Influence of hydrostatic pressure and temperature on the water dielectric strength and on the dynamic pressure wave

The paper presents experimental results for breakdown voltage in water gaps as a function of water hydrostatic pressure and temperature. Low applied electric field and high switching energy ensure the development of subsonic electrical discharges. For these discharges, the vapour bubbles involved during the pre-breakdown phase are initiated by joule heating effect. The dependencies of the U50 breakdown voltage on hydrostatic pressure up to 5MPa and on the temperature up to 90°C are investigated. The pre-breakdown phase of the discharge is characterised by the different power consumption behaviours and by the energy losses according to hydrostatic pressure and temperature. A minimum threshold value of the discharge energy losses can be highlighted. Experimental measurements concerning the shock wave generated by the subsonic discharges are presented. Results point out that the dynamic wave is not dependent from the hydrostatic pressure. On the other hand, for a constant energy at breakdown time, the dynamic pressure wave increases with the temperature. These results will allow the optimization of the electrical energy ratio converted into acoustic energy.