Visual Critical Voltage for Corona Formation – Formula, Definition and Explanation

Visual critical voltage is defined as the minimum phase-neutral voltage at which corona glow appears all along the line conductors.

the corona glow does not begin at the disruptive voltage Vc, rather it occurs at a higher voltage called visual critical voltage.

Visual critical voltage is abbreviated using Vv.

The phase-neutral effective value of visual critical voltage is given mathematically by the following empirical formula:

Where in above equation:

δ = air density factor

mv = irregularity factor

value of mv = 0.72 to 0.82 for rough conductors

value of mv = 0.72 to 0.82 for polished conductors

go = breakdown strength of air at 76 cm of mercury and 25ºC = 30 kV/cm (max) or 21·2 kV/cm (r.m.s.)

r = radii of conductors

d = spacing between conductors

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