Effects of discharge area on PD patterns in voids

Unlike the case of a void with a larger diameter, no great reduction of PD magnitude was observed in a narrow void in the PD aging process. This suggested that the reduction of PD magnitude in a large void might be caused by the reduction of the discharge area of PD (or the region to which the carriers can diffuse instantaneously in a PD process). In a narrow void, the discharge area seems to be limited by the void size, and may not decrease much with the reduction of the time delay of PD in the aging process. Further experiments on a void between two metal surfaces also agreed with this consideration. Because the discharge area was always equal to the metal surface due to the high conductivity of the metal, the PD magnitude showed very small randomness, and the PD pattern did not change much with the reduction of the void size