Corona is a Phenomena of hissing noise and violet glow of surrounding Power conductor. Power Transmission for long distance is not possible without high voltage. So high voltage use for transmission 132KV , 220KV and 440KV .The Phenomena Start from Above 33KV  to Above Voltage. Why is  Corona Phenomena Produce in Power Transmission lines Discuss here.

Air is not a Work Perfect Insulator  under bad weather and also  normal condition. In Corona Phenomena Air is ionizing surrounding the Power conductor. Free Electrons present in free space air. Assume the two Parallel  Conductors. As the Potential Between the conductor is increased, The Gradient around the surface of  the conductor is increases. Spacing between the conductors is large as compare to diameter of conductors. The free electrons is move with certain velocity. These free electron will collide with the  molecular of air and in case of speed is high. they will dislodge electrons from molecular. Number of electrons will increase. The process of ionization as form of avalanche electrons. The result is Ionization of Surrounding the Power conductor. A point will  be reached. Hence curry Current in air along with Conductor surface also hissing noise, a glow and   and smell of  Ozone gas  Generated from Breakdown and recombination of O2 Molecular.

The Corona Phenomena can be Examined by Stroboscope and See by Stroboscope. When The Corona Phenomena See By Stroboscope that time see, The Positive Conductor Red Glow  and Negative Conductor Blue Glow.

Critical Disrupting  Voltage Vc
The Disrupting Critical Voltage is minimum  phase to neutral voltage at which Corona function is begins.

In Air  go  = 30 KV/cm  [Max.]
                = 21.2 KV/cm  [rms.]
r  = reduis of conductor
d = distance between conductors
V = Vc
 This Formula Valid for 25 °C and 76 cm of Hg

Any other temperature and  pressure air density factor 𝛅0 and irregularity mo factor are including then critical disrupting voltage is given by
                                                                            
b is  barometric pressure cm of Hg and t temperature in °C.


Critical Visual Voltage Vv 

The Visual Critical Voltage is minimum  phase to neutral voltage at which Corona appear at the conductor surface.

Factor Effecting Corona: 

Atmosphere : Corona Is less in Fair Weather Because Present of ions is less in Free space air. In Stormy Weather Corona is more. rain, Dust  and temperature  effect the Corona increasing ionization of air.

Conductor Size and Surface: If Conductor diameter size in small and surface of conductor is irregular than corona is more. So choose Diameter of conductor is large and Smooth Surface.

Spacing of conductor: If Space Between the conductors is less  that means  corona is more. So space between the conductor is choose more and specific design to reduce to the corona.

Electrical Factor:  Low Voltage lines Corona is not appear Corona is appear Above 33 KV Lines. and Frequency of line effect the corona losses. if frequency is high that means corona losses is high

Corona Power Loss: 

The Electrical field produce around the conductor due To corona effect . It has some Power loss which is power of conductor. In order to maintain the flow of energy over conductor. it is necessary to supply this additional loss from the supply system. These loss given by this formula. this formula also called peek's formula.

Corona Loss In Fair weather
     

Corona Loss In Stormy weather



Method For  Reducing Corona Loss 
  1. Increasing Conductor Diameter Size.
  2. Increasing Spacing Between Conductors.
  3. Composite Conductor , it is Use in high voltage Transmission lines.
  4. Bundle conductor ,   it is Use in Extra high voltage Transmission lines.
  5. Hollow  conductor ,   it is Use in Ultra high voltage Transmission lines. 

Advantage of Corona:
  • It Reduce the steepness of Surgs
  • Due to Corona Virtual diameter of the conductor increase so electrostatic stress between the Conductors Reduced.

Disadvantage of Corona:
  • Loss of Power
  • Non Sinusoidal current flow at the surface of conductor due to this interference with near communication lines acoure.

Application Of Corona: 
  • In Safety Valve
  • In Ozone gas Production Industries.

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