Evaluation of a model for prebreakdown at the cathode in a DC-stressed liquid

A nonlinear model is simulated for a partial discharge, or low density region (LDR), at a DC-stressed needle cathode in hexane for several ambient pressures from subatmospheric to 3 atm. It assumes a void driven in the liquid from the cathode by electrical force on the void´s charged liquid boundary (LDR wall). The effects of varying certain parameters on the simulation results are discussed. Simulation results are compared with earlier experimental values of LDR size, pulse charges, and pulse duration as functions of time and pressure. The results suggest that the LDR is driven by electrical pressure which is initially much larger than typical ambient pressures but which drops during the LDR expansion to below ambient pressure, resulting in the demise of the LDR. Current pulses are then produced as a result of the expansion (rather than being its cause), and they serve as externally detectable telemetry signals characterizing the LDR state without invading it. The pulses result when the LDR grows and its trapped charge spreads over larger wall area, changing the LDR wall potential