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2015 International Symposium on Lightning Protection (XIII SIPDA), Balneário Camboriú, Brazil, 28 th Sept. – 2nd Oct. 2015.
Development of shield-type multi-chamber lightning
arrester for 35kV OHL
Streamer Electric Company, Saint-Petersburg, Russia
[email protected]
Podporkin, E.Yu. Enkin, V.V. Zhitenev, R.I. Zainalov, V.E. Pilshchikov, D.O. Belko.
Abstract – the paper presents an alternative to the traditional
method of lightning protection of 35 kV overhead lines based on
shield-type multi-chamber arresters. The main stages of the design
of arrester, and also shows the test results confirming compliance
with required characteristics.
second end of MCS is equipped with a rod lead directed
upwards.
а)
Keywords—component;
insulators-arresters,
lightning
protection, multi-chamber arresters, overhead power lines, power
arc, multi-chamber system, direct lightning strike, arc interruption.
I.
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INTRODUCTION
In order to ensure lightning protection of high-voltage
overhead lines (OHL) for 35-220kV, multi-chamber insulator
arresters (MCIA) [1] have been developed which are installed
in place of the existing suspended insulation. However, in
some cases replacement of insulation might be unreasonable
or complicated. In view of the above a goal of development of
multi-chamber arresters (MCA) for OHL protection has
become urgent. These arresters will be installed in parallel to
the protected insulation without its replacement.
4
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1
c)
The main working element of both MCIA and MCA being
developed is a multi-chamber system (MCS) (Fig. 1). It
contains a number of electrodes integrated in the profile of
silicone rubber. Between the adjoining MCS electrodes
cylindrical arc quenching chambers of specially designed
configuration are molded. Spark gaps are formed inside the
chambers.
d)
Fig. 1. Fragment of multi-chamber system:
a) plan view; b) side view, initial stage of spark discharge; c) side view,
last stage of spark discharge; d) discharge shaft cross-section, end view;
1 – silicon rubber profile; 2 – intermediate electrodes; 3 – arc suppression
chambers; 4 – spark discharge channel.
The arrester consists of two parts which look similar to
toroidal shields (hereinafter are referred for short to as
“shields" (see Fig. 2). Due to this, the arrester obtained its
name: shield-type MCA for 35kV OHL (or SAd35z in the
international market).
1
6
5
8
MCS’s are installed on a support structures made of
insulation material. The shields are fastened by insulation rods
to the upper and lower ends of the insulator string.
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1
The upper shield is installed on the string strap, the lower
one – on the eyelet. Shield to shield orientation can be
changed in order to provide the required value of the spark gap
between the tap leads. The shields support structures are
manufactured of insulating material and integrated in MCS by
means of hot moulding. It results in having a unified cast
structure.
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2
10
а)
b)
Fig. 2. SAd35z: a) general view; b) photograph of testing:
The first end of the lower MCS shield, via spark gap and
string mountings, is connected with line conductor, and the
978-1-4799-8754-2/15/$31.00 ©2015 IEEE
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b)
1– upper and lower shields with MCS; 2 – lower incoming electrode;
3 – lower tap lead; 4 – intermediate tap leads; 5 – upper incoming electrode;
6 – traverse; 7 – conductor; 8 – insulator; 9, 10 – spark gaps.
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Under the impact of voltage surge on the OHL conductor,
for instance, in case of a direct lightning stroke on the
conductor, the spark air spaces between the mountings and the
lower MCS shield and between the rod electrodes of the upper
and lower shields and MCS’s of both shields will be activated.
The current caused by lightning-caused overvoltage flows
from the conductor through the spark discharge gap of the
lower shield, and further through the MCS of this shield,
discharge gap between the intermediate tap leads, through the
MCS of the upper shield, along its metal rod, the tower and
goes to the ground (Fig. 2b)
TABLE 1. SAD35Z TESTING PROGRAM
No.
Electrical tests
At MCS operation sequential breakdown of spark gaps in
each arc quenching chamber occurs with formation of
conducting plasma channels (Fig. 1 a,b). Further on, under the
impact of applied voltage the current starts increasing in the
chambers. It causes heating of the arc channel, increase of its
diameter and, as a consequence, pressure increase inside the
chambers with arc carry-over from the discharge gap (Fig. 1
c,d). Arc effluence causes its elongation, displacement in cold
air, cooling and increase of channel electrical resistance.
1
Checking of arrester coordination with insulation in dry and
rain condition in case of voltage surge with a steep leading
edge.
2
Power frequency voltage withstand test in dry and rain
conditions.
3
Determination of 50% discharge characteristics under the
impact of lightning impulses of standard shape 1.2/50 μs.
