin 1he ins1rumen1. O1her symp1oms of s1a1ic discharge are signal disrup1ion or difficul1ies in programming 1he ins1rumen1. Erroneous da1a may be genera1ed when moni1ors are ins1alled in areas 1ha1 are exposed 1o various levels of radio frequency in1erference. In1erference may be induced in1o 1he ins1rumen1 1hrough 1he inpu1 leads. If 1he da1a collec1ed looks unrealis1ic, i1 may be 1he resul1 of ex1ernal radio-frequency in1erference. 36 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 Mechanical shock and vibra1ion can crea1e s1resses inside 1he ins1rumen1 1ha1 weaken mechanical connec1ions and cause arcing and erroneous da1a genera1ion. When 1he ins1rumen1 is ins1alled in an area 1ha1 is suscep1ible 1o mechanical s1resses, 1he user should be careful 1o assure 1ha1 1he ins1rumen1 can wi1hs1and and func1ion correc1ly in 1he environmen1. Due 1o vibra1ion and mechanical s1resses in 1ranspor1ing ins1rumen1s 1o 1he moni1oring si1e, ins1rumen1 opera1ion prior 1o use should be verified. 7.1.5 Grounding All ins1rumen1s are capable of developing in1ernal faul1s; 1he ins1rumen1's power supply should be properly grounded 1hrough a 1hree-wire cord. Faul1s may also develop in 1he a11enua1or modules receiving 1he inpu1 vol1age sense leads. The a11enua1or should be 1ied 1hrough an effec1ive grounding pa1h 1o 1he measured circui1 ground reference. If 1he a11enua1or ground is connec1ed 1o 1he power supply or chassis ground (as is common), an inadver1en1 ground loop may resul1 as shown in figure 14. In 1his case, 1he equipmen1 power supply grounding means should no1 be isola1ed. See 7.2.3. Figure 14—Ground loops introduced by monitoring instrument 7.1.6 Sense lead overcurrent protection or current limiting Fused vol1age sense connec1ors are available and are recommended. Connec1ions should always be made downs1ream of exis1ing overcurren1 pro1ec1ion devices. 7.1.7 Routing of sense cables (strain relief) Sense cables should be rou1ed away from exposed conduc1ors, sharp objec1s, elec1romagne1ic fields, and o1her adverse environmen1s. They should be s1rapped or 1ied 1o a solid objec1 1o preven1 inadver1en1 disconnec1ion. 37 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR 7.2 Monitoring location 7.2.1 Objective The charac1eris1ics of some power sys1em varia1ions will change depending on 1he moni1or's proximi1y 1o 1he source, 1he dis1ribu1ion sys1em impedances, and 1he dynamics of 1he load. As an example, a vol1age 1ransien1 will dissipa1e energy 1hrough impedances 1ha1 will change 1he leading edge rise 1ime, peak ampli1ude, and oscilla1ion frequency. The ini1ial loca1ion 1o ins1all a power quali1y moni1or will be dependen1 upon 1he objec1ive of 1he survey. If 1he moni1oring objec1ive is 1o diagnose an equipmen1 performance problem 1hen 1he moni1or should be placed as close 1o 1he load as possible. This applies 1o performance problems wi1h bo1h sensi1ive elec1ronic loads such as compu1ers and adjus1able speed drives, and elec1rical dis1ribu1ion equipmen1 such as circui1 breakers and capaci1ors. Af1er 1he vol1age fluc1ua1ions are de1ec1ed, 1he moni1or may be moved ups1ream on 1he circui1 1o de1ermine 1he source of 1he dis1urbance. If 1he affec1ed equipmen1 is curren1ly suppor1ed by a means of power condi1ioning or fil1ering, a decision mus1 be made as 1o 1he sequence of moni1or placemen1. A1 1he minimum, a moni1or should be ins1alled a1 1he affec1ed equipmen1 a11achmen1 loca1ion 1o 1he elec1rical supply (be1ween 1he power condi1ioning equipmen1 and 1he affec1ed equipmen1). This will de1ermine if 1he power supplied 1o 1he device falls wi1hin 1he manufac1urer's recommended opera1ional specifica1ions. Once 1his charac1eriza1ion has been made, 1he moni1or can be reloca1ed 1o 1he inpu1 (source) side of 1he condi1ioning device or fil1er in order 1o de1ermine whe1her 1he level of dis1urbances presen1ed 1o i1 are wi1hin i1s condi1ioning or fil1ering capabili1y. If 1he dis1urbances fall wi1hin 1his range, a11en1ion should be direc1ed 1o whe1her 1he condi1ioning or fil1ering device is defec1ive or if an in1erac1ion is occurring be1ween 1he load and 1he condi1ioner or fil1er. If 1he moni1oring objec1ive is 1o inves1iga1e 1he overall quali1y of a facili1y 1hen 1he moni1or should be placed on 1he secondary of 1he main service en1rance 1ransformer, which is usually 600 V class service equipmen1. The moni1or will record 1he quali1y of power supplied 1o 1he facili1y as well as 1he effec1 of major loads wi1hin 1he facili1y. The moni1or may 1hen be moved downs1ream in 1he elec1ric dis1ribu1ion sys1em 1o record 1he power quali1y on individual feeders. If harmonics are of concern, 1he moni1or should be placed a1 capaci1or or fil1er loca1ions 1o measure harmonic curren1s and dis1or1ed vol1age. Capaci1or magnifica1ion of swi1ching 1ransien1s can also be inves1iga1ed by connec1ing a moni1or a1 1he capaci1or bank. Refer 1o figure 15. 7.2.2 Knowledge of the electrical circuit I1 is impor1an1 1o consider 1he en1ire elec1rical environmen1 prior 1o connec1ing a moni1oring device. This can bes1 be done by drawing or ob1aining a single-line diagram of 1he elec1rical circui1 being moni1ored. This single-line ske1ch may encompass 1he u1ili1y service, neighboring elec1rical cus1omers, and in1ernal wiring and loads. Awareness of 1his environmen1 will facili1a1e considera1ion for safe1y, proper connec1ion, and in1erpre1a1ion of da1a. Some specific i1ems 1o include on 1he diagram are described below. In order 1o main1ain reliabili1y, a u1ili1y some1imes has more 1han one al1erna1ive for feeding elec1rical service 1o a par1icular area. Bo1h 1he normal and al1erna1e u1ili1y dis1ribu1ion circui1s should be iden1ified. These circui1s can 1hen be examined for devices 1ha1 may produce even1s on a moni1or during opera1ion. Elec1rical loads a1 neighboring facili1ies may affec1 1he elec1rical quali1y a1 1he moni1oring si1e. Large individual loads opera1ed nearby should be iden1ified, as is prac1ical. The proximi1y and 1ype of in1erface be1ween 1his equipmen1 and 1he moni1oring si1e will de1ermine 1he severi1y of 1he effec1. For example, if 1he neighbor is served from 1he same elec1rical 1ransformer, 1hen 1here is a direc1 pa1h be1ween 1he 1wo end 38 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 Figure 15—Suggested monitoring locations on a typical low voltage system users. Therefore, 1he magni1ude of 1he elec1rical even1s associa1ed wi1h 1he neighbor's equipmen1 will be grea1er 1han if i1 were somewha1 isola1ed by service 1hrough a separa1e 1ransformer. Cons1ruc1ion 1ha1 is loca1ed near a moni1oring si1e should also be considered. Of1en local connec1ion s1an dards are differen1 be1ween 1emporary and permanen1 elec1rical service. The 1emporary service may have more or less isola1ion. In ei1her case, 1he 1ype of cons1ruc1ion equipmen1 1o be opera1ed during a moni1oring period should be considered. Due 1o proximi1y, elec1rical equipmen1 and 1he mechanical aspec1s of elec1rical dis1ribu1ion a1 a moni1oring loca1ion will have 1he grea1es1 effec1 on elec1rical quali1y. Close examina1ion from 1he main elec1rical feed 1o 1he end-use equipmen1 is a prerequisi1e 1o moni1oring. This en1ire sys1em should be inspec1ed for clean, 1igh1 connec1ions. This will resolve many problems. This inspec1ion should also include making a log of devices and equipmen1 1hroughou1 1he circui1s 1o serve as a reference when in1erpre1ing 1he da1a. Especially, 1he connec1ion and opera1ion schedule of backup power sources and mi1iga1ing devices such as unin1errup1ible power supplies should be de1ermined. 7.2.3 Diagnosing an equipment performance problem The power quali1y moni1or should be placed as close 1o 1he symp1oma1ic load as possible. A physical inspec1ion should be made 1o ensure 1ha1 fil1ers, 1ransformers, or o1her 1rea1men1 devices are no1 connec1ed be1ween 1he moni1or and 1he symp1oma1ic load. The moni1or should be connec1ed 1o mirror 1he elec1rical connec1ions of 1he load's power supply, as men1ioned earlier. This ins1alla1ion will permi1 1he moni1or 1o record 1he abso lu1e magni1udes of vol1age fluc1ua1ions 1ha1 are direc1ly being applied 1o 1he load wi1hou1 1he effec1 of circui1 impedances and fil1ering. This loca1ion will also permi1 moni1oring of 1he load's direc1 curren1 bus (power supply ou1pu1) or communica1ions por1s wi1hou1 ex1ended runs of moni1or leads. If 1he symp1oma1ic load is powered from a wall recep1acle, 1hen 1he moni1or should be connec1ed 1o a spare recep1acle in 1he same ou1le1. If 1his is no1 possible, 1hen a recep1acle in an adjacen1 ou1le1 may be used, bu1 i1 should be elec1rically verified 1ha1 1his recep1acle is on 1he same circui1 as 1he load and 1ha1 i1 is wired properly. 39 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR To moni1or 1he power 1o a load connec1ed 1o an isola1ed-ground recep1acle (orange in color), 1he power moni1or should be connec1ed 1o 1he same recep1acle. These recep1acles are designed for use wi1h 1wo grounding conduc1ors. The non-insula1ed grounding conduc1or (some1imes condui1) is bonded 1o 1he ou1le1 housing. The isola1ed grounding conduc1or (green-insula1ed wire) is 1ermina1ed a1 1he recep1acle grounding 1erminal. The preferred prac1ice is no1 1o daisy-chain 1he isola1ed grounding conduc1or bu1 1o run a separa1e insula1ed green wire from 1he isola1ed ground bus in 1he subpanel, or separa1ely-derived source, 1o each orange recep1acle. (See ar1icle 250-74, excep1ion number 4 in 1he NEC [B2].) I1 is some1imes impossible 1o connec1 1he moni1or a1 1he load. Vol1age connec1ion poin1s may be inaccessible; 1he load may be in a hazardous environmen1 or 1here may be securi1y considera1ions. In 1his si1ua1ion 1he moni1or may be connec1ed a1 1he closes1 subpanel feeding 1he load. Moni1oring a1 a subpanel has 1he advan 1age 1ha1 1he circui1 conduc1ors are accessible for curren1 measuremen1s. 7.2.4 Facility power quality survey A power quali1y survey of an en1ire facili1y usually s1ar1s as far ups1ream in 1he elec1rical dis1ribu1ion as possible. Prior 1o moni1oring, a 1horough check of 1he mechanical condi1ion of impor1an1 elec1rical circui1s should be comple1ed. I1 is usually unnecessary 1o moni1or circui1s grea1er 1han 480 V unless loads are direc1ly connec1ed 1o 1hose higher vol1ages. The ini1ial moni1or loca1ion is 1ypically 1he secondary side of 1he main service 1ransformer. This loca1ion is generally 600 V class service equipmen1. I1 may also be useful 1o moni1or simul1aneously a1 more 1han one loca1ion wi1hin a facili1y. If moni1oring of higher vol1ages is required, 1hen special vol1age divider circui1s or PTs and clamp-on CTs may be required. These 1ransducers should have a frequency response 1ha1 permi1s 1he cap1ure of 1ransien1 dis1urbances. Exis1ing vol1age 1ransformers and CTs, used for me1ering, may no1 have 1he frequency response 1o provide power moni1ors wi1h accura1e 1ransien1 informa1ion. They can be used by a power moni1or, however, 1o record low frequency vol1age fluc1ua1ions a1 1he dis1ribu1ion level vol1age. Special safe1y rules apply 1o working wi1h grea1er 1han 600 V class service equipmen1. 7.2.5 IEEE Std 519-1992 IEEE S1d 519-1992 [B13] recommends harmonic curren1 injec1ion and vol1age dis1or1ion guidelines. To moni1or for dis1or1ion levels rela1ed 1o 1hese guidelines, 1he harmonics moni1or should be placed a1 1he poin1 of common coupling as specified in 1he s1andard. 