Corona discharge is an inherent and unique phenomenon in the high voltage transmission lines. When an alternating current of high and very high potential difference is applied to the conductors whose spacing is large as compared to their diameter than the atmospheric air surrounding the wires is subjected to electro-statìc stresses.These stresses are proportional to the potential gradient at low voltage these are less and at higher voltage are higher. The stresses of air because of hissing sound and sometimes the bluish colour glow around the conductor. This effect of the higher or very higher voltage is termed as corona discharge (corona effect).
So we can say that corona is the phenomenon of hissing sound or noise, in the over head line conductors. It also produces the bluishing glow and production of ozone gas around the conductor.
It is an important factor for designing the transmission lines which actually decides the spacing between the conductors, otherwise at higher potential difference small flash over may take place between the conductors of transmission line.
Factors effecting Corona Discharge
The shape of the conductor i.e., a stranded conductor will have more corona than the solid single conductor. The atmosphere also plays an important role, as the ionisation of air is the main cause so the physical condition and state of the atmosphere for example stormy weather, moisted atmosphere, will carry more ions resulting corona at even much less voltage compared to fair weather conditións. Spacing between the conductors also reduces voltage gradient reducing corona to occur. Finally the voltage of transmission line will affect the intensity of corona, less voltage less corona and high voltage more corona.
Advantages of Corona Discharge
The virtual diameter of the conductor due to corona (conductive ariana around the conductor) is increased which decreases the electrostatic stresses between the conductors.
As the electrostatic stresses are reduced the probability of flash over is reduced, this improves the performance of the system. It also reduces the effects of transients produced by lightning.
Disadvantages of Corona Discharge
The loss of energy in electrostatic charge. It is dissipated in the forms of heat, light, sound and chemical reactions. The corona causes the corrosion of the line conductors. It affects the sinusoidal wave of the voltage this effects as an interference in the near by communication lines.
How to reduce the Corona Discharge?
The corona effect which may cause flash over instead of hissing sound. should be carefully studies and its effects be reduced. It can be reduced by increasing the conductor size and by increasing the spacing between the conductors.