Combined ?-radiation and heat effects on transformer oil

An experimental study on the combined γ-radiation and heat effects on the electrical properties of transformer oil is presented. Several samples of fresh unused transformer oil of the type used in Egypt is irradiated in a γ-cell for different time periods, at the same radiation conditions. Each sample, one at a time, is then raised to a different pre-specified temperature. At this temperature, we measure the dielectric constant of the oil sample using a very accurate optical technique, ellipsometry, employing a laser beam. Also, at this temperature, we measure the breakdown voltage of the sample using a standard oil tester. Several measurements are taken and results are statistically analyzed. Other samples of used oil, for several years, in a distribution transformer (11 kV/380 V) are also tested under the same conditions as the fresh unused samples. In this condensed form of paper some of the obtained results for the unused and used samples are presented along with a brief discussion. Results and discussion provide more information on the combined effects of the γ-radiation and heat.