基于虚拟阻抗模型的电流互感器饱和判据

Current transformer saturation criterion based on virtual impedance model

提出一种虚拟阻抗模型的电流互感器饱和判别方法,它可以有效地识别区内外故障因电流互感器(TA)饱和对差动保护的影响。在电力系统的线路、母线、主设备等一些差动保护中,区外故障时,在大的短路电流作用下TA饱和容易造成保护误动。基于RL模型的短数据窗算法可以测得保护安装点的二次等效系统阻抗,它可以等效到在系统故障增量模型中虚拟一条阻抗支路。区内外故障TA饱和时,该支路虚拟阻抗会发生明显的变化。分析该阻抗在TA饱和与否情况下的变化规律,利用这种变化规律可以可靠、灵敏地判别出区内外故障TA饱和,是否闭锁差动保护,提高差动保护的可靠性。

An algorithm based on virtual impedance model is presented,which can effectively detect CT （Current Transformer） saturation caused by in-zone or out-zone fault to avoid its effect on differential protection. In some differential protections for transmission line,bus bar,main equipment,etc.,CT saturation caused by the big short-circuit current when an out-zone fault occurs may result in their misoperation. The secondary equivalent impedance at the protection installation location can be measured using short- data window algorithm based on RL model,which is treated as a virtual impedance branch added to the fault increment model. Its virtual impedance is obviously changed when CT saturation happens during out-zone or in-zone fault. The law of impedance change under CT saturation is analyzed and used to distinguish the CT saturation of out-zone fault from the CT saturation of in-zone fault for blocking differential protection.