Effect of electrode geometry and rate of voltage rise on streamer propagation in mineral oil

Experimental data on the propagation of streamers in mineral oil is important for the design of high-voltage systems in the power and pulsed-power industries. In the present study, prebreakdown delay times were measured for plane-parallel electrodes, and for two types of non-uniform electrode arrangement. For each geometry, the breakdown characteristics were determined for impulses of rise-time 100 ns, and also risetime 1 μs. The maximum applied voltage magnitude was 400 kV, giving a maximum dV/dt of 4 kV/ns. For the non-uniform geometries with inter-electrode gap length of 8.5 mm, the time to breakdown was 2.5-3 times longer for impulses of rise-time 1 μs than for 100 ns rise-time. The time-to-breakdown data suggest that streamer propagation velocity increases with higher values of dV/dt. For example, the estimated propagation velocity for pin-plane geometry with a 1 μs rise-time is 10-12 km/s. At 100 ns rise-time for the same electrode geometry, the average propagation velocity exceeds 40 km/s. The results presented are intended to provide reference data for designers of oil-immersed high-voltage systems in both the power and pulsed-power industries.