Field Experiments and Analysis on the Faults Caused by Switching Shunt Reactors Using 10 kV Vacuum Circuit Breakers

In recent years, vacuum circuit breakers (VCBs) have been widely used for switching reactive power equipment such as shunt reactors in distribution systems. However, the overvoltage accidents such as short-circuit faults and insulation breakdown of the transformers caused by switching shunt reactors with the VCBs are common in the operation of the power grid, which makes great impacts on the power grid. Therefore, it is necessary to study the transient process of chopping current and arc re-ignition when VCBs switch shunt reactors in the actual process and to analyze the formation mechanism of overvoltage. In this paper, the analysis of the series of grounding and short-circuit faults of the substation transformer occurred in a 10 kV bus is carried out. Based on the experiments and simulations, the study of the characteristics of the switching overvoltage (shunt reactors) was carried out. Based on the field test results of the VCBs switching shunt reactors and the back-factory test of the VCBs, it could be concluded that the failed mechanical performance of the VCBs caused the high chopping current, which induced high transient recovery voltage appeared between the contact gap of this VCBs and the re-ignition occurred. Then the high overvoltage propagated to the substation transformer in the 10 kV bus, eventually led to the occurrence of grounding faults.