Observations of partial discharges in hexane under high magnification

Partial discharges are observed in hexane by shadow photography under the application of DC voltages. A nonuniform field geometry is used and the growth of cavities associated with partial discharges at a point cathode was photographed at 200× magnification. The use of an image-preserving optical delay allows a record of the conditions which exist in the liquid prior to the initiation of the low-density streamer to be obtained. The cavity growth at a point cathode is anisotropic, which suggests that electrostatic forces are of primary importance in driving its expansion. The onset of instabilities in the cavity wall is suggested. The initial partial discharge current pulse precedes or is concurrent with the growth of the cavity. An upper bound of 60 ns between first current pulse and the growth of the cavity is obtained