Power loss due to corona

When corona occurs between two parallel lines of an overhead transmission line, energy is dissipated in form of light, heat, sound and chemical action. After exceeding the disruptive voltage, the power loss due to corona is given by

$$P=242.2(\frac { f+25 }{ δ } )\sqrt { \frac { r }{ d } \quad } { (V-Vc }^{ 2 })\quad X\quad { 10 }^{-5 }\quad$$ KW/Km/PH.

Where, f = frequency in Hz.
V =Rms phase voltage,
Vc = Rms disruptive voltage per phase.

Radio interference of corona

Wireless signals like A.M broadcasting, carrier signal etc, are adversely affected by corona discharges. It may create interference to communication line within even few kilometers. When system voltage becomes high, corona interference also increases. It also depends on conductor surfaces and diameter. Smooth conductor has lower interference.

The radio interference created by transmission line varies inversely with the radio frequency. Hence, high frequency transmission like, T.V, microwave, F.M broad casting are less affected.

Advantage and Disadvantage of corona


► The diameter of the conductor increases due to corona formation. The conducting air surrounding the conductor, increases virtual diameter which reduces electrostatic stresses between the conductors.
► It reduces the effect of indirect lightning. The loss of induced energy in the form of corona, save the conductor from lightning.


► Corona is nothing but the power loss, so, it reduces the efficiency of transmission line.
► Corona produces ozone gas. This gas is responsible for corrosion of conductor.
► Due to corona, third harmonic current, which is non sinusoidal flows, which produce inductive interference with communication line.

Methods of reducing corona effect

Corona effect may cause power loss in transmission circuit as well as reducing efficiency. But intense corona observed in the voltage range from 33 KV and above. So, proper design is required for 33 kV and above voltage level, to avoid ionization of air which may cause damage the equipment by flashover. This effect may reduced by
(a) Increasing the size of conductor: If we raise the critical disruptive voltage, that means, the voltage at which corona starts, corona effect may reduced to a considerable limit.

It is possible, if we increase the size of conductor. So, higher the cross sectional area, lesser the corona loss. A.C.S.R conductor has this advantage.

(b) Increasing conductor spacing: If we increase the space between two conductors, corona effect may be eliminated. But too much spacing may increase supporting structure cost highly.


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