The repetitive breakdown and flashover properties of solid dielectric materials under DC and pulsed conditions

This paper reports on the results of a test programme to investigate the material limits of solid dielectric insulation at potentials in excess of 100 kV. This comparative study of various materials was not an attempt to optimise the material breakdown voltage but to make a direct sample comparison under identical, representative pulsed power conditions. The electrical breakdown characteristics of various materials were studied using kV pulses which are representative of those generated in a typical high voltage transmission line system. The investigation was carried out for both DC and pulsed voltages, the latter operating at repetition rates of up to 100 pps. The broad aims of this test programme were to compare the flashover and breakdown performance of different materials in air and in oil, to compare the voltage characteristics of insulating tubes and insulating films for different materials and to investigate the effect of repetitive operation and pulse charging upon solid insulation. The breakdown voltage of PTFE, acrylic, Pyrex glass and polycarbonate tubes was measured and compared using a standard test arrangement. This enabled direct comparison to be made between the different materials. The flashover potential of these materials was also measured as a function of gap spacing in silicone oil and air. Breakdown tests were also carried out for tubes made from many layers of polypropylene and polyester films. These were wound under vacuum and impregnated with silicone oil to minimise trapped air effects. Electrostatic modelling of the test set up was also carried out.