Modelling of current and temperature rise during discharge initiation in water

The conduction current recorded when a high voltage impulse is applied to a rod-plane gap containing water is modelled. The electro/thermal model considers the coupling between electric field, Joule dissipation, temperature rise, and variation of liquid resistivity with temperature. A fairly good agreement between current measurements and calculations are obtained. The model also shows the evolution of temperature and field distributions in the gap versus time. The calculated average temperatures appear insufficient to explain liquid boiling. Boiling can be explained by considering the influence of local surface defects. Values of the bubble pressure at discharge ignition are evaluated, with the hypothesis that discharges occur in vapor following Paschen's law.