Studies on the applicability of the Pockels technique to measure surface discharge in liquid dielectrics

This paper studies the feasibility of applying the electro-optical Pockels technique to measure surface discharge at a solid-liquid insulation interface. The principle of the method is based on the Pockels characteristic of the bismuth silicon oxide (BSO) sensing crystal. The presence of surface charge induces an electric field across the crystal which in turn linearly changes the polarisation state of the incoming polarised light. This change in the light polarisation state can be deduced from the recorded light intensity and hence surface charge density can be calculated. The distribution of charge generated from a needle electrode immersed in mineral oil under two cycles of AC voltage was measured and results are compared with those obtained in gas and gas-liquid structures.