Corona Inception in the Presence of Insulators in a Rod-Plane Gap Under Positive Switching Impulse Voltages

Results are presented concerning corona inception in air and in the presence of a porcelain insulator in a non-uniform field under positive switching impulse voltages. It is shown that in the presence of the insulator both first and second coronas start earlier, under lower inception voltages and with smaller associated charges compared to corona inception in air alone. Where the insulator is present, the first and second corona inception voltages and the required voltage increase during dark period increase linearly with the applied voltage. This is not so in the case of corona inception in air alone where the second corona inception voltage was found roughly constant, independent of the applied voltage variations. The apparent first and second corona charges were found to increase with the corresponding inception voltages according to a power and an exponential law respectively