Research On EHV Transimission Line Protection Based On Adaptive Residual Current Compesnsation Method And Concerned Problems

Along with the power system development such as power transmitted form west china toeast china, power grid interlink project,ultra high voltage transmission, large numbersof EHV transmission line has been commissioned in china.In order to keep the stabilityof the power system,the higher demand of the characteristics of high voltagetransmission line protection has been put forward. This dissertation mainly concernsabout the study of how to research and development an EHV transmission line protectionwith high performance. The significant achievements are as follows:(1) How to measure the impedance with voltage and current at relay location is thefundamental question to distance relay. In order to accurately measure theimpedance, the residual current for impedance measurement in ground distancerelay is compensated in a fixed way. It has been shown that the above compensationmanner may have negative impact on the phase selection in Mho elements in a singlepole trip scheme. A new residual current compensation method based on the currentmagnitude of each phase for Mho elements is presented in this paper.(2) For 750kv and 1000kv system, the influence of the distributed capacitance currentto the characteristics of the relay cannot be ignored. The influence to the differentialequation algorithm and the current differential relay has been considered in this paper.Based on the electromagnetic transient model of the distributed transmission line, anew method based on the Bergeron model of the transmission line has been putforward. The influence of the distributed capacitance current has been considered inthis new model.(3) How to get the correct phase selection result is still a difficult question for the backupprotection of the transmission line protection. The main problem for phase selector isthat the performance of the phase selector based on steady component is notsatisfying. A new method for phase selection based on impedance in microprocessorbased protective relay is presented in this paper. New scheme has been put forwardfor the single line and double-circuit line, respectively. .It may be one of thesolutions for the phase selection based on steady component.(4) The power swing blocking for distance relay has always been one of the difficultiesfor transmission line protection. Based on the idea of adaptive relay, a definiteanalytic equation about the impedance changing with time has been deduced. Thesetting of the threshold to distinguish power swing from short circuit has beendetermined not by the practice but by the rule. An algorithm based on the magnitudeand phase angle of the generalized phasor for measuring instantaneous frequency andswing frequency is presented in this paper. Extensive simulation studies show thatthe algorithm has a fast response and high accuracy.(5) The influence of the HVDC commutation failure to the fault component relay isdiscussed in this dissertation. For the relay near the HVDC inverter, the influence ofthe communication failure caused by the AC system fault to the fault componentrelay is still a question needed to be considered. In order to avoid the misoperation offault component direction element, some measure has been put forward in thispaper.