This standard is a revision of ANSI C37.06-1997. It reflects small editorial changes needed to coordinate with the final wording contained in the defining standards ANSI/IEEE C37.04-1999 and ANSI/IEEE C37.09-1999. Some ratings have also been updated. Because this revision is primarily editorial in nature, this Foreword describes the substantive and editorial changes between this revision and the 1987 version. The format of the tables remains very much the same, except that some ratings, which had been given in the notes (sometimes on a different page from the table of preferred ratings), have been listed explicitly in the tables.