Scatter reduction of the 50-60 Hz breakdown voltage test for insulating liquids

There are several reasons to test the breakdown voltage of insulating liquids: acceptance tests on new deliveries, testing of treated liquids prior to or during filling into electrical equipment, and monitoring and maintaining oil-filled apparatus in service. Among others, the test for the determination of breakdown voltage at 50 or 60 Hz is one of the most important. In fact, it is worldwide accepted that this test gives quickly very useful information even if mainly related with moisture and particle content than the intrinsic properties of the insulating liquids. This test is standardized by IEC and ASTM but has some limitations in terms of the statistical scatter of mean value of the breakdown voltage. The present paper presents an improvement on the scatter of the mean values of the breakdown voltage by increasing the number of requested shots and discarding the most disperse results. In addition, it is presented as a revised test cell having stirring device on the top and round edges at the bottom may further reduce the standard deviation of the same breakdown voltage. Others experimental parameters which may still influence the scatter of the same standardized test are also examined and discussed.