Effect of overvoltage on the risetime and amplitude of PD pulses

A two-dimensional mathematical model has been employed to characterize the pulse or spark breakdown behavior of a short gap in air. It has been established that the form or shape of a breakdown current pulse is very much determined by the overvoltage developed across the gap. Large overvoltages lead to intense space charge effects, which appreciably modify the breakdown current pulse form, leading to more rapid rise times, greater peak current amplitudes and reduced pulse widths. In so far as the overvoltage across a given cavity affects the rise time and amplitude of the pulse resulting from a spark type discharge, the response of a conventional partial discharge pulse detector is necessarily a function of the overvoltage developed across the cavity.>