复合阻抗对线路零序电流保护的影响

为了降低逐杆接地的光纤复合架空地线(OPGW)上的能量损耗,防止其因长期发热而迅速老化,同时保证线路遭受雷击和发生接地故障时OPGW的大电流迅速入地,可在OPGW与地间安装复合阻抗。为方便分析考虑复合阻抗全部导通和全未导通两种极限情况,利用卡松理论分析了复合阻抗安装前后输电线路的零序参数,并研究了220 kV输电线路零序参数的变化对零序电流保护的影响。分析表明,随安装的复合阻抗导通个数的增加,输电线路的零序阻抗趋于减小,零序电流保护的范围趋于增大,但一般不超过复合阻抗安装前的保护范围。

Influence of Composite Impedances on Zero-sequence Current Relay of Transmission Lines

OPGW(Optical fiber composite overhead ground wires) is often connected to the ground tower by tower in practice and it can not be broken for many sections due to its particularity.This will bring about considerable power loss and make OPGW aging rapidly when the transmission lines are operating,even the parameters of system are balanceable,and the loss will increase with the transmitted voltage and the length of the transmission line.In order to reduce the power losses of OPGW installed tower by tower,to prevent aging rapidly due to long-term heating;and to ensure that large currents in the OPGW can flow into ground rapidly when the lines are subject to lightning and grounding fault at the same time,composite impedances are installed between OPGW and ground.This paper analyzes the zero sequence parameters of the transmission lines with the Carson Theory,when composite impedances are installed on the OPGW or not.Two ultimate conditions,namely,all the composite impedances are conducted or not,are considered to study easily the change of the zero sequence parameters.By combining with a practical 220kV transmission line,the influence of the system on zero-sequence current relay due to variable zero-sequence parameters is analyzed.Analysis shows that the zero sequence impedance is not constant due to composite impedances,and it is greater when the numbers of switched composite impedance are increased.The protection range of the zero sequence current of the transmission lines are increased accordingly,but the protection range does not exceed the protection range before composite impedance is installed.