Converting substations in basements and sub-basements

This paper treats principally of methods of overcoming the difficulties attendant upon the installation of synchronous converter and battery substations in the basements of large office buildings in the down-town district of a large city. The development covers a period of fifteen years during which time the capacity of the units has been increased as many fold. The combined capacity of such substations is 42,000 kw., serving 0.81 sq. mi. (2.1 sq. km.) of area in which are many high commercial buildings with a connected load of 1,940,000 lamps (50-watt equivalent). This type of substation is divided into two classes: I — the basement type, referring to those located directly below street level, and II — the sub-basement type, referring to those located in the first or second sub-basement. Description and illustration of a typical machinery intake for a Class II substation are given, also methods and difficulties of bringing in apparatus. The air supply for the apparatus as compared with a substation above grade is next considered. A special air cleaning device is described. Description and illustration of a supply and exhaust system for ventilating the apparatus are given. The temperature of a 5000-kw. substation was lowered 11 deg. cent. by directing the exhaust air from the units. The difficulty in providing air cooling equipment for larger units for sub-basement substations has been more or less responsible for the adoption of the oil and water cooling system, particularly for the stationary apparatus, such as transformers and the regulators. The diagram and description of the oil and water piping system show how 3850-kv-a. transformers, each containing 3100 gal. (11,730 1.) of oil, are cooled. The nature of the foundation structure of large buildings limits the adaptation of the floor construction for the electrical apparatus, which is the reason for the comparatively high structural cost. The floor space required for small units of 500 kw. capacity is 0.95 sq. ft. (0.088 sq. m.) per kw., and for large units of 3500 kw. capacity is 0.54 sq. ft. (0.05 sq. m.) per kw. The plan and elevation of one of the largest and most modern substations of the sub-basement type are shown. The ultimate capacity of this substation is 16,000 kw. with a 1875-kw. battery. The floor space is 10,600 sq. ft. (985 sq. m.) and the head-room is 26 ft (7.9 m.).