Research On A High Pulse Current Fault Line Selection Method In The Neutral Point Non-effectively Grounded Manner

The neutral point non-effectively grounded manner is widely applied in the power distribution systems of 6k V to 35 k V in China.But the problem of line selection of single-phase-to-earth fault in the neutral point non-effectively grounded system has not been well settled for a long time.Maintaining the advantages of the neutral point non-effective grounding manner with high reliability,while solving the problems of this manner is a major research topic of medium voltage system.The key of solving this problem is the accuracy of fault line selection when single-phase grounding fault occurs.Due to the impact of the grid structure,line type,fault conditions and other factors,the current line selection method still have shortages,so it is important to find a strong adaptability detection method.In this paper,the neutral point non-effective grounding system is modeled and simulated.The neutral point non-effective grounding system and neutral point grounding system through arc suppression coil are analyzed.At the same time,analyse the transient characteristics and the steady-state characteristics of the single-phase grounding fault in the neutral-point non-effectively grounded manner.On this basis,this paper studies a method of pulsed high current line selection and develops a device of pulse line selection.The device of thyristor is connected between neutral point and ground of small current grounding system.When single phase grounding fault occurs,the system detects bus voltage change,judges that single phase grounding fault occurs in distribution network.And then the neutral point thyristor is connected to the ground to form a circuit between the neutral point and the fault phase.The low current grounding system is changed to the high current grounding mode in a short time.The voltage and current monitoring devices installed on each 10 k V outgoing line detect the high current signal of the fault line and accurately complete the fault line selection.The voltage and current monitoring devices installed on each 10 k V outgoing line detect the high current signal of the fault line and accurately complete the fault line selection.Results of simulation and experiment verify the effectiveness of the method,and the corresponding engineering prototype is developed based on the method.