SOLUTION

Corona loss can be reduced by the use of hollow conductors because for a given cross-section, the radius of the conductor is increased.

When the surface potential gradient of the conductor exceeds a certain critical value, causing the air ionization around the conductor, and the movement of charged ions forming into the corona current on the line, resulting in energy loss which is called the corona loss. The size of the conductor and their spacing have a considerable effect on corona loss.

Corona loss is given by

Where, f = Supply frequency

δ = Air density factor

r = Radius of the conductor

D = Distance between the conductors

V = Operating voltage of the transmission line

Vo = Critical disruptive voltage

• Corona loss increases with frequency.
• Corona loss increases very fast with an increase in system voltage since the loss is dependent on (V – V_o)²

Method of reducing corona

The corona loss can be reduced by using:

Conductors with large diameters: The voltage at which the corona occurs can be increased by increasing the size of the conductor and hence, the corona loss can be reduced.

Hollow conductors: These are used to increase the effective diameter of the conductor without using any additional material. Since corona loss is inversely proportional to the diameter of the conductor, corona loss decreases with an increase in the diameter.

Bundled conductors: These are made up of two or more sub-conductors and are used as single-phase conductors. When using two or more sub-conductors as one conductor, the effective diameter of the conductor increases, resulting in reduced corona loss.