Research On Line Selection And Ranging Of Small Current Ground Fault Based On ESMD

At present,the distribution network in China widely adopts the method of small current grounding.The main fault type is a single-phase grounding fault.At this time,the fault current flowing in the line is small,which will not have a large impact on the normal operation of the system.The fault state may expand the single-phase ground fault to a two-phase short circuit or even a three-phase short circuit,resulting in damage to the relay protection device and endangering the safe operation of the system.Therefore,it is of great significance to quickly and accurately determine the fault line and accurately locate the fault point to protect the reliable and safe operation of the power grid.Therefore,in this thesis,the single-phase grounding fault line selection and distance measurement method of the small current grounding system is studied in depth.This thesis first analyzes the advantages and disadvantages of the existing fault line selection and ranging methods,and focuses on the steady-state and transient characteristics of the system when a single-phase ground fault occurs.The research results show that non-stationary and non-linear transient signals are not affected by the neutral grounding method and contain a large amount of fault feature information,which provides a theoretical basis for subsequent fault line selection and range.To solve the problem that the transient component fault feature extraction is difficult and is greatly affected by the fault condition,which leads to the poor adaptability of the line selection method,the Extreme-point Symmetric Mode Decomposition(ESMD)is introduced to extract the information features,effectively avoiding the traditional information extraction method empirical mode Decomposition(EMD)has the shortcomings of modal aliasing and end effect,which can completely and accurately extract the fault information of the original signal.Combined with the relative entropy that can identify and expand the energy difference between the faulted line and the non-faulted line,the maximum integrated energy relative entropy(ERE)of the line is proposed as the criterion for fault line selection.The simulation results show that the line selection method is less affected by transition resistance,fault distance,fault initial phase angle,noise,and has greater margin and higher sensitivity than the EMD-ERE method.Aiming at the problem that the fault transient traveling wave head is difficult to identify and the traveling wave ranging accuracy is not high,a wave head information extraction algorithm combining ESMD and Teager energy operator(TEO)is proposed.First,the ESMD decomposition of the transient line mode current collected after the line fault is used to obtain multiple intrinsic mode functions(IMF),and then the TEO has the characteristics of reflecting the instantaneous energy fluctuation of the signal to calculate the IMF1 component,and the wave head reaches the measurement end The time difference is finally substituted into the single-ended traveling wave method to obtain the fault distance.The simulation results show that the ranging method can achieve accurate ranging under different fault initial phase angle,transition resistance,fault distance,grounding method,and environmental noise.it has stronger adaptability and higher ranging accuracy than the EMD-TEO method.