A New Approach to Define Internal Partial Discharge Intensity

The results of measurements of internal partial discharge intensity generally are used to assess the risk of failure of electrical insulation due to internal discharges. However, with the use of present definitions ions of discharge intensity, there is as yet quatenadeuate information for specifying acceptable levels of intensity. The effectiveness of indicators of discharge intensity has been checked while maintaining "similar conditions" at all discharging cavities belonging to a set of insulation arrangements. Each arrangement consists of solid insulation with one air-filled cavity. A new, nonmeasurable quantity, the average discharge current transferred across the discharging cavity, has been introduced and its value is used to verify the fact that similar conditions exist in the cavity. Furthermore, a new and more accurate pattern of recurrence of discharges has been used to identify four groups of discharges, which in turn leads to a new definition of discharge intensity. The results of computations of theoretical values of the new and presently used indicators are presented and the advantages associated with use of the new definition are explained.