负荷电流下并联电抗器差动误动现象及解决措施

Phenomenon and resolution of differential protection mal-operation for shunt reactor under load current

针对并联电抗器差动保护在空投电抗器时的误动实例,对电流互感器(CT)在负荷电流下的饱和现象进行了分析和论述。指出大故障电流并不是CT发生饱和的必要条件,在非周期分量的作用下,正常负荷也可能导致CT饱和。分析了CT饱和的原因,指出在空投电抗器时,如果负荷电流中含有非常大的衰减直流分量,CT也会发生饱和现象。阐明了这种情况与大电流引起的CT饱和现象的不同特点,即这种饱和现象具有持续时间长,波形畸变不明显,谐波含量小,产生差流的主要原因是相位发生了偏移等特点。同时指出了这种现象对电抗器的分相电流差动和零序电流差动均有非常不利的影响,差动保护应该采取措施防止发生误动,提出了电抗器分相电流差动解决方案和电抗器零序电流差动解决方案。

Aiming at the examples of mulfunction of differential protection of shunt reactors when the reactor is energized on no-load, this paper analyzes and discusses the current transformer （CT） saturation under the load current. It points out that a large fault current is not a necessary condition for CT saturation occurrence, under the condition of non-periodic component, the normal load may also cause CT saturation. This paper analyzes the reason of CT saturation, points out in the reactor dropped, if the load current contains a very large decaying, CT saturation will occur. It illustrates the difference between the case and CT saturation caused by carge current, that is, such a saturation phenomenon has the characteristics of long duration, no significant waveform distortion, less harmonic content, and the poor flow is mainly caused by the phase shift occurred. The paper also points out that the phenomenon has a very negative impact on the reactor current differential and zero-sequence current differential, differential protection should take measures to prevent the occurrence of malfunction. And reactor current differential solution and the reactor zero-sequence current differential solution are proposed.