Temporal development of the electric field within a stressed oil gap

Extensive high-resolution electrooptic Kerr field-mapping measurements have been taken with transformer oil near 20 degrees 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 observation. Evidence suggests that polarity-dependent asymmetries in the gap field distribution arise primarily from differences in the mobilities of the two polarities off charge carrier rather than from injection of carriers at the electrodes.