The Study On The Very Fast Transient Overvoltage Induced By Incomplete Opening Of Circuit Breaker

Gas-Insulated Switchgear(GIS)has been widely applied in power system because of their advantages such as high reliability,less space occupation,low maintenance workload,long maintenance peiod and so on.However,the multiple arc reignitions will occur between the moving and static contact during the operation of disconnecting switch and circuit breaker in GIS,and the very fast transinet overvoltage(VFTO)will cause by high frequency oscillation,which will be poses a serious threat to the insulation of the electrical equipment,influence the stability of power system.The breakdown characteristic of the circuit breaker is different from the breakdown characteristic of the traditional circuit breaker when the circuit breaker is incomplete opening.In this paper,the circuit breaker repetitive breakdown model when the circuit breaker is not completely opened is established,and the transient process of the system is simulated when the circuit breaker is not completely opened to find the transient change law of over-voltage and over-current of the system.The main work of this paper is as follows:(1)The arc model was studied and the parameters of the KEMA arc model were identified using the particle swarm algorithm.Through the analysis of the mechanism of repetitive breakdown of the fracture gap when the circuit breaker is not completely opened,a repetitive breakdown model of circuit breakers is built based on the combination of exponential decay model and KEMA model.The results show that the identification results of KEMA arc model parameters by particle swarm optimization are in good agreement with the original waveform,which shows that the parameter values obtained by this identification method are practical.And through the combination of the exponential decay model and the KEMA model,the repeated breakdown model of the circuit breaker can fully describe the three stages of the breakdown,arcing and arc extinguishing of the single discharge in the break gap of the circuit breaker.(2)According to the actual structural characteristics of GIS,a reasonable equivalence was made for each component.The simulation analysis is made of the repeated breakdown of the breakers when the circuit breaker is not completely opened,to study the transient process of repeated breakdown,and the reasons for the formation of the very fast transient overvoltage are explored.The results show the incomplete opening of the circuit breaker will result in a substantial reduction in the breakdown voltage of the fracture below the system operating voltage,causes the repeated discharges happened in the fracture and then the high-frequency oscillations would generate VFTO.Because the high amplitude and steepness of very fast transient overvoltage,it will cause serious harm to the insulation of power equipment.(3)The current VFTO suppression measures were discussed,and the simulations and comparative analysis of the effect of the addition of ferrite core and split-resistor resistor at the circuit breaker on the VFTO of GIS equipment were performed.The results show that the addition of the ferrite magnetic ring and the added switch resistor will have a good suppression effect on the very fast transient overvoltage,but the system structure will be complicated and the stability of the power system will be affected by adding the switch resistance.Therefore,it is suggested that the very fast transient overvoltage can be suppressed by adding ferrite magnetic loop,so as to effectively reduce the danger of very fast transient overvoltage in GIS.In this paper,the formation principle of VFTO is analyzed in detail when the circuit breaker is incomplete opening,and the risk of incomplete opening of circuit breaker is established.Related suppression measures were discussed to provide support for the selection of inhibitory measures,to improve the suppression measures,reduce the occurrence of such accidents and ensure the safe operation of power equipment,it will be of great significance for the overvoltage protection and insulation design of GIS.