Research on the Measurement of Electric Field in Liquid Dielectric under Lightning Impulse Voltage

The insulating performance of the liquid dielectric plays an important role in the operation of the transformer. It has been verified by numbers of fault cases occurred in the release testing on transformers, that flashovers and breakdowns of insulating pressboard occurred in the angle rings, shielding rings and outlet device frequently, while an impulse routine test was processing. Study on the distribution of space electric field in the liquid dielectric under the impulse voltage is helpful to optimize the design of insulation structures, with rich theoretical and engineering value. The ex post fault analyses are usually based on a simulation result instead of experimental measurement. Kerr effect method is a non-contact online electro-optical measurement on the electric field in liquid dielectric. We established a rapid measuring system consisting of optical system, test cavity, impulse power supply and photo-detector, the whole system calibrated in propylene carbonate with a high Kerr constant. The calibration result indicates that the measuring system has a fine response rate and the deviation between the measured electric field and the applied electric field is less than 3.65%.