What is Corona Loss ?

                   What is Corona Loss ?

When an alternating potential difference is applied across two conductors whose spacing is large in
compares ion with their diameter then the atmosphere air surrounding the conductor realize electrostatic stress. At low voltage there is no change in the condition of atmospheric air around the conductors but when the potential difference is gradually increased, a stage arrive when fan is luminous glow of violet color appears with the hissing sound . This phenomenon is known as visual corona. If the potential difference raised still further, the glow and the noise will increase eventually a spark over of air insulation will take place. This phenomenon is lies in transmission line of 100KV and above.

  • What is corona loss effect
  • Effect of corona 

It produces localized break down around the conductors.
It produces hissing sound s.
It produce luminous glow around the conductor.
It produces ozone as dew to chemical action.
The size and brightness of glow and intensity of hissing sound increase with increase in voltage across the conductor.
The corona glow is brightest at those surface of the conductor surface is rough or dirty.
It results in energy loss which is dissipated in the form of heat, light sound and chemical action.
It generates harmonics and radio interference.
In case of DC the glow around the positive wire is uniform wide the glow around negative wire as spotty.
In case of A.C the glow around the two conductors is same science the conductor are alternately positive and negative.


The magnitude of fair weather corona loss is generally small for mosr of the EHV (extra high voltage) line.
The corona loss in fair weather can be calculate by using peak / Peterson formula . the corona loss under bad weather condition may be as high as hundred times the fair weather corona loss. The bad weather persist only for a short time during air.
For estimating the corona loss developing load weather the following formula
is used
Sum of Power(P):  = Pfw + { V/1.6*J*r2* log(1+10R)*sum of E5

Where P id total fair weather corona loss
V. line to neutral voltage
J. this is standard value
r. sub conductor radios
R rain rate in mm/hour
E. gradient at the bottom of each sub conductor
the above formula can be used for calculating the corona loss under the condition of snow at that time the value of J is     1.27x 10-9     
    for  snow and first condition and the following equivalent ran rate may be used  for this condition    
for heavy snow R= 2.54 mm/hour
for medium Snow R= .636 mm/hour
for light snow   R=.0127 mm/hour
thus with way then corona loss can be calculate under the poor weather condition.

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