We measured the partial discharge (PD) characteristics by means of a bridge circuit when a rectangular pulse voltage or an ac voltage is applied. The qmax for the rectangular pulse voltage increased with the applied voltage, however, the qmax for the ac voltage did not depend on the applied voltage. We believe it is affected by the delay time of the PD occurrence. We also measured the PD characteristics when the width of the rectangular pulse voltage was changed. At a range shorter than 10 mu s, we found one PD at the pulse top and a few small PDs or no PDs after the trailing part. We consider that the interval time between the PDs that occur at the pulse top and after the trailing part will affect the PD characteristics.
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