The conduction current and breakdown under normal conditions and under forced circulation of insulating liquids

The work described in this paper is concerned with the investigation of conduction current and breakdown of insulating liquids, both for stationary liquids and when the liquid is in motion. It is generally thought that bubble and bridge formation are involved at some stage in the breakdown process of a liquid. The present work was undertaken to compare the conduction current and breakdown under normal conditions and under forced circulation of the oil where favourable conditions for bubble and bridge removal exist. Most of the experiments were conducted with transformer oil. In order to assess the generality of effects being studied, several electrode geometries were used. In all cases examined the conduction current increased and in most of them the breakdown voltage decreased with the speed of test liquid flow. The observed polarity effect for both uniform and non-uniform fields would indicate that the motion is the result of the interaction of the applied field and charge carriers in the liquid. The proposed physical explanation qualitatively agrees with the experimental results.