Summary of the ``Guide for Protective Relay Applications to Power Transformers´´ ANSI C37.91

The ``Guide for Protective Relay Applications to Power Transformers,´´ ANSI/IEEE Standard C37.91, has been expanded and updated recently by the Power System Relaying Committee to assist in the effective application of relays and other devices for the protection of power transformers. The various protective considerations and methods of protection for the most commonly used power transformer configurations are covered. The purpose of this paper is to review some of the highlights of the guide, to familiarize the industry with the scope and usefulness of this revised document, and to invite considered discussion for the purpose of improving future revisions of the guide.