4
Power Arc Follow (PAF) current quenching test.
5
Measuring of industrial radio interference level.
Climatic tests
Contact of the arc with chamber walls causes silicon
rubber evaporation (ablation). In addition to pressure increase
it modifies the chemical composition of the discharge. During
evaporation the silicon rubber (C2H6SiO)n adds therein the
components with high output activity (for instance, for
hydrogen H 13.6 eV) reducing the discharge channel
conductivity.
6
Impact of ambient temperature change
7
Salt fog test
8
Accelerated weathering test (IEC 62217)
Mechanical tests
9
Withstanding load
10
Vibration resistance test
III.
Impact of all these factors causes restoration of the
discharge gap electrical strength upon the follow current zero
crossing and prevents repetitive arc ignition.
DEVELOPMENT OF ARRESTER DESIGN
Diameter of SAd35z shield is selected based on the
requirement to install thereon the required number of MCS
discharge chambers capable to ensure stable quenching of the
PAF current with the specified greed voltage applied.
It is worth mentioning that the capability of arc quenching
chambers to displace the arc outside MCS allows dispersing
most of follow current energy in the ambient space. This
makes the design of MCS resistant to electrodynamic and
thermal impacts of the direct lightning strike surge current and
the follow current arc.
II.
Types of inspections and tests
SAd35z is intended for lightning protection of OHL 35kV
with insulated neutral or neutral grounded with resistance at
the substations. In both cases single-phase short circuit current
is significantly less than in case of phase-to-phase short
circuit. Due to this the case of phase-to-phase short circuit is
the defining one. Overvoltage occurring on the conductors of
OHL 35kV due to the lightning discharge effect may cause a
simultaneous operation of two SAd35z arresters of different
phases. The maximum operating line voltage in the 35kV grid
is Um.o.l= 35х1.15= 40.3 kVeff. (effective value). It is equally
divided between two arresters. Because of that each SAd35z
should ensure interruption of the follow current arc with 20.2
kVeff voltage, and one shield – with 10.1 kVeff voltage.
GENERAL MISSION STATEMENT
In the development of SAd35z it is necessary to resolve
several electrical engineering and design problems. Electrical
characteristics of the arrester should ensure reliable
coordination with the protected insulation and let it quench the
follow current caused power arc in case of any lightning
impact, including direct lightning strikes to the phase
conductor, backflashovers and induced overvoltrages. The
arrester should have a resistance to long-term weather
exposure (temperature, humidity, solar radiation), as well as to
mechanical impacts of wind and ice loads under low ambient
temperatures.
The length of spark gap between the shield tap leads (see
Fig. 2) should ensure insulation protection by coordinated
arrester operation in case of surge impact and allow preserving
the rated insulating strength under the normal operating
conditions.
In order to confirm the compliance of SAd35z with the
required specification, a testing program has been developed.
It includes all the main electrical, mechanical and climatic
tests (Table 1).
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IV.
POWER ARC FOLLOW (PAF) CURRENT INTERRUPTION
V. CHECKING OF ARRESTER COORDINATION WITH DRY
INSULATION AND IN THE RAIN IN CASE OF VOLTAGE SURGE
WITH A STEEP FRONT
TEST
The PAF current interruption test was conducted on a
high-voltage test bench represented by a high-voltage impulse
and current generator which imitates lightning impulse and a
generator imitating the grid current of power frequency. Both
generators work in parallel (Fig. 3). The lightning generator
parameters: current – up to 30kAа (a- amplitude), voltage –
300kVа, duration of current impulse till a half-value – 50 μs.
Grid generator has voltage amplitude up to 30kVа with follow
current up to 5 kAа (3.5 kAeff of effective value).
The coordination is checked to determine the maximum
value of spark gap between the intermediate tap leads of
shields at which a stable coordinated operation of the arrester
complete with the string is observed. The test was conducted
in dry conditions and in the rain by voltage surges with the
steepness of 2000kV/μs, which are more complicated
conditions for the coordinated arrester discharge than a
standard lightning impulse.
Fig. 3. Principal diagram of test bench
In case of direct lightning strike to the phase conductor,
lightning current is divided into two parts flowing to the
opposite direction from the point of strike. Depending on the
lightning current value and tower grounding resistance,
arresters installed on the neighboring towers may also operate
together with arresters installed on the towers nearest to the
strike location. Calculations made in [2] demonstrated that
with lightning currents less than 100kA, which happen in 95%
of cases, the current passing through the arrester does not
exceed 30kA.
Fig. 4. Typical voltage and current oscillograms for PAF current
quenching at zero point.
