Computation Program for Breakdown Voltages of a Gas Insulation under Different Pressures and Slightly Nonuniform Electric Fields

This paper proposes a program for computing the breakdown voltage of a gas insulation under slightly nonuniform electric field. The development of the program is based on the knowledge of gas ionization and streamer breakdown theories, so it can compute the breakdown voltage of an ideally-simulated gas-insulated system. under a certain gas pressure level that the streamer constant is known. To verify this program, several simulations of sphere-sphere electrode systems were made using COMSOL Multiphysics with differences in sphere dimensions and gap spacings referred from IEC-60052 standard. Then the AC breakdown voltage of each simulation was computed using the breakdown voltage computation function under the pressure of 101.3 kPa according to the standard. Next, the computed AC breakdown voltages were compared with the AC breakdown data from the standard. The differences between the computed and the standard AC breakdown voltages were less than 3% in all simulated cases. Then the program was developed further by creating a new function that could estimate the streamer constant of a practical gas-insulated system under various gas pressure levels and slightly nonuniform electric field. Since the streamer constant of a practical gas-insulated system with any gas pressure level could be estimated using the streamer constant estimation function, the breakdown voltage of any practical gas-insulated system should be able to be computed pragmatically. To verify the ability to compute the breakdown voltage of a practical gasinsulated system, several practical gas-insulated systems with slightly nonuniform electric field were set up under certain gas pressure levels. Then several simulations were made to represent the practical gas-insulated system those were set up. Next, the streamer constant of each simulation was estimated using the developed streamer constant estimation function. After that, the gap spacings of both practical and simulated systems were changed. Then AC breakdown test was conducted on each practical system, while AC breakdown voltage of each simulated system was computed using the breakdown voltage computation function. Finally, the computed breakdown voltages were compared with the breakdown voltages those were practically tested. The comparison was satisfactory with less than 3% differences between the computed and the tested AC breakdown voltages in all cases.