Electrical Breakdown of Oil-Impregnated Pressboard under AC and DC Voltages Ramp

In this work, we present an experimental study on electrical breakdown, also called dielectric failure on a material widely used as insulation in oil transformers and other equipment. This material is pressboard paper impregnated with insulating oil. The breakdown tests are carried out under three types of voltage and for several voltage rise speeds. Dielectric breakdown is a random phenomenon, many tests are carried out on a large number of samples and the results obtained have been subjected to statistical processing. The material is cut into square plates of 7.5 cm in length from a set of plates 2 m² in length and 500 µm in thickness. Prior to the tests, the samples were conditioned in a desiccator with silicone gel for at least 24 hours in order to eliminate any presence of moisture. Then they were impregnated with Borak22 insulating oil for at least one week. The tests consist of placing the sample concerned between two cylindrical bronze electrodes and applying a voltage ramp at constant speed until breakdown. After failure, the value of the breakdown voltage is taken. These tests are carried out in the laboratory at room temperature. However, we have tried to reproduce the s