Qualitative comparison of optoelectric and current measurements of streamer propagation in new and aged ester liquids and mineral oil under lightning

This study deals with the streamer characteristics of natural and synthetic ester compared to mineral oil by presenting the results of current and light measurements. The liquids were stressed with positive and negative lightning impulse voltage. Pre-breakdown phenomena were studied using a point-plate electrode configuration. Streamer propagation current was measured by a current shunt, light emission via an avalanche photo diode system. From the registered current and light signals stepwise propagation discharges could be made visible, which differ when changing polarity and liquid type. The influence of ageing on the propagation characteristics is found to be less than the influence of polarity and type of liquid.