Research On Single Phase Grounding Fault Location Based On Fault Indication System

In order to improve the reliability of power supply system,the neutral point non-effective grounding mode is generally adopted in the distribution network in China.When a single-phase ground fault occurs in the system,the fault signal is often weak.Therefore,the problem of single-phase grounding precise positioning in distribution networks has not been well solved.So,the research of fault line selection,section location and distance measurement technology of single phase to ground fault in distribution network is of great theoretical and practical significance for improving power supply reliability and ensuring the safe operation of power grid.In this paper,the steady and transient characteristics of a single phase grounding fault in a small current grounding system are analyzed and compared.After the single-phase grounding fault occurs,the steady-state signal is weak because of the compensation of the arc suppression coil,so the accuracy of the fault location is not high by using the steady state signal.Compared with the steady-state components,the transient components of faults are obviously enhanced.Therefore,fault location based on transient signals is more conducive to overcome the adverse effects caused by arc suppression coils.In order to obtain a more complete and more accurate fault information,this paper proposes an intelligent fault indicator and fault location system based on the study of traditional fault indicator,D-dot voltage sensor and precise synchronization theory.They not only have the advantages of precise synchronization and high frequency sampling,but also have additional functions of measuring voltage signals.The intelligent fault indicator has smaller volume and better dynamic performance,so it is suitable for measuring transient signals.In this paper,we choose wavelet theory of the time-frequency analysis tool to process data.In order to determine the time of fault occurrence,a method based on wavelet modulus maxima is put forward.Aiming at the problem of determining the characteristic frequency band,the frequency band with most obvious transient characteristic mutation is selected as the characteristic frequency band,which is more reliable than the method based on the maximum principle of energy based on integral and square calculation.For fault line selection,the fault line is determined by judging the positive and negative of the product of the wavelet packet decomposition coefficient corresponding to the zero sequence voltage and zero sequence current in the characteristic frequency band.This method makes full use of transient information,it can effectively suppress interference,and has high reliability.On the problem of fault section location,the fault section is determined by judging the positive and negative of the product of the modulus extreme value of the wavelet transform corresponding to the zero sequence.Aiming at the problem of measuring the fault distance,a two terminal asynchronous fault location method based on parameter identification for single-phase grounding fault is adopted.The method eliminates the measurement errors due to the uncertainty of line parameters and the asynchrony of two terminal data.An equal sequence network is used to eliminate the influence of the data synchronization angle,and then the fault location equations are set up,whose unknown variables are the line parameter and the fault distance.The above equations are solved by particle swarm algorithm leapfrog to obtain the fault distance.At last,simulation,experiment and analysis are carried out.A simulation model is built to verify the transient and steady state response of the intelligent fault indicator.At the same time,a simulation model is built to verify the accuracy of the fault location method proposed in this paper.