Corona Effect

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Corona Effect in Overhead Transmission Line

The phenomenon of violet glow, hissing sound and production of ozone gas in an overhead transmission line is known as corona.

When a very high voltage is applied across two conductors of the overhead transmission line whose spacing is large as compared to their diameters.

 When this applied voltage exceeds a certain value (called critical disruptive voltage), then the conductors are surrounded by a faint violet glow that is known as corona effect.

In practice, the corona effect is accompanied by a hissing sound, production of ozone, power loss and radio interference. The higher is the transmission voltage, the larger and higher the luminous envelope becomes and the higher are the power loss and the radio interference. 

If the applied voltage attained the breakdown value, then a flashover will occur between the conductors due to breakdown of the insulation of air.

If the transmission conductors are polished and smooth, then the violet glow will be uniform throughout the length of the conductors, otherwise the rough points will appear brighter.

In case of DC transmission lines, there is a difference in the appearance of corona glow for the two conductors, i.e. the positive wire has uniform corona glow about it and the negative wire has spotty glow.

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