What is the Corona Effect in Transmission Lines? How Engineers Overcome it?

Corona Effect in TX Lines
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What is corona effect?

Disadvantages & advantages of corona effect:

1. Disadvantages:

  • A non-sinusoidal voltage drop occurs in transmission line due to non-sinusoidal corona current, which causes interference with neighboring communication circuits due to electromagnetic transients and electrostatic induction effects.
  • Ozone gas is produced due to the formation of corona, which chemically reacts with the conductor and causes corrosion.
  • The energy dissipated in the system due to corona effect is called as Corona loss. The power loss due to corona is undesirable and uneconomical. The efficiency of transmission line is highly reduced due to the loss of power or energy.

2. Advantages:

  • Due to corona across the conductor, the sheath of air surrounding the conductor becomes conductive which rises the conductor diameter virtually. This virtual increase in the conductor diameter, reduces the maximum potential gradient or maximum electrostatic stress. Thus, probability of flash-over is reduced.
  • Effects of transients produced by lightning or electrical surges are also reduced due to corona effect. As, the charges induced on the line by surge or other causes, will be partially dissipated as a corona loss. In this way, corona protects the transmission lines by reducing the effect of transients which are produced by voltage surges.

Factors affecting corona discharge:

  1. Supply voltage: As the electrical corona discharge mainly depends upon the electric field intensity produced by the applied system voltage. Therefore, if the applied voltage is high, the corona discharge will cause excessive corona loss in the transmission lines. On contrary, the corona is negligible in the low-voltage transmission lines, due to the inadequate amount of electric field required for the breakdown of air.
  2. Conductor surface: The corona effect depends upon the shape, material and conditions of the conductors. The rough and irregular surface i.e., unevenness of the surface, decreases the value of breakdown voltage. This decrease in breakdown voltage due to concentrated electric field at rough spots, give rise to more corona effect. The roughness of conductor is usually caused due to the deposition of dirt, dust and scratching. Raindrops, snow, fog and condensation accumulated on the conductor surface are also sources of surface irregularities that can increase corona.
  3. Air density factor: Air density factor also determines the corona loss in transmission lines. The corona loss in inversely proportional to air density factor. Power loss is high due to corona in Transmission lines that are passing through a hilly area because in a hilly area the density of air is low.
  4. Spacing between conductors: Design engineers calculate the spacing between the two conductors in the transmission line after careful and extensive research. As the phenomenon of corona discharge is affected by the conductor spacing. If the distance between two conductors is very large as compared to the diameter of conductor, the corona effect may not happen. It is because the larger distance between conductors reduces the electro-static stress at the conductor surface, thus avoiding corona formation.
  5. Atmosphere: As corona is formed due to ionization 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 weather. The decrease in the value of breakdown voltage is followed by the increase in the number of ions. As a result of it, corona occurs at much less voltage as compared to the breakdown voltage value in fair weather.
By Iantresman — CC BY 3.0, Link

Methods of reducing corona effect:

  1. By increasing conductor size
  2. By increasing conductor spacing
  3. By using Corona Ring

Important parameters in corona analysis:

  1. Critical disruptive voltage: The minimum phase-neutral voltage at which corona occurs is known as ‘Critical disruptive voltage’.
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