Surface-time enlargement law for gas breakdown

This paper investigates, through theory and experiment, the applicability of the results obtained in laboratory tests of relatively short duration performed on model structures, as a part of the process of designing high-voltage equipment intended for lasting exploitation. Possibilities and limitations of applying these results to practical structures are examined using the methods of mathematical statistics. Special attention is devoted to the influence of electrode surface enlargement and pulse load (overvoltage) prolongation on the statistical behaviour of the pulse breakdown voltage random variable, expressed in the form of the enlargement law. In the theoretical part of the paper, the general four-dimensional (space-time) enlargement law is derived, along with its simplified three-dimensional (surface-time) variant. In the part of the paper related to the experiment, performed with the aim of testing the applicability of the derived surface-time enlargement law to SF₆ gas-insulated two-electrode systems, a description of the experimental equipment and procedure is provided, along with the details of measurement data processing. Comparison of experimental results with those predicted by the surface-time enlargement law proved its validity for a two-electrode configuration with a homogenous and radial electric field, insulated by SF₆ gas under pressure (with gas pressure as a parameter).