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The Scientific World Journal
Volume 2014, Article ID 724529, 10 pages
Research Article

Method to Eliminate Flux Linkage DC Component in Load Transformer for Static Transfer Switch

State Key Laboratory of Advanced Electromagnetic and Technology, Huazhong University of Science and Technology, Wuhan 430074, China

Received 27 February 2014; Revised 15 June 2014; Accepted 16 June 2014; Published 17 July 2014

Academic Editor: Antonio García-Zambrana

Copyright © 2014 Yu He et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Many industrial and commercial sensitive loads are subject to the voltage sags and interruptions. The static transfer switch (STS) based on the thyristors is applied to improve the power quality and reliability. However, the transfer will result in severe inrush current in the load transformer, because of the DC component in the magnetic flux generated in the transfer process. The inrush current which is always 2~30 p.u. can cause the disoperation of relay protective devices and bring potential damage to the transformer. The way to eliminate the DC component is to transfer the related phases when the residual flux linkage of the load transformer and the prospective flux linkage of the alternate source are equal. This paper analyzes how the flux linkage of each winding in the load transformer changes in the transfer process. Based on the residual flux linkage when the preferred source is completely disconnected, the method to calculate the proper time point to close each phase of the alternate source is developed. Simulation and laboratory experiments results are presented to show the effectiveness of the transfer method.