This type of effect can be noticed that near the overhead lines there exists a hissing noise and sometimes a faint violet glow.
CORONA EFFECT:
When normal alternating voltages is applied across two conductors which conductors are enough spacing in between,then there is no change in the atmospheric conditions surrounding conductors.but if the applied voltage exceeds a particular limits value then the air surrounding the conductors gets ionized due to which hissing noise or faint violet glow appears.
The phenomenon of violet glow, hissing noise and production of ozone gas in an overhead transmission line is known as corona.
If the conductors are polished and smooth, the corona glow will be uniform throughout the length of the conductors, otherwise the rough points will appear brighter. With d.c. voltage, there is difference in the appearance of the two wires. The positive wire has uniform glow about it, while the negative conductor has spotty glow.
Theory of corona formation in transmission lines :
The corona effect takes place when applied voltage exceeds the particular value which is called critical disruptive voltage.
