A novel transformer protection principle based on the change of inductances

For the problem of discrimination between inrush current and internal fault current, this paper presents the basic principle of the novel transformer protection principle based on the change of inductances. Its operation equations of two-winding and three-winding transformer are derived from this principle. And the transformer protection method is presented. The method can´t be acted on the inrush current and does not need the internal parameters got difficultly. The results of tests confirmed that the method is able to clear the internal fault reliably and quickly.