This standard lists essential elements and commonly used components in excitation control systems and contains new and revised definitions for excitation systems as applied to electric utility synchronous machines, generally above 5000 kVA, with particular emphasis given to applications of solid-state devices. Primary purposes are to provide a basis for (1) writing excitation system specifications, (2) evaluating excitation system performance, (3) specifying methods for excitation system tests, and (4) preparing excitation system standards. The definitions will also serve as an educational means for people becoming acquainted with excitation systems.