Surface Partial Discharge Characteristics Under Repeated Positive Triangular High Voltages (1 kV/s)

In DC insulation systems, surface partial discharge activity is of major concern, in addition to the normal operating conditions, under transient stress conditions relating to energization and de-energization, voltage polarity reversal, and overvoltage surges. In this study, surface partial discharges in a short sphere-plane gap bridged by polymeric insulating surfaces are investigated under positive triangular high voltages. Discharge modes and their salient characteristics as affected by the applied electric field and insulating material are evaluated and discussed based on current measurements. Emphasis is further given to assess the dependence of surface partial discharge activity on the rise and fall of the applied voltage, repeated testing as well as upon surface charging. Surface discharges are initiated in pulse mode at significantly lower voltages than that observed in air alone; however, the stable glow discharge is established and maintained at markedly higher voltages although related to lower continuous current with greater fluctuation, especially for insulating materials with lower relative permittivity. These are attributed to space and surface charges associated with preceding discharges.