一种距离保护Ⅲ段防过负荷误动的方法

A Method of Distance Protection ZoneⅢ Capable of Preventing Overload Maloperation

针对传统距离保护Ⅲ段不能正确识别过负荷和故障的问题,详细研究了过负荷和故障情况下电流不对称度、Ucosφ和电压相位变化等电气特点的特征差异,提出了一种识别过负荷和故障的新方法。此方法基于电流不对称度、故障处电弧电压与系统中最低电压的差异以及电压相位变化,不仅实现了对称过负荷与各种故障的识别,而且通过比较不对称过负荷和单相高阻接地时电压相位变化差异解决了不对称过负荷和单相高阻接地故障的识别技术难题。通过RTDS仿真试验,验证了该方法既可有效防止对称和不对称过负荷时距离保护Ⅲ段误动,又能够保证在各种故障时可靠开放距离保护Ⅲ段。

In view of the inability of traditional distance protection zone Ⅲ to correctly identify the difference between overload and fault,this paper specifically analyses the differences in electrical characteristics such as overload and fault from current asymmetry degree,Ucos φ and the variation of voltage phase.A new method for identification of overload and fault is proposed,which is based on current asymmetry degree and the difference between fault arc voltage and the minimum system voltage and voltage phase change.This method not only realizes the identification of symmetric overload and fault,but also solves the identification of the asymmetric overload and the high resistance grounding fault by comparison of changes in voltage phase.Through real-time digital system (RTDS) simulation,the results show that the method is capable of preventing maloperation of distance protection zone Ⅲ caused by overload while unblocking distance protection zone Ⅲ when fault does happen.