What is Corona Effect ?

Hissing noise with violet glow near conductor termed as corona effect which is usually in high voltage transmission lines. Due corona effects there is high voltage drop and energy loss along with release of ozone gas.

Definition of corona :

The ionization of air surrounding the high voltage transmission lines causing the conductors to glow and producing a hissing noise is called Corona Effect.

Corona effect reason :

In transmission lines conductors are bare and surrounded by the air. Air acts as a dielectric medium, When the electric field intensity is less than 30kV/cm,the conductor is not sufficient to ionize the air.

When the voltage of air surrounding the conductor exceeds the value of 30kV/cm, the charging current starts to flow through the air and air get ionized. The ionized air also starts working as conductor and start producing a hissing sound with a violet glow.

What is Advantage of Corona Effect ?

Due to corona across the conductor air surrounding the conductor becomes conductive which rises the conductor diameter virtually. This virtual increase in the conductor diameter reduces the maximum potential gradient or maximum electrostatic stress. Thus, the probability of flash-over is reduced.

Corona reduces the effect of transient produced by Surge

What is Disadvantage of Corona Effect ?

Due to Corona effect Ozone gas is prodcued , which chemically reacts with conductor and cause corrosion

The energy dissipated in the system due to Corona effect is called as Corona loss. The efficiency of transmission line is highly reduced due to the loss of power or energy.

Factors effecting Corona .

1. Supply Voltage: Corona Effect depends on electrical field intensity. So greated the supplied volatge, greater the Corona loss in lines.
2. Conducto Surface : The corona effect also depends upon surface of conductor .The rough and irregular surface i.e., unevenness of the surface, decreases the value of breakdown voltage. This decrease in breakdown voltage due to concentrated electric field at rough spots, give rise to more corona effect.
3. Air Density :  Air density factor also effect the corona loss in transmission lines. The corona loss is ininversely proportional to air density factor. Power loss is high due to corona in Transmission lines that are passing through a hilly area because in a hilly area the density of air is low compare to ground/ plane area.

How reduce the Corona Effect ?

1. By increase the conductor size, We used ACSR condcutor with larger cross-sectional area.
2. By increasing the spacing between conductors that increases the voltage at which corona occurs. But increase in conductor spacing is limited because to the cost of supporting structure also increase as bigger cross arms and supports cost increase.
3. The intensity of electric field is high at the point where the conductor curvature is sharp. SO corona discharge occurs first at the sharp points, edges, and corners in transmission lines.