The 60-cycle distribution system of the Commonwealth Edison company

The purpose of this paper is to describe the Commonwealth Edison Company´s 60-cycle distribution system. Energy for this system is generated in five stations and transmitted at 12,000 volts, three-phase, to manually-operated and remote-control substations, the operation of the remote-control substations being under the control of the manually-operated substations by means of control wire and selector switch operation. The larger customers are supplied by means of industrial substations located upon their premises and fed from 12,000-volt, three-phase, underground loop circuits; the general load is supplied by means of 2300/4000-volt, three-phase, four-wire radial circuits from the various manually-operated and remote-control substations. The generator capacity was 420,000 kv-a. and the maximum load 379,000 kv-a., as of January 1,1925, for the 60-cycle portion of the system, exclusive of load carried upon the 25-cycle and d-c. portions of the plant. Reliability of service is provided by relay-controlled oil switches, current-limiting reactors, duplicate supply lines, and lie points for interconnection of different parts of the system. The rapid growth of load density in some sections of Chicago will soon necessitate modification of the present distribution system by either an increase of distribution voltage or an increase of circuit capacity. The advantages and disadvantages of the two proposed new systems are now under consideration.