Effects of temperature on partial discharges and streamers in an ester liquid under AC stress

Insulating liquids in transformers experience the transformer operational temperature rather than the ambient temperature that is often used in discharge studies in laboratories. This paper presents the effects of temperature on partial discharge (PD) and streamer characteristics of a synthetic ester liquid under AC stress. A needle-to-plane electrode configuration was employed to perform the PD and streamer measurements. The PD pattern, streamer images, current signals were chosen to explore the PD and streamer characteristics at temperatures of 20, 40, 60 and 80 °C. It was found that both PD and streamer characteristics of the synthetic ester are temperature dependent. As the temperature increased, the magnitude and repetition rate of positive PDs increased slightly, but both the magnitude and repetition rate of negative PDs dropped dramatically. In addition, it was observed that when the temperature increased, the stopping length of positive streamers did not change appreciably while a significant reduction of negative streamer length and area was witnessed. A mechanism based on the electrohydrodynamics (EHD) phenomenon and the space charge theory has been used to explain the different effects of temperature on positive and negative PDs.