Volt age transmission line Conductor s, when the Electric Field strength is high enough to cause a breakdown of the surrounding air. Once ionized the air becomes a conductor of Electricity .
Corona is visible at night as a luminous glow close to the conductors.
The use of bundled conductors and appropriate hardware on EHV and UHV lines keeps corona to acceptable limits if the equipment is installed correctly. The line conductors must be kept clean and free from damage that results in rough or pointed projections. Grease on a conductor can cause the generation of corona. However, corona is generally less on DC lines and does not increase as much during bad weather compared with conditions on AC lines. Corona involves Power loss, which may be serious in some cases.