The breakdown of liquid dielectrics and its dependence on oxidation of the electrodes

The dependence of the impulse breakdown strength of a liquid dielectric on the natural oxide layer on the electrodes used for the test is considered. It is shown that an electric field may exist in the oxide layer owing to the chemisorption of oxygen, and that this would be expected to reduce the probability of electron emission from the cathode and thus increase the recorded breakdown strength. Results are given of experiments on the breakdown of pretreated transformer oil using stainless steel, brass, and aluminium electrodes which support this conclusion.