The non-destructive testing of electric strength of liquids

The development of an 80 kV breakdown testing equipment, designed for the non-destructive breakdown testing of liquids, is described. The equipment is so designed that, within one or two microseconds from the initiation of a breakdown, the source of high voltage is short-circuited by means of a special form of three-sphere gap, and consequently the energy dissipated in the breakdown path is little more than that stored in the self-capacitance of the electrode assembly. The equipment is particularly suited to the testing of transformer oil, and about 5000 breakdown tests have been carried out on one sample of oil without any evidence of the formation of carbon. Some data are included of test results obtained during a current programme of research into the mechanism of oil breakdown. Provision has been made to enable the equipment to be transported easily as two units, one weighing about 2 cwt and the other 25 lb; this does not represent the minimum attainable size.