Electric strength of transformer oil for large electrode areas

Carefully controlled measurements of the electric strength of transformer oil are reported. Electrodes of large-diameter cylindrical geometry are used to obtain substantially uniform fields with an electrode area of up to 2m2. The results indicate the important influence of oil volume on the electric strength both for supply-frequency and 1/50¿s-impulse voltages. The effects of temperature, forced oil motion and the nature of gas in solution are also studied, and it is concluded that the oil flow is an important parameter in determining the statistical distribution of breakdown measurements. The test results have been explained on the basis of gas-initiated breakdown.