トラック型ZCTの巻線方法改善による残留電流低減の検討

摘要

ZCT (Zero-phase-sequence Current Transformer) is used widely for the detection of the ground fault current in low or high voltage distribution power line. Especially, the use of pole air switches equipped with ZCT is increasing to prevent the extended accident caused by the ground fault. The accurate detection of low level ground fault is needed from the view of early stage discovery. The internal residual current of ZCT must be small as possible for the detection of low level ground fault. Generally, the magnetic shield around the core of ZCT is used to reduce the internal residual current. Also, the core material and shield effect is related to the reduction of the internal residual current. In this paper, the reducing method of the internal residual current is proposed by using new winding method of the core. In new winding method, the secondary and tertiary windings are provided, and each winding is divided into two or three sections with parallel connection. The leakage magnetic flux caused by the primary current is changed to the cross current in parallel winding. This cross current is used to offset the leakage magnetic flux caused by the primary current. It is observed by the examination that the cross current is effective to reduce the internal residual current without influence to the zero phase current detection.