The testing method was represented by application of
impulses with gradual reduction of tap leads length by the
method of half-division until the first uncoordinated discharge
took place.
In the Russian Federation most of OHLs 35kV are
operated with three glass insulators in a string, but in certain
areas with high pollution level four insulators can be used.
Due to the above, the coordination test was conducted on two
types of strings (Fig. 5).
The arc interruption tests were conducted in three modes
with various amplitudes of impulse currents:
–
high impulse current 30kA of direct lightning strike
with t = 8/50 μs;
–
medium impulse current 10kA of direct lightning
strike with t = 8/50 μs;
–
back flashover mode 2.5 kA with t = 1/50 μs.
Impulse current and grid voltage of power frequency 10.5
kVeff were simultaneously applied to each test object (it was a
little higher than the necessary level of 10.1 kV eff, mentioned
above). Measuring instruments recorded the results –
quenching or failure to quench the follow current arc.
Each of 12 tested shields demonstrated stable follow
current arc interruption at zero level (Fig. 4) in all the variants
of pulse current with the stable of MCS mechanical integrity.
Fig. 5. Test of SAd35z for discharge coordination
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U, kV
Based on the results of the test, maximum values of spark
air gaps between the discharge elements were determined: 220
mm for three-insulator string and 300 mm for four-insulator
string.
VI.
400
POWER FREQUENCY WITHSTAND VOLTAGE TEST IN DRY
AND RAIN CONDITION
The test objective is to determine the minimum value of
the spark gap with which during one minute of application of
power frequency voltage at the level of 80 kV in the rain there
is no flashover. The test was conducted by the incremental
reduction of the spark gap by increasing tap leads up to the
mark of the value preceding the occurrence of the flashover.
The minimum value of the spark gap was 10 mm.
300
200
100
Summarizing the results of the coordination test and power
frequency withstand voltage test, the mean values of spark
gaps (200 mm for three-insulator string and 280 mm for fourinsulator string) with the constant length of coordination tap
leads of the upper and lower shields equal to 130 mm have
been determined.
L, mm
0
440
200
400
570
600
800
Fig. 6. Graph of dependence of 50% discharge voltage on the connecting
dimension of SAd35z on strings with three (440 mm) and four (570 mm)
insulators.
In order to determine a possibility to use SAd35z with
types of insulation other than the ones described above,
analysis of 50% arrester discharge characteristics was
conducted. It was conducted in dry conditions and in the rain
at six SAd35z arresters with three- and four-insulator strings
using tap leads of constant length. Averaged data of 50%
discharge voltages after their processing are presented in
Table 2.
VII.
MEASURING OF INDUSTRIAL RADIO INTERFERENCE
LEVEL
Initial design of SAd35z supposed the voltage
delivery to upper and lower MCS shields via carrying
electrodes executed as flat steel rods (Fig. 7а). This solution
seemed promising, because it looked simple and significantly
increased mechanical strength of the base structure.
TABLE 2. 50% DISCHARGE VOLTAGES AT SAD35Z UNDER THE
IMPACT OF LIGHTNING-CAUSED OVERVOLTAGES
50% discharge voltage
Number
of
insulators
in the
string
Connecting
dimension of
SAd35z
Three
440 / 200
Four
570 / 280
Insulation
condition
Positive
polarity
Negative
polarity
Dry
190
257
Rain
234
233
Dry
247
359
Rain
314
290
Based on the obtained data, graphs of dependence of 50%
discharge voltage on the connecting dimension of SAd35z on
strings with three (440 mm) and four (570 mm) insulators
were built (Fig. 6). By extending straight lines on the graph in
the opposite directions a possibility was obtained to estimate
applicability of SAd35z with various types of insulation
knowing their 50% discharge voltages and arrester connecting
dimensions. On the graph 50% discharge voltages of
insulation should be at least 20% above the arrester
characteristics.
а)
b)
Fig. 7. Design of input electrodes of SAd35z arrester:
a) input electrode without spark gap; b) with spark gap;
1 – steel rod; 2 – intermediate tap leads; 3 – insulation rod; 4 – lower
input electrode; 5 – additional spark gap; 6 – traverse; 7 – conductor ; 8 –
insulator.
