Corona
INTRODUCTION
Corona phenomenon is defined as a self-sustained electric discharge in which the field intensified ionization is localized only over a portion of the distance between electrodes.
CRITICAL DISRUPTIVE VOLTAGE
The voltage at which complete disruption of dielectricoccurs is called critical disruptive voltage.
Remember:
Remember:
Where mo is the roughness factor of conductor surface.
Note:
Where r is the radius of conductors spaced by distance D.
VISUAL CRITICAL VOLTAGE
Visual corona does not occurs when the electric intensity becomes equal to ciritical value Eo but startsat a higher value of intensity Ev, because the charged ions in the air must receive some finite energy to cause further ionization by collisions.
Where mv is the irregularity factor of the conductor surface.
For 3-f line
Note:
CORONA LOSS
It is the amount of electric power lost in high voltage lines due to the rediation of energy by corona discharge.
Remmber:
Peek’s Formula
Where Pc = Corona loss in kW/km/phase
V = Rms value of phase voltage in
kV Vd = RMS value disruptive critical voltage in
kV r = Radius of conductor in metres
D = Spacing (or equivalent spacing) between conductor in metres
f = System frequency
Note:
Peterson’s Formula
Where F is a factor which varies with ratio
Remember:
Factors Affecting Corona Loss
Effect of Frequency
Effect of System Voltage
Effect of Conductivity of Air
Effect of Density of Air
Effect of Rain, Dust, etc.
Effect of Conductor Radius
Remember:
Effect of Conductor Surface
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