A Review of Research Progress on Residual Magnetism Detection Methods for Power Transformer Cores

When the power transformer is out of operation, due to the inherent hysteresis characteristics of the core material, residual magnetism will appear in the iron core, so that the inrush current is randomly generated when the transformer is reclosed, resulting in a closing failure. Therefore, the accurate detection of residual magnetism and effective demagnetization can avoid the harm of inrush currents to the power grid. In this paper, the formation mechanism and detection principle of residual magnetism are first analyzed. Then, a variety of residual magnetism detection methods are introduced, and the principles of existing detection methods are analyzed and summarized, which are divided into five categories, including estimation method, voltage integration method, pre-charging method, DC and AC indirect detection method. In addition, the accuracy, directionality and applicability of the above methods are compared and discussed. Finally, the problems and development trends of the five methods are summarized and prospected.