电流互感器二次回路阻抗不匹配对差动保护的影响
卢庆港1，乐晓蓉2，解军3
1 苏州热工研究院有限公司，江苏 苏州 215004；2 苏州工艺美术职业技术学院，江苏 苏州 215104；3 广州工程技术职业学院，广东 广州 510925
摘 要：在电动机启动过程中由于非周期分量及高倍数电流的综合作用，当电流互感器(CT) 二次回路阻抗不匹配时，两侧的二次电流存在差异而形成差流，导致差动保护误动作。通过对多组录波数据进行分析，重现了不同二次回路阻抗下的差动动作轨迹，并研究了二次回路阻抗不匹配对差动保护的影响，认为只有在设计阶段对CT 及二次电缆按照标准进行严格计算及选型，保证CT 的暂态特性满足工程要求，使差动两侧CT 的二次负荷尽量平衡，减少可能出现的差电流，才能有效避免此类误动的发生。
关键词：电动机；启动；差动保护；误动；动作轨迹；二次回路；阻抗；不匹配
中图分类号：TM452 文献标识码：B 文章编号：1007-3175(2014)02-0037-04
Mismatch Impact of Current Transformer Secondary Circuit Impedance on Differential Protection
LU Qing-gang1, LE Xiao-rong2, XIE Jun3
1 Suzhou Nuclear Power Research Institute Co., Ltd, Suzhou 215004, China;2 Suzhou Art & Design Technology Institute, Suzhou 215104, China; 3 Guangzhou Institute of Technology, Guangzhou 510925, China
Abstract: In motor starting process, due to the synthetic function of non-cycle component and high times current, secondary currents at both side will form differential current due to existing difference, to cause differential protection unwanted operation when the current transformer (CT)secondary circuit impedance mismatching. Via analysis to multi-groups recorded wave data, the action tracks under different secondary circuit impedance reappeared and this paper researched on mismatch impact of secondary circuit impedance on differential protection, pointing out that only if in design stage the CT and secondary cables were carried out strict calculation and model selection according to standards to ensure transient characteristics of CT to meet engineering requirements, making differential action secondary load of CT at both side in balance as possible and reducing differential current taking place possibly, thus the differential protection would effectively avoid such a kind of unwanted operation.
Key words: motor; start-up; differential protection; unwanted operation; action track; secondary circuit; impedance; mismatch
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