An Investigation by Fluid Analysis of Decrease of Breakdown Voltage due to Arc in SF₆ Gas

Abstract

Considering the unanticipated increase in contact resistance in Gas Insulated Switchgear, an investigated result on the reduction of the breakdown voltage due to the arc is reported.
At first, incompressible fluid analysis is applied to calculate profiles of fluid velocity, gas density, etc. In experiment, the arc is generated on the gas gap between a pair of conductors located in the center of the tank. The breakdown voltage between them and the disc electrode located above them is measured.
Results are as follows.
(1) The transit time of the hot gas from the condutors to the disc electrode is 235ms in calculation and 233ms in experiment, respectively.
(2) The breakdown voltage between the conductors and the disc electrode is estimated by the gas density and the electric field strength at the surface of the conductors. Because the gas density, which is calculated by the fluid analysis, is lowest and the electric field strength, which is calculated by FEM, is largest.
Consequently, it is proved that condition of these calculation is similar to that of the lowest breakdown voltage in experiment.