Corona will be higher when the weather condition is Poor.
Factor Affecting Corona: Atmospheric condition:
Temperature: Temperature increases the corona also increases
Pressure: atmospheric pressure increases the density of the air increases which reduces the corona.
Rain, Snow Fog, Dust and Dirt: All are opposite side of electrical stability, so ultimately all increases the corona in the transmission line.
Factors Affecting corona:
Frequency: the corona power losses Pc is directly proportional to the frequency. Therefore, corona power losses less where the system frequency is less. That’s why in DC transmission line has less corona losses as compared with AC transmission line.
The corona power loss is high when the voltage is high.
Method of reducing Corona:
Increasing the distance between the conductor
Increasing the diameter of the conductor.
Using hallow conductor. That’s why in Switchyard, you can see that mostly use hallow conductor.
Shape pf the conductor: Round or Solid has less corona loss but flat conductor has high corona losses.
Surface condition: Polished Surface where the corona loss is less and Rough surface has corona loss is more.
Using Bundled conductor: In EHV lines, bundled conductors are used, So effective radius increases. Vc increases and corona loss reduces.
Temperature of the conductor: Decreasing the temperature of the conductor, reduces the corona loss.
Using corona discharge ring on high voltage. The corona ring is electrically connected to the high voltage conductor, encircling the points where corona would form. Since the ring is at the same potential as the conductor, the presence of the ring reduces the potential gradient at the surface of the conductor greatly, below the disruptive potential gradient, so corona does not form on the metal points.