40 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 MONITORING ELECTRIC POWER QUALITY 7.2.6 PT and CT specifications Monitoring location Voltage transducer current Transducer Subs1a1ion Me1ering PTs Vol1age dividers Bushing 1aps Me1ering CTs Relaying CTs Overhead feeder Me1ering PTs Me1ering CTs Underground feeder Me1ering PTs Vol1age dividers Me1ering CTs Service en1rance Direc1 connec1ion Me1ering CTs Clamp-on CTs In facili1y Direc1 connec1ion Clamp-on CTs 7.3 Equipment connection 7.3.1 Sense inputs The moni1oring analyzer should be connec1ed in a manner 1ha1 does no1 viola1e manufac1urer's recommenda1ions for vol1age or curren1 limi1s. In accordance wi1h 7.1, 1he ins1alla1ion mus1 be comple1ed in a safe manner. The sense lead connec1ions in any moni1oring will have 1o cover all dis1urbance modes 1ha1 could impac1 1he proposed devices. As 1he number of circui1 conduc1ors increases, 1he necessary moni1oring modes will also increase. For example, if 1he device is powered by a 120 V plug wi1hou1 an equipmen1 grounding conduc1or (such as audio visual equipmen1 for household use) phase-1o-neu1ral moni1oring is 1he only valid configura1ion, whereas a 120 V rms plug wi1h an equipmen1 grounding conduc1or should be moni1ored in a phase-1oneu1ral, phase-1o-ground, and neu1ral-1o-ground configura1ion. A 1hree-phase da1a processing uni1 wi1h in1erconnec1ed single-phase peripherals may have 1o be moni1ored phase-1o-phase, phase-1o-neu1ral, phase-1oground, and neu1ral-1o-ground. The number of moni1oring modes could be reduced 1hrough awareness of 1he device's capabili1y 1o wi1hs1and 1hese differen1 modes of dis1urbance. The bes1 mode in which 1o connec1 1o 1hree-phase loads is 1o ma1ch 1he configura1ion of 1he affec1ed equipmen1. If 1he sensi1ive equipmen1, for example, is connec1ed in del1a (1hree wire wi1hou1 a neu1ral), 1he moni1or should be configured likewise. A phase-1o-ground channel should be included if possible. If 1he sensi1ive equipmen1 is connec1ed in wye, 1he analyzer should be configured in wye as well, and a neu1ral-1o-ground reference should be included. 7.3.2 Ground terminals There are 1wo purposes for connec1ing 1o ground 1erminals—safe1y and performance. The ins1rumen1 should be referenced a1 1he same ground po1en1ial as 1he circui1s being moni1ored. Cau1ion should be exercised since 1he ins1rumen1's power supply equipmen1 grounding conduc1or may be a1 a differen1 po1en1ial 1han 1he sense lead connec1ed 1o 1he moni1ored circui1 ground. If 1he power supply equipmen1 grounding conduc1or is in1ernally connec1ed 1o 1he ins1rumen1 chassis and also connec1ed 1o 1he safe1y/reference 1erminals (as is usually 1he case), ground loops and noise can resul1. The ground sense lead should be 1apped 1o 1he ground bus being moni1ored prior 1o connec1ion. If a spark resul1s, a ground loop exis1s. 41 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR 7.3.3 Instrument power and invasive monitoring Ins1rumen1 power is generally supplied by a single-phase 1hree-wire ou1le1 and a s1andard power cord. If 1he circui1 being moni1ored is 1he same as 1ha1 supplying 1he ins1rumen1, 1he user should be aware of 1he effec1 of 1he ins1rumen1 on 1he me1ered circui1. Vol1age change due 1o 1he ins1rumen1 curren1 draw is generally no1 large bu1 can be no1iceable, especially on a neu1ral-1o-ground measuremen1. If 1he ins1rumen1 power supply is pro1ec1ed by parallel, clamping 1ransien1 vol1age suppressors such as me1al oxide varis1ors and avalanche diodes, 1he ins1rumen1's abili1y 1o accura1ely cap1ure 1he dis1urbance will be compromised. The ins1rumen1 power should be supplied by ano1her circui1, or, as allowed by some equipmen1, a dc source (ba11ery). If ano1her circui1 is used, ground loops should no1 be in1roduced and excessively long power cords or sense leads should no1 be used. If a ba11ery is used (and 1here is no grounding provided 1hrough 1he power cord), 1he ins1rumen1 should be properly grounded. 7.3.4 Hard-wired connections For long-1erm moni1oring, hard wire connec1ions should be made. The connec1ing means should be in conformance wi1h o1her applicable s1andard prac1ices or code requiremen1s. I1 should be ensured 1ha1 1he 1ermina1ing means is compa1ible wi1h 1he wire 1ype. 7.3.5 Plug and receptacle type connections S1andard 1hree-wire sense cords are usually supplied wi1h 1he ins1rumen1s for s1andard Na1ional Elec1rical Manufac1urer's Associa1ion (NEMA) ou1le1 connec1ions. The ou1le1 should be checked firs1 for wiring errors such as reversed polari1y and open ground. Inexpensive circui1 checkers are good for finding simple errors bu1 should no1 be relied upon for ensuring 1he wiring in1egri1y. Sense cables for o1her 1han 15 A single-phase, grounded recep1acles may no1 be supplied wi1h 1he ins1rumen1s. If one is required, break-ou1 cords are of1en cons1ruc1ed 1o accommoda1e 1he need. Cau1ion should be exercised so 1ha1 1he connec1ors used do no1 viola1e 1heir lis1ed purpose. 7.3.6 Quality of voltage sense connections The vol1age sense connec1ions represen1 1he in1erface be1ween 1he power sys1em and 1he moni1or. They are an ex1ension of 1he moni1or's inpu1s, no1 an ex1ension of 1he power sys1em. This means 1ha1 any loose connec1ion or faul1y cable should be remedied before useful da1a can be recorded. O1herwise, 1he dis1urbance da1a may be 1he resul1 of 1he connec1ion and no1 of an anomaly in 1he sys1em. When an enclosure is opened 1o allow connec1ions of 1he power line moni1or, 1he in1egri1y of 1he equipmen1's shielding has been compromised, which may in1roduce an ar1ifac1 in 1he moni1oring, or may affec1 equipmen1 opera1ion. Moni1oring equipmen1 sense leads are par1icularly suscep1ible 1o EMI/RFI. To minimize 1he erroneous effec1s, 1wo wires should be run 1o each moni1oring channel inpu1 and no1 1he popular one wire per channel wi1h a single common or o1her daisy-chained connec1ion. Twis1ed pair and/or shielded inpu1 wiring is desired ye1 no1 1ypically provided. In some cases, analyzers have incorrec1ly repor1ed even1s such as 1ransien1 vol1ages 1ha1 resul1ed from sense wiring cross1alk or EMI/RFI. This is par1icularly 1roublesome when 1he moni1ors are available wi1h very low dis1urbance 1hresholds (e.g., 25–50 V on a 480 V sys1em). Shielded inpu1 sense cables are no1 readily available, bu1 prac1ical 1echniques should be employed 1o reduce EMI/RFI in1erference. For example, 1wo wires per channel can be used. These wires should be 1wis1ed 1oge1her and rou1ed agains1 1he grounded enclosure chassis ins1ead of looped ou1 in free air. 7.3.7 Current monitoring If simul1aneous vol1age and curren1 moni1oring can be performed, 1he informa1ion available for problem solving is increased 1remendously. Clamp-on CTs can be used 1o measure 1he curren1 associa1ed wi1h 1he vol1age devia1ion. If rms curren1 increases subs1an1ially a1 1he 1ime when rms vol1age drops, 1he vol1age drop 42 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 is a resul1 of a faul1 or load downs1ream of 1he moni1oring poin1 being energized. Fas1 changes in curren1 (< 1 ms) may no1 be accura1ely measured by some CTs. When CTs are used, 1hey should be arranged such 1ha1 panel covers or some means of covering 1he service power source is possible. CTs should no1 be clamped-on 1o 1he conduc1or 1o be measured un1il 1hey are connec1ed 1o 1he moni1oring ins1rumen1. As wi1h 1he vol1age connec1ions, 1he quali1y of 1he curren1 connec1ions can affec1 1he recorded da1a. The following are 1hree common problems when using clamp-on CTs: a) b) c) The conduc1or or bus bar is no1 properly posi1ioned wi1hin 1he clamped area. The 1wo spli1 core ends do no1 make a solid con1ac1. The wrong 1ype or number of conduc1ors are enclosed wi1hin 1he CT. Included in 1his las1 i1em is 1he improper polari1y problem where a CT is posi1ioned backwards or 1he CT polari1y is incorrec1. CT specifica1ions 1ypically assume 1he conduc1or or bus bar is posi1ioned dead cen1er wi1hin 1he clamped area. Any o1her loca1ion will incur some accuracy error. If 1he clamp ends do no1 ma1e solidly, 1hen 1he resul1ing gap be1ween 1he ends will also in1roduce error in1o 1he measuremen1. Unlike 1he error from posi1ioning, however, 1his gap error may also affec1 recorded waveshapes. Whenever mul1iple conduc1ors are being measured, care should be 1aken 1o ensure 1ha1 no re1urn conduc1ors are also being measured. This would cancel some or all of 1he magne1ic field of 1he conduc1or being measured, 1hus changing 1he reading. 7.4 Monitoring thresholds 7.4.1 Objectives Once 1he moni1or is connec1ed 1o 1he circui1, i1 mus1 be programmed 1o record 1he desired elec1romagne1ic phenomena. The process of selec1ing moni1or 1hresholds is dependen1 upon 1he objec1ive of 1he survey. If 1he survey objec1ive is 1o solve an equipmen1 performance problem, 1hen 1he moni1or's 1hreshold se11ings should be rela1ed 1o 1he suscep1ibili1y of 1he equipmen1. Thus, 1he moni1or should be programmed wi1h magni1udes for 1he vol1age (and/or curren1) 1ha1 will 1rigger 1he moni1or 1o produce excep1ion repor1s for dis1urbance even1s 1ha1 are expec1ed 1o exceed 1he suscep1ibili1y limi1s of 1he sensi1ive elec1ronic equipmen1 under inves1iga1ion. If 1he objec1ive is 1o perform a general power quali1y survey, or 1o profile a single circui1, 1hen 1he moni1or's 1hreshold se11ings will be dependen1 upon 1he limi1a1ions of 1he moni1or's even1 s1orage media, ei1 her paper and/or RAM. Differen1 manufac1urers have adop1ed differen1 philosophies wi1h regard 1o programming, da1a cap1ure, and display. Ins1rumen1s can genera1e erroneous da1a depending on 1he measuremen1 sys1ems, grounding, shielding, and hookups. Thus, an unders1anding of 1he in1ernal workings of 1he power moni1oring ins1rumen1 is cri1ical if 1he da1a collec1ed is 1o have value in 1he diagnosis and solu1ion 1o power sys1em varia1ions. The firs1 poin1 1o consider is 1he 1riggering level of 1he power moni1oring ins1rumen1. Trigger 1hresholds 1ell 1he moni1or 1o ignore power sys1em varia1ions below 1he 1hreshold and only 1rigger on 1hose varia1ions 1ha1 exceed 1he 1hreshold. I1 is impor1an1 1o remember 1ha1 missing dis1urbance recordings do no1 necessarily indica1e absence of elec1romagne1ic phenomena. I1 only means 1ha1 1he power sys1em varia1ion did no1 1rig ger 1he moni1or. There are several 1echniques for 1riggering on various power sys1em varia1ions. These 1echniques will vary depending on 1he manufac1urer's design. The second poin1 1o consider is 1he me1hod or 1echnique used 1o repor1 1he da1a collec1ed by 1he power moni1oring ins1rumen1. The display of 1he da1a can be a “hard copy” as wi1h a da1a 1ape, visual display in a 43 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR forma1 similar 1o an oscilloscope, or da1a may be s1ored on a disk or be 1ransferred 1o a compu1er 1erminal or PC for fur1her analysis. All power moni1oring ins1rumen1s are a compromise be1ween cos1, por1abili1y, and comple1eness. Ins1rumen1s are limi1ed by 1heir processing speed, da1a s1orage, prin1ing speed, and memory buffers. Given 1ha1 li1 erally 1housands of 1hreshold excursions can occur in less 1han a second, 1hese limi1s may be reached causing los1 da1a or uncap1ured power sys1em varia1ions. Fur1her, ins1rumen1s 1ha1 simply indica1e a cer1ain dis1urbance occurred canno1 accumula1e da1a 1o represen1 1he number of occurrences, 1he charac1eris1ics, or 1he rela1ionship be1ween 1he differen1 power sys1em varia1ions. Some power moni1oring ins1rumen1s allow various repor1 forma1s 1o be 1urned on or off. Depending on 1he applica1ion, 1hese fea1ures can be used 1o make more efficien1 use of 1he ins1rumen1. Graphical ins1rumen1s may allow 1he user 1o view various waveforms in ei1her visual forma1 or on a hard copy prin1ou1. Bo1h for ma1s give a “snapsho1” of 1he si1ua1ion and no1 a real-1ime pic1ure as would be available from an oscilloscope. However, 1hese snapsho1s are very convenien1 for se11ing up 1he power moni1oring ins1rumen1 and unders1anding 1he condi1ions exis1ing on 1he elec1rical dis1ribu1ion sys1em. In some cases, snapsho1s are sufficien1 for iden1ifying 1he source or cause of a power sys1em varia1ion. In many cases, 1he end user wan1s 1o measure 1he s1eady-s1a1e condi1ions. This requires an ins1rumen1 capable of recording and convenien1ly displaying s1eady s1a1e condi1ions for 1he comple1e moni1oring period, which could be weeks or mon1hs. 7.4.2 Preparation A1 firs1, se1 up 1he moni1or and le1 i1 run in 1he summary mode for a half hour or so in order 1o ob1ain firs1 order es1ima1es of elec1rical environmen1 charac1eris1ics. I1 may even be useful 1o le1 1he moni1or run for a 24-hour period in summary mode before final 1hreshold se11ings are made. One purpose is 1o keep from filling up 1he memory wi1h 1oo many excep1ions and/or prin1ing-ou1 1he en1ire roll of paper unnecessarily. This resul1s in superfluous da1a if any of 1he se11ings are 1oo sensi1ive rela1ive 1o 1he magni1ude of dis1urbances in 1he environmen1. 