Investigating the relationship between the hold-off voltage of gas insulation for industrial applications and the discharge self-sustainment voltage

If the degree of non-uniformity of the electric field is sufficiently low, then the breakdown voltage may be approximately estimated by computing the voltage of ignition of a self-sustaining discharge in the same setup. The latter is a much simpler computational task: an accurate evaluation of the discharge ignition voltage for a given setup usually takes no more than half an hour on a personal computer. High-voltage insulating gaps are typically designed without sharp edges or small protrusions, in order to reduce the electric field non-uniformity as much as possible. Then the question is whether the electric field non-uniformity in a particular industrial device is low enough for the breakdown voltage to be close to the ignition voltage. This work aims to answer this question with respect to breakdown in air under typical conditions of exterior of vacuum interrupters. This is done in two ways, computationally and experimentally. The ignition voltage was computed using a plasmachemical model of low-current discharges in air at atmospheric or higher pressure. The breakdown voltage was computed for the same setup by means of standard time-dependent modeling with the use of the same plasmachemical model and was found to differ from the ignition voltage by no more than a few percent. Experiments specifically designed for investigation of breakdown in the exterior of vacuum interrupters have been performed, and a good agreement between the experimental hold-off voltage and the computed ignition voltage was found for different experimental designs and various air pressures.