Effect of instantaneous voltage change rate on appearance of swarming pulsive microdischarges

The study investigates the time variation of SPMD characteristics and the effect of the instantaneous voltage change rate on SPMD in a CIGRE Method-II specimen by using the computer aided partial discharge analyzing system (CAPDAS). The following conclusions were obtained. (1) SPMD did not occur at first, but increased with the aging time and finally almost all PDs turned into SPMD. The appearance of SPMD was concerned with the degradation of insulator. The void surface roughness was one of the main factors for the appearance of SPMD. From these results it would be possible to find the degradation of insulating materials by the SPMD ratio. (2) SPMD is less likely to occur under the application of the very low frequency voltage. The charge integral at 0.1 Hz measured with the conventional pulse method was almost equal to the bridge value at 60 Hz. Therefore the quantitative analysis of SPMD characteristics becomes possible using only the conventional PD detector under the voltage application of both very low and power frequency.