We can categorize the factors affecting the corona loss in three groups.

1. Electrical factors
2. Atmospheric factors
3. Physical factors related to conductors

The equation for power loss due to corona loss is,

where,

• $f$ is the supply frequency
• $\delta$ is the air density correction factor
• $V_p$​ is the operating voltage in kV
• $V_0$ is the critical disruptive voltage.

From the equation it is clear that the corona loss is a function of supply frequency. If the frequency increases, the loss increases. In AC power there is always a third harmonic present. Hence the actual corona is always somewhat greater than the calculated value for 50 Hz supply.

Field around the conductor is larger for the conductors situated at the middle of two or more conductors than that of the outer conductors. Whatever may be the configuration of the conductors, vertical or horizontal, the middle conductor has lower critical disruptive voltage. Therefore, the corona loss of middle conductor is always more than that of outer conductors.

Corona loss is also higher if the ground clearance of the conductor reduces.

Atmospheric Factors

The expression of corona voltage as well as corona loss does use the air density factor. The air density factor depends upon both pressure and temperature of atmosphere, hence the corona loss is affected by these conditions of surrounding air.

The equation of air density factor is

where,

• $b$ is the pressure measured with height of Hg column
• $t$ is the temperature in degree centigrade

So, at hilly area $b$b reduces and also $t$t reduces. Therefore overall ratio $\delta$δ increases. This is why the corona loss of conductors is somewhat higher than it is on plane land.

Dust Particles

Deposition of dust on the conductor surface increases the roughness of the surface. Therefore corona loss increases.

Humidity

Due to weather conditions such as rain, snow, if the humidity of air rises, the value of disruptive voltage $V_0$V0​ of the corona loss expression reduces. Therefore, the corona loss increases.

Factors Related to the Conductors

The diameter of the conductor is directly related to the loss expression as we have already shown. From that expression we can write,

Therefore, the loss is directly proportional to square root of radius of the conductors. And from the expression of critical disruptive voltage, it is found that the disruptive voltage decreases with decreasing diameter of the conductor.

The relation tells us

So, with decreasing $r$, $V_0$​ decreases, hence $(V_p – V_0)$ increases. Therefore the loss increases.