Fluctuations of DC Conduction in Mineral Oil under High Electrical Fields

Pulses of conduction current in transformer oil under high electrical fields were studied by recording them on magnetic tapes and then subjecting them to pulse-height analysis. It was found that for the degassed oil, small-magnitude pulses increased, whereas large-magnitude ones decreased with the duration of the stress conditioning period. With air dissolved in the oil, pulses of all magnitudes decreased during stress conditioning. The electrode material affected the current pulses only at relatively low stresses. The pulses were found to be sensitive to hydrostatic pressure only for relatively large gaps at high applied fields. The results support the theory that a gaseous phase is involved at some stage in the breakdown process of liquids.