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The chances of corona are maximum in
Domestic wiring
Distribution lines
Transmission lines
All of the above
Transmission lines
Corona is a discharge phenomenon that occurs when the electric field intensity at the surface of a conductor exceeds the dielectric strength of the surrounding air, leading to partial ionization. This effect is predominantly observed in high-voltage transmission lines because the operating voltages are significantly higher compared to distribution or domestic systems.
Corona is a discharge phenomenon that occurs when the electric field intensity at the surface of a conductor exceeds the dielectric strength of the surrounding air, leading to partial ionization. This effect is predominantly observed in high-voltage transmission lines because the operating voltages are significantly higher compared to distribution or domestic systems.
VcтАЛ=g0тАЛm0тАЛ╬┤rln(rdтАЛ) тАФ Critical disruptive voltage formula
PcтАЛ=244тЛЕ(f+25)тЛЕdrтАЛтАЛтЛЕ(VтИТVcтАЛ)2тЛЕ10┬░тИТ5 тАФ Power loss due to corona per phase
The critical disruptive voltage VcтАЛ is the voltage at which corona starts. It is defined by VcтАЛ=g0тАЛтЛЕm0тАЛтЛЕ╬┤тЛЕrтЛЕln(rdтАЛ), where g0тАЛ is the dielectric strength of air, r is the conductor radius, and d is the spacing. Since VcтАЛ increases with higher operating voltage and larger spacing, transmission lines operating at EHV/UHV levels are the most susceptible to reaching these ionization thresholds compared to lower voltage distribution circuits.
Corona is accompanied by a hissing sound, ozone production, and light glow.
Higher atmospheric pressure and lower temperature reduce corona.
Stranded conductors increase the surface area and reduce the electric field intensity compared to solid conductors.
Corona loss is frequency-dependent and increases with higher operating frequencies.
Reduces magnitude of steep fronted surges (acting as a shunt)
Provides a protective layer of ionized air around the conductor
Power loss reducing efficiency
Radio interference with communication lines
Ozone generation causes corrosion of conductors
High Voltage Transmission (EHV/UHV)
Bundled conductors in transmission lines
Standard atmospheric conditions correspond to ╬┤=1 (pressure = 76cm Hg, temp = 25┬░C).
Option B (Distribution lines) usually operates at lower voltages (e.g., 11kV, 415V), which are typically below the critical disruptive voltage of air, making corona negligible.
C is correct тАФ Transmission lines operate at very high potentials, often exceeding the breakdown strength of air, which is the primary requirement for corona discharge.
Always remember that corona is directly proportional to (VтИТVcтАЛ)2; therefore, even a small increase in voltage above the critical value results in a quadratic increase in power loss.