Study of streamer propagation in mineral oil in overvolted gaps under impulse voltage

This paper presents a study of prebreakdown phenomena in mineral oil under impulse voltage (up to 500 kV) in point-plane geometry, with gap distances up to 30 cm. In these experiments, we have studied the behaviour of positive streamers in highly overvolted gaps (up to four times the breakdown voltage). The experiments presented concern the visualization with a still or streak camera, the recording of transient currents, light emission, and electric charge associated to the propagation of streamers. The influence of voltage and gap distance is presented for positive streamers. The measurements show that above a critical voltage, a large increase in propagation velocity is recorded (from 2 km/s up to about 100 km/s), correlated to large modifications in the shape, currents, light and charge recordings