The Protective Equipment on the System of the Commonwealth Edison Company

The use of protective devices is based primarily on the desire to maintain a high continuity of service rather than to protect apparatus. The tendency in the development of large systems is toward interconnection, and to make this practicable, satisfactory relays are necessary. The paper describes briefly the system of the Commonwealth Edison Company of Chicago with special reference to the protective devices installed thereon. Generators are equipped with balanced relays, lines with induction-type inverse-time-element relays, some of them of the uni-directional type, and balanced relays, while substation apparatus has the usual equipment of overload relays, speed-limit devices, etc., and outgoing feeders the instantaneous type of relays. The arrangement of these relays is shown and some of the settings described.