Effect of polarity and gap length on the breakdown characteristics of mineral oil for non-uniform fields

Abstract

The direct breakdown voltage of degassed transformer oil has been measured as a function of gap length using point-sphere electrodes, for both polarities of the point. Although changing the material of the sphere electrode altered the magnitude of the breakdown voltage for both point polarities, the critical gap length at which the breakdown voltage was the same for both polarities remained unchanged. This critical gap length was markedly reduced by the presence of dissolved oxygen.