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The good effect of corona on overhead lines is to
Increase the line carrying capacity due to conducting ionized air envelop around the conductor
Increase the power factor due to corona loss
Reduce the radio interference from the conductor
Reduce the steepness of surge fronts
Reduce the steepness of surge fronts
Corona is a discharge phenomenon occurring on overhead lines when the potential gradient exceeds the dielectric strength of air. While usually considered a loss mechanism, one beneficial effect is its ability to dissipate transient surges by acting as a high-frequency resistance, effectively rounding off or reducing the steepness of surge wavefronts.
Corona is a discharge phenomenon occurring on overhead lines when the potential gradient exceeds the dielectric strength of air. While usually considered a loss mechanism, one beneficial effect is its ability to dissipate transient surges by acting as a high-frequency resistance, effectively rounding off or reducing the steepness of surge wavefronts.
PcтАЛ=244(f+25)drтАЛтАЛ(VтИТVcтАЛ)2├Ч10тИТ5 тАФ Empirical formula for Corona loss per phase in kW/km
When a voltage surge travels along a transmission line, it possesses a very steep wavefront. Corona discharge initiates ionized paths around the conductor, which increases the effective conductor diameter and provides a non-linear resistance path to ground. This ion sheath absorbs energy from the surge, causing the wave to flatten, thereby reducing the stress on transformer and equipment insulation.
Corona is accompanied by ozone gas, hissing noise, and light.
It occurs when the surface voltage gradient exceeds the disruptive critical voltage of air, approximately 30 kV/cm (peak).
Corona discharge behaves like an ohmic resistance for high-frequency transient waves.
The surge front attenuation protects terminal equipment from steep voltage gradients.
Reduces the steepness of surge fronts caused by lightning or switching
Limits transient overvoltage peaks
Causes power loss (I2R loss equivalent)
Produces ozone gas leading to corrosion of conductor surface
Generates radio interference and audible noise
High Voltage (HV) and Extra High Voltage (EHV) transmission line insulation coordination
The disruption voltage VcтАЛ is dependent on conductor surface roughness (irregularity factor moтАЛ) and air density factor ╬┤.
Option A is incorrect because corona causes power loss, not an increase in power transfer capacity; in fact, it limits the practical voltage limit.
Option B is incorrect because corona loss is a non-linear loss, which generally degrades the power factor.
Option C is incorrect because corona is a primary source of radio frequency interference, it does not reduce it.
D is correct тАФ Corona discharge acts as a non-linear resistance during high-voltage transients, which flattens the wavefront and reduces its steepness.
Always remember that corona is generally a parasitic effect, but the reduction of surge steepness is its only notable technical 'benefit' in power system transient protection.