Research On Method Of Fault Traveling Wave Location And Adaptive Protection For Distribution Network

Distribution network is a key part to maintain the connection between power system and users.It undertakes the important responsibility of power tran smission,ensuring the national economic development and the people’s normal life.Therefore,the reliability and continuity of power supply in distribution network is the important support for the rapid development of society,the improvement of national economic efficiency,and the improvement of people’s living and production standards.However,distribution network is susceptible to environments and human activities,resulting in line faults,power outages,and safety accidents of people and equipment,due to the large power distribution range,complex line structure and operation scenarios.Rapid location and reliable removal of fault points in distribution network is the key to reducing fault recovery time and the scope of power outages.It can improve the reliability of power supply for distribution network.Nowadays,the fault location methods for distribution network are mainly divided into three categories,i.e.,the selection of fault line,the identification of fault section and the location of fault point.Compared with the selection of fault line and the identification of fault section,the fault location method based on traveling waves is low sensitive to the system operation mode and fault types,and has better fault location accuracy and reliability.It can help to reduce the losses of power outage,and improve the service capability of power supply.However,the reliability of the existing fault traveling wave location methods still needs to be improved due to the impact of multi-branch nodes,hybrid lines,abnormal measurement data,limited traveling wave devices,and uncertainty of line parameters.Besides,owing to the influence of neutral point grounding method,the traditional current protection method is not good at removing the line with grounding fault,and it is difficult to meet the development requirements of distribution network.Therefore,in order to improve the reliability and continuity of power supply,this paper focuses on the precise location of fault point and the reliable protection of lines for distribution network.The main research results and innovations are as follows:1、In order to solve the problems of decomposition scale or modal aliasing in the existing time-frequency analysis methods for the detection of traveling wave wavefront,a novel fault traveling wavefront detection method is proposed based on the extreme-point symmetric mode decomposition(ESMD)algorithm.According to the frequency characteristics of fault traveling wave signal,the fault traveling wave signal is decomposed by ESMD to filter out the low frequency components in the fault signal.Then,the teager energy operator(TEO)is used to enhance the transient characteristics of the wavefront and determine the arrival time of traveling wavefronts.Simulation results show that the proposed method can effectively determine the fault traveling wavefront,and has a better detection ability than wavelet transform(WT)and HHT methods.Besides,considering the influence of line parameters for traveling wave velocity,an identification rule of reflected traveling wave from the fault point is established according to the fault traveling wave transmission path for multi-branch distribution network.Then,a fault location method without traveling wave velocity is proposed by the use of initial fault traveling wave and initial reflected fault traveling wave.Further,according to the numerical relationship between the length of branches and fault distance to each terminal,the terminal element value Q is defined.The corresponding fault location determination principle is proposed to achieve fault location.Simulation results show that the proposed method can accurately identify the reflected traveling wave from fault point,and is low sensitive to traveling wave velocity and time synchronization error between devices,and effectively improves the location accuracy for multi-branch lines.2、In order to solve the problem of fault location for distribution network with hybrid lines,a novel fault location method is proposed employing the offset value of traveling wave fault distance.According to the transmission characteristics of fault traveling wave in distribution network,the fault offset value D of line terminal is defined by employing the fault distance offset relationship between the virtual fault point and the real fault point.Then,an optimization model based on the minimum fault offset value is established,where the virtual fault position and traveling wave velocity are variables.The fault locat ion process is converted to solve the optimization problem of the preset fault offset value.Further,considering the influence of hybrid lines on fault offset value,according to the gray wolf optimization(GWO)algorithm,the principle of solving the opt imal fault offset value is analyzed.And the selection methods of the preset fault positions and the preset traveling wave velocity are proposed to achieve the fault location accurately.Besides,to reduce the influence of abnormal measurement data on fault location,an abnormal data processing method based on multi-dimensional scaling analysis and local outlier factor is proposed.Simulation results show that the proposed method can effectively identify the fault branches and accurately locate faults.The fault location results are not easily affected by the change of traveling wave velocity,fault distances and types.3、 In order to solve the shortcomings of existing distribution network fault location methods,which are difficult to implement due to high costs,a fault location algorithm based on distance matrix and branch coefficient is proposed.By analyzing the topology of distribution network and the transmission path characteristics of fault traveling wave,the effective branch and reference nodes of the distribution network are defined.Before and after fault occurs,an inherent distance matrix(IDM)and a fault distance matrix(FDM)are established,and then the difference between IDM and FDM is calculated to obtain the fault branch decision matrix(FBDM).A corresponding fault branch determination principle and a location method were proposed.Further,considering the economical operation of distribution network,the optimal configuration principle of fault traveling wave devices is proposed.Then,the branch coefficient function W is defined to realize the accurate determination of fault non-effective branch,and an improved traveling wave method is proposed to locate the fault point.Simulation results show that the proposed algorithm is simple and can be easily realized.Compared with existing location method for distribution networks,with a limited number of traveling wave devices,the proposed method can accurately determine the fault lines,and the locat ion results are not easily affected by fault types and transition resistances.It can help to improve the engineering application of traveling wave location methods in distribution networks.4、In order to solve the problem of fault location for multi-section hybrid lines with the uncertain of line parameters,a fault location method is proposed based on characteristic coefficients of node amplitude.According to the refraction and reflection transmission characteristics of the fault traveling wave at junction nodes of the multi-section hybrid line,the amplitude characteristics of the fault traveling wave at the line terminal are analyzed.Considering the uncertainty of line parameters,the node amplitude characteristics coefficient K of hybrid line is defined.Then,according to the node amplitude characteristic coefficients relationship between junction nodes and fault points,a fault section identification principle is proposed to determine th e fault line section for hybrid lines.Further,according to the identification results of fault section line,the traditional double-ended fault location method is revised by using the traveling wave transmission time of different sections,and a fault lo cation method without traveling wave velocity is proposed.Simulation results show that the proposed method can determine the fault line section and locate fault positions correctly.Compared with the existing fault section identification methods for hybri d lines,the fault section identification results of the proposed method are not affected by line length and traveling wave velocity,and effectively improve the fault location accuracy for multi-section hybrid lines.5、In order to improve the sensitivity and reliability of current protection for distribution network,an adaptive protection method is proposed based on current waveform matching weight.By analyzing the fault cur rent waveform matching characteristics of distribution network,a line fault identification threshold is established.Then,according to waveform matching characteristics of dynamic time warping(DTW)algorithm,a protection method is proposed based on curre nt waveform matching DTW value.Besides,according to the principle of full-length protection,an adaptive overcurrent threshold is proposed to reduce the real-time calculation burden of waveform matching values between protection devices.Further,considering the abnormal situations of communication and sampling between protection devices,the virtual measurement device of line protection is defined.Then,a protection scheme based on waveform matching weight is established to improve the reliability of line protection,and realize the fast and accurate removal of fault lines for distribution network.Simulation results show that the proposed protection method is not easily affected by fault types and system load changes,and can effectively identify fault lines.Compared with the existing adaptive protection methods,the proposed method has a better performance of protection and is less susceptible to abnormal sampling,abnormal communication and current transformer(CT)saturation,which is more applicable for engineering.