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Tuesday, 14 January 2020

What is Corona Effect? Its Advantages and Disadvantages,

Corona Effect

Corona Effect

Corona Effect


When an alternating potential difference is applied across two conductors whose spacing is large as compared to there diameter there is a no effect in change in atoms air surrounding the conductor.

When applied voltage is  exceeds a certain value then conductors are surrounded by faint violate glow and hissing noise and ozone gas called Corona.
The phenomenon of violate glow, hissing noise and ozone gas in an overhead transmission line called corona.

Theory of Corona Formation 

  • Some ionization is always present in air due to cosmic ray's, radioactivity and ultraviolet radiation under normal condition. 
  • The air around the conductor contains some free electrons and positive ions. 
  • When potential difference is applied potential gradient is set up in the air which will have maximum at the conductor surface under the influence of potential gradient, the existing free electrons acquire greater velocity. 
  • The greater the applied voltage greater, greater potential gradient and greater the velocity of electrons. 
  • When potential gradient reaches about 30Kv per cm the velocity acquire by free electrons is sufficient to strike the neutral molecule with enough force to dislodge more electron from it this process of ionization cumulative.
  • The result of this ionization is that either corona either corona is form or spark is takes place between the conductors.

Factors Affecting the Corona

Atmosphere
In stormy weather the number of ions is more than normal and such a corona occurs at much less voltage as compare to fair weather.

Conductor Size
The rough and irregular surface will give rise to more corona thus a stranded conductors has irregular surface and hence give rise to more corona.

Spacing between conductors 
If the spacing between conductors made very large as compare to their diameter  there may not be any corona effect. 

Line voltage
If the line voltage is low the corona corona effect is less because of less electrostatic stress. 

Advantages of Corona 

1) Due to corona formation the air surrounding of conductor becomes conducting and hence virtual diameter of conductor increases.

2) Corona reduces effect of transient produces sugar.

3) It reduces effect of high voltage travelling wave due to lightening. 

Disadvantages of Corona

1) Because of corona effect energy loss will occur in transmission line which affect efficiency of line.

2) Ozone gas is produces due to corona and may causes corrosion of conductor due to chemical action. 

3) Interference with neighboring communication line because current drawn by the line due to corona is no sinusoidal. 

Important terms related to corona

Critical disruptive voltage
It is minimum phase to neutral voltage at which corona occur.

Visual critical voltage 
It is minimum phase to neutral voltage at which corona glow will appear surrounding the conductor.

Power loss due to corona 

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