Field Experiments And Overvoltage Mechanism Of Switching 10kV Shunt Reactors By Vacuum Circuit Breakers

In recent years, vacuum circuit breakers(VCBs) have been widely utilized in 10/35 k V distribution systems to switch reactive power compensation equipment because of big breaking capacity, suitable for frequent operation and being easy to maintain. However, switching 10 k V shunt reactors when vacuum circuit breakers(VCBs) are applied,under certain system conditions may cause multi-prestrike and multi-reignition. The transient process often comes with high-frequency(HF) and high-amplitude overvoltage surges in the 10 k V side of a 220 k V substation in Chongqing, China. Insulation failures in VCBs, shunt reactors, dry-type distribution transformer occur frequently and severely. However, the reason for this phenomenon is unclear.Based on the test platform for the failure circuit of a running 10 k V power system, a series of field tests were conducted to investigate the overvoltage mechanism of this type of failure in this paper. Field tests successfully recorded the prestrike and reignition waveforms during the switching transient processes of shunt reactors, and the innovative conclusions have been presented, such as multi-prestrikes and multi-reignitions, cable length, switching conditions, and system configurations were the main reasons for the severe overvoltages.In order to model the accurate simulation model of VCB, The required characteristic parameters of VCB model were extracted from the waveform data of field test. The prestrike and reigniton model of VCBs switching in 10 k V shunt reactors is set up via ATP-EMTP, and a three-phase simulation of the VCB switching shunt reactors was established in ATP-EMTP to verify the accuracy of the VCB model. The main research contents of the thesis are as follows:Combined with the test where the distribution characteristics of power equipment, a switching operation transient test system of 10 k V shunt reactor circuit was invented, and a signal trigger control system of the switching operation transient test system for reactive power device was proposes. Field experiment successfully captured the switching voltage current waveform data, transient process in operation.By field tests, the paper successfully got a series of three-phase voltage and current waveforms during the entire transient process of switching operation, based on which transient process and phenomena were analyzed. The mechanisms of overvoltage generation of the switching transient processes were analyzed based on circuit analysis. According to the experimental results and analysis, good effects of restraining overvoltage can be achieved by adopting several measures for switching 10 k V shunt reactors by VCBs.The VCBs models, including the closing operation characteristics of different period,the dielectric dynamic strength recovery curve and high-frequency current quenching characteristics, were set up in ATP-EMTP based on the field experimental results. The paper established a three-phase simulation of the VCB switching in shunt reactors in ATP-EMTP to simulate the field tests based on the models, and cable parasitic parameters is considered in the simulation. The simulation results agree well with the experimental results.In a word, the paper comes to the following conclusions: single-phase prestrike phenomena occurred frequently when VCBs were applied to switch in 10 k V shunt reactors and high amplitude and high frequency transient overvoltage can also be formed in the system under this condition. The probability of reignition was relatively low, but the magnitude and the rise rate of the recovery voltage of the reigniton caused overvoltage during the transient process were higher, was the most possible reasons for the scene of the accident. Vacuum switch simulation model was built based on the field experiment data. The simulation results are basically consistent with the experimental results. This work further improvement of the formation mechanism of transient overvoltage during switching operations processes under this condition and the VCB simulation model. Therefore, the research work of this paper has important significance to improve the insulation coordination for power equipment in substation application and the VCB simulation model.