Research On Single Phase High Impedance Grounding Fault Detection And Protection Method Of Small Resistance Grounding Distribution Network

The operation environment of distribution networks is complex,as they usually are connected to residential areas.So distribution lines are prone to intermittently contact with branches,or fall on the surface of non-ideal media such as asphalt,lawn,san d,concrete buildings,etc.,which will cause single-phase high-impedance grounding faults(HIGF).The transition resistance of this kind of fault is large,and the fault characteristics are not obvious,so that it is difficult to be detected by the ordina ry relays.Unfortunately,if the fault exists for a long time,it may cause serious consequences,such as fire,two-phase ground short circuit,large-scale blackout,etc.HIGF detection is becoming one of the challenges faced by power engineers and researchers.Given that,this paper focuses on the characteristic analysis of HIGF,its detection methods and its protection schemes.Based on the zero-sequence equivalent model of the single-phase grounding fault in a small resistance grounded system,the paper first analyses the transient and steady-state characteristics of the single-phase low-resistance grounding fault and HIGF,and then compares the relationship between the zero-sequence current of each feeder of the single-phase grounding fault and the curr ent flowing across the small neutral resistor(later referred to as neutral resistance current).In addition,a simulation model of a small resistance earthed distribution network is constructed to order to obtain the voltage and current simulation wavefor m under different fault conditions.After combining theoretical analysis and numerical simulation,the characteristics of single-phase HIGF in small resistance earthing systems are summarised,which provides a basis for the detection and protection of sing le-phase HIGF.A method based on the skewness coefficient of the neutral resistance current is proposed to detect HIGF in small resistance grounding system.As the neutral resistance current and the zero sequence current of each feeder caused by single-phase low-resistance earth fault and non-fault causes are sinusoidal,the calculated skewness coefficients of the full and half-frequency cycles are equal and both are about-0.5.However,for single-phase HIGF,the neutral resistance current is small and the waveform undergoes non-linear distortion,the skewness coefficients of the full and half-frequency cycles are not equal and both deviate from-0.5.Therefore,based on the above fault characteristics,it is able to quickly detect HIGF by calculating the skewness coefficient of the neutral resistance current.Finally,simulation analysis verifies the effectiveness of the proposed method.Based on the waveform similarity between the neutral resistance current and the feeder current,a HIGF protection method for small resistance grounding system is proposed.When a HIGF occurs in the small resistance grounding system,the impedance of the fault line is close to the resistance,while the impedance of the healthy line is close to the capacitance.The neutral res istance current and the zero sequence current of the faulty feeder have nonlinear distortion near the zero crossing point(the waveform is the vertex sharp waves),while the zero sequence current of the healthy feeder has distortion near the peak value(th e waveform is the sag wave).It is found that the waveform similarity between the healthy feeders and the neutral is weak,while the waveform similarity between the fault feeder and the neutral is strong.By calculating the correlation coefficient after on e cycle of the fault,a protection scheme for the HIGF is proposed.Finally,the proposed scheme is evaluated using simulation data.Test results show that the proposed scheme can work properly under low signal-to-noise ratio and different fault scenarios without misoperation,which shows a strong applicability.