Research On Fault Diagnosis And Traveling Wave Fault Location Methods For Short Circuit Fault In Power Network

Quality of power supply and economical efficiency of system operation are improved by enhancement of power network interconnection.However,secure operation of the whole system will be destroyed when the short circuit fault of local power network occurs.Therefore,rapid fault diagnosis and accurate fault location after short circuit faults occurring in power network are important to speed up power restoration and insure secure and steady operation of power system.With the development of smart grid,the higher requirements are put forward for secure operation of power network.Existing fault diagnosis and fault location methods for short circuit fault in power network are confronted with severe challenges in diagnosis accuracy,diagnosis reliability and location accuracy.In this dissertation,the researches about application of the model-based diagnosis method in power network,modeling and solving of the analytical model for fault diagnosis of power network,and fault location based on transient traveling wave are done.The detailed research works are shown as following:(1)In order to overcome the limitation of the traditional expert system applied in fault diagnosis of power network,a model-based diagnosis method is proposed to diagnose power network faults.Power network is decomposed into several independent subsystems according to distribution of measurement points.By searching the analytical redundancy relations in each subsystem,model-based diagnosis models are established.After that,with a diagnosis acquiring method based on the causal relation,the preparation candidate diagnoses are obtained according to presupposed fault output.Candidate diagnoses are determined by the matched presupposed fault output,according to electric data after faults occurring.Actual alarm data is introduced to logic framework of model-based diagnosis,and then,the scheme based on the bayes theorem is proposed to identify optimal diagnosis from the candidate diagnoses.(2)An improved complete analytic model is proposed,in order to solve the problem of multiple solution and misdiagnosis within the existing complete analytical model for fault diagnosis.An evaluation index of event is introduced by analyzing the uncertainty about the operation of circuit breaker and protective relay,the reception of alarm.Different weight factors are assigned to various circuit breakers and protective relays according to evaluation indexes,making the analytic model more reasonable.Additionally,in order to improve the universality of the model solving technique,a novel method based on association rules is developed to solve analytic model.Basic rules are derived from the causal relation between the operation status and alarm data of circuit breakers and protective relays.After correlating basic rules in accordance with the corresponding logic relationship,association rules are established to accomplish model solving.(3)In order to overcome main technology limitations of current single ended fault location method based on traveling wave for transmission line,the fault location method based on initial coupling traveling wave is proposed.The arrival time sequence of coupling and non-coupling line module traveling waves is determined by analyzing four types of traveling wave propagation paths.According to the time sequence,the initial coupling line module traveling wave reflected or refracted from fault point can be identified.The polarity relation between the second line module reverse traveling wave and the initial coupling line module traveling wave is used to confirm the nature of the second reverse traveling wave.As soon as the nature of the second reverse traveling wave is confirmed,the fault location for transmission line can be accomplished.The proposed location method is not affected by busbar structure,traveling wave attenuation and coupling traveling wave.The sufficient reliablity is achieved by the proposed location method,and the application scope of the single ended method based on traveling wave is broadened to a large extent.(4)To solve the problems of existing traveling wave fault location methods for distribution power network,a novel fault location method is proposed for distribution power network with complex structure.After the line structure normalization is implemented,the distribution power network is split up into several equal segments.The traveling wave path matrix is constructed according to the distance between the dividing node and branch terminals in the network,after that,the time difference matrix of traveling wave propagating is established for every dividing node.When fault occurs,the arrival time of initial traveling wave is determined by traveling wave detection method based on TDQ.Based on the arrival time determined,the time difference matrix of traveling wave arrival is established for fault point.Respectively,comparing each time difference matrix of traveling wave propagating with time difference matrix of traveling wave arrival,the dividing node can be identified as fault point when the difference between the two matrixes is minimized.The proposed method is not influenced by line structure,branch quantity and branch layer,and large errors of measured time can be accepted.