Stressed oil Volume theory

            In commercial liquids where minute traces of impurities are present, the breakdown strength is determined by the "largest possible impurity. On a statistical basis it was proposed that the electrical breakdown strength of the oil is defined by the weakest region in the oil, namely, the region which is stressed to the maximum by the volume of oil included in that region. In non-uniform fields, the stressed oil volume is taken as the volume which is contained between the maximum stress (Emax) contour and 0.9 Emax contour. According to this theory the breakdown strength is inversely proportional to the stressed oil volume.