Research On Single-phase Ground Fault Location Method Based On Controllable Signal Injection In Small Current Grounding System

When a single-phase grounding fault occurs in neutral ungrounded system(neutral ineffectively grounded system),the distribution system can continue to operate with fault within a period of time because of the week fault current and symmetrical system line-to-line voltage.At present,with the enlargement of distribution system scale and the increasing applying of cable lines,the fault current flowing through earth point increases and the fault arc is hard to extinguish,as a result,long-time operating with fault seriously affects the insulation life of electrical equipment,or expends the fault and leads to power blackout.Therefore,fast and timely fault location in neutral ungrounded system(neutral ineffectively grounded system)is the focal research point in the field.A new method based on injecting active signals which have notable feature and ease of detection,or making good use of the harmonic information of active signals for fault distance measurement with impedance method,has to be researched urgently.Based on the location principles of medium-resistance method,this paper proposed a new fault location method based on power electronic devices,which injects active signals with adjustable amplitude and notable feature by triggering the thyristor between any healthy phase and ground in the power supply side.The equivalent circuit model of signals injection after a fault occurs in neutral ungrounded system is built,theoretical formula of controllable signal is derived,the controllable signal strength is estimated by theory and simulation study,and the feature of signal waveform,phase position and frequency spectrum are analyzed to evaluate the feasibility of this method.In the study of fault location based on feeder detection method,the double-subtract algorithm for signal extraction is proposed,the controllable signal strength and phase position feature are selected as identification characteristics,the detection threshold are determined based on actual running data and simulation data of load fluctuation,the sensitivity and selectivity of this method are analyzed through simulation study,and dynamic simulation test is conducted to verify the reliability and practicability of this method.At last,the running condition and function of 10 kV device are tested in 10 kV testing system.In the study of fault location based on single-ended detection method,the sequence components of controllable signal harmonic are extracted based on fast Fourier analysis and symmetrical component method,the fault location algorithm is determined by obtaining the simultaneous equations derived from the relation between harmonic voltage and harmonic current in each sequence network of the distribution system.Then the fault location algorithm is corrected by considering the influence of earth capacity of distribution lines and terminal load based on the distributed parameter model,the sensitivity analysis of the fault location algorithm is conducted through simulation study,and resonance circumvention measures are proposed to improving the accuracy of fault location.