SOLUTION

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.

The frequency of supply: Corona loss decrease as the supply frequency decrease.

The distance between the two conductors: To prevent corona spacing between the conductors must be increased.

Air Pressure: In hilly areas, the corona effect is more dominant due to reduced pressure.

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.

Using Smooth conductor: Since corona loss is higher at sharp corners of the conductors, due to the presence of the highly non-uniform field, increasing the conductor radius as a whole can reduce the corona effect significantly. More the imperfections on the conductor surface more will be Corona.

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.