Determination of electric field distribution in oil using the Kerr-effect technique after application of DC voltage

A technique based on the Kerr electrooptic effect is used for the measurement of electric field strength in dielectric liquids such as transformer oil. An elliptically polarized laser beam is used as incident light and the applied DC voltage is modulated with an AC voltage. Using this technique, low-level electric fields are measured in liquids with small Kerr constants using a short electrode length. The change of electric field distribution with respect to time after application of a DC step voltage and the nonuniformity of the electric field in water-saturated transformer oil are also studied. The electric field in water-saturated transformer oil is shown to be distorted, and the charge density is shown to be about 1 nC/cm³ when the applied step DC voltage is 2 kV. However, electric field distribution is found to be uniform in dry transformer oil, dry silicone oil, and water-saturated silicone oil