The London Underground Tube network is the oldest mass transit system in the world and carries in excess of 1.25 billion passengers per annum. The system is split into eleven lines and runs for 7 days a week with only a short period each night for track, station and train maintenance. To service and maintain the trains, each line has its own maintenance depot (or depots) where repairs, cleaning and routine maintenance all take place over night. In total there are 14 depots and the equipment they require presents a variety of challenges for manufacturers and installation designers.
The environment within depots is very harsh (with indoor and outdoor locations, washdown areas, etc.) and electrical supplies to users of portable tools and specialist plant must be protected to the highest standard. In addition, equipment must be durable and supplies resilient, to ensure disruption is minimised and work is completed on time. Blakley Electrics have designed specialist assemblies for installation in LUL maintenance depots for many years. Whilst assemblies change in detail to meet the requirements of different locations, there are a number of common themes that influence the basic design of equipment for depots.
London Underground’s safety policy dictates the widespread use of 110 volts to power maintenance equipment. The restricted space in the pits prevents the installation of local transformers, which results in long circuits from transformers to the pit sockets. These long runs create a number of issues. Firstly, to overcome volts drop, the pit sockets have to be capable of looping-in and out over sized cables. This can result in the need to terminate 16mm2 or 35mm2 cables (in and out) in a socket rated at only 16A. Secondly, if the specification requires multiple sockets on a circuit to be fed at full load, simultaneously, the supply protection will exceed the socket rating, necessitating an MCB to be fitted into each socket.
Thirdly, in order to achieve disconnection times, there is a need to incorporate RCD protection in the Transformer Distribution Cubicles, which supply the 110V power to the socket circuits. In order to ensure a fault on one tool or machine does not trip the supply RCD in the transformer, individual sockets need to incorporate RCD protection to discriminate with the RCDs installed in the transformers (the RCDs in the transformers need to be Selective type with time delay).
In addition to the electrical design, there are also mechanical design requirements. Assemblies need to have a high IP rating (IP55) and enclosures for wet areas need to be made from stainless steel. Unlike equipment installed in Underground Stations, the use of moulded sockets is permissible, which makes it possible to meet higher IP ratings. The pdf document shows drawings and images of typical assemblies for depots.
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SP21_Tube Train Maintenance Depot.pdf (297.33 KB)