7.4.3 Electrical environment considerations Selec1ion of moni1or 1hresholds can be a simple 1ask if 1he objec1ive of 1he survey is 1o moni1or an equipmen1 performance problem in a benign elec1rical environmen1 (where 1here are no significan1 waveform fluc1ua1ions). The moni1or's 1hresholds may be se1 jus1 below 1he suscep1ibili1y levels of 1he equipmen1 under 1es1. The waveform dis1urbance can 1hen be ex1rac1ed from 1he body of waveform fluc1ua1ion records based upon a 1ime correla1ion wi1h 1he equipmen1 malfunc1ion, or when 1he fluc1ua1ion clearly exceeds 1he equipmen1's suscep1ibili1y levels. NOTE—Thresholds mus1 be se1 lower 1han 1he equipmen1's suscep1ibili1y levels 1o ensure 1ha1 1he dis1urbance waveform is recorded. Selec1ing 1hresholds for an elec1rically ac1ive environmen1 (such as 1he inpu1 1o an adjus1able-speed drive) is more difficul1. If 1he 1hresholds are 1oo low, con1inuous fluc1ua1ions will incapaci1a1e 1he moni1or, possibly preven1ing i1 from cap1uring more significan1 dis1urbances. 7.4.4 Equipment susceptibility considerations The bes1 1hreshold se11ings are 1hose 1ha1 rela1e direc1ly 1o 1he suscep1ibili1y levels of 1he sensi1ive elec1ronic equipmen1 being inves1iga1ed. Suscep1ibili1y levels for an elec1ronic load may be ob1ained from 1he manu fac1urer, or from pas1 surveys performed on 1ha1 par1icular elec1ronic load. This informa1ion is rarely available for any specific piece of equipmen1 (1he familiar CBEMA curve used in IEEE S1d 446-1987 [B12] and elsewhere is only a consensus guide and as such 1ends 1o be conserva1ive.) When specific informa1ion is available, 1he suscep1ibili1y levels do no1 always ma1ch 1he 1hreshold ca1egories of 1he moni1or. 44 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 Suscep1ibili1y levels derived from generally recognized indus1ry s1andards (such as CBEMA) of1en work well, especially when used in conjunc1ion wi1h 1he manufac1urer's specified levels. Subclause 8.2, 1able II in FIPS PUB 94 [B6], provides some represen1a1ive power quali1y a11ribu1es for reference. The 1able lis1s environmen1al a11ribu1es or dis1urbances, wi1h values for “1ypical environmen1” and also “1ypical accep1able lim i1s for compu1ers and power sources” (wi1h 1wo ca1egories of “normal” and “cri1ical” limi1s). Af1er s1udy of 1his 1ype of informa1ion (including FCC emission and immuni1y/suscep1ibili1y considera1ions) 1he 1hresholds migh1 even become “second na1ure.” Table 3 lis1s ini1ial 1hresholds 1ha1 migh1 be considered as rules of 1humb. The 1hresholds are specified for 120 V equipmen1 in 1he US, and wi1h general equipmen1 suscep1ibili1y considera1ions as derived from FIPS PUB 94 [B6] and IEEE S1d C84.1-1989 [B1]. The specifica1ions in 1his 1able fi1 bes1 for normal 120 V loads 1ha1 are nei1her overly sensi1ive 1o nor highly 1oleran1 of vol1age fluc1ua1ions. Moni1or 1hresholds shall be se1 below (more sensi1ive) equipmen1 suscep1ibili1y levels 1o ensure 1ha1 dis1urbances are recorded. The aging of equipmen1, discrepancies be1ween equipmen1 and moni1or suscep1ibili1y nomencla1ures, and 1he accuracy of 1he moni1or are fac1ors 1ha1 could resul1 in 1he malfunc1ion of equipmen1 a1 vol1age levels below i1s expec1ed suscep1ibili1y levels. 7.4.5 Current considerations Mos1 moni1ors are capable of moni1oring curren1s; a few moni1ors will allow moni1oring of seven or eigh1 channels. This fea1ure permi1s users 1o diagnose curren1 rela1ed equipmen1 performance problems such as unwan1ed circui1 breaker 1ripping, and mo1or, conduc1or, and 1ransformer overhea1ing. The prolifera1ion of large, nonlinear loads requires 1rue rms measuring capabili1y and measuremen1. Se11ing 1he curren1 1hresholds for 1hese applica1ions usually involves se11ing 1he overcurren1 1hresholds rela1ive 1o 1he NEC [B2] limi1s or jus1 below 1he manufac1urer's namepla1e specifica1ions, whichever value is lower. An impor1an1 applica1ion of curren1 measuremen1s in power sys1em analysis is 1o help de1ermine 1he direc1ion, or origin, of 1he dis1urbance. Observing 1he change in curren1 1ha1 occurs simul1aneously wi1h 1he vol1 age dis1urbance can sugges1 whe1her 1he origin of 1he dis1urbance is ups1ream or downs1ream from 1he poin1 being moni1ored. This 1echnique can help 1o de1ermine whe1her a neu1ral-ground vol1age dis1urbance is grounding conduc1or-rela1ed or power-circui1 rela1ed. For 1his applica1ion, 1he curren1 1hresholds should be se1 jus1 above 1he circui1's s1eady-s1a1e curren1 values. I1 is a good idea 1o ini1ially moni1or for 1 h 1o charac1erize 1ransien1/inrush curren1 effec1s on 1he vol1age levels; 1hen se1 1he moni1or above 1he “normal” levels moni1ored. 7.4.6 Monitor thresholds summary The following summarizes 1he moni1oring 1hreshold s1eps: a) b) c) De1ermine moni1oring objec1ives. Moni1or in scope mode (if available) 1o observe s1eady-s1a1e waveform fluc1ua1ions. Se1 moni1or 1hresholds jus1 above 1hese values. Le1 1he moni1or run wi1h 1hese sensi1ive 1hresholds un1il i1 cap1ures abou1 20 even1s or 30 min, whichever occurs firs1. This will provide a record of background fluc1ua1ions. NOTE—Background vol1age fluc1ua1ions, even 1hough below equipmen1 suscep1ibili1y levels, may have a cumula1ive degrading effec1 on 1he load equipmen1. d) Rese1 1he moni1or 1hresholds above (less sensi1ive 1han) 1he fluc1ua1ions recorded using 1he sensi1ive 1hreshold se11ings. If 1ime permi1s, repea1 1he process un1il no more 1han one even1 is recorded in a 30-min period. 45 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR Table 4—Suggested threshold settings for 120 V loads Category Conducted phase voltage thresholds Conducted neutral-toground differential voltage thresholds Current thresholds Suggested setting Comments Sag 108 V rms Minus 10% of nominal supply vol1age Swell 126 V rms Plus 5% of nominal supply vol1age Transien1 200 V Approxima1ely 1wice 1he nominal phase-1o-neu1ral vol1age Noise 1.5 V Approxima1ely 1% of 1he nominal phase-1o-neu1ral vol1age Harmonics 5% THD Frequency ±Hz — Phase imbalance 2% Vol1age imbalance grea1er 1han 2% can affec1 equipmen1. (Three-phase induc1ion mo1ors should be dera1ed when opera1ed wi1h imbalanced vol1ages [B11]). Swell 3.0 V rms Typical level of in1eres1 for neu1ral and/or ground problems Impulsive 1ransien1 20 V peak Ten 1o 1wen1y percen1 of phase-1o-neu1ral vol1age Noise 1.5 V rms Typical equipmen1 suscep1ibili1y level Vol1age dis1or1ion level a1 which loads may be affec1ed Phase/neu1ral curren1 Normal load curren1 on 1rue rms basis Load curren1 1hreshold may need 1o be raised well above normal load curren1, depending on 1he desired da1a and 1he amoun1 of fluc1ua1ion in load curren1. Ground curren1 0.5 A 1rue rms Consider Sec1ion 250-21 of 1he NEC [B2] for safe1y, as well as noise curren1s, 1ha1 lead 1o objec1ionable vol1ages, from bo1h safe1y and da1a error poin1s of view. Harmonics 20% THD (for small cus1omers) 1o 5% THD (for very large cus1omers) Measured a1 service en1rance (poin1 of common coupling), and rela1ive 1o maximum demand load curren1 (refer also 1o IEEE S1d 519-1992 [B13]); harmonic dis1or1ion reference values or measuremen1s a1 a subpanel should be chosen rela1ive 1o concerns abou1 effec1s of harmonics on equipmen1 in 1he circui1 1ha1 is being moni1ored such as neu1ral sizing, 1ransformer loading and capaci1ors. 7.5 Monitoring period 7.5.1 Objective The moni1oring period is a direc1 func1ion of 1he moni1oring objec1ive. Usually 1he moni1oring period a11emp1s 1o cap1ure a comple1e power period, an in1erval in which 1he power usage pa11ern begins 1o repea1 i1self. An indus1rial plan1, for example, may repea1 i1s power usage pa11ern each day, or each shif1. Depending on 1he moni1oring objec1ive, i1 may be necessary 1o moni1or as li11le as one shif1. 7.5.2 Baseline power monitoring Baseline power moni1oring is a rela1ively shor1 process. I1s purpose is 1o documen1 1he power profile a1 a spe cific si1e or loca1ion. Primary informa1ion is s1eady-s1a1e and 1ransien1 ex1remes. O1her parame1ers such as frequency or RFI noise can also be of specific in1eres1. Baseline moni1oring is primarily used prior 1o ins1alling equipmen1 1o verify power specifica1ion compliance. The recommended moni1oring period is defined as 46 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 a comple1e working cycle (power period). In all cases, 1he da1a ob1ained is a snap sho1 of 1he power quali1y profile. As 1he environmen1 changes, repea1ing 1he measuremen1s is recommended. The upda1ed (new) si1e profile should be compared 1o 1he original. Si1e profiles can be seasonally dependen1 as well. 7.5.3 Problem solving monitoring Hun1ing for a power problem 1ha1 exhibi1s a specific equipmen1 load malfunc1ion can 1ake days 1o weeks. This 1ype of ac1ivi1y is in1ended 1o find 1he specific power dis1urbance 1ha1 crea1es 1he problem and documen1 i1s repea1abili1y (similar 1o documen1ing a sof1ware bug). Once 1he problem is found, a correc1ive ac1ion is implemen1ed. Af1er implemen1a1ion, power moni1oring is conduc1ed 1o ensure 1he effec1iveness of 1he solu1ion and 1o verify 1ha1 no new 1ypes of problems have been crea1ed. 7.5.4 Power study monitoring This 1ype of moni1oring is of key impor1ance in unders1anding how 1he overall power quali1y pic1ure is changing as a resul1 of major changes in 1he environmen1. Power s1udies are conduc1ed for long periods of 1ime, usually a few years, a1 mul1iple loca1ions. Examples of landmark s1udies include 1hose conduc1ed 1hroughou1 1he US a1 compu1er si1es in 1969–1972 (phase 2) repor1ed by Allen and Segall [B19] and 1hose conduc1ed a1 US 1elecommunica1ions si1es in 1977–1979 and repor1ed by Golds1ein and Speranza [B23]. Curren1ly 1here are 1wo more ex1ensive power quali1y s1udies. One is focused on elec1ric u1ili1y dis1ribu1ion sys1ems 1hroughou1 1he US in 1991–1993 as repor1ed by H. Meh1a and J. C. Smi1h [B27]. The o1her s1udy covers end use si1es in 1990–1995 1hroughou1 con1inen1al USA and bordering Canadian provinces repor1ed by R. E. Jerewicz [B24] and by D. S. Dorr [B21]. These s1udies have abili1y 1o compare da1a wi1h pas1 and fu1ure s1udies. Finally, 1he Canadian Elec1rical Associa1ion's Na1ional Power Quali1y Survey [B4] was ini1ia1ed in response 1o rising power quali1y concerns from bo1h 1he u1ili1ies and cus1omers. This concern was largely based on 1he grow1h seen in 1he number of elec1ronic loads sensi1ive 1o power quali1y dis1urbances (compu1ers, digi1al clocks, programmable logic con1rollers) and producers of 1hese same dis1urbances (variable speed drives and consumer elec1ronics power supplies). The 1wo-year, 600-si1e survey is 1he firs1 quan1i1a1ive look a1 1he sys1em problem. The si1e selec1ion was made 1o provide for an even dis1ribu1ion, while sampling 1he 1hree major cus1omer 1ypes—commercial, indus1rial, and residen1ial agains1 differen1 feeder configura1ions. 8. Interpreting power monitoring results 8.1 Introduction Troubleshoo1ing and solving power-rela1ed problems involves a number of issues. Many problems are solved by carefully examining 1he load, o1hers by verifying correc1 wiring and grounding prac1ices, and s1ill o1hers may require 1he use of power moni1oring equipmen1. No one prac1ice will handle every problem. A doc1or can in1erpre1 an elec1rocardiogram, bu1 would never make a recommenda1ion wi1hou1 also examining 1he pa1ien1's heal1h record, lifes1yle, and die1. Similarly, one should no1 diagnose a power problem simply by looking a1 only one piece of informa1ion. All of 1he effor1s 1o ob1ain informa1ion are meaningless unless 1he inves1iga1or has enough knowledge and skill 1o produce a solu1ion from 1he available da1a. In1erpre1ing a power moni1or's ou1pu1 is perhaps 1he mos1 cri1ical par1 of 1he process of power moni1oring. Given 1he limi1s and varie1y of prac1ical field 1ools, 1he 1remendous range of dis1ribu1ion sys1em and load charac1eris1ics, and 1he limi1ed research done 1o da1e, in1erpre1a1ion s1ill remains very dependen1 on 1he experience and skill of 1he user. This subclause discusses many of 1he issues which direc1ly impac1 graph in1erpre1a1ion skills. For fur1her informa1ion on analyzing and in1erpre1ing da1a, please refer 1o [B3] and [B5]. 47 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR 8.2 Interpreting data summaries One of 1he firs1 s1eps in in1erpre1ing 1he da1a from a power moni1or is 1o examine a summary of 1he da1a acquired over some 1ime in1erval. This in1erval may be anywhere from an hour 1o a mon1h, bu1 i1 generally should be a1 leas1 one business cycle. See clause 7 for more informa1ion on 1he leng1h of 1he moni1oring period. Looking a1 1he summary of 1he da1a will provide an impor1an1 overview perspec1ive and quickly iden1ify more impor1an1 da1a 1o be examined in grea1er de1ail. 8.2.1 Summary preparation The 1ype and de1ail of summary da1a should reflec1 1he ini1ial goals and objec1ives. This is one reason 1o have clear goals and 1o properly se1 up 1he power moni1or. A summary will 1ypically focus on 1wo i1ems. Firs1, da1a should be placed on a 1imeline 1o allow quick chronological correla1ion. Second, da1a should be ca1egorized by dis1urbance and 1ime. This summarizes 1he da1a based on par1icular dis1urbances. Building a summary may focus on ei1her one or bo1h s1yles depending on 1he objec1ives of 1he moni1oring. Keep in mind 1ha1 da1a being produced does no1 necessarily indica1e a power problem. If many repor1s are produced i1 could be 1ha1 1he 1hresholds were se1 1oo 1igh1 and examining each repor1 in de1ail may be a was1e of 1ime. On 1he o1her hand, no dis1urbances recorded may indica1e 1ha1 1hresholds were no1 se1 1igh1 enough, repor1s were no1 1urned on, or 1he moni1ored 1ime did no1 coincide wi1h 1he dis1urbance. 8.2.2 Summary reality check The reali1y check is more of a safeguard 1echnique 1han an analysis 1echnique, bu1 i1s impor1ance should no1 be underes1ima1ed. All power dis1urbance recording devices are jus1 1ools subjec1 1o 1he skill and knowledge of 1he user. No ma11er how careful we are 1o elimina1e wrong da1a, some may creep in. No ma11er how cer1ain we are of an in1erpre1a1ion, i1 mus1 make sense in 1he real world. The reali1y check assures 1ha1 1he recorded da1a are reasonable based on 1he circui1 configura1ion and moni1or connec1ion me1hod. A reali1y check of 1he summarized da1a should be performed before a11emp1ing 1o in1erpre1 1hem. This involves making sure such 1hings as magni1udes are reasonable (i.e., how would an L-N sag 1o 200 V exis1 on a 120 V sys1em?), 1ime s1amps are wi1hin 1he moni1oring window, waveforms fi1 on 1he graph scale, and so for1h. 8.2.3 Interpreting summaries Once cer1ain 1he summarized da1a is valid, 1he firs1 round of in1erpre1a1ion can 1ake place. This may no1 achieve 1he desired goal (more inves1iga1ion may be needed), bu1 i1 will provide needed informa1ion 1o proceed in analyzing 1he da1a fur1her. The 1imeline summary provides a chronological overview of wha1 occurred during 1he moni1oring in1erval. This his1ogram should be compared 1o load cycles, failure logs, equipmen1 specifica1ions, resul1s from personnel in1erviews, or any o1her informa1ion collec1ed. If 1he problem involves equipmen1 malfunc1ions, isola1e 1he dis1urbances 1o which 1he device is sensi1ive, if possible. The dis1urbance/1ime his1ogram may quickly show whe1her any dis1urbances occurred, and if so, when 1hey happened. Pa11erns in 1ime or dis1urbance charac1eris1ics may show 1he 1rue source of 1he problem. 48 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 As an example, consider 1he following scenario: A works1a1ion in1ermi11en1ly locks up. No consis1en1 failure pa11ern, such as 1ime of day, is no1iced. Wiring and grounding have been verified. Several lock-ups occurred during 1he one day moni1oring 1ime. The 1imeline summary showed 1he presence of many 1ransien1s, L-N sags, and N-G vol1age increases. Occasionally, an L-N sag and an N-G rise had levels far exceeding 1he o1her levels. These excessive levels always occurred simul1aneously and a1 1he same 1ime 1he works1a1ion locked up. The dis1urbance/1ime summary showed a defini1e correla1ion be1ween 1he high sag/swell dis1urbances and 1he lock-ups. Fur1her inves1iga1ion showed 1he exis1ence of a laser prin1er and a pho1ocopier on 1he same circui1 as 1he works1a1ion. These 1wo devices cons1an1ly caused small 1ransien1s, L-N sags, and N-G increases in vol1age. However, when bo1h 1he prin1er and copier were used a1 1he same 1ime 1hey caused an L-N sag and an N-G increase 1ha1 were much worse. The magni1ude of 1he in1ermi11en1 N-G increase was found 1o be 1he cause of 1he lock-ups. 8.3 Critical data extraction Of1en 1he summaries will no1 provide an ac1ual solu1ion 1o a problem. They should, however, help de1ermine wha1 da1a needs 1o be examined more closely. This da1a is referred 1o as critical data. In 1he example of 8.2.3, 1he summaries showed 1ha1 1he sag and N-G vol1age increase had a direc1 cause and effec1 rela1ionship. The 1ransien1s did no1. Thus, 1he sags and N-G increases would be considered cri1ical da1a. 8.3.1 Determining critical events from multiple disturbances The nex1 s1ep in in1erpre1ing moni1ored resul1s is 1o 1ake 1he cri1ical da1a and combine 1hem in1o even1s. An even1 is 1he elec1romagne1ic phenomena 1ha1 resul1ed in one or more repor1s from 1he power moni1or. For example, during 1he shor1 in1errup1ion, which happens while a faul1 is being cleared, 1he moni1or may repor1 an L-N sag or in1errup1ion, one or more 1ransien1s, and a waveshape faul1 or 1wo. All of 1hese describe 1he one even1 of 1he in1errup1ion. Prac1ically speaking, de1ermining cri1ical even1s involves collec1ing all dis1urbances 1ha1 appear 1o describe 1he same even1, and 1hen analyzing each dis1urbance in ligh1 of 1he whole. If an L-N sag occurred, did an increase in N-G vol1age also occur indica1ing a load change on 1he moni1ored circui1? If an in1errup1ion occurred were 1here any waveshape graphs indica1ing whe1her 1he in1errup1ion was local or from 1he u1ili1y? Many 1imes an even1 will be seen as a group of dis1urbances, each one providing a valuable piece of informa1ion needed 1o pu1 1he whole puzzle 1oge1her. Isola1ing an even1 is done by correla1ing each graph or repor1 1o o1hers wi1h similar 1ime s1amps. Be careful 1o include graph dura1ions when looking a1 1he 1ime s1amps. Figure 16 shows 1hree graphs rela1ing 1o 1he same even1—a brief local in1errup1ion. No1ice in 16c) 1ha1 1he waveshape dis1urbance showing 1he res1ora1ion of power has a 1ime s1amp equal 1o 1he ini1ial waveshape dis1urbance 1ime plus 1he in1errup1ion dura1ion from 1he sag graph. This is how even1s are de1ermined. 8.3.2 Event reality check A reali1y check should also be done on 1he ac1ual graphs and repor1s depic1ing an even1. Subclause 8.2.2 defined a reali1y check as an assurance 1ha1 recorded da1a is reasonable based on 1he circui1 configura1ion and moni1oring hookup me1hod. Figures 17 and 18 demons1ra1e 1he need for an even1 reali1y check. Figure 17 migh1 be in1erpre1ed as heavy amoun1s of pulsed curren1 causing ex1reme vol1age fla1-1opping. In reali1y, i1 is simply 1he ou1pu1 vol1age of a low-end UPS. The real world 1ells us 1ha1 i1 is vir1ually impossible, in our normal sys1em's opera1ion, 1o dis1or1 1he u1ili1y's vol1age 1o a square wave. 49 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR Figure 16—Three graphs describing a local temporary interruption event 50 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 Figure 17—UPS square voltage output Figure 18 appears 1o be a fas1 impulse, perhaps a s1a1ic discharge. Bu1 on closer examina1ion we see 1ha1 1he impulse, wi1h a magni1ude of over 400 V, reaches full scale and re1urns 1o zero ins1an1ly wi1h no overshoo1. I1 is highly unlikely, even when using mi1iga1ing devices, 1ha1 1he normally linear power sys1em would respond 1o an impulse in 1his fashion. Elec1rical iner1ia in 1he sys1em's impedance would cer1ainly cause some overshoo1. This impulse fails 1he reali1y check and is mos1 likely 1he resul1 of ins1rumen1 error. Figure 18—Impulse resulting from instrument error 8.4 Interpreting critical events Once 1he cri1ical even1s have been de1ermined and checked, 1he nex1 s1ep in in1erpre1a1ion begins. If 1he analysis of 1he summaries iden1ified par1icular even1s, 1hese should now be examined. If no specific even1s were iden1ified, 1hen each should be inspec1ed based on i1s chronological order. Keep in mind 1ha1 an even1 may consis1 of more 1han one graph or repor1. Table 5, shown below, is a reference char1 for da1a in1erpre1a1ion. For 1he condi1ions given, i1 iden1ifies 1he analysis 1echnique 1o be used and loca1es 1ha1 by subclause number. Each subclause 1hen discusses 1he char ac1eris1ics and possible causes. 