基于过渡电阻评估的灵活接地系统暂态故障选线方法

Transient Fault Line Selection Method for Flexible Grounded System Based on Transition Resistance Evaluation

灵活接地系统发生单相高阻接地故障后,并联小电阻的投入将导致故障稳态分量变小,同时各馈线零序电流稳态幅值变化量差异较小,存在选线难题。分析并联小电阻投入后灵活接地系统暂态故障特征,得到馈线暂态零序电流与母线暂态零序电压及其导数的固有关系,分析小电阻投入时刻与暂态故障特征幅值的关系,从而提出一种基于过渡电阻评估的灵活接地系统暂态故障选线方法。该方法通过小电阻投入产生的低频暂态电压电流评估过渡电阻,进而实现故障选线,不受故障初相角影响,耐过渡电阻能力强,对互感器精度要求低;同时,通过小电阻投入时刻的选择可实现暂态故障特征的最大化调控,可为灵活接地系统选线与保护方法提供新思路。最后,通过仿真和实时数字仿真(RTDS)实验验证了所提方法的正确性。

After the single-phase high-resistance grounding fault occurs in the flexible grounded system,the input of the parallel low resistor will lead to the reduction of the steady-state fault component.At the same time,the variation of the steady-state amplitude of the zero-sequence current of each feeder is small,so it is difficult to select the fault line.The transient fault characteristics of the flexible grounded system after the parallel low resistor is connected are analyzed;the inherent relationship between the feeder transient zero-sequence current and the bus transient zero-sequence voltage and their derivatives is obtained;and the relationship between the time when the low resistor is connected and the transient fault characteristic amplitude is analyzed.Thus a transient fault line selection method for the flexible grounded system based on the transition resistance evaluation is proposed.This method evaluates the transition resistance through the low-frequency transient voltage and current generated after the connection of the low resistor,so as to realize the fault line selection,which is not affected by the initial phase angle of the fault,has strong resistance to the transition resistance,and has low requirements for the accuracy of the transformer.At the same time,the maximum regulation of transient fault characteristics can be realized by selecting the connection time of low resistor,which can provide a new idea for flexible grounded system line selection and protection methods.Finally,the correctness of the proposed method is verified by simulation and real time digital simulation(RTDS)experiments.