Outdoor Switching Equipment at Northwest Station Commonwealth Edison Company

This paper describes the switching equipment and its arrangement in an outdoor switching center at 132, 66, and 12 kv., in connection with an installation of three-winding transformers. This installation is a junction point on an interconnected system, from which energy is distributed at the lower voltage. The development of the original 12-kv. installation with indoor type of equipment enclosed in metal housings and concrete cells is described. The reasons leading to its extension with metal-clad oil-filled gear are also discussed. A feature of this metal-clad oil-filled installation is that it is laid out on an isolated phase basis with wide separation between phases, which is the first time that this arrangement has been attempted with this type of equipment. Included in the design are complete facilities for grounding and testing of the equipment, which are fully interlocked to insure maximum safety in their use. A brief discussion of costs as compared with indoor installations is also given.