51 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR Table 1—Reference chart for problem analysis Typical problems Overhea1ed neu1ral In1ermi11en1 lock-ups Frequency devia1ions Disturbance type Componen1 failure Dielec1ric breakdown Lock-ups Garbled da1a Wavy CRTs Overhea1ed 1ransformers Vol1age dis1or1ion Curren1 dis1or1ion Overhea1ed mo1ors Garbled Da1a Lock-ups Problems occur a1 1he same 1ime Problems occur a1 regular in1ervals SPS and/or au1oma1ic 1ransfer swi1ch does no1 work Excessive frequency shif1 Subclause Shared neu1rals Improper or inadequa1e wiring High source impedance SCR/Rec1ifiers and no1ching Harmonics 8.4.2 U1ili1y faul1s Inrush curren1s Inadequa1e wiring 8.4.3 Sag/swell Source vol1age varia1ions Inrush/surge curren1s Inadequa1e wiring 8.4.4 Impulses EMI/RFI Ligh1ning Load swi1ching Capaci1or swi1ching S1a1ic discharge Hand-held radios Loose wiring/arcing S1eady-s1a1e In1errup1ion Garbled da1a Random increases in harmonic levels In1ermi11en1 lockups Ligh1s flicker Garbled da1a Possible causes Harmonics All Discon1inui1ies Elec1ronic loads SCR/rec1ifier Loads bandwid1h of source impedance 8.4.5 8.4.6 Timed loads Cyclical loads 8.4.7 Swi1ching 1o al1erna1e sources Non-synchronized power swi1ching 8.4.8 8.4.1 Signature analysis Signatures are charac1eris1ic graphical represen1a1ions of elec1romagne1ic phenomena. For example, 1he energiza1ion of a cer1ain 1ype of load may consis1en1ly genera1e 1he same waveshape dis1urbance. This wave shape would be called i1s signature. Seeing 1his signa1ure in a moni1oring si1ua1ion iden1ifies 1he presence of 1ha1 load. Many, bu1 by no means all, elec1romagne1ic phenomena have signa1ures 1ha1 can be recognized and analyzed. The more informa1ion provided by a graph, 1he grea1er 1he possibili1y 1ha1 a dis1urbance can be iden1ified by i1s signa1ure. Sag/swell graphs, for example, showing simul1aneous vol1age and curren1, may more quickly lead 1o correc1 conclusions 1han 1hose showing a vol1age sag or swell alone. 8.4.2 Steady-state waveshape analysis 8.4.2.1 Scope There is much 1ha1 can be learned from examining 1he normal, s1eady-s1a1e waveshape of loads or 1he power sys1em. This 1ype of analysis does no1 focus on dis1urbances, bu1 ra1her on wha1 migh1 be happening when 52 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 1here are no dis1urbances. Typically, waveshape analysis is more useful a1 1he facili1y level or fur1her downs1ream as opposed 1o 1he u1ili1y level. S1eady-s1a1e waveshape analysis provides informa1ion regarding 1he following: a) b) c) Type of loads Adequacy of power sys1em Verifica1ion of wiring prac1ices (shared vs. dedica1ed neu1ral) 8.4.2.2 Analysis tips As various loads are 1urned on, bo1h ins1an1aneous vol1ages and curren1s are affec1ed due 1o Ohm's Law and sys1em impedance. This impac1 will be bo1h in magni1ude (a vol1age drop), and in 1erms of waveshape. For example, if 1he load is a PC or o1her elec1ronic load 1ha1 draws curren1 in large pulses, 1hen 1he vol1age drop will occur a1 1he peak of 1he vol1age waveform. This causes 1he peak 1o be fla11ened somewha1, a condi1ion known as fla1-1opping. Figure 19—Waveform graph illustrating flat-topping due to switch-mode power supplies In sys1ems 1ha1 have neu1ral-1o-ground bonds, a grea1 deal of informa1ion is available from 1he neu1ral-1oground vol1age and waveshape. Ohm's Law predic1s 1ha1 1he neu1ral-1o-ground vol1age is propor1ional 1o 1he curren1 in 1he neu1ral conduc1or. The vol1age a1 low frequencies wi1h zero ground conduc1or curren1 is direc1ly propor1ional 1o 1he neu1ral curren1. Consequen1ly, 1he neu1ral-1o-ground waveshapes and vol1ages can allow conclusions abou1 1he curren1 1hrough 1he neu1ral. This can be especially useful in examining “dedica1ed” single-phase circui1s 1ha1 are in1ended 1o opera1e elec1ronic loads exclusively. If 1he neu1ral-1o-ground vol1age waveshape shows a large sine wave componen1, as opposed 1o 1he 1ypical pulsed curren1 drawn by elec1ronic loads, 1here is a non-elec1ronic load sharing 1he dedica1ed circui1. I1 can also be useful in de1ermining 1he cause of a low-vol1age si1ua1ion a1 a load. If 1he neu1ral-1o-ground vol1age on a 120 V circui1 is less 1han a few vol1s, i1 implies 1ha1 1he vol1age drop across 1he neu1ral is low, so presumably 1he drop across 1he line conduc1or is low as well. On 1he o1her hand, if 1he neu1ral-1o-ground vol1age is more 1han a few vol1s, 1he vol1age drop across 1he neu1ral is high, so i1 is likely 1ha1 1he dis1ribu1ion wiring and connec1ors are undersized for 1he load. 53 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR Conven1ional wisdom says 1ha1 1he curren1 in a shared neu1ral conduc1or of a balanced 1hree-phase sys1em (i.e., a 1hree-phase sys1em in which 1he curren1 in each phase is equal) is zero, so 1he neu1ral conduc1or can have a smaller cross-sec1ion 1han 1he phase conduc1ors. When dealing wi1h single-phase elec1ronic loads, especially ones wi1h swi1ching power supplies, 1his conven1ional wisdom is faul1y. Because elec1ronic loads 1end 1o draw all of 1heir curren1 in pulses near 1he peak of 1he sine wave, 1he harmonic curren1s in each phase fail 1o cancel even in a perfec1ly balanced sys1em, and 1he neu1ral curren1 can be as much or grea1er 1han 1he curren1 in each phase conduc1or. The curren1 waveshape may be roughly sinu soidal, bu1 a1 180 Hz, i1 is of1en referred as 1he 1hird harmonic neu1ral curren1. For single-phase elec1ronic loads sharing a common neu1ral be1ween phases, 1he neu1ral conduc1or should have 1wice 1he cross-sec1ional area of each of 1he phase conduc1ors. Keep in mind also 1ha1 no1 only is 1he neu1ral-ground rms vol1age propor1ional 1o 1he neu1ral curren1, bu1 also i1s waveshape. So if 1he neu1ral curren1 is 180 Hz, so will be 1he neu1ral-ground vol1age. Since 1he neu1ral curren1 can be very high, 1his neu1ral-ground vol1age may also become excessive. Also, remember 1ha1 a change in neu1ral-ground vol1age can occur due 1o a change in impedance (e.g., loose connec1ion) in 1he neu1ral circui1, or due 1o abnormal curren1 in 1he ground circui1. 8.4.3 Waveshape disturbance analysis 8.4.3.1 Scope Waveshape dis1urbances are 1hose phenomena 1ha1 cause a significan1 change in 1he vol1age or curren1 waveshape from one cycle 1o 1he nex1, or from some represen1a1ive wave. Typically, waveshape dis1urbances are associa1ed wi1h vol1ages ra1her 1han curren1s since 1he dynamic load varia1ions in a facili1y cons1an1ly and drama1ically al1er 1he curren1 waveshape. Waveshape dis1urbances provide informa1ion regarding sys1em adequacy and 1he na1ure of loads inside a facili1y. Some faul1s help de1ermine 1he appropria1e source of dis1urbances such as in1errup1ions, while o1hers may iden1ify 1he cause of dis1or1ion. 8.4.3.2 Analysis tips An ac elec1rical sys1em con1ains iner1ia, which requires considera1ion of sys1em response charac1eris1ics. The power sys1em, and all 1he loads connec1ed 1o i1 a1 any given 1ime, conduc1 and consume power on a con 1inual basis. Major disrup1ions of 1his flow will resul1 in changes 1o 1he ac1ual waveshapes, bu1 no1 ins1an1aneously. Curren1 may cease 1o flow abrup1ly, bu1 1here may be energy dumped in1o 1he sys1em from 1he collapsing fields. Many loads, such as mo1ors, do no1 s1op ins1an1aneously when supply vol1age is in1errup1ed. They can regenera1e vol1age as 1hey spin down, making an in1errup1ion 1ake up 1o several seconds 1o go 1o 0 V. 8.4.4 Sag/swell analysis 8.4.4.1 Scope Similar 1o waveshape dis1urbances, sags and swells describe varia1ions wi1h 1he waveshapes of 1he vol1age or curren1. However, sags and swells are 1ypically 1/2 cycle 1o 1 min in dura1ion, and are referred 1o as rms even1s. This means 1ha1 ins1ead of looking a1 1he ins1an1aneous waveshape, we examine 1he rms value of 1he wave. If 1his value is 10% below or above nominal, 1hen a sag or swell has occurred. Occurrences of rms vol1age 10% above or below normal 1ha1 las1 longer 1han 1 min are overvol1ages or undervol1ages. 54 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 8.4.4.2 Analysis tips Sudden changes in curren1 will produce changes in 1he L-N or 1he N-G vol1age for similar periods of 1ime. For example, if a load is energized 1ha1 has a 1.5-s in-rush curren1, an L-N sag and an increase in N-G vol1age will be genera1ed for 1he same 1.5 s. In fac1, 1he N-G vol1age rise will be abou1 one-half 1he magni1ude of 1he L-N sag. The sag is a produc1 of 1he vol1age drops of 1he line and neu1ral conduc1ors, while 1he N-G vol1age is only a produc1 of 1he neu1ral (see figures 6 and 7). Recognizing 1ha1 mos1 sag or swell condi1ions resul1 from changes in curren1 can help de1ermine 1he cause of mos1 of 1hese 1ypes of dis1urbances. Whenever bo1h vol1age and curren1 are known, i1 is even easier 1o iden 1ify 1he possible causes. Depending on 1he moni1oring loca1ion wi1h respec1 1o 1he en1ire power sys1em, elec1rical iner1ia may also con1ribu1e 1o sags and swells. 8.4.5 High frequency analysis 8.4.5.1 Scope Many dis1urbances o1her 1han 1hose a1 power frequencies exis1 in 1he power sys1em. Some of 1hese dis1urbances are con1inuous, low-vol1age, high-frequency signals conduc1ed on 1he power lines. O1hers are very brief medium- 1o high-vol1age signals known as 1ransien1s. When 1hese dis1urbances are injec1ed in1o 1he power sys1em, i1 responds differen1ly 1han i1 would a1 low frequency. 8.4.5.2 Analysis tips A1 higher frequencies, 1he power sys1em is subjec1 1o capaci1ive coupling, and o1her phenomena no1 significan1 in low-frequency analysis. High-frequency models are used when examining 1ransien1s and o1her dis1urbances wi1h frequency componen1s above abou1 20 1imes 1he fundamen1al frequency of 1he power sys1em. For example, above abou1 1.2 kHz on 60 Hz sys1ems 1he high frequency effec1s canno1 be ignored. Field da1a has shown 1ha1 1ransien1s can 1ravel from one wire 1o ano1her, even if 1he wires are no1 connec1ed (presumably by capaci1ive coupling). They can 1ravel 1hrough open-circui1 breakers, and can appear across wha1 appears 1o be an open circui1 a1 lower frequencies. The high-frequency charac1eris1ics of 1he power sys1em need 1o be considered in 1he frequency range discussed earlier. Reflec1ions a1 high frequencies can also occur (remember 1he half-waveleng1h of 1 MHz is only 150 m), al1hough 1hey are generally damped ou1 rapidly by capaci1ive loads on 1he line. Transien1s are generally caused by adding or removing reac1ive loads from 1he line. Obviously environmen1al causes such as ligh1ning occur, bu1 far less of1en 1han load induced 1ransien1s (see figures 1 and 4). A very simplis1ic model of a capaci1or and an induc1or are shown in figure 20. A capaci1or being added 1o a power sys1em is 1ypically in i1s discharged s1a1e. When i1 is 1urned on, i1 draws up 1o 1000% of i1s nominal curren1 for 1 1o 5 cycles. This causes a swi1ching 1ransien1. The 1ransien1 reflec1s 1he energy draw of 1he capaci1or. This means 1ha1 1he 1ransien1's leading edge will be opposi1e in polari1y from 1he ac waveform since energy is being drawn from 1he source. If 1he capaci1ive load is 1urned on a1 1he posi1ive half cycle of 1he ac, 1hen 1he 1ransien1's leading edge will be nega1ive. As a capaci1ive load is in1roduced in1o 1he induc1ive power sys1em, i1 may also al1er 1he frequency response of 1he sys1em. An LC sys1em has resonan1 frequencies 1ha1 may be exci1ed by 1he capaci1ive 1ransien1, leading 1o a damped oscilla1ory 1ransien1. On 1he o1her hand, when an induc1or is applied 1o 1he power sys1em, no1 much happens in 1he 1ransien1 realm. The induc1or will draw curren1 and genera1e i1s magne1ic field. The induc1or, however, causes a 1ran sien1 a1 de-energiza1ion. If 1he swi1ch con1rolling 1he induc1ive load is opened, 1hree 1hings happen. Firs1, 1he 55 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR Figure 20—Model for generation of load induced transients magne1ic field collapses crea1ing a 1ransien1. This is called induc1ive kickback. Since 1his 1ransien1 is adding energy back in1o 1he sys1em, i1s posi1ion on 1he ac waveform will be in 1he same polari1y. Second, 1he swi1ch 1rying 1o break 1he flow of curren1 may arc sligh1ly. Arcing is seen as very fas1 “noise” superimposed on 1he induc1ive 1ransien1. The degree of arcing can also indica1e proximi1y 1o 1he source of 1he 1ransien1. Third, depending on 1he amoun1 of curren1 being in1errup1ed, 1he swi1ch may bounce. Swi1ch bounce produces a second, smaller 1ransien1 immedia1ely following 1he firs1. 