Research On Single-phase Earth Fault Protection For Radial Distribution Systems With Distributed Generators

In traditional distribution systems,the neutral point with non-solid earthing such as ungrounded and grounding via Petersen-coil are commonly used.For such systems,single-phase earth fault is the most common fault type.However,the single-phase earth fault is very difficult to detect because of its low magnitude of the fault current.In addition,as a result of low carbon and energy-saving demand,the increasing number of distributed generators including the inverter-based distributed generator and the synchronous-based distributed generator has been connected to the systems recently which introduces lots of new challenge to detect and locate the single-phase earth fault.Therefore,in the thesis,the new problems of single-phase earth fault protection in distribution systems with distributed generators are studied,and the the protection scheme based on clustering theory and relay agent is proposed to improve the accuracy and robustness of fault detection.In this thesis,the protection principle of single-phase earth fault for distribution systems with distributed generators is studied as follows:First,based on the characteristic differences between the traditional distribution systems and the distribution systems with distributed generators for single-phase earth fault,the zero sequence network of single-phase earth fault of distribution systems with distributed generators is analyzed to describe the distribution of fault current.And the traditional protection schemes based on different fault features are analyzed in order to get the most informative fault features to discriminate fault for this system.Second,traditional protections for distribution systems only use the single fault information like fault current to set the setting values in a certain extent,which are difficult to effectively restrain the effects of different fault conditions.In order to improve the reliability of traditional protection methods above,in this thesis,a novel single-phase earth fault protection based on clustering theory and relay agent is presented for distribution systems with distributed generators,which can fuse all fault information,and has high fault tolerance,sensitivity and robustness.Finally,the proposed protection scheme is evaluated in a radial distribution systems with distributed generations using PSCAD simulation.In here,the influence factors including different distance calculation methods,fault resistance,position of the fault point,fault initial angle,output power of inverter-based distributed generator and different operational states of distribution systems,etc.are consider.Simulation results have shown that,under different fault conditions,the new scheme can distinguish the faults happened in distribution systems with distributed generations.The protection scheme is proposed to solve the protection issues for distribution systems with high penetration of distributed generators,and to create the conditions for the further development of distributed generation and the implementation of the protection of intelligent distribution systems.