The Research Of The Influence To Relay Protection Caused By Transmission Line's Sequence Paremeters

The power frequency paremeters of transmission line mainly contain positive sequence impedance, positive sequence admittance, zero sequence impedance , zero sequence admittance and the coupling capacitance between several parallel transmission lines. At the incipient stage when the transmission lines were constructed,their power frequency paremeters must be actual measured.But in practice these paremeters are affected by many factors.And considering of the interference of coupling electromagnetism and electrostatic, it's difficult to judge the precision of the actual measurement data. In some severe situations the relay protection's precision will be affected.The error of 500kV transmission line'ssequence paremeters will affect the relay protection. After investigating different length of the transmission lines and stochastic error of the sequence paremeters, conclusions were put forward.At fault's steady state the distance protection's obscure action zone is as wide as the bound of the error of line's sequence paremeters.The setting must have some redundancies in order to avoid mis-operation. The obscure action zone of fault's transient state is wider than that of fault's steady state.We need to take actions to avoid mis-operation from the protection's principle and setting calculation.Meanwhile the different zero sequence mutual impedance's intensity of parallel lines and coupling lines of different voltage grades cause many effection to the relay protection. This issue discussed this problem and suggestions were given hereafter. According to the zero sequence mutual impedance's intensity of parallel lines, we can increase the setting value appropriately when the two lines are working at the same time,in order to keep the stability of protection zone.The protection zone will be wider than the setting zone because of the coupling lines'zero sequence mutual impedance.We need to decrease the setting value according to the zero sequence mutual impedance's intensity,in order to keep the protection's selectivity.In pace with the development of the grid and load,short transmission lines of high voltage appeared constantly.And most of them were not transposed.In this issue,different length of these lines,different loads and different faults,including ground fault of single phase and faults between phases, are concerned.This kind of short lines caused great impact to the distance protection and make their obscure action zone as wide as 16 percent of the lines'full length maximally. And when the short-circuit fault occurred near the setting point,the measured impedance could be 10 percent more than the setting impedance.We need to consider this influence and narrow the protection zone,in order to avoid mis-operation when the fault was out of the protection zone.