| The actual operating environment of the power grid is complex,and a large number of switching operations are required to ensure reliable operation of the system.The typical operation is switching reactive power compensation equipment with vacuum circuit breakers in the substation to compensate the system reactive power.During the operating transient state of the vacuum circuit breakers,there are uncertain factors such as current chopping and arc reignition.There are also certain stochastic laws in the switching time and phase.Therefore,there is a certain stochastic distribution law for the switching overvoltage.Traditional circuit breaker switching transient models often perform overvoltage simulation under some extreme switching conditions.The model parameters are relatively fixed,and the simulation results are often quite different from the measured overvoltage.Therefore,it cannot play a good role in tracking and analyzing the risk of switching overvoltage.In order to solve this problem,a statistical switching model of circuit breaker can be constructed according to the digital twin idea.The model parameters are continuously modified based on the data obtained from online monitoring,so that the simulation results continuously approach the measured overvoltage level,and finally make the model meet the requirements of tracking analysis.Data and models are the two major prerequisites for achieving this goal.In this paper,a 10 k V vacuum circuit breaker switching parallel capacitor bank is taken as an example.The acquisition of switching transient voltage and current data was achieved by building an online monitoring system.The key parameters and its statistical characteristics required for the vacuum circuit breaker switching model are studied,and the model is modified through the measured data,and the statistical characteristics of the switching overvoltage are obtained through a simulation example.The main work of this paper is as follows:(1)Aiming at the problems in the existing monitoring equipment of the substation and the characteristics of the switching overvoltage,a switching electromagnetic transient online monitoring system was proposed to realize the online and synchronous monitoring of voltage and current at the key nodes of the switching circuit of the capacitor bank.The installation and commissioning of the system was completed in the substation,and the transient voltage and current waveforms of the switching operation process were successfully captured.(2)The existing circuit breaker switching model is improved,and important modeling parameters such as the circuit breaker switching time,chopping current,fracture breakdown condition,and high-frequency extinguishing condition are considered.A statistical model of circuit breaker switching under multiple random factors is built in MATLAB software.This model is convenient for data access of random variables,and can implement model parameter correction based on online monitoring data and statistical research functions.(3)Based on the statistical model of circuit breaker switching,an overall equivalent three-phase simulation circuit for the actual switching circuit of the parallel capacitor bank is established,and the key parameters of the model are modified using online monitoring data.This model is used to statistically study the overvoltage generated during the process of vacuum circuit breakers switching the parallel capacitor bank,and the statistical characteristics of this type of operating overvoltage are analyzed.In this paper,the online monitoring data of circuit breaker switching has been successfully obtained.Considering the multi stochastic factors and statistical laws of the circuit breaker switching process,the existing circuit breaker switching model is improved.By using the analysis method proposed in this paper,the accuracy of the simulation model can be continuously improved by simply modifying the values of the model parameters according to the online monitoring data until the requirements of the tracking analysis are reached.The research results in this paper can not only provide a certain basis for the tracking and analysis of the overvoltage risk of the circuit breaker,but also have a certain guiding significance for the insulation coordination under the switching overvoltage. |
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