基于改进零序导纳法的单相接地故障选线原理

Fault Line Selection Principle of Single-phase-to-ground Fault Based on Improved Zero-sequence Admittance

传统零序导纳法的故障选线方案由于没有考虑到配网系统中三相零序不对称的情况,因此在发生单相接地故障尤其是高阻故障时,零序导纳的计算会出现较大的误差。基于此,提出了计及线路三相零序不对称的改进零序导纳的计算方法和选线方案。首先,分别推导了中性点不接地系统和经消弧线圈接地系统中,考虑线路不对称条件下的零序导纳的计算公式。其次,根据零序导纳的计算提出了2种接地方式下的改进导纳法的选线方案,同时提出了基于零序导纳的相角差系数的概念并构造了选线判据。最后,通过配电网单相接地故障仿真以及现场试验数据,验证了改进导纳法的选线方案可在线路不对称情况下有效选出故障线路。

The protection scheme of the single phase-to-ground fault based on the traditional zero-sequence admittance method does not consider the three-phases zero-sequence asymmetry in the distribution network.Therefore,the calculation of zero-sequence admittance will have a large error when a single-phase ground fault occurs,especially a high-impedance fault.For this problem,an improved zero sequence admittance calculation method and the protection scheme of the single phase-to-ground considering the three-phase zero-sequence asymmetry are proposed.Firstly,the calculation formulas of zero-sequence admittance for ungrounded and resonant grounded systems under the condition of line asymmetry are derived respectively.Secondly,according to the calculation of zero-sequence admittance,the protection scheme based on improved admittance method under two grounded systems is proposed.At the same time,the concept of phase difference coefficient based on zero-sequence admittance is proposed,and the fault feeder selection criterion is established.Finally,simulation of a single-phase-to-ground fault model for the distribution network,and field test data verified that the protection scheme based on improved zero-sequence admittance method can select the fault feeder under the condition of line asymmetry effectively.