基于零序导纳变化的灵活接地系统接地故障方向判别算法

目前灵活接地系统的接地保护大多直接采用小电阻接地系统的定时限零序过电流保护,存在高阻接地时保护灵敏度不足以及故障信息利用不充分等问题。通过分析灵活接地系统发生单相接地故障时,并联小电阻投入前后故障点上、下游及健全线路的零序测量导纳特征,发现并联小电阻投入前后故障点下游及健全线路的零序测量导纳不变,模值比为1,而故障点上游线路零序测量导纳的模值比远大于1,基于此提出了基于零序导纳变化的灵活接地系统接地故障方向判别算法。数字仿真和现场试验数据表明,该方法准确率高,不易受线路参数和过渡电阻等因素影响,可与定时限零序过电流保护配合使用,能满足现场实用要求。

Dicrimination Algorithm of Grounding Fault Direction Based on Variation of Zero-sequence Admittance in Flexible Grounding System

At present, grounding fault protection of most flexible grounding system directly adopts the zero-sequence time-limit overcurrent protection of traditional low-resistance grounding system, which has problems including insufficient protection sensitivity and insufficient utilization of fault information when grounding via high-resistance. When single-phase grounding fault occurs in flexible grounding system, the characteristics of zero-sequence admittance measurement of healthy lines, upstream and downstream line of the fault point before and after switch-in of parallel small resistance are analyzed. It is found that the zero-sequence admittance measurement of healthy lines and the downstream line of the fault point remain unchanged, and the modulus ratio of admittance before and after switch-in of parallel resistance is 1, while the ratio of the upstream line of the fault point is much greater than 1. Based on this, a discrimination algorithm of grounding fault direction based on variation of zero-sequence admittance in flexible grounding system is proposed. Digital simulation and field experiment data show that this method has high accuracy, and it will not be easily affected by factors such as line parameters and transition resistance. The proposed method can be used in conjunction with zero-sequence time-limit overcurrent protection, which can meet practical field requirements.