Elucidation of DC magnetic deviation in converter transformers used for a self‐commutated BTB system during single‐line‐to‐ground faults

This paper deals with a 50‐MW self‐commutated BTB (Back‐To‐Back) system intended for power flow control between transmission networks. It focuses on the dynamic behavior of the BTB system during single‐line‐to‐ground (SLG) faults. During an SLG fault, a DC magnetic deviation appears in the converter transformers used for the BTB system just after the occurrence and restoration of the fault. It is indispensable to understand the magnitude of the deviation, because it may bring about magnetic saturation as well as subjecting the transformers to a large magnetizing current. This paper derives theoretical equations related to the deviation during the SLG fault. The theoretical analysis developed in this paper may make significant contributions to designing the transformers. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 168(2): 48–59, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20805