Pre-breakdown conduction current pulses in insulating oils under non-uniform field conditions

Abstract

The pre-breakdown conduction current pulses in degassed transformer oil were studied using needle-sphere electrodes. The current pulses were recorded on a magnetic tape and then analysed using a pulse height analyser. The results showed that these current pulses were sensitive to the applied hydrostatic pressure as well as to the liquid temperature. With the needle positive the number of larger pulses reached a minimum at a pressure between 250 and 500 torr, while with the needle negative the pulse rate was greatest in this range of pressure. Increasing the temperature of the liquid or the applied voltage increased the pulse activity. When a needle-needle electrode system was used, pulse activity also showed a pronounced response to the applied hydrostatic pressure. It is suggested that a gaseous phase is involved in the breakdown process of liquids, which is most likely to be due to dissociation of the liquid molecules by energetic electrons.