Investigation of correlation between vacuum breakdown phenomena and field emission current during shunt capacitor switching

In the case of interrupting capacitive loads, the most challenging problem for vacuum interrupters is to withstand recovery voltage during opening operation. In addition, the field enhancement factor of vacuum contacts is assumed to be high due to the damage of contacts caused by making the inrush current. In this paper, simulated shunt capacitor switching tests are carried out and the field emission current across the contact gap is measured to research the influence of the inrush current on the breakdown phenomena during opening operation. All breakdowns occur before the gap spacing reaches the maximum value and it is determined that there is a correlation between the electric field breakdown and the field emission current measured before the breakdowns. Furthermore, the found correlation is independent of the amplitude of the inrush current. The electric field breakdown is nearly invariant under the condition that the measured field emission current is constant regardless of the inrush current. However, the field emission current tends to be high in the presence of a large inrush current. The difference in the expected field emission current is believed to affect the electric field breakdown.