灵活接地系统小电阻退出暂态特征及对暂态故障选线方法影响

Transient Characteristics of Small Resistor Exit in Flexible Grounding System and Implications for Transient Faulty-line Selection Methods

灵活接地系统发生高阻接地故障时,中性点小电阻并联阶段保护往往拒动,仍需考虑小电阻退出时的暂态特征对已有暂态故障选线方法的影响。并联小电阻退出时伴随一定的暂态过渡过程,文中针对此过程建立灵活接地系统单相接地故障暂态等值电路。分析了并联小电阻退出时系统各暂态电气量特征、不同故障情况对暂态电气量幅值的影响、暂态零序电流与暂态零序电压的约束关系,明确并联小电阻退出后暂态量对暂态故障选线方法稳定性的影响。当灵活接地系统高阻接地故障小电阻退出时,产生的暂态电气量将导致暂态幅值比较法、暂态极性选线法、暂态功率方向法误动,但暂态零序电流投影法选线正确,仿真验证了分析结果的正确性。

When a high-resistor grounding fault occurs in a flexible grounding system,the protection during the parallel stage of neutral point small resistor often refuses to activate,so it is still necessary to consider the impact of the transient characteristics of small resistor exit on the existing transient faulty-line selection methods.The exit of the parallel small resistor is accompanied by a certain transient transition process.For this process,a transient equivalent circuit for a single-phase grounding fault in a flexible grounding system is established.The characteristics of transient electrical quantities of the system when the parallel small resistor exits,the impact of different fault conditions on the amplitude of transient electrical quantities,and the constraint relationship between transient zero-sequence current and transient zero-sequence voltage are analyzed.The impact of transient quantities after the parallel small resistor exits on the stability of the transient faulty-line selection methods is clarified.When the small resistor exits during a high-resistor grounding fault in a flexible grounding system,the generated transient electrical quantities will cause misoperation in the transient amplitude comparison method,transient polarity selection method,and transient power direction method,but the transient zero-sequence current projection method for the line selection is correct.The simulation verifies the accuracy of the results.