Dissolved gas analysis of liquid insulation under ac and impulse breakdown voltage tests

This paper represents the study of dissolved gas analysis in mineral oil compared with natural ester (FR3) under AC and impulse breakdown voltage tests. Liquid insulation was heated at 60°C with 200 mbar for 12 hours. Liquid test samples were divided into three groups. The first group was tested with AC voltage using the spherical electrodes with the gap distance of 1.0, 1.5, and 2.0 mm. The AC test procedure was in accordant with IEC 60156. The second and the third group of liquid samples was tested with standard positive lightning impulse and standard negative lightning impulse voltage using the needle - sphere electrode with the distance of 10, 15, and 20 mm. The impulse test procedure was according to IEC 60897. Testing experiments were performed 5, 10, and 15 times consecutively for each test sample. Then dissolved gas analysis of each test sample was performed. From the test results, the type of breakdown voltage and the number of breakdowns effected on the quantity of the dissolved gas in the liquid insulation.