Influence of Temperature and Pressure on Conduction Currents in Transformer Oil

This paper gives the results of an experimental study of the dependence of conduction currents in transformer oil on temperature and hydrostatic pressure (10-760 torr) using direct fields up to 680 kV/cm. Results of measurements with degassed oil and oil containing dissolved oxygen suggest that electrons move through the liquid partly as free electrons and partly as negative ions. The dependence of current on pressure under certain experimental conditions is interpreted as indirect evidence for the existence of an ionization process in the liquid bulk at stresses well below breakdown. The view that a gaseous phase is involved in the process provides a consistent explanation of the results.