Temporal development of the electric field within a stressed oil gap

Abstract

Extensive high resolution electro-optic Kerr field mapping measurements have been taken with transformer oil near 20°c using parallel plane electrodes and field strengths near 0.2 MV/m. Static field measurements have been extended to the transient period following the application of a step voltage. Significant space charge effects resulting in electrode fields being enhanced by a factor of up to 2.5 over the average field are observed. This factor is dependent on the gap length. A simple model based on charge carrier generation mainly by dissociation of ion pairs in the liquid bulk is used in the discussion of the observations. Evidence suggests that polarity dependent asymmetries in the gap field distribution arise primarily from differences in the mobilities of the two polarities of charge carrier rather than from injection of carriers at the electrodes.