Novel Method Of Hybrid Arc Suppression Control And Fault Phase Selection For Single-Line-to-Ground Faults In Distribution Network

Residual current and overvoltage of the ground fault in distribution system are serious threats to the safety of people and power supply equipment.Nearly 70%of power failure accidents are caused by grounding fault,leading to huge loss of economy with bad influence for society.Ground fault is characterized by transient,intermittent and other complex modes and evolvement,which makes fault detection and protection very difficult.The intermittent arc overvoltage caused by SLG fault endangers the safety of personal equipment,and even causes dangerous accidents such as substation deflagration and cable ditch fire,which may lead to large-scale and long-term power outage accidents and seriously affect the safety of distribution network and power supply reliability.Aiming at the existing problems of fault phase selection and arc suppression,the proposed paper innovatively proposes faulty phase recognition method based on three-phase voltage magnitude-phase characteristics,combined with hybrid arc suppression control strategy,which realizes rapid and accurate faulty phase judgment and reliable arc suppression under different grounding fault conditions of distribution network.In this paper,arc suppression mechanism of single-phase-to-ground fault in distribution network is analyzed,and the overall design scheme is proposed.Based on the analysis of the characteristics of three-phase voltage amplitude and phase angle,a set of faulty phase identification method applied the variation law of three-phase voltage magnitude and phase angle is proposed.Then,hybrid arc suppression method is proposed.Through the booster transformer,the two-phase power supply of A,B and C of the auxiliary side of the grounding transformer is selected to directly connect to the neutral point,which can compensate most of the fault current based on the result from faulty phase recognition.The low-power active arc suppression device is matched to compensate the ground residual current.The full compensation of the fault current is achieved,and the problem of the low cost of the harmonic,the high cost of the active arc,and the phase error of the transformer leakage are effectively overcome.The analysis and comparison of the hybrid arc method and other arc suppression methods are analyzed with comparisons,and the comprehensive advantages of the hybrid arc method are emphasized.On the basis of theoretical analysis,the proposed faulty phase selection method and hybrid arc suppression method are modeled and simulated on PSIM and MATLAB/Simulink software respectively,and hybrid arc suppression experimental platform is built in a 10kV distribution network laboratory to verify the proposed method experimentally.The simulation and experimental results show that the fault phase selection method proposed in this paper can effectively solve the oscillation of three-phase relative ground voltage caused by the change of ground resistance during the faulty phase grounding,as well as the three-phase unbalance caused by the sudden change of single-phase load.Through applying special synchronization mechanism and synthesizing the magnitude and phase angle of the three phase-to-ground voltages,the real-time performance of fault phase detection is effectively enhanced.Simulation results show that the proposed hybrid arc suppression method makes full use of passive arc suppression and active arc suppression,carrying the advantages of both the rapidity and accuracy of arc suppression.It realizes zero sequence voltage control efficiently,for arc suppression,further it constrains the capacitance current down to zero,achieving completely arc suppression compensation.In addition,the hybrid arc suppression method greatly reduces the power capacity requirement of the active inverter,with decreasing of the equipment cost,and improves the reliability of the arc suppression system.