PARTIAL DISCHARGES AND STREAMERS IN LIQUID DIELECTRICS - THE SIGNIFICANCE OF THE INCEPTION VOLTAGE

Recent studies have concerned themselves with the determination of the partial discharge (PD) inception voltages (PDIV) of several practical insulating oils using conventional PD measurements. They showed that the PDIV was a reasonably reproducible quantity. Independently, using electro-optical techniques, the streamer inception voltages (SIV) in t hese liquids have been measured. Again these SIV values were found to be reproducible, within experimental error. Both techniques yielded si milar inception values. These results suggest that the PD and streamer phenomena are closely related. Furthermore, it has been shown that th e PDIV is independent of the gap and hence the average electric field. The SIV has also been found to be independent of the applied voltage. These observations suggest that the inception of both phenomena are c ontrolled by the local rather than the average applied field. The expe rimental observations are interpreted and a theory is advanced to expl ain them. It is suggested that the inception voltage coincides with th e onset of electron tunneling which increases drastically the charge c arrier supply as well as their energy distribution. This process incre ases the local field, facilitates the onset of streamer formation and hence of PD.