电网不对称条件下小电流接地系统接地相辨识

Grounding Phase Determination in Non-Effective Grounding Systems in Case of Unsymmetrical Voltage

当中压电网发生单相接地故障时,在电网不对称和存在较大过渡电阻情况下确定接地相是比较复杂和困难的。传统判据往往忽略电网不对称的影响。本文运用相量图分析了发生单相接地故障后电网不对称电压和过渡电阻对中性点电压和相电压的影响,认为中性点电压的轨迹不是半圆,而是一段圆弧,并且在某些情况下辨识故障相的传统判据并不适用。在此基础上,本文提出通过构造一种新的"相"矢量的方法进行接地相辨识。理论分析和仿真结果表明该方法能够克服传统方法的缺点,准确判断接地相。

When a single-line-to-ground fault happens in the power grid, it is complex and difficult to determine the ground phase especially in the case of an unsymmetrical voltage and a large transition resistance. And the unsymmetrical voltage is often ignored because of simplified analyses in the previous literature. In this paper, with these factors considered a detailed analysis of the single-line-to-ground fault and the phasor diagram of the line-to-neutral voltages are presented firstly. It is concluded that the trajectory of the neutral voltage is no longer a semi-circular, but a circular arc. What is worse, in some cases it is not suitable to apply the traditional criterions that the previous literature proposed. A new method of constructing three new ＂phase＂ vectors is presented to identify the ground phase. Theoretical analyses and simulations show that the method can overcome the shortcomings of traditional methods and determine the grounding phase accurately.