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Corona discharge

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Tugas Teknik Tegangan Tinggi
Nama : Ericka Rhamadianty
NIM : 2016 11 258
Corona discharge
A corona discharge is an electrical discharge brought on by the ionization of a fluid such as
air surrounding a conductor that is electrically charged. Spontaneous corona discharges occur
naturally in high-voltage systems unless care is taken to limit the electric field strength. A
corona will occur when the strength of the electric field (potential gradient) around a
conductor is high enough to form a conductive region, but not high enough to cause electrical
breakdown or arcing to nearby objects. It is often seen as a bluish (or another color) glow in
the air adjacent to pointed metal conductors carrying high voltages, and emits light by the
same property as a gas discharge lamp.
In many high voltage applications, corona is an unwanted side effect. Corona discharge from
high voltage electric power transmission lines constitutes an economically significant waste
of energy for utilities. In high voltage equipment like Cathode Ray Tube televisions, radio
transmitters, X-ray machines, and particle accelerators the current leakage caused by coronas
can constitute an unwanted load on the circuit. In the air, coronas generate gases such
as ozone (O3) and nitric oxide (NO), and in turn, nitrogen dioxide (NO2), and thus nitric
acid (HNO3) if water vapor is present. These gases are corrosive and can degrade and
embrittle nearby materials, and are also toxic to humans and the environment.
Corona discharges can often be suppressed by improved insulation, corona rings, and making
high voltage electrodes in smooth rounded shapes. However, controlled corona discharges are
used in a variety of processes such as air filtration, photocopiers, and ozone generators.
A corona discharge is a process by which a current flows from an electrode with a
high potential into a neutral fluid, usually air, by ionizing that fluid so as to create a region
of plasma around the electrode. The ions generated eventually pass the charge to nearby areas
of lower potential, or recombine to form neutral gas molecules.
When the potential gradient (electric field) is large enough at a point in the fluid, the fluid at
that point ionizes and it becomes conductive. If a charged object has a sharp point, the
electric field strength around that point will be much higher than elsewhere. Air near the
electrode can become ionized (partially conductive), while regions more distant do not. When
the air near the point becomes conductive, it has the effect of increasing the apparent size of
the conductor. Since the new conductive region is less sharp, the ionization may not extend
past this local region. Outside this region of ionization and conductivity, the charged particles
slowly find their way to an oppositely charged object and are neutralized.
Along with the similar brush discharge, the corona is often called a "single-electrode
discharge", as opposed to a "two-electrode discharge"; an electric arc.[1][2][3] A corona only
forms when the conductor is widely enough separated from conductors at the opposite
potential that an arc cannot jump between them. If the geometry and gradient are such that
the ionized region continues to grow until it reaches another conductor at a lower potential, a
low resistance conductive path between the two will be formed, resulting in an electric
spark or electric arc, depending upon the source of the electric field. If the source continues to
supply current, a spark will evolve into a continuous discharge called an arc.
Corona discharge only forms when the electric field (potential gradient) at the surface of the
conductor exceeds a critical value, the dielectric strength or disruptive potential gradient of
the fluid. In air at atmospheric pressure, it is roughly 30 kilovolts per centimeter[1] but
decreases with pressure, so Corona is more of a problem at high altitudes.[4] Corona discharge
usually forms at highly curved regions on electrodes, such as sharp corners, projecting points,
edges of metal surfaces, or small diameter wires. The high curvature causes a high potential
gradient at these locations so that the air breaks down and forms plasma there first. On sharp
points in air corona can start at potentials of 2 - 6 kV.[2] In order to suppress corona
formation, terminals on high voltage equipment are frequently designed with smooth large
diameters rounded shapes like balls or toruses, and corona rings are often added to insulators
of high voltage transmission lines.
Coronas may be positive or negative. This is determined by the polarity of the voltage on the
highly curved electrode. If the curved electrode is positive with respect to the flat electrode, it
has a positive corona, if it is negative, it has a negative corona. (See below for more details.)
The physics of positive and negative coronas are strikingly different. This asymmetry is a
result of the great difference in mass between electrons and positively charged ions, with only
the electron having the ability to undergo a significant degree of ionizing inelastic collision at
common temperatures and pressures.
An important reason for considering coronas is the production of ozone around conductors
undergoing corona processes in air. A negative corona generates much more ozone than the
corresponding positive corona.
Corona discharge has a number of commercial and industrial applications:
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Removal of unwanted electric charges from the surface of aircraft in flight and thus
avoiding the detrimental effect of uncontrolled electrical discharge pulses on the
performance of avionic systems
Manufacture of ozone
Sanitization of pool water
In an electrostatic precipitator, removal of solid pollutants from a waste gas stream, or
scrubbing particles from the air in air-conditioning systems
Photocopying
Air ionisers
Production of photons for Kirlian photography to expose photographic film
EHD thrusters, Lifters, and other ionic wind devices
Nitrogen laser
Ionization of a gaseous sample for subsequent analysis in a mass spectrometer or an ion
mobility spectrometer
Static charge neutralization, as applied through antistatic devices like ionizing bars.