However, performed calculations of electric field
distribution between the arrester structural elements
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discovered that when the maximum amplitude voltage of 32.9
kVа is applied thereto, then, in case of high potential input
directly in the MCS, the maximum electric field strength
occurred at the electrode of the lower shield first chamber, and
its value in this point was E ≈ 50kV/cm (Fig. 8а). This
significantly exceeded the level of corona ignition of
30kV/cm. With such electric field strength, in several first
chambers under the impact of operational voltage partial
discharges will continuously occur. They will cause radio
interference making not acceptable the initial voltage delivery
unit design.
shield is impacted by the distributed load of 15 kg. In order to
check shield base strength, a withstand load test under the
temperature minus 70˚С was conducted in the CNII RTK
laboratory. Shields were placed on the compact mountings,
which allowed the application of the required distributed load,
and this assembly was held for four hours in a climatic
chamber under the temperature below 70˚С. Immediately after
the chamber opening a two-fold load of 30kg was applied and
retained till complete defrosting. The test demonstrated that
the shield base material preserved its mechanical strength and
elasticity under the impact of 30-kg distributed load, which
twice exceeded ice weight with the wall thickness of 40 mm.
Reduction of electric field strength at the lower MCS
shield to 8kV/cm (Fig. 8 b) is achieved by the provision of the
air gap between the MCS and current-carrying accessories
(Fig. 7 b).
The shield was tested for vibration survival with
application of 15-kg distributed load, which imitated a
combined impact of wind and ice loads. In order to determine
the stiffness level, the analysis of resonance characteristics
was conducted according to 100-1 method of GOST
20.57.406-81. In the process of test object resonance
characteristics measuring Fres from 30 to 60Hz was revealed
with mechanical Q-factor up to 10. Based on the obtained
results the sixth degree of stiffness was selected according to
GOST 16692.2-90 and a test for vibration survival with the
frequency range from 10 to 80Hz was performed with
acceleration of 5 m/s² in one direction. The total duration of
the test was 6 hours. No damage to shield bases and
weakening of fasteners were observed.
For the upper shield, which has ground potential, due
to the shielding effect of the traverse the electric field strength
in the first chamber of the MCS is reduced to the acceptable
level of 20kV/cm.
Main characteristics of the arrester are provided in Table 3.
TABLE 3. MAIN TECHNICAL CHARACTERISTICS OF SAD-35Z
ARRESTER
Characteristic
а)
b)
Fig. 8. Visualization of electric field intensity in the first three chambers of the
lower shield:
Value
Voltage class, kV
35
Short circuit current effective value, kA
3.5
OHL protection against:
direct
strikes
a) input electrode of the lower shield without spark gap; b) with spark gap.
lightning
backflashovers
Measuring of industrial radio interference level at SAd35z
with the arranged spark gap at the lower shield demonstrated
that, when the voltage 1.1Ul.op = 44.5 kV is applied, radio
interference level was 32 dB (the norm is 55 dB).
Minimum commutation life, number of discharges
induced
overvoltages
10
Diameter of shield with MCS, mm
435
Length of intermediate tap leads, mm
130
Spark gap length with connecting dimensions of:
VIII. TEST OF RESISTANCE TO EXTERNAL IMPACT FACTORS
Required mechanical characteristics of the shield base are
ensured due to use of structural plastic Polyphenylene Sulfide
(PPS). This material is used in many industries, including
space, automotive, aircraft building, and has a high strength
and resistance to aggressive environmental impacts.
In the process of SAd35z operation the greatest concern is
caused by the mechanical strength of shield base material
under the impact of ice load in combination with extremely
low value of the ambient temperature. Based on the estimated
data, in case of ice wall of 44 mm (the highest degree), one
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440 mm…………………………………
200
570 mm…………………………………
280
Level of industrial radio interference, dB
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IX.
CONCLUSIONS
1. Multi-chamber shield-type arrester (SAd35z) is
designed for 35kV OHL protection against lightning-caused
overvoltages, including direct lightning strikes to the
conductor;
2. SAd35z is intended for use in the grids with shortcircuit current up to 3.5 kAeff;
3. The arrester is easy to install and operate on OHLs.
Implementation doesn’t require insulation replacement;
4. SAd35z successfully passed all electrical and
mechanical tests;
5. At the time of this article delivery additional climatic
tests for the impact of temperature change, solar radiation and
salt fog were not completed.
X.
REFERENCES:
[1] G. V. Podporkin, E. Yu. Enkin, E. S. Kalakutsky, V.E. Pilshikov, A.
D. Sivaev. “Overhead Lines Lightning Protection by Multi-chamber Arresters
and Insulator-arresters", IEEE Transactions on Power Delivery, vol. 26, No. 1,
January 2011, pp.214-221.
[2] G. V. Podporkin, E. Yu. Enkin, E. S. Kalakutsky, V. E. Pilshikov and
A. D. Sivaev. “Development of Multi-Chamber Insulator-Arresters for
Lightning Protection of 220kV Overhead Transmission Lines”, XI
International Symposium on Lightning Protection (SIPDA), 3-7 October
2011, Fortoleza, Brazil, Rep. 7-2.
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