地磁感应电流作用下的CT饱和特性及其引起的变压器差动保护误动

Research on CT Saturation Characteristics Affected by Geomagnetically Induced Current and Resulting Malfunction of Transformer Differential Protection

电流互感器(current transformer,CT)的饱和特性对继电保护的动作性能会产生重要影响。地磁感应电流(geomagnetically induced current,GIC)在区域电网中具有高幅值、低频率、时变性等特点,它对CT饱和特性的影响与外部故障的穿越性电流、涌流中的非周期分量、高压直流输电引起的直流偏磁都不完全相同,值得引起人们的重视。根据GIC的典型波形特征构建GIC等效源模型,在PSCAD/EMTDC中对GIC作用下的CT饱和特性进行了仿真分析,并研究了与其相关的变压器差动保护受到的影响。研究结果表明,GIC可能导致CT的严重饱和,使CT二次侧电流的波形畸变特征消失,导致变压器差动保护计算出的不平衡电流增大,且差流中二次谐波含量很低,造成差动保护误动。针对该误动情况,可采用基于差流及其二次谐波含量趋势的措施来进行防范。

There is a close relation between the saturation characteristic of current transformer （CT） and the performance of protective relayings. In regional power grid the geomagnetically induced current （GIC） possesses the feature of high-amplitude, low-frequency, time-variance and so on, its impact on saturation characteristic of CT is not so identical with the impacts of through-current due to external fault, non-periodic component in inrush current and DC magnetic biasing caused by HVDC power transmission, so it is worthy of attention. Based on typical waveform feature of GIC an equivalent source model of GIC is constructed, and using PSCAD/EMTDC the saturation characteristic of CT under the affect of GIC is simulated, and the resulting affect on transformer differential protection is researched. Research result shows that GIC may lead to serious saturation of CT＇s magnetic path and it makes the waveform distortion characteristic in the current at CT＇s secondary side disappeared, so the unbalanced current calculated by transformer differential protection is enlarged and the content of the second order harmonic in the differential current will drop below the restraint threshold, and finally the malfunction of transformer differential protection occurs. To prevent such a malfunction, the measure based on differential current and the variation tendency of the content of second order harmonic in it can be adopted.