Three-terminal Line Fiber-optic Differential Protection And Related Issues

The dispersed phase current differential protection is a simple principle and immune to the influence of power system oscillation,series capacitance,double lines mutual inductance,two phase operation and single power supply system.The protection has fault phase choice ability and short operation time.So it is suitable for main protection.Optical fiber pilot differential protection will be adopted widely on UHV transmission line with the development of communication technology and the cost reduction of communication device such as optical fiber etc.This dissertation solves several problems as follows: Three Terminal Synchronization AdjustmentIn this dissertation,protection terminals installed on three ends of lines freely sample external AC signals with the same sampling frequency and simultaneously attach a sample sequence number for every sample.By adjusting sample sequence number but not sample time,the scheme can simply achieve sampling synchronization of three terminals. After finding the corresponding sample sequence number,adjust its vector. Characteristics of Three Terminals Differential ProtectionMaster-master and Master-slave are the two mode of three terminals differential protect.In master-master mode the three terminal device can trip Independents.In master-slave mode,only the master terminal device can trip,the two slave device trip after the master have done.The Three Terminals Differential Protection can easy compatible two terminals. Three Terminal Distance MeasuringMaking fully use of the characteristics of transmitting voltage and currents phasors of opposite side of phase-segregated current differential protection relays,the dissertation employs a three terminal distance measuring technique and accurately determines the location of fault points.This scheme has been applied on DF3320ET digital transmission line protection.The feasibility and advantage of this scheme was verified by the results on 110KV system model of dynamic modeling test in National centre for quality supervision & testing of relay Electric Power Research Institute.The relays succeeded in run on 66KV system.