Influence of grading capacitors on breakdown characteristics of a double-break vacuum interrupter

The objective of this paper is to determinate the influence of grading capacitance on breakdown characteristics of a double-break vacuum interrupter. A prototype of double-break vacuum interrupter was built up as a U-type configuration with two 12 kV vacuum interrupters in series. The double-break vacuum interrupter is stressed by a power frequency withstand voltage and a lightning impulse withstand voltage, respectively. The lightning impulse breakdown voltage U
50
is obtained by an up-and-down method. Five grading capacitance are designed. One is with no grading capacitors, which is as a benchmark. The other four capacitances are 100 pF, 500 pF, 1500 pF, and 10 nF, respectively. The experimental results show that there is an optimum grading capacitance which leads to a maximum impulse breakdown voltage. As the grading capacitance increases, the number of successive breakdown increases when breakdown occurs. With grading capacitance increasing, the power frequency breakdown voltage increases and finally reaches saturation.