发电机中性点电压互感器断线的检测方法

Detecting the PT secondary circuit open at the neutral of generator

分析了发电机中性点电压互感器断线故障对定子单相接地保护的影响,指出中性点电压互感器断线将导致三次谐波电压比值型定子单相接地保护误动,但现有电压互感器断线判断方法不易检测该处的断线故障。利用单相接地故障发生时机端和中性点三次谐波电压故障分量近似相同的变化特点区分中性点电压互感器断线与中性点金属性接地故障,防止定子单相接地保护误动。

This paper analyses the effect of PT secondary circuit open at the neutral on the stator ground protection, and points out that this kind of PT fault will cause the maloperation of the stator ground protection, which adopts the ratio of third harmonics. However, it is hard for the present method to detect the PT secondary circuit open at the neutral. In the paper, the variations of the fault components of third harmonic at the terminal and neutral, which are nearly the same, are used to distinguish faults between the PT secondary circuit open and the direct grounding at the neutral to prevent the stator grounding protection from maloperation.