Partial discharges and streamers in liquid dielectrics-the significance of the inception voltage

Recent studies have determined the partial discharge inception voltage (PDIV) of several practical insulating oils using conventional PD measurements. They show that the PDIV is a reasonably reproducible quantity. Independently, using electrooptical techniques, the streamer inception voltages (SIVs) in these liquids have been measured. These SIV values are found to be reproducible, within experimental error. Both techniques yield similar inception values. These results suggest that the PD and streamer phenomena are closely related. It is shown that the PDIV is independent of the gap and hence the average electric field. The SIV is found to be independent of the applied voltage. These observations suggest that the inception of both phenomena is controlled by the local rather than the average applied field. The experimental observations are interpreted and a theory is advanced to explain them