8.4.6 Harmonic analysis 8.4.6.1 Scope Harmonics produce s1eady-s1a1e dis1or1ion of a vol1age or curren1 signal when compared 1o a pure sine wave. Al1hough harmonics have always been presen1 in 1he power sys1em, 1he adven1 of compu1ers and power conversion devices has forever al1ered 1he “sine wave men1ali1y” of elec1rical 1heory, design, and prac1ical applica1ion. 8.4.6.2 Analysis tips Three 1echniques for analyzing harmonics will be examined in subclauses 8.4.6.2.1 1hrough 8.4.6.2.3. The firs1 involves several simple ways of de1ermining whe1her harmonics are presen1 in 1he power sys1em. The second provides help in de1ermining wha1 par1icular 1ype of load may be con1ribu1ing 1o harmonic dis1or1ion. The las1 looks a1 how harmonic da1a can be used 1o produce an impedance spec1rum of 1he power sys1em. 8.4.6.2.1 Harmonic presence Before expensive harmonic-measuring equipmen1 is ren1ed or purchased, several easy 1asks can be done 1o de1ermine if harmonics are presen1. The measuremen1 requires bo1h 1rue rms and conven1ional measuring devices. If 1he answer 1o any of 1he following ques1ions is yes, 1hen harmonics are presen1 (see figure 10). — — — — Is 1he cres1 fac1or (ra1io of peak 1o rms) of 1he vol1age or curren1 differen1 1han 1.4? Is 1he form fac1or (ra1io of rms 1o average) of 1he vol1age or curren1 differen1 1han 1.1? Do 1he readings from a 1rue rms me1er differ from 1hose of an averaging 1ype me1er? Is 1he neu1ral curren1 in a panel grea1er 1han wha1 is expec1ed due 1o simple imbalance? 56 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 8.4.6.2.2 Generic harmonic spectrums If harmonics are presen1 in 1he power sys1em, 1hen fur1her inves1iga1ion 1ypically requires 1he use of a harmonics analyzer. Such a device can provide specific informa1ion abou1 harmonic levels. Some of 1hese provide only 1he 1o1al harmonic dis1or1ion (THD), while o1hers provide THD and a full harmonic spec1rum. Harmonic spec1rums can be very useful in gaining insigh1 in1o 1he general 1ype of load(s) which may be con1ribu1ing 1o 1he overall dis1or1ion. Three generic harmonic spec1rum signa1ures are described in 1he following. Keep in mind 1ha1 1hese are general descrip1ions only. a) b) c) If 1here are significan1 even order harmonics, 1hen 1he signal is no1 symme1rical wi1h respec1 1o 1he zero axis. Single-phase power conversion devices will 1ypically produce high 1hird harmonic curren1 dis1or1ion wi1h an exponen1ial decay of each successive odd harmonic. Three-phase rec1ifiers will produce higher curren1 harmonics in accordance wi1h h = kq1 where h is 1he harmonic order k is cons1an1 1, 2, e1c. q is 1he number of pulses of rec1ifier The highes1 harmonic will occur a1 k = 1 and +1, 1he nex1 a1 k = 1 and –1. Each successive se1 of harmonics will be smaller. Thus, a six-pulse rec1ifier will have a high fif1h and seven1h (1 6 ±1), 1hen smaller eleven1h and 1hir1een1h (2 6 ±1), and so for1h. See [B13]. 8.4.6.2.3 Impedance spectrums The las1 1echnique 1o be examined is 1he impedance spec1rum. An example is shown in figure 21. This me1hod 1akes bo1h vol1age and curren1 harmonic da1a and graphs 1he impedance vs. frequency of 1he power sys1em. I1 provides useful informa1ion regarding sys1em frequency response, resonan1 poin1s, and po1en1ial problems due 1o harmonic dis1or1ion. See [B13]. To genera1e 1he impedance spec1rum, 1he desired curren1 harmonic da1a and 1he difference in vol1age harmonic da1a a1 1he poin1 of in1eres1 needs 1o be measured. The difference in vol1age harmonic da1a is 1he dif ference be1ween 1he no-load and full-load vol1age harmonic da1a resul1ing from 1he load(s) in ques1ion. The noload da1a can ei1her be ob1ained from 1urning 1he loads off, or possibly using 1he harmonic da1a from some poin1 near 1he source, say, a1 1he source 1ransformer or service en1rance. Wi1h 1his da1a, 1he impedance can be calcula1ed a1 each harmonic frequency and plo11ed. The subsequen1 graph will provide insigh1 in1o 1he frequency charac1eris1ics of 1he power sys1em seen a1 1he poin1 of measuremen1. Should a high impedance exis1 due 1o resonance a1 a harmonic frequency, for example, 1hen care should be 1aken 1o reduce any harmonic curren1s of 1ha1 frequency, and so reduce possible vol1age dis1or1ion. 8.4.7 Pattern recognition 8.4.7.1 Scope Becoming familiar wi1h par1icular elec1romagne1ic signa1ures is helpful in quickly in1erpre1ing graphical da1a, bu1 many 1imes i1 is no1 1he graphs 1ha1 are 1he mos1 impor1an1 issue. O1her pa11erns, such as 1ime of 57 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR Figure 21—Z vs. F example showing resonant frequencies due to power factor correction capacitor day, of1en provide 1he key 1o da1a in1erpre1a1ion. Pa11erns do no1 have 1o be graphical, bu1 can also be 1ex1ual in na1ure. Recognizing 1hese addi1ional pa11erns will be of grea1 benefi1 in solving 1he power sys1em puzzle. 8.4.7.2 Analysis tips The key 1o pa11ern recogni1ion is 1ha1 few dis1urbance pa11erns occur na1urally—mos1 are man-made. Analyzing 1hem involves simply 1racking down wha1 migh1 be 1he cause and how migh1 1his cause impac1 1he opera1ion of o1her equipmen1. The following 1able shows some 1ypical examples of 1hese 1iming rela1ionships. Table 2—Pattern recognition Patterns Possible causes Time of day Power fac1or correc1ion capaci1ors being 1urned on au1oma1ically Parking lo1 ligh1s 1urning on or off ei1her au1oma1ically or wi1h pho1oelec1ric swi1ches HVAC/Ligh1ing sys1ems on au1oma1ic con1rol Dura1ion of dis1urbance Cyclical loads such as pumps and mo1ors Laser prin1er hea1ing elemen1s cycling on for only 10–30 s Timing con1rols on process/manufac1uring equipmen1 Frequency of occurrence Con1inuous cycling of hea1ing elemen1 in laser prin1er, copiers Transien1s from SCR con1rolled devices occurring every cycle Vending/Soda machine compressor mo1or crea1ing 1ransien1s a1 1urn on 8.4.8 Discontinuities 8.4.8.1 Scope Discon1inui1ies refer 1o 1he radical depar1ure of some sys1em componen1 from 1he norm, which 1he models canno1 explain. In a sense 1hey are a subse1 of signa1ures because 1hey do exhibi1 a graphical pa11ern, ye1 1hey are differen1 because 1hey represen1 1he exis1ence of ou1side influencing fac1ors. The 1wo mos1 prominen1 ou1side fac1ors are mi1iga1ing devices and al1erna1e sources. 58 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 8.4.8.2 Analysis tips The single mos1 impor1an1 1echnique 1o iden1ify discon1inui1ies is an unders1anding of how 1he power sys1em should behave. Depar1ures from normal elec1rical sys1em response (forced or na1ural) usually indica1e 1he exis1ence of some ou1side fac1or. The following lis1 is helpful in discovering whe1her or no1 1here has been ou1side influence. — Did 1he frequency of 1he signal abrup1ly change? — Do 1he zero crossings of 1he signal remain con1inuous? — Did a magni1ude change occur ins1an1aneously, or did i1 1ake a li11le 1ime 1o se11le? — Did 1he signal suddenly lose a por1ion of a cycle consis1en1 wi1h loose wiring? 8.5 Verifying data interpretation Al1hough 1his is 1he las1 subclause of 1his clause, i1 is by no means 1he leas1 impor1an1. This clause has primarily focused on 1aking clues, piecing 1hem 1oge1her, and arriving a1 a solu1ion, or a1 leas1 a very good guess. The final s1ep in 1he process of da1a in1erpre1a1ion is 1o double check 1he solu1ion (or guess) 1o see if i1 is, indeed, 1he righ1 one for 1he problem. This can be easily done 1hrough examining 1he following guidelines in 8.5.1 and 8.5.2 for pos1-moni1oring. An al1erna1ive verifica1ion is 1o u1ilize compu1er simula1ion 1ools. Many such programs are available 1ha1 allow a user 1o “1es1” 1he validi1y of a proposed solu1ion, especially if 1rial and error me1hods are risky or 1oo expensive. 8.5.1 Post-monitoring for verification Once a solu1ion has been implemen1ed, pos1-moni1oring de1ermines 1he success of 1he solu1ion. I1 a11emp1s 1o answer 1he following ques1ions: — Is 1he failing equipmen1 now opera1ing correc1ly? — Is 1here a reduc1ion or elimina1ion of 1he dis1urbance(s) in ques1ion? If 1he answer is “no” 1o ei1her of 1hese ques1ions, 1hen fur1her inves1iga1ion is warran1ed. This is no1 1o say 1ha1 1he solu1ion is wrong. Some1imes i1 may be, bu1 of1en, solving one problem simply allows 1he nex1 1o surface. 8.5.2 Post-monitoring for system interaction Since 1he power sys1em is jus1 1ha1, a sys1em, changing one par1 of 1he sys1em may affec1 o1her par1s. I1 is en1irely possible 1ha1 1he “solu1ion” 1o a problem may ac1ually in1roduce ano1her problem in1o 1he sys1em. For example, if 1he problem is 1ha1 a vending machine injec1s 1ransien1s in1o 1he power lines and disrup1s a work s1a1ion, 1he solu1ion may be 1o plug 1he vending machine in1o a differen1 recep1acle. This works fine for works1a1ion #1, bu1 now works1a1ion #2 has problems because 1he vending machine is now plugged in1o i1s recep1acle. Pos1-moni1oring helps 1o de1ermine if any o1her concerns have come up due 1o 1he implemen1a1ion of a solu1ion. 59 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR Annex A (informative) Calibration and self testing A.1 Introduction Elec1rical measuremen1s and 1he ancillary field of me1er calibra1ion are 1wo aspec1s of 1he same indus1ry. As new advances are made in measuremen1 ins1rumen1 1echnology, new calibra1ion 1echnology is demanded 1o keep 1hese ins1rumen1s a1 peak performance and main1ain 1heir 1raceabili1y 1o na1ional s1andards. Calibra1ion requiremen1s should be based upon moni1oring objec1ives and 1he na1ure of loads, no1 on 1he specific ins1rumen1 used. We should ask ourselves, “Wha1 are 1he consequences if 1he measuremen1s do no1 mee1 specifica1ion?” If we are measuring vol1age 1o ANSI C84.1-1989 [B1] specifica1ions, 1he 1olerance is ±5%, s1eady s1a1e. There can be occasional excursions ou1side 1his boundary. Wha1 are 1he accuracy and calibra1ion requiremen1s for compliance wi1h ANSI C84.1-1989? The documen1 does no1 describe any. I1 does say 1ha1 1he measured values mus1 be in rms values bu1 does no1 indica1e whe1her 1he values can be de1er mined by means of peak recording vol1-me1er 1echnology 1ha1 uses an algori1hm 1o conver1 1o rms. This me1hod is no1 accura1e wi1h dis1or1ed waveshapes. ANSI C84.1-1989 defines s1eady-s1a1e as sus1ained vol1age levels and no1 momen1ary vol1age excursions. Wha1 if, however, we use an ins1rumen1 1ha1 1akes periodic snapsho1s and 1hen calcula1es an average? Is 1ha1 me1hod accura1e? How can one say 1ha1 calibra1ion has meaning 1o 1ha1 ins1rumen1 in an absolu1e sense? O1her fac1ors 1o be considered include 1he assump1ions of 1he ins1rumen1 maker. If we are 1o measure 1rue rms values accura1ely under all dis1or1ed condi1ions, 1hen 1here are only 1wo op1ions 1o consider—we can ei1her digi1ally sample mul1iple poin1s on 1he wave of a whole cycle and calcula1e 1he 1rue rms value, or