The Research Of The Backup Protection For Double-circuit Transmission Lines On Same Tower

As same-tower double circuit line has the technical and economic advantages of largetransmission capacity, less occupying of power transmission corridors, lower towerconstruction investment, it is widely used in the power system of china. The fault types andtransient characteristics of parallel line on the same tower are match more complex than thatof single circuit transmission line and paralleled double circuit line as the same-tower circuitline has more wires and the wires are very close to each other. Moreover, as the transmissioncapacity of same-tower double circuit line is large, cutting off both the wires should be avoidin other to ensure high stability of the system in the case of interline fault, and that will sethigher requirement for fault phase selection and auto-reclosing scheme. Although the study onrelay protection of same-tower circuit line has made great progress, there are still manyproblems to be studied and discussed as the fault characteristics are so complex. In other toenhance the performance of protection devices and ensure stability of the power system,carrying out further research on relay protection is significant in both theory and practice.The study on same-tower circuit line protection involves many aspects, problems aboutdistance protection, fault phase selector and zero sequence over current protection are mostprominent among them, these problems are also the key point of researching on same-towercircuit line protection, and this paper will focus on these problems.Firstly, the paper analyzes the researching and application status of same-tower doublecircuit line protection, reviews and summarizes the problems of distance protectioncomponent, fault phase selector and zero sequence over current component faced in practicalapplication. On this basis, key points and main contents of this paper are presented.The paper analyzes the characteristics of the distance protection component that apply tosame-tower double circuit line. As the Single-phase interline non-earthing fault is not a realsingle-phase earth fault, the normal grounding distance protection would not operate correctly.This paper studies the operation behavior of ground protection and phase-to-phase distanceprotection in case of all kinds of interline faults, points out that the distance relay settingcalculation obeys the normal principle, and it is inappropriate to introduce zero sequence current of adjacent lines.The performance of fault phase selector has an important effect on the protection’soperation behavior and the correct operating of auto-reclosing. This paper conducts a study onthe operation behavior of common used phase-current-difference fault phase selector andnegative-zero sequence fault phase selector in case of all type of interline fault, and points outthe problems exist.This paper discusses the zero sequence over current protection from the aspect of zerosequence direction components and setting calculation, points out the issues should be noticewhen applying to same-tower double circuit line, and suggestions are given in this paper.In the end of this paper, a summary is made, and the works should done next step arepresented.