The dielectric testing of gaseous and liquid insulation has a long tradition and devices for breakdown testing have improved during the past 40 years. Special liquids like silicone oil, have made it necessary to develop special methods. As a result, methods to recognize the disruptive discharge have changed, as have methods to determine switchoff characteristics and to generate test voltages.
The dielectric breakdown voltage is a variable with a statistical distribution. The test procedure involves a number of single test sequences. To get reliable results, it is of paramount importance to have a minimum of influence from one sequence to the next. This depends on breakdown energy and therefore on breakdown recognition, maximum short-circuit current and also on the switch-off characteristic of the testing device. The development of new, sensitive testing devices enable the energy which is sent into a test sample to be kept at a very low level. This permits a clear differentiation between partial discharge and disruptive discharge.
Investigations in breakdown characteristics and switch-off methods of devices with different techniques across several gaseous and liquid samples with special consideration of the comparability of testing results have been made to improve testing. This article describes new ways of breakdown recognition and switch-off techniques, discusses advantages and disadvantages of the new and better-known methods and discusses the problems of standardization.