The selection of transformers for use on an underground railway

London Underground Limited has reviewed its specifications for the construction and installation of all types of transformers. This review has considered the three installation environments applicable to London Underground: (1) outdoors-exposed to local ambient conditions; (2) indoors-protected from extremes of temperature and weather, but possibly having a restricted flow of cooling air (this sometimes being dust laden), located in a segregated substation building; and (3) underground station-adjacent to an underground passenger station and subject to special requirements in terms of fire safety. Indoors and usually below street level. The third of these environments is particular to underground railways and in the United Kingdom is subject to legislation in the form of the Fire Precautions (Sub-surface Railway Stations) Regulations 1989. In view of the special needs of the underground station environment, a much wider review of practices for this area was undertaken; this review and the findings from it are described.