Propagation mechanism of discharge on oil surfaces

THIS study of the propagation mechanism of impulse creepage discharges over oil-immersed Kraft board was carried out using Leica and high-speed Boys cameras to record the progression of the discharges, as well as a special probe technique to measure the discharge potentials at various points along the channel. The electrode configuration used in these experiments consisted of a rod electrode on one side of a sheet of 1/8-inch Kraft board and a grounded copper surface deposited on the opposite side. Capacitance probes were imbedded in the copper surface to measure the approximate potentials of streamers passing along the rod side of the insulation. Impulse waves of 1.5 × 7,000 microseconds were applied to the rod at 120 kv which was about three times the corona starting level. The entire test structure was placed in a lucite tank filled with commercial-quality insulating oil. Photographs of the discharges were made through the walls of the tank by means of a slit and mirror arrangement. The Kraft board insulation used in these tests was first impregnated with oil under vacuum, and transferred to the testing tank just before tests were begun.