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The restricted earth fault (REF) relay is one of the protection units of the transformer digital protection system which typically has a fast response and thus is prone to maloperation. Based on measurement results and time-domain simulation results, this paper provides a comprehensive performance evaluation of the REF relay which is an augmented-based adaptive restraint current approach for performance stabilization. The investigation results provide justifications to introduce modification to the relay to improve its performance during transients and, thus, improve the relay security. This paper also introduces and evaluates a scheme to modify the REF relay performance. The proposed scheme has been implemented in the field, and the results indicate performance improvement.