we can measure 1he hea1 genera1ed in a resis1or. Can one sample a 1oken number of cycles and average 1hem? Possibly, excep1 1ha1 voids in 1he da1a may resul1. The accuracy of measuring 1he magni1ude of 1he ac vol1age bo1h s1eady-s1a1e and 1ransien1 dis1urbances canno1 be separa1ed from 1he process of how 1he ins1rumen1 records 1he measuremen1. Peak de1ec1ing, averaging and special algori1hms only work where 1here is limi1ed waveform dis1or1ion. 60 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 Figure A.1—Instrument accuracy is the combination of (a) random errors and (b) systematic component errors A.2 Calibration issues A.2.1 Drift rate The 1ime span of a specifica1ion indica1es 1he leng1h of 1ime an ins1rumen1 can be expec1ed 1o remain wi1hin 1he specified limi1s. One 1o 1wo years are common 1ime spans for por1able ins1rumen1s. Uncer1ain1ies will increase for longer 1ime spans due 1o a drif1 ra1e. If a drif1 ra1e specifica1ion is included, a buyer can calcula1e 1he uncer1ain1y for 1he 1ime span required. A.2.2 Temperature coefficient This represen1s 1he amoun1 1ha1 uncer1ain1y increases wi1h 1empera1ure varia1ion from a specified 1empera1ure spread. A 1ypical 1empera1ure spread is 23 °C (73°F) ±5 °C. A wide 1empera1ure spread and a small 1em pera1ure coefficien1 permi1 on-si1e calibra1ion since 1he ins1rumen1s are ou1side 1he pro1ec1ed environmen1 of 1he calibra1ion labora1ory. A.2.3 Where to calibrate Calibra1ing a working ins1rumen1 in i1s real environmen1 is inheren1ly more accura1e because local affec1s are 1aken in accoun1, and on-si1e calibra1ion is safer since 1he ins1rumen1 is no1 subjec1 1o damage in 1ransi1. Also, 1he ins1rumen1 is ou1 of commission a shor1er 1ime. Con1rary argumen1 says, “should ‘local effec1s' be included or purposely dele1ed from calibra1ion?” If i1 affec1s and crea1es a more accura1e measuremen1 a1 one si1e, does no1 1ha1 na1urally mean i1 may produce less accura1e da1a a1 ano1her si1e? A.2.4 Calibration intervals A broad guideline is provided by mili1ary specifica1ion MIL-L-45662B [B28]. Tes1 equipmen1 and s1andards should be calibra1ed a1 in1ervals es1ablished on 1he basis of s1abili1y, purpose, degree of usage, precision, accuracy and skills of personnel u1ilizing 1he equipmen1. 61 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR Some ins1rumen1s offer buil1-in calibra1ion. I1 is impor1an1 1o know exac1ly wha1 a buil1-in calibra1or is 1es1ing. In1ernal self-1es1 can be limi1ed by i1s own processing procedure, so i1 is impor1an1 1o de1ermine wha1 1ype i1 uses. In1ernal 1es1ing can be limi1ed by providing only a couple of poin1s on a spec1rum 1o 1ry 1o valida1e performance whereas a labora1ory calibra1or would genera1e a whole spec1rum of poin1s; 80 poin1s migh1 be an average. In1ernal 1es1 may only 1es1 one sec1ion a1 a 1ime and a1 low signal levels. The user mus1 de1ermine if 1ha1 me1hod is adequa1e. Buil1-in self-calibra1ion and self-1es1 may no1 be able 1o genera1e high vol1ages necessary 1o 1es1 1he fron1 end circui1ry of 1he ins1rumen1. A calibra1ion labora1ory would normally use a s1andard 1ha1 is four 1imes more accura1e 1han 1he ins1rumen1 being calibra1ed 1o valida1e accuracy. This s1andard is difficul1 1o reproduce wi1h a buil1-in device. A.2.5 Calibration points Manufac1urer's manuals for 1he ins1rumen1s 1ha1 will be calibra1ed are an impor1an1 reference. Normally, 1hese manuals include recommended calibra1ion procedures along wi1h a se1 of calibra1ion poin1s, for example, a DMM's calibra1ion poin1s would include vol1age levels, frequencies, and resis1ances. A.2.6 Self testing Self 1es1ing is a buil1 in fea1ure of some ins1rumen1s 1ha1 by means of firmware and special circui1ry i1 can make some limi1ed in1ernal checks. The abili1y 1o run in1ernal calibra1ion checks be1ween ex1ernal calibra1ion allows 1he opera1or 1o moni1or 1he performance be1ween calibra1ions and helps 1o avoid da1a problems. If 1he ins1rumen1's in1ernal references are well con1rolled and impervious 1o environmen1al changes, 1hen 1hese calibra1ion checks can be performed wi1h 1he ins1rumen1 in i1s working environmen1. This ins1ills confidence wi1hou1 1he need 1o re1urn 1he ins1rumen1 1o 1he calibra1ion lab. No1e 1ha1 1hese calibra1ion checks do no1 adjus1 1he ins1rumen1's ou1pu1, bu1 merely evalua1e 1he ins1rumen1's ou1pu1 agains1 in1ernal references. Comparison of 1he in1ernal reference values 1o ex1ernal 1raceable s1andards is necessary 1o make 1raceable in1ernal adjus1men1s. A.2.7 Practical field checks On mul1i-channel analyzers, link all channels 1oge1her and crea1e a dis1urbance. If all channels indica1e same even1/magni1ude/dura1ion 1hen calibra1ion is probably adequa1e. 62 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 Annex B (informative) Bibliography B.1 Definitions and general [B1] ANSI C84.1-1989, American Na1ional S1andard for Elec1ric Power Sys1ems and Equipmen1—Vol1age Ra1ings (60 Hz). [B2] ANSI/NFPA 70-1993, Na1ional Elec1rical Code (NEC). [B3] “Basic Measuring Ins1rumen1s,” Handbook of Power Signatures, Second Edi1ion, 1993. [B4] “Canadian Elec1rical Associa1ion Na1ional Power Quali1y Survey,” CEA Publica1ion Number 220D711A, 1995.5 [B5] “Drane1z Technologies,” The Dranetz Field Handbook for Power Quality Analysis, 1991. [B6] FIPS PUB 94, Guideline on Elec1rical Power for ADP Ins1alla1ions, 1983. [B7] IEC 1000-2-2 (1990) Elec1romagne1ic Compa1ibili1y (EMC)—Par1 2: Environmen1. Sec1ion 2: Compa1ibili1y levels for low-frequency conduc1ed dis1urbances and signalling in public low-vol1age power supply sys1ems, Sec1ion 2, 1990. [B8] IEC 1000-3-3 (1994) Elec1romagne1ic compa1ibili1y (EMC)—Par1 3: Limi1s. Sec1ion 3: Limi1a1ion of vol1age fluc1ua1ions and flicker in low-vol1age supply sys1ems for equipmen1 wi1h ra1ed curren1 16 A. NOTE—This s1andard supersedes IEC 555-3 (1982). [B9] IEC 1000-4-7 (1991) Elec1romagne1ic Compa1ibili1y (EMC)—Par1 4: Tes1ing and Measuremen1 Techniques. General guide on harmonics and in1erharmonics measuremen1s and ins1rumen1a1ion, for power supply sys1ems and equipmen1 connec1ed here1o, Sec1ion 7. [B10] IEC Technical Commi11ee 77, Working Group 6 (Secre1aria1) 110-R5, Classifica1ion of Elec1romagne1ic Environmen1s. Draf1, January 1991. [B11] IEEE S1d 141-1993, IEEE Recommended Prac1ice for Elec1ric Power Dis1ribu1ion for Indus1rial Plan1s (Red Book) (ANSI). [B12] IEEE S1d 446-1987, IEEE Recommended Prac1ice for Emergency and S1andby Power Sys1ems for Indus1rial and Commercial Applica1ions (Orange Book) (ANSI). [B13] IEEE S1d 519-1992, IEEE Recommended Prac1ices and Requiremen1s for Harmonic Con1rol in Elec1ric Power Sys1ems (ANSI). [B14] IEEE Surge Pro1ec1ion S1andards Collec1ion (C62), 1992 Edi1ion. 5Canadian Elec1rical Associa1ion publica1ions are available from 1he Canadian Elec1rical Associa1ion, 1 Wes1moun1 Square, Sui1e 1600, Mon1real, Canada H3Z 2P9. 63 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR [B15] UIE-DWG-2-92-D, UIE Guide 1o Measuremen1s of Vol1age Dips and Shor1 In1errup1ions Occurring in Indus1rial Ins1alla1ions, Oc1ober 1993. [B16] UIE-DWG-3-92-G, Guide to Quality of Klectrical Supply for Industrial Installations, “Par1 1: General In1roduc1ion 1o Elec1romagne1ic Compa1ibili1y (EMC), Types of Dis1urbances and Relevan1 S1andards,” Advance UIE Edi1ion, Dis1urbances Working Group GT 2, 1994. [B17] UL 1478 (1989), Fire pump relief valves. [B18] UL 1950 (1993), Safe1y of informa1ion 1echnology equipmen1, including elec1rical business equipmen1. B.1.1 Introductory [B19] Allen and Segall, “Moni1oring of Compu1er Ins1alla1ions for Power Line Dis1urbances,” IKKK PKS, C74 199-6, 1974. [B20] Burke, James; Griffi1h, David; and Ward, Dan, “Power Quali1y—Two Differen1 Perspec1ives,” IKKK Transactions on Power Delivery, vol. 5, no.3, pp. 1501–1513, July 1990. [B21] Dorr, D. S., “AC Power Quali1y S1udies IBM, AT&T and NPL,” INTKLKC '91, Koyo1o, Japan. [B22] Douglas, John, “Quali1y of Power in 1he Elec1ronics Age,” Klectric Power Research Institute KPRI Journal, Nov. 1985. [B23] Golds1ein and Speranza, “The Quali1y of US Commercial Power” INTKLKC, CH1818-4/82-0000002B, 1982. [B24] Jerewicz, R. E., “Power Quali1y S1udy 1990-1995,” INTKLKC, CH 29289-0/90/0000/0443. [B25] Key, Thomas S., “Diagnosing Power-Quali1y-Rela1ed Compu1er Problems,” IKKK Transactions on Industry Applications, IA-I5, No. 4, July/Aug. 1979. [B26] Lawrie, Rober1 J., Ed., Klectrical Systems for Computer Installations. New York: McGraw-Hill, 1988. [B27] Meh1a, H. and Smi1h, J. C., “Impor1an1 Power Quali1y Concerns on 1he Supply Ne1work,” PQA '91, Paris, France, 1991. [B28] MIL-L-45662B, Calibra1ion Sys1ems Requiremen1s. [B29] Nailen, Richard L., “How To Comba1 Power Line Pollu1ion,” Klectrical Apparatus, Dec. 1984. [B30] Reason, John, “End-Use Power Quali1y: New Demand on U1ili1ies,” Klectrical World, Nov. 1984. [B31] Rechs1einer, Emil B., “Clean, S1able Power for Compu1ers,” KMC Technology & Interference Control News, vol. 4, no. 3, July–Sep1. 1985. B.1.2 In-depth overview [B32] Clemmensen, Jane M. and Ferraro, Ralph J., “The Emerging Problem of Elec1ric Power Quali1y,” Public Utilities Fortnightly, Nov. 28, 1985. 64 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 [B33] Mar1zloff, François D. and Gruzs, Thomas M., “Power Quali1y Si1e Surveys: Fac1s, Fic1ion, and Fallacies,” IKKK Transactions on Industry Applications, vol. 24, no. 6, Nov./Dec. 1988. [B34] Smi1h, J. Charles, “Power Quali1y: End User Impac1s,” Proceedings of Knergy Technology Conference XV, Washing1on, D.C., Feb. 1988. B.2 Susceptibility and symptoms—voltage disturbances and harmonics B.2.1 Voltage disturbances [B35] S1andler, Ronald B., “Transien1s on 1he Mains in a Residen1ial Environmen1,” IKKK Transactions on Klectromagnetic Compatibility, vol. 31, no. 2, May 1989. B.2.2 Harmonics [B36] Arrillaga, Bradley, and Bodger, Power System Harmonics. John Wiley & Sons, 1985. [B37] Fuchs, E. F., “Inves1iga1ions on 1he Impac1 of Vol1age and Curren1 Harmonics on End-Use Devices and Their Pro1ec1ion,” The U.S. Department of Knergy, con1rac1 no. DE-AC02-80RA 50150, Jan. 1987. [B38] Lowens1ein, Michael Z., Holley, Jim, and Zucker, Myron, “Con1rolling Harmonics While Improving Power Fac1or,” Klectrical Systems Design, March 1988. [B39] Shu1er, T. C., Volkommer, Jr., H. T., and Kirkpa1rick, T. L., “Survey of Harmonic Levels on 1he American Elec1ric Power Dis1ribu1ion Sys1em,” IKKK Transactions on Power Systems, Oc1., 1989, pp. 2204–2210. B.3 Solutions B.3.1 Utility approach [B40] Clemmensen, Jane M. and Samo1yj, Marek J., “Elec1ric U1ili1y Op1ions in Power Quali1y Assurance,” Public Utilities Fortnightly, June 11, 1987. [B41] Tempchin, Richard S. and Clemmensen, Jane M., “Transforming Power Quali1y Problems in1o Marke1ing Oppor1uni1ies,” Klectric Perspectives, July-Aug. 1989. B.3.2 Wiring and electrical design [B42] Freund, Ar1hur, “Double 1he Neu1ral and Dera1e 1he Transformer—Or Else,” KC&M, Dec. 1988. [B43] Lazar, Irwin A., “Designing Reliable Power Sys1ems for Processing Plan1s,” Klectrical Systems Design, July 1989. [B44] Lewis, Warren, “Applica1ion of 1he Na1ional Elec1rical Code 1o 1he Ins1alla1ion of Sensi1ive Elec1ronic Equipmen1,” IKKK Transactions on Industrial Applications, vol IA-22, May/June 1986. [B45] McLoughlin, Rober1 C., “Power Line Impedance and I1s Effec1 on Power Quali1y,” KMC Technology & Interference Control News, vol. 7, no. 6, Sep1. 1988. 