Assessment of insulating liquid deterioration by laser measurements

Samples of two types of insulating oil used in transformers and switch-gear components in Egypt are experimentally tested to determine the breakdown-change of their dielectric constant and of their breakdown voltage. A standard oil tester is used to apply high voltage to the samples at two different rates and two different time intervals. The breakdown voltage of each sample is measured at the two rates. At each value of the breakdown voltage we measure the dielectric constant of the oil sample by a novel method using a laser beam. This method employs a research ellipsometer composed of a polarizer, a compensator, and an analyzer. The ellipsometer is used in the straight-through position and in the null mode. Selected experimental results obtained for one type of oil (GSA) at one time interval between successive breakdowns (one minute) at two different rates of application of the high voltage (500 and 3000 V/sec) are presented in this condensed form. Other results for the same type of oil at two-minutes time intervals, and for samples of Diala B insulating oil at the same test conditions are obtained and referred to.