Partial discharge patterns and surface deterioration in voids in filled and unfilled epoxy

Results are presented from analyses of pulses from partial discharges (PDs) in single spherical voids in filled and unfilled epoxy plastic and related to the observed surface deterioration. The filler types used were dolomite, alumina, and silica. Long-time aging tests including pulse phase/height analyses were performed over a period of 2400 h and showed very characteristic discharge patterns for each material combination. A unique behavior with regard to changes of pulse repetition rate and maximum apparent charge was observed for PD in alumina- and silica-filled epoxy. The void surfaces were investigated by scanning electron microscopy for voids exposed to PD as well as voids without discharges. Different kinds of surface deterioration were found. An attempt was made to establish a relationship between aging phenomena as exhibited by void surface changes and discharge patterns