Experimental Research on Overvoltage Suppressing Measures Caused by 10-kV Vacuum Circuit Breakers Switching-off Shunt Reactors

When the vacuum circuit breakers (VCBs) switch the shunt reactors (SRs), the overvoltage with high amplitude and frequency will be produced by multiple restrikes. It is easy to cause switchgear explosion and insulation breakdown of power equipment. These accidents are detrimental to the stable operation of the power system. This work is based on the 10 kV side of a 220 kV substation. The VCB was operated multiple times to switching-off the SR in the substation, and the overvoltage characteristics were analyzed. The experimental result shows that the maximum overvoltage amplitude at substation transformer (ST) and SR side caused by VCB multiple separating SRs can reach 8.16 p.u. and 6.43 p.u. without any suppression measures. To suppress the overvoltage, surge arresters were and resistance-capacitance (RC) snubbers were installed. The experimental results show that the VCB opening process will produce three different frequency oscillation processes, and will cause multiple restrikes between the contacts. RC snubber can suppress the oscillating frequency, and the number of restrikes between the contacts compare with installing the surge reactor. The influence of lightning arrester and RC snubber on the transient process of overvoltage is discussed. It is showed that the RC snubber suppresses the three-stage oscillation frequency and the restrike between the VCB contacts. Finally, as for the 220 kV substation, the reasonable suppression measure is installing a RC snubber at the end of the SR cable, which has an excellent suppression effect on overvoltage transient process.