利用零序电流相位变化特征的灵活接地系统故障选线方法

Fault Line Detection of Flexible Grounding System Based on Phase Variation Characteristics of Zero-sequence Current

针对配电网灵活接地系统高阻接地故障选线困难的问题,提出一种利用零序电流相位变化特征的故障选线方法。详细分析了单相接地故障时各线路与中性点零序电流的相位差变化特征。并联小电阻投入前,各线路与中性点零序电流相位差为180°;并联小电阻投入后,健全线路与中性点零序电流相位差约为90°,而故障线路与中性点零序电流相位差约为180°。通过互相关系数反映各线路与中性点零序电流相位差,并且构造互相关系数差动判据,进一步增强故障特征差异。同时,利用中性点零序电流计算幅值微弱的健全线路零序电流,有效降低零序CT无法准确采集导致故障选线装置误判的风险。PSCAD仿真结果表明,该方法适用于过渡电阻3000Ω以内的接地故障,在零序CT反接、强噪声干扰等极端工况下,依然具有较高的可靠性。

Aiming at the difficulty in selecting the fault lines when the high resistance grounding fault occurs in the flexible grounding system of a distribution network,a method of the fault line selection is proposed using the characteristics of the phase change of the zero-sequence current.The characteristics of the phase differences of the zero-sequence current between each line and the neutral point are analyzed in detail when a single-phase grounding fault occurs.Before the parallel small resistance is put into use,the phase difference of the zero-sequence current between each line and the neutral point is 180°.After the parallel small resistance is put in,the phase difference of the zero-sequence current between the sound line and the neutral point is about 90°,while the phase difference of the zero-sequence current between the fault line and the neutral point is about 180°.The cross-correlation coefficient reflects the phase differences of the zero-sequence current between each line and the neutral point,and the differential criterion of the cross-correlation coefficient is constructed to further enhance the differences in the fault characteristics.At the same time,the neutral zero-sequence current is used to calculate the zero-sequence current of a sound line with a weak amplitude,effectively reducing the risks of misjudgment by the fault line selection devices due to the failure of accurately collecting the zero-sequence CT.Simulation results of the PSCAD show that this method is suitable for the ground faults with a transition resistance less than 3000 ohms.It has rather high reliability under the extreme conditions such as a zero-sequence CT reverse connection and a strong noise interference.