变压器零序差动保护灵敏度分析

Sensitivity Analysis of Zero-sequence Differential Protection of Transformers

超高压和特高压变压器组一般由三个单相变压器组成,变压器内部基本上不会发生相间短路,主要的内部故障形式为单相接地和匝间短路。零序差动保护为y0/Y0/Y0或0Y/△接线变压器的Y0侧单相接地主保护,其灵敏度一般很高;但在非常接近中性点处发生单相接地短路时,如果短路的匝数很少,短路电流很小,零序差动保护的灵敏度可能不足,需要校验。该文用多回路分析的方法分析了0Y/△接线变压器Y0侧非常接近中性点处单相接地时零序差动保护的差电流,提供了一种用于工程实践中校验零序差动保护灵敏度的方法。

Extra-high voltage (EHV) and ultra-high voltage (UHV) transformer banks are generally composed of three single-phase transformers, in which interphase fault will not happen basically. The main form of internal fault is single-phase grounding and turn-to-turn fault. Zero-sequence differential protections of transformers are the main protections for single-phase grounding faults of Y0 side of 0 0Y /Y or 0Y /?connected three phase transformers. They usually have high sensitivity. But if the single-phase grounding fault is near the grounded neutral, and the number of short circuit turns is very small, the short-circuit current will be very small. The sensitivity of the zero-sequence differential protection will be very small it may refuse to operate, which needs to be verified. The differential current of zero-sequence differential protection when single-phase grounding faults of Y0 side of 0Y /?connected three phase transformers are close up to the grounded neutral point is analyzed through multi-loop analysis. And a method which may be used in engineering practice for verifying the sensitivity of zero-sequence differential protection is proposed.