Characteristics of the threshold coordinate for high stress conduction in transformer fluid

Above a specific threshold coordinate on the V-I characteristic, prebreakdown conduction current flows through transformer oil in direct proportion to a simple power of the applied voltage when this rises and falls linearly in time. The threshold coordinate for this power law regime as well as the power law exponent has been shown to be dependent on the electrode geometry, gap separation, and electrode material for dimethyl siloxane, but transformer oil exhibits in addition a sensitivity to the value of the maximum stress value per cycle. At high maximum stress the characteristic V-I loop is seen to divide into two, and above the turnover point V_th behaves differently with respect to the ramp rate than below it. This phenomenon is described in its relationship to gap separation and electrode material and compared with similar data observed with dimethyl siloxane