Corona Effect
Corona phenomenon is the ionization of the surrounding air near power conductor. Free electrons are always present in free space because of radioactivity and cosmic rays. As the potential between the conductors is increased, the gradient around the surface of the conductor increase. The free electrons will move with certain velocity depending upon the field strength.These free electrons will collide with molecules of air and in-case they have high velocity they will dislodge the electrons from molecules and which will leads to increase in no. of electrons. This will form a electron avalanche.
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