65 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR [B46] Schram, Pe1er J., “Coping wi1h 1he Code— Ano1her Revision is Jus1 Around 1he Corner,” Klectrical Systems Design, July 1989. [B47] Sopkin, Louis, “Capaci1ors Correc1 Power Fac1or, Line Vol1age, and Wave Dis1or1ion,” Klectrical Systems Design, March 1988. B.3.3 Surge suppression [B48] Mar1zloff, François D., “Ma1ching Surge Pro1ec1ive Devices 1o 1heir Environmen1,” IKKK Transactions on Industrial Applications, vol. IA-21, no. 1, Jan./Feb. 1985. [B49] Shakarjian, D. R. and S1andler, “AC Power Dis1urbance De1ec1or Circui1,” IKKK Transactions on Power Delivery, vol. 6: pp. 536-540, April 1991. [B50] Smi1h, S.B. and S1andler, “The Effec1s of Surges on Elec1ronic Appliances,” IKKK Transactions on Power Delivery, vol. 7, pp. 1275–1282, July 1992. [B51] S1andler, Protection of Klectronic Circuits from Overvoltages. New York: Wiley-In1erscience, May 1989. B.3.4 UPS and power conditioning [B52] Cooper, Edward, “Power Line Condi1ioning,” Measurements and Control, June 1985. [B53] Edman, James, “Selec1ing a UPS for Today's Sys1ems Requiremen1s,” KMC Technology & Interference Control News, vol. 4, no. 3, July–Sep1. 1985. [B54] Griffi1h, David C., “Selec1ing and Specifying UPS Sys1ems,” Klectrical Consultant for Designers and Specißer of Klectrical Systems, May/June and July/Aug., 1981. [B55] Madoo, Timo1hy and Rynone, William, “Choosing a UPS Sys1em—Consider Before You Buy,” Klectrical Systems Design, May 1987. [B56] Madoo, Timo1hy and Rynone, William, “Choosing a UPS Sys1em,” Klectrical Systems Design, June 1987. [B57] Madoo, Timo1hy and Rynone, William, “Wha1 You Can Tell Your Clien1 Abou1 High-Powered UPS Sys1ems,” Klectrical Systems Design, April 1987. [B58] Meirick, R. P., “The Evolu1ion of Unin1errup1ible Power Supplies,” PCIM Power Conversion & Intelligent Motion, Oc1. 1989. [B59] S1urgeon, Jeffrey B., “UPS—Providing Power You Can Coun1 On When Things Go Wrong,” Klectrical Systems Design, May 1989. [B60] Walsh, John J., “UPS/M-G: Quali1y Compu1er Power,” Klectrical Systems Design, May 1989. B.3.5 Electrostatic discharge [B61] Boxlei1ner, Warren, “How 1o Defea1 Elec1ros1a1ic Discharge,” IKKK Spectrum, Aug. 1989. 66 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 B.3.6 Harmonics solutions [B62] Griffi1h, David C. and Resch, Rober1 J., “Working wi1h Waveform Dis1or1ion in Digi1al Sys1ems,” Powertechnics, Sep1. 1986. [B63] McGranaghan, Mark and Mueller, Dave, Designing Harmonic Filters for Adjustable Speed Drives to Comply with New IKKK Std 519 Harmonic Limits. IEEE Indus1rial Applica1ions Socie1y, 401h Annual Conference, 1993. [B64] McGranaghan, Mark; Grebe, Thomas; and Samo1yj, Marek, “Solving Harmonic Problems in Indus1rial Plan1s and Harmonic Mi1iga1ion Techniques for Adjus1able-Speed Drives,” Paper Presen1ed a1 Elec1ro1ech 92, Mon1real, Canada, 1992. B.4 Existing power quality standards Exis1ing power quali1y s1andards are lis1ed in 1his subclause in order 1o provide resource informa1ion 1ha1 may be of par1icular in1eres1 when making power quali1y measuremen1s. S1andards rela1ing 1o power quali1y 1ha1 exis1 or are under developmen1 a1 1his 1ime are lis1ed below. A brief scope is anno1a1ed following mos1 of 1he sources, and availabili1y informa1ion is lis1ed in 1he foo1no1es. [B65] ANSI C84.1-1989, Elec1ric Power Sys1ems and Equipmen1—Vol1age Ra1ings (60 Hz).6 [Voltage rating for power systems and equipment.] [B66] ANSI C141 Flicker (1975 Edi1ion). [B67] ANSI/NFPA 70-1993, Na1ional Elec1rical Code (NEC). [Installation grounding, ADP equipment, interconnected electric power production sources.] [B68] FIPS PUB94, Guideline on Elec1rical Power for ADP Ins1alla1ions, 1983.7 [Klectric power for ADP installations.] [B69] IEC 1000 Series, Elec1romagne1ic Compa1ibili1y (EMC). [B70] IEEE S1d 141-1993, IEEE Recommended Prac1ice for Elec1ric Power Dis1ribu1ion for Indus1rial Plan1s (IEEE Red Book) (ANSI). [Industrial electrical power systems.] [B71] IEEE S1d 142-1991, IEEE Recommended Prac1ice for Grounding of Indus1rial and Commercial Power Sys1ems (IEEE Green Book) (ANSI). [Industrial and commercial power system grounding.] [B72] IEEE S1d 241-1990, IEEE Recommended Prac1ice for Elec1ric Power Sys1ems in Commercial Buildings (IEEE Gray Book) (ANSI). [Commercial electric power systems.] [B73] IEEE S1d 242-1986, IEEE Recommended Prac1ice for Pro1ec1ion and Coordina1ion of Indus1rial and Commercial Power Sys1ems (IEEE Buff Book) (ANSI). [Industrial and commercial power system protection.] 6ANSI publica1ions are available from 1he Sales Depar1men1, American Na1ional S1andards Ins1i1u1e, 11 Wes1 42nd S1ree1, 131h Floor, New York, NY 10036, USA. 7FIPS publica1ion are available from 1he Na1ional Technical Informa1ion Service, US Depar1men1 of Commerce, Springfield, VA 22161. 67 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR [B74] IEEE S1d 399-1990, IEEE Recommended Prac1ice for Indus1rial and Commercial Power Sys1ems Analysis (IEEE Brown Book) (ANSI). [Industrial and commercial power system analysis.] [B75] IEEE S1d 446-1987, IEEE Recommended Prac1ice for Emergency and S1andby Power Sys1ems for Indus1rial and Commercial Applica1ions (IEEE Orange Book) (ANSI). [Industrial and commercial power system emergency power.] [B76] IEEE S1d 487-1992, IEEE Recommended Prac1ice for 1he Pro1ec1ion of Wire Line Communica1ions Facili1ies Serving Elec1ric Power S1a1ions. [B77] IEEE S1d 493-1990, IEEE Recommended Prac1ice for 1he Design of Reliable Indus1rial and Commercial Power Sys1ems (IEEE Gold Book) (ANSI). [Industrial and commercial power system reliability.] [B78] IEEE S1d 518-1982, IEEE Guide for 1he Ins1alla1ion of Elec1rical Equipmen1 1o Minimize Noise Inpu1s 1o Con1rollers from Ex1ernal Sources (Reaff 1990) (ANSI). [Guide on noise control.] [B79] IEEE S1d 519-1992, IEEE Recommended Prac1ices and Requiremen1s for Harmonic Con1rol in Elec1ric Power Sys1ems (ANSI). [Recommended practice on harmonics in power systems.] [B80] IEEE P519a (D4, 9/95), Guide for Applying Harmonic Limi1s on Power Sys1ems.8 [B81] IEEE S1d 602-1986, IEEE Recommended Prac1ice for Elec1ric Sys1ems in Heal1h Care (ANSI). [Industrial and commercial power system in health facilities.] [B82] IEEE S1d 739-1984, IEEE Recommended Prac1ice for Energy Conserva1ion and Cos1-Effec1ive Planning in Indus1rial Facili1ies (IEEE Bronze Book) (ANSI). [Knergy conservation in industrial power systems.] [B83] IEEE S1d 929-1988 (Reaff 1991), IEEE Recommended Prac1ice for U1ili1y In1erface of Residen1ial and In1ermedia1e Pho1ovol1aic (PV) Sys1ems (ANSI). [Interconnection practices for photovoltaic power systems.] [B84] IEEE S1d 1001-1988, IEEE Guide for In1erfacing Dispersed S1orage and Genera1ion Facili1ies wi1h Elec1ric U1ili1y Sys1ems (ANSI). [Interfacing dispersed generation and storage.] [B85] IEEE S1d 1035-1989, IEEE Recommended Prac1ice: Tes1 Procedure for U1ili1y-In1erconnec1ed S1a1ic Power Conver1ers (ANSI). [Test procedures for interconnecting static power converters.] [B86] IEEE S1d 1050-1989, IEEE Guide for Ins1rumen1a1ion and Con1rol Equipmen1 Grounding in Genera1ing S1a1ions (ANSI). [Grounding of power station instrumentation and control.] [B87] IEEE S1d 1100-1992, IEEE Recommended Prac1ice for Powering and Grounding Sensi1ive Elec1ronic Equipmen1 (Emerald Book) (ANSI). [Power and grounding sensitive equipment.] 8S1andard projec1 IEEE P519a was no1 approved by 1he IEEE S1andards Board a1 1he 1ime 1his wen1 1o press. I1 is available from 1he IEEE. 68 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. MONITORING ELECTRIC POWER QUALITY IEEE Std 1159-1995 [B88] IEEE S1d 1250-1995, IEEE Guide for Service 1o Equipmen1 Sensi1ive 1o Momen1ary Vol1age Dis1urbances (ANSI). [B89] IEEE P1346 (D2.0, 9/95), Recommended Prac1ice or Evalua1ing Elec1ric Power Sys1em Compa1ibili1y Wi1h Elec1ronic Process Equipmen1.9 [B90] IEEE S1d C57.110-1986 (Reaff 1992), IEEE Recommended Prac1ice for Es1ablishing Transformer Capabili1y When Supplying Nonsinusoidal Load Curren1s (ANSI). [B91] IEEE S1d C62.41-1991, IEEE Recommended Prac1ice on Surge Vol1ages in Low-Vol1age AC Power Circui1s (ANSI). [B92] IEEE Dis1ribu1ion, Power, and Regula1ing Transformers S1andards Collec1ion, 1995 Edi1ion (C57) (ANSI). [B93] IEEE Surge Pro1ec1ion S1andards Collec1ion, 1995 Edi1ion (C62) (ANSI). [B94] NEMA-PE1 (1992), Unin1errup1ible Power Sys1ems.10 [Uninterruptible power supply specißcations.] [B95] NEMA MG1 (1993), Mo1ors and Genera1ors. [Polyphase induction motors.] [B96] NFPA-75 (1995), Pro1ec1ion of elec1ronic compu1er da1a processing equipmen1.11 [Protection of electronic computer data processing equipment]. [B97] NFPA-780-95, Ligh1ing pro1ec1ion code. [Lighting protection code for buildings.] [B98] NIST-SP768, Informa1ion pos1er on power quali1y.12 [Overview of power quality with respect to sensitive electrical equipment.] [B99] UL 1449 (1995), Transien1 vol1age surge suppressors.13 [Standards for safety of transient voltage surge suppressors (tvss).] 9S1andard projec1 IEEE P1346 was no1 approved by 1he IEEE S1andards Board a1 1he 1ime 1his wen1 1o press. I1 is available from 1he IEEE. 10NEMA publica1ions are available from 1he Na1ional Elec1rical Manufac1urers Associa1ion, 2101 L S1ree1 NW, Sui1e 300, Washing1on, DC 20037, USA. 11NFPA publica1ions are available from Publica1ions Sales, Na1ional Fire Pro1ec1ion Associa1ion, 1 Ba11erymarch Park, P.O. Box 9101, Quincy, MA 02269-9101, USA. 12NIST publica1ion SP868 (order number PB89237986) is available from 1he Na1ional Technical Informa1ion Service 1-800-553-6847. 13UL publica1ions are available from Underwri1ers Labora1ories, Inc., 333 Pfings1en Road, Nor1hbrook, IL 60062-2096, USA. 69 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply. IEEE Std 1159-1995 IEEE RECOMMENDED PRACTICE FOR The following 1able lis1s 1opics wi1h corresponding relevan1 s1andards. For addi1ional informa1ion on 1hese s1andards, refer 1o 1he no1ed bibliography references. Table B.1—Power quality standards by topic Topics Relevant standards Grounding IEEE S1d 446 [B75] IEEE S1d 141 [B70] IEEE S1d 142 [B71] IEEE S1d 1100 [B87] ANSI/NFPA 70 [B67] Powering ANSI C84.1 [B65] IEEE S1d 141 [B70] IEEE S1d 446 [B75] IEEE S1d 1100 [B87] IEEE S1d 1250 [B88] Surge pro1ec1ion IEEE C62 series [B93] IEEE S1d 141 [B70] IEEE S1d 142 [B71] NFPA 78 [B97] UL 1449 [B99] Harmonics IEEE S1d C57.110 [B90] IEEE S1d 519 [B79] IEEE P519a [B80] IEEE S1d 929 [B83] IEEE S1d 1001 [B87] Dis1urbances ANSI C62.41 [B91] IEEE S1d 1100 [B87] IEEE S1d 1159a IEEE S1d 1250 [B88] Life/fire safe1y FIPS PUB94 [B68] ANSI/NFPA 70 [B67] NFPA 75 [B96] UL 1478 [B17] UL 1950 [B18] Mi1iga1ion equipmen1 IEEE S1d 446 [B75] IEEE S1d 1035 [B85] IEEE S1d 1100 [B87] IEEE S1d 1250 [B88] NEMA-UPS [B94] Telecommunica1ions equipmen1 FIPS PUB94 [B68] IEEE S1d 487 [B76] IEEE S1d 1100 [B87] Noise con1rol FIPS PUB94 [B68] IEEE S1d 518 [B78] IEEE S1d 1050 [B86] U1ili1y in1erface IEEE S1d 446 [B75] IEEE S1d 929 [B83] IEEE S1d 1001 [B84] IEEE S1d 1035 [B85] Moni1oring IEEE S1d 1100 [B87] IEEE S1d 1159 (see no1e f) Load immuni1y IEEE S1d 141 [B70] IEEE S1d 446 [B75] IEEE S1d 1100 [B87] IEEE S1d 1159a Sys1em reliabili1y IEEE S1d 493 [B77] IEEE P1346 [B89] a IEEE S1d 1159-1995 is 1his s1andard. 70 Authorized licensed use limited to: UNIV OF ALABAMA-BIRMINGHAM. Downloaded on December 04,2012 at 15:37:33 UTC from IEEE Xplore. Restrictions apply.
