When high ac voltage is applied across two conductors of overhead transmission line whose spacing is large as compared to their diameter exceeds a certain value (called critical disruptive voltage) then, the conductors are surrounded by a faint violet glow called the corona effect.
The phenomenon of ionization of air surrounding the conductors of high voltage transmission lines causing the conductors to glow faint violent with a hissing noise and production of ozone gas around the conductor is called corona discharge or corona effect.
Occurrence of Corona Effect
The corona effect occurs naturally because normal air is not a perfect insulator as it contains many free electrons and ions. When an electric field is established between two conductors in the air, the free electrons and ions present in the air will experience a force. Due to this force, the free electrons and ions get accelerated and start moving in the opposite direction.
The charged particles during their motion collide with one another and also with slow moving uncharged particles then, the number of charged particles rapidly increases. If the electric field is strong enough, a dielectric breakdown of air will occur and an arc will form between the conductors.
At low value of the supply voltage, corona loss does not occurs as stress is not enough to ionize the surrounding air. But when the voltage reaches critical disruptive value of about 30kv, the stress become strong enough to ionize the surrounding air making it partially conductive resulting corona effect.
Effect of Corona Effect
The corona effect result in power loss as light, heat, sound and ozone layer production reducing the efficiency of the system and increasing the operating cost.
Factor Affecting Corona Effect
- Atmospheric Conditions
- Air Density Factor
- Condition, Size and Nature of the Conductors
- Spacing between Conductors
- Magnitude of the flowing current
Methods to Reduce Corona Effect
- Increasing the size of the conductor
- Increasing the space between conductor
- Using bundled conductors
- Using corona rings
Advantages of Corona Effect
- Reduces the probability of the corona effect
- Reduces the effect of transient produced by the voltage surge and lightening.
Disadvantages of Corona Effect
- Corrosion
- Insulation Damage
- Corona Loss
- Reduces Efficiency
- Interference with Communication equipment
Application of Corona Effect
- Removal of unwanted electric charges from the surface of the aircraft.
- Sanitation of pool
- Manufacture of ozone
- Air ionizers