THE INFLUENCE OF PRESSURE AND CONDUCTIVITY ON THE PULSED BREAKDOWN OFWATER

The influence of hydrostatic pressure and liquid conductivity the diel ectric breakdown of water solutions subjected to high amplitude electr ic fields of sub-microsecond duration has been investigated. Well-defi ned pulses (80 kV, 3 ns risetime, 100 ns duration) have been applied t o a gap (0.4 to 2.1 mm), between Rogowski profile electrodes (thus ens uring a uniform electric field), containing de-ionized water (non-dist illed, and distilled and ultrasonically treated), sodium chloride solu tions (0.001 to 1.0 molar), or magnesium sulfate solutions (0.01 to 0. 1 molar). Breakdown in these liquids has been studied at pressures fro m atmospheric up to 40 MPa. The inter-electrode potential and the curr ent response were measured indicating the time lag to breakdown, break down voltage, and temporal characteristics of the breakdown process. T he breakdown time lag increases with increasing pressure, and is insen sitive to the liquid conductivity. These findings have relevance to th e ongoing discussion concerning 'thermal' vs. 'electronic' mechanisms for dielectric breakdown in Liquids. In particular, the results sugges t that breakdown evolves via 'bubble' formation by field emitted curre nts near asperities on the cathode, and that the time for the change i n liquid conductivity as a result of breakdown is limited by processes other than ionization growth (due to electron impact ionization of mo lecules in the 'bubble') of prebreakdown electron currents.