Coronas can be used to generate charged surfaces, which is an effect used in electrostatic
copying (photocopying). They can also be used to remove particulate matter from air streams
by first charging the air, and then passing the charged stream through a comb of alternating
polarity, to deposit the charged particles onto oppositely charged plates.
The free radicals and ions generated in corona reactions can be used to scrub the air of certain
noxious products, through chemical reactions, and can be used to produce ozone.
Terjemahan
Korona merupakan proses dimana arus, mungkin diteruskan, muncul dari sebuah elektrode
berpotensial tinggi di dalam sebuah fluida yang netral, biasanya udara,
dengan mengionisasi fluida hingga menciptakan plasma di sekitar elektrode. Ion-ion yang
dihasilkan akhirnya akan melampaui muatan listrik menuju area-area berpotensi rendah terdekat,
atau bergabung kembali untuk membentuk molekul-molekul gas netral.
Saat gradien potensialnya fluida cukup besar pada sebuah titik, maka fluida itu akan mengalami
ionisasi dan menjadi bersifat konduktif. Udara di dekat elektrode bisa terionisasi (sebagian
bersifat konduktif). Saat udara di dekat titik menjadi bersifat konduktif, ia memiliki efek
meningkatkan ukuran konduktor. Di luar wilayah ionisasi dan konduktivitas ini, partikel-partikel
bermuatan perlahan-lahan mencapai benda yang muatannya berlawanan dan dinetralkan.
Jika wilayah terionisasi terus bertambah luas dan tidak berhenti pada radius tertentu,
terbentuklah jalur yang betul-betul bersifat konduktif yang berakibat pada terciptanya latu elektrik
yang muncul sekejap atau busur elektrik yang berkesinambungan.
Lucutan korona biasanya melibatkan dua elektrode asimetris; elektrode yang satu memiliki
permukaan yang sangat melengkung (seperti ujung sebuah jarum atau kawat berdiameter kecil)
dan elektrode satunya lagi memiliki kelekukan yang rendah (seperti piring atau permukaan
tanah). Kelengkungan yang tinggi memastikan potensial gradien yang tinggi di sekitar
sebuah elektrode, untuk menciptakan sebuah plasma.
Korona bisa bermuatan positif atau negatif. Hal ini ditentukan oleh polaritas tegangan di
elektrode yang kelengkungannya tinggi. Jika elektrode melengkung bemuatan positif berkenaan
dengan elektoda rata terciptalah korona positif, tetapi jika negatif yang tercipta adalah korona
negatif. Ketidaksamaan sifat korona positif dengan korona negatif yang amat berbeda
disebabkan oleh jauh berbedanya massa elektron dengan ion bermuatan positif, dengan
hanya elektron memiliki kemampuan mengalami tingkat benturan taklenting pengion yang
signifikan pada temperatur dan tekanan bersama.
Fungsi lucutan korona yang utama adalah terciptanya ozon di sekitar konduktor yang mengalami
proses korona. Korona negatif menghasilkan ozon jauh lebih banyak daripada korona positif.
Berikut ini adalah penerapan lucutan korona di bidang komersial dan industri.
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Menghilangkan muatan listrik yang tidak diinginkan dari permukaan pesawat yang sedang
terbang dan dengan begitu menghilangkan efek yang merugikan dari pulsa lucutan elektris
tidak terkontrol pada kinerja sistem avionik
Pembuatan ozon
Sterilisasi air kolam
Pembersih dengan mengosokan partikel-partikel dari udara dalam HVAC (lihat Pengendap
elektrostatik)
Menghilangkan berbagai organik teruap yang tidak diinginkan, seperti pestisida kimia,
pelarut, atau bahan senjata kimia, dari atmosfer
Meningkatkan kelembapan atau ‘energi tegangan permukaan’ dari film polimer untuk
meningkatkan kesesuaian dengan tinta cetak atau perekat.
Membuat fotokopi
Pengion udara yang baik buat kesehatan
Fotografi Kirlian menggunakan foton yang dihasilkan oleh lucutan untuk mengekspos film
fotografik.
EHD thruster, Lifter, dan peranti ion wind yang lain
Laser nitrogen
Perlakuan Permukaan untuk Kultur Jaringan (Polistirena)
Ionisasinya cuplikan gas untuk analisis subsekuen dalam sebuah spektrometer
massa maupun spektrometer mobilitas ion.
Korona bisa digunakan untuk menghasilkan permukaan bermutan, yang merupakan sebuah efek
yang digunakan dalam pengopian elektrostatik (membuat fotokopi). Korona juga dapat
digunakan untuk menghilangkan materi kepartikelan dari aliran udara dengan terlebih dahulu
mengisi udara dengan muatan listrik, lalu melewatkan aliran udara bermuatan melalui sisir
polaritas bolak-balik, untuk mengendapkan partikel-partikel bermuatan ke lempengan dengan
muatan yang berlawanan.
Ion serta radikal bebas yang dihasilkan dalam reaksi korona bisa dipakai untuk membersihkan
udaranya produk-produk merugikan tertentu, melalui reaksi kimia, dan bisa digunakan untuk
memproduksi ozon.
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