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Corona is affected by
Size of conductor
Shape and surface condition of the conductor
Operating voltage
All of above
All of above
Corona is a partial discharge phenomenon occurring when the voltage gradient at the conductor surface exceeds the dielectric strength of the surrounding air. It is influenced by the physical geometry of the conductor, its surface finish, and the magnitude of the applied operating voltage.
Corona is a partial discharge phenomenon occurring when the voltage gradient at the conductor surface exceeds the dielectric strength of the surrounding air. It is influenced by the physical geometry of the conductor, its surface finish, and the magnitude of the applied operating voltage.
VcтАЛ=g0тАЛтЛЕ╬┤тЛЕm0тАЛтЛЕrln(rDтАЛ) тАФ Critical disruptive voltage formula
PcтАЛтИЭ(f+25)DrтАЛтАЛ(VтИТVcтАЛ)2 тАФ Empirical power loss due to corona
Corona occurs when the electric field intensity E at the surface of a conductor exceeds the disruptive critical voltage gvтАЛ of air (approx. 30 kV/cm peak). The air molecules are ionized, leading to the formation of ozone, light emission, and audible noise. Since the electric field E=rln(D/r)VтАЛ, it is directly proportional to operating voltage V and inversely proportional to conductor radius r. Surface roughness (e.g., nicks, dust) creates localized high-stress regions that initiate discharge at lower nominal voltages.
Corona is more prominent in AC systems compared to DC systems at the same RMS voltage.
Higher surface roughness (lower m0тАЛ) reduces the voltage at which corona starts.
Bundled conductors increase the effective radius r, thereby reducing the surface potential gradient and corona loss.
Atmospheric conditions like rain, fog, or high humidity significantly increase corona discharge.
Provides a natural relief mechanism against high-voltage surges (limited effect)
Can be used as a design indicator for voltage stress limits
Results in power loss along the transmission line
Generates radio and television interference
Produces ozone, causing chemical corrosion of metallic hardware
Designing EHV (Extra High Voltage) transmission lines
Used in electrostatic precipitators and xerography
The irregularity factor m0тАЛ is 1 for smooth polished wires and varies between 0.82-0.92 for weathered or stranded conductors.
The 'All of above' option is correct because the electric field intensity, which governs the inception of corona, is mathematically dependent on the conductor radius (size), the surface state (irregularity factor), and the potential difference (operating voltage).
D is correct тАФ All listed factors directly influence the electric field stress at the conductor surface, which determines the inception and magnitude of corona discharge.
Remember that corona loss increases with frequency (f) and is proportional to the square of the over-voltage (VтИТVcтАЛ)2; always prioritize increasing conductor diameter to mitigate this.