The Impact of Electrode Area and Surface Roughness on the Pulsed Breakdown Strength Water

Experimental results are presented on the degree to which electrode surface area and surface roughness impacts the dielectric strength of water. A 2 mm water gap was tested under pulsed conditions with maximum electric fields in excess of 1 MV/cm and maximum currents of more than 5 kA. Six different pairs of stainless steel electrodes, each having a unique Bruce profile and thus a different effective surface area, were used to achieve a uniform electric field across the gap. The differing electrode pair profiles, with effective areas ranging from 0.5 cm² to 76 cm², were designed to minimize the change in gap capacitance. Prior to each test, a different roughness average, ranging from 0.26 mum to 1.96 mum, was applied to the electrodes. Conclusions are made as to the effect both electrode surface area and surface roughness has on the holdoff voltage of water dielectric systems. In addition, shadowgraph images of pre-breakdown events are presented.