D-C Cleanup in Insulating Oils

Three unusual types of behavior of insulating oils have been subjected to a series of experiments which indicate that all 3 are closely related. These types of behavior are the reduction of conductivity and a-c dielectric loss following a sustained application of continuous potential (called ``d-c cleanup´´), the current-time relation under continuous potential and the unequal potential distribution under continuous stress due to the accumulation of space charges toward the electrodes. Theories regarding a common cause of these different types of behavior are drawn from the experiments.