Observations of pre- and post-breakdown events in polydimethylsiloxanes

The effect of viscosity and rate of voltage application on the electrical breakdown process in four polydimethylsiloxane fluids has been investigated under non-uniform field conditions using a high-speed image converter camera. The viscosity of these fluids ranged from 10 to 10,000 cSt, and the rate of rise. of the approximately trapezoidal voltage pulse varied from 10 to 42 kV/µs. It was noted that, within experimental error, viscosity had no effect on the breakdown process. When the cathode was a point, pre-breakdown streamer propagation was shown to be related to the rate of rise of the applied voltage and the breakdown voltage was highest for the highest rate. When the anode was a point, the streamer. propagation was approximately independent of applied voltage. The time to cross the gap of 3 mm was determined to be 0.6 ± 0.1 µs independent of the fluid's viscosity. The implications of those findings are discussed in the light of existing theories.