Factors affecting corona and advantages and disadvantages of corona

Factors affecting corona :-

The phenomenon of corona is affected by the physical state of the atmosphere as well as by the conditions of the line. The following are the factors upon which corona depends :

Corona effect

1. Atmosphere:  As corona is formed due to ionisation of air surrounding the conductors, therefore, it is affected by the physical state of atmosphere. In the stormy weather, the number of ions is more than normal and as such corona occurs at much less voltage as compared  with fair weather.
2. Conductor size: The corona effect depends upon the shape and conditions of the conductors. The rough and irregular surface will give rise to more corona because unevenness of the surface decreases the value of breakdown voltage. Thus a stranded conductor has irregular surface and hence given rise to more corona that a solid conductor.
3. Spacing between conductors: If the spacing between the conductors is made very large as compared to their diameters, there may not be any corona effect. It is because larger distance between the conductors reduces the electro-static stresses at the conductor surface, thus avoiding corona formation.
4. Line voltage: The line voltage greatly affects corona. If it is low, there is no change in the condition of air surrounding the conductors and hence no corona is formed. However, if the line voltage has such a value the electrostatic stresses developed at the conductor surface make the air around the conductor conducting, then corona is formed.

Advantages and disadvantages of corona :

Corona has many advantages and disadvantages. In the correct design of a high voltage overhead lien, a balance should be struck between the advantages and disadvantages.

Advantages

1. Due to corona formation, the air surrounding the conductor becomes conducting and hence virtual diameter of the conductor is increased. The increased diameter reduces the electrostatic stresses between the conductors.
2. Corona reduces the effect of transients produced by surges.

Disadvantages:

1. Corona is accompanied by a loss of energy. This affects the transmission efficiency of the line.
2. Ozone is produced by corona and may cause corrosion of the conductor due to chemical reaction.
3. The current drawn by the line due to corona is nonsinusoidal voltage drop occurs in the line. This may cause inductive interference with neighbouring communication lines.

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