Effects of hydrostatic pressure, temperature and impurity on electric conduction in liquid dielectrics

The conduction currents in nhexane, carbon tetrachioride and transformer oil have been found to be dependent on field strength, temperature and impurity content, but independent of hydrostatic pressure up to a gauge pressure of 150lbf/in2 for field strengths up to 90% of the normal breakdown stress. It is suggested that the decrease of conduction current with time is associated with the decrease of concentration and drift velocity of charge carriers, and that the linear portion of conduction-current/field-strength characteristics is attributable to ionic conduction, while the nonlinear portion is attributable to Schottky-type electron emission from the cathode. The strong pressure dependence of electric strength indicates that breakdown is initiated by bubbles formed in the liquid.