Corona in Transmission Lines

 Corona in Transmission Lines

In transmission lines when an alternation potential difference is applied across two conductors, whose spacing is large in comparison with their diameter, And then the atmosphere air surrounding the conductor is subjected to electric – static stresses. At low voltages these is no change in condition of atmosphere air around the conductions.

When the potential is gradually increased, the air between the conductor starts ionization and a stage arrives a faint luminous glow of violet color appears along the lines with hissing noise. This phenomenon is called “Visual Corona” and is accomplished by production of OZONE gas. If the potential difference is further increases, the glow and noise will increases rapidly until a spark over. The whole phenomenon of hissing noise, the violet glow and production of Ozone gas is known as CORONA.

Corona can be simply summarized as:

1.      A violet glow is observed around the conductor.

2.      It produces a hissing noise.

3.      It produces ozone gas.

4.      The glow is maximum over rough and dirty surfaces of the conductor.

5.      It is accomplished by a power loss.

6.      Under corona conditions the charging current in the line gets increased.

7.      Interference will occur in the Radio and communication lines.

Factors affecting corona

Corona in the transmission lines occurs due to ionization of the air surrounding the line conductors. Hence, it is affected by the physical state of the atmosphere as well as conditions of the line.

Corona is affected by the following factors, namely.

1. Atmosphere: In stormy weather conditions, the number of ions in the atmosphere is more as compared to fair weather conditions. Hence, the corona will occur at much less voltage compared with fair weather.

2. Conductor size :

a)      Corona decrease with increase in diameter of the conductor.

b)     Corona is more in case of stranded conductors as compared to solid conductors.

c)      Corona is more in case of rough and dirty surface of the conductors as compared to smooth conductors.

3.             Spacing between Conductors: If the spacing between the conductors is large as compared with their diameters. Then there is no formation of corona in transmission lines.

4.  Line Voltage: At low voltages, there is no corona effect, but at higher line voltage corona effect will appear.`