電流互感器二次回路阻抗不匹配對差動保護的影響
盧慶港1，樂曉蓉2，解軍3
1 蘇州熱工研究院有限公司，江蘇 蘇州 215004；2 蘇州工藝美術職業技術學院，江蘇 蘇州 215104；3 廣州工程技術職業學院，廣東 廣州 510925
摘 要：在電動機啟動過程中由于非周期分量及高倍數電流的綜合作用，當電流互感器(CT) 二次回路阻抗不匹配時，兩側的二次電流存在差異而形成差流，導致差動保護誤動作。通過對多組錄波數據進行分析，重現了不同二次回路阻抗下的差動動作軌跡，并研究了二次回路阻抗不匹配對差動保護的影響，認為只有在設計階段對CT 及二次電纜按照標準進行嚴格計算及選型，保證CT 的暫態特性滿足工程要求，使差動兩側CT 的二次負荷盡量平衡，減少可能出現的差電流，才能有效避免此類誤動的發生。
關鍵詞：電動機；啟動；差動保護；誤動；動作軌跡；二次回路；阻抗；不匹配
中圖分類號：TM452 文獻標識碼：B 文章編號：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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