New principle for using full-wave rectifiers in differential protection of transformers

In the paper, a new principle is proposed for blocking the transformer differential relay during magnetising inrush time. The relay differential current is rectified at first, and the fundamental component of the rectified current is then filtered and used for blocking the relay. Discrimination between the magnetising inrush current and the sinusoidal short-circuit current is secured by the presence of the fundamental component in the rectified inrush current, and the absence of that component in the rectified sinusoidal current.