Study on transformer inrush current and CT saturation as well as the impact of their coupling effect on protection

For the construction of the smart grid, protection needs to be accurately measured, and the current transformer needs to correctly transfer the transient process. The transient process of nonlinear ferromagnetic elements mainly includes the transformer inrush current and CT saturation. Differential protection misoperation is rarely caused by a single factor. It involves the coupling effect between the transformer inrush current and CT saturation. In this paper, the magnetizing inrush current and sympathetic inrush current and the CT saturation are studied from the aspects of principle analysis and digital simulation. Based on an accident, the coupling between the transformer inrush and CT saturation and its impacts on the differential protection are analyzed. Finally, methods to this problem are discussed.

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