The conductivity of insulating oils

Continuous-current characteristics of several insulating oils are studied for time intervals beginning 0.001 sec. after the application of voltage or short circuit. Essential equipment is the amplifier oscillograph in connection with a quick-acting switch. It is found that in one group of oils there is an initial conductivity which is constant over the period of the first second following the application of the voltage. Thereafter there is a slow decrease of conductivity to a final value much lower than the initial value. It is shown that this initial constant conductivity is sufficient to account for all of the dielectric loss under alternating stress.