利用电压变化特征的识别电力系统振荡的方法

Method for Identifying Power System Swing by Using Voltage Variation Characteristics

电力系统发生振荡时交流线路距离保护的测量阻抗会进入动作区,导致距离保护误动作。目前我国线路距离保护I段和II段采取了振荡闭锁措施,以防止保护误动作,但是需要人工计算静稳电流定值,整定难度大;此外,线路处于重负荷状态时,会误闭锁距离保护,闭锁期间,线路故障无法切除。该文分析了系统振荡期间保护安装处电压余弦分量(Ucosφ)特征,系统振荡期间,Ucosφ变化范围是[-1 p.u.,1 p.u.];正常运行时,|Ucosφ|变化范围是[0.707 p.u.,1 p.u.];线路发生故障后,Ucosφ固定且数值较小,根据上述特征差异,提出了利用Ucosφ识别系统振荡与线路故障的方法。该方法利用Ucosφ替代静态稳定电流,无需人工整定,自适应识别系统振荡及线路故障,在系统振荡且会导致距离保护误动时,闭锁距离保护;线路故障时,可靠不闭锁距离保护,利用实时数字仿真系统进行了仿真验证。

During the power system swing,the measured impedance of the transmission line distance protection may enter the protection action area,resulting in the wrong action of the distance protection.At present,the power system swing blocking is adopted in the line distance protectionⅠandⅡsections in China to prevent the wrong action of the protection.However,the setting value of the static stable current needs to be manually calculated,which is difficult to set.In addition,when the line is under heavy loads,it will mistakenly lock the distance protection.Therefor,we analyzed the characteristics of the voltage cosine component(Ucosφ)at the protection installation during system oscillation.The variation range of Ucosφduring system oscillation is[−1 p.u.,1 p.u.].In normal operations,|Ucosφ|varies in[0.707 p.u.,1 p.u.].After a line fault occurs,Ucosφis fixed and the value is small.According to the above characteristic differences,a method is proposed to identify system oscillation and line fault by using Ucosφ.The method uses Ucosφinstead of static stable current,without manual tuning,and adaptively identifies system oscillations and line faults.When the system oscillates and the distance protection may misoperate,the distance protection can be blocked;meanwhile,when the line fails,the distance protection can reliably be in non-block state.The real-time digital simulation system is used for simulation verification.