Transient Characteristics Of Uhv Transmission Lines And The Analysis Of Impacts On Protections

UHV transmission lines have the advantages of large transmission capacity,long transmission distance and low loss,which have been greatly developed in recent years.Relay protection is the first defense line for grid security and its importance is self-evident.Compared with HV/EHV transmission lines,UHV transmission lines require higher reliability and speed of protection.In addition,because the parameters and structures of UHV transmission lines are different from those of conventional transmission lines,the electromagnetic transient characteristics of UHV transmission lines will change,which will affect the operation characteristics of protection.The maloperation or misoperation of UHV transmission line protection will bring serious consequences to the stability of power system and the safety of power equipment.Therefore,the relay protection of UHV transmission lines is studied in this paper.Firstly,the configuration principles,methods and performance improvement requirements of UHV transmission line protection are summarized.Through the introduction of protection configuration examples of 1000 kV Huaiwu line and the analysis of protection action accidents,the problems of UHV transmission line protection and the corresponding performance optimization requirements are summarized.The parameters of UHV transmission line from southeastern Shanxi to Nanyang to Jingmen are obtained by consulting the literature.The equivalents of 500 kV power grid in central China and North China are made.Based on PSCAD/EMTDC simulation software,the simulation model of UHV transmission line is built.The electromagnetic transient characteristics of UHV transmission line under normal operation,fault and fault removal scenarios are analyzed respectively.It is concluded that the UHV transmission line has large capacitive current and decay time constant of DC component of fault current is large.Considering the high requirement of protection speed for UHV transmission lines,and the problem that the DC component of large decay time constant can easily lead to saturation of current transformer(CT)and the misoperation of current differential protection,a novel main protection scheme for UHV transmission lines with high reliability and speed is proposed.The proposed scheme can reliably distinguish between the internal fault and the external fault,and will be blocked when CT is saturated under external fault and be quickly opened when the external fault develops to an internal one.The research work in this paper has certain reference significance for the construction and development of UHV transmission lines.