Relation between swarming pulsive microdischarges and surface roughness of dielectric materials in terms of surface potential distribution

Partial discharge (PD) degradation phenomena are one of the important factors in deciding the performance and the lifetime of high-voltage apparatus. Swarming pulsive micro-discharges (SPMD) appeared during PD degradation tests of an epoxy specimen with an internal void. The appearance of SPMD is concerned with the degradation of insulating materials, therefore insulation diagnosis in terms of the detection of SPMD becomes possible. However, the details of SPMD are not clear yet. SPMD is too difficult to detect with a conventional PD detector because the PD magnitudes are too small to be detected. The authors have developed a PD detecting system named the computer aided partial discharge analyzing system (CAPDAS) to detect and to analyze SPMD quantitatively. The purpose of this study is to clarify the factor of the appearance of SPMD. To this end, the surface potential distribution of dielectric materials after PD exposure and its time dependence were measured in connection with surface roughness