28-06-2012, 01:09 PM
What Is Corona?
Corona.ppt (Size: 3.48 MB / Downloads: 110)
Corona is a luminous discharge due to ionization of the air surrounding an electrode, caused by a voltage gradient exceeding a certain critical value.
CORONA FORMATION
In order that corona formed ,the value of “g” (critical disruptive voltage = V/[r loge d/r]) must be made equal to the break down strength of air .The breakdown strength of air at 76 cm pressure and temperature of 25 degree Celsius is 30 kv/cm(max),or 21.2 kv/cm
What’s The Fuss?
Corona from conductors and hardware may cause audible noise and radio noise
Corona from conductors and hardware may cause audible noise and radio noise
Audible noise from conductors may violate noise standards
Corona from conductors and hardware may cause audible noise and radio noise
Audible noise from conductors may violate noise standards
Radio noise from conductors may interfere with communications or navigation
Corona from conductors and hardware may cause audible noise and radio noise
Audible noise from conductors may violate noise standards
Radio noise from conductors may interfere with communications or navigation
Corona loss may be significant when compared with resistive loss of conductors
Mechanism of corona discharge
A neutral atom or molecule of the medium, in a region of strong electric field is ionized by an exogenous environmental event
The electric field then operates on these charged particles, separating them, and preventing their recombination, and also accelerating them, imparting each of them with kinetic energy. As a result of the energisation of the electrons (which have a much higher charge/mass ratio and so are accelerated to a higher velocity), further electron/positive-ion pairs may be created by collision with neutral atoms. These then undergo the same separating process creating an electron avalanche. Both positive and negative coronas rely on electron avalanches.
Corona and the Electric Field
Corona is NOT solely a function of the Electric Field
Corona is a function of the electric field on the surface of the electrode (conductor)
Corona is also a function of the radius of curvature of the electrode (conductor)
For the preceding reasons, selecting the conductor with the smallest electric field at its surface is not correct.
One utility found out (the hard way) that simply choosing large diameter conductors did not work well because the electric field decayed slowly away from the surface