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Corona is
Partial breakdown of air
Complete breakdown of air
Sparking between line
Good for line
Complete breakdown of air
Corona is an electrical discharge brought on by the ionization of a fluid such as air surrounding a conductor that is electrically charged. When the potential gradient at the conductor surface exceeds the dielectric strength of air (approximately 30 kV/cm peak), the air undergoes a complete breakdown, leading to ionization and the formation of a luminous glow.
Corona is an electrical discharge brought on by the ionization of a fluid such as air surrounding a conductor that is electrically charged. When the potential gradient at the conductor surface exceeds the dielectric strength of air (approximately 30 kV/cm peak), the air undergoes a complete breakdown, leading to ionization and the formation of a luminous glow.
VcтАЛ=g0тАЛтЛЕmтЛЕrтЛЕln(rDтАЛ) тАФ Disruptive critical voltage formula
EmaxтАЛ=rln(rDтАЛ)VтАЛ тАФ Maximum potential gradient at conductor surface
The electric field intensity at the surface of a circular conductor is non-uniform. When the applied voltage reaches the 'critical disruptive voltage', the air molecules adjacent to the conductor gain enough energy to ionize, releasing free electrons. These electrons accelerate and collide with neutral air molecules, creating an avalanche effect that renders the air locally conductive (a complete local breakdown).
Corona is accompanied by a hissing sound, ozone production, and light emission.
It causes power loss and radio interference in transmission lines.
Occurs primarily in high-voltage AC overhead lines.
Increased by surface roughness, dust, and inclement weather conditions.
Power loss in transmission lines
Radio and television interference
Chemical degradation of insulation due to ozone
Vibration of conductors
The air near the conductor undergoes a complete local breakdown, hence 'complete breakdown' refers to the dielectric failure of the air gap immediately surrounding the conductor.
Option A is misleading because while the effect is localized, it involves a complete dielectric breakdown of the air layer adjacent to the conductor.
B is correct тАФ Corona discharge is the phenomenon involving the complete dielectric breakdown (ionization) of the air surrounding a high-voltage conductor.
Always remember that corona losses are proportional to (f+25) in some empirical formulations, making frequency a significant factor in loss calculations.