一起电抗器差动保护误动事故的分析和对策

Analysis on Mal － operation of Ｒeactor Differential Protection and Its Strategy

摘要:

分析了一起在变压器低压侧投入并联电抗器时电抗器差动保护的动作行为，指出 CT 暂态饱和是引起差动保 护误动的根本原因。电抗器差动保护采用比率制动特性和二次谐波闭锁，在一定程度上可以防止 CT 饱和所引起的 误动，当电抗器相电流比较小、制动电流比较小时，比率制动特性不能起到应有的作用。此外，CT 饱和后，差流中二次 谐波含量很低，导致二次谐波闭锁失效。提出了一种利用差动电流的直流分量和基波分量的比值来修正差动电流的 方法，该方法可以有效地防止 CT 暂态饱和所引起的差动保护误动。理论和实践表明，采用该方法后该电抗器再未发 生投入电抗器的误动事故。

Abstract:

The behavior of reactor differential protection is analyzed when switching on shunt reactor at the low voltage side of transformer，and it is pointed out that CT transient saturation is the root cause of triggering mal － operation． Applying ratio － brake characteristic and second harmonic blocking can avoid mal － operation to a large extend，however，in the case of small phase current and small brake current，the ratio － brake characteristic cannot play its due function． Furthermore，after CT saturation，second harmonic in differential current is very low，which will cause second － harmonic blocking invalid． A new algorithm is presented to avoid mal － operation caused by CT transient saturation． This algorithm makes use of the ratio of DC and fundamental component to get a correction factor，and then get a corrected differential current． Theory and practice show that there is not any mal － operation of shunt reactor differential relaying since this new algorithm is applied．