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LONDON UNDERGROUND & OVERGROUND


to reaching capacity. Meticulous design and planning is required to ensure all cables are installed correctly and serious gauging issues are prevented so that there is no possibility that passing trains might make contact with any part of the cabling route.


On a larger scale, the challenges are mainly brought about by the greater size and weight of the upgraded equipment that the scheme demands. At each substation the existing 1.5MVA transformers will be upgraded to 2.5MVA and that means an increase in physical size. Under normal circumstances, this would not present a problem, but in the constricted working areas of the Underground it takes a great deal of planning, and no small degree of lateral thinking.


At one central London site it means removing part of the roof of the substation and craning the old transformers out and replacing them in a single night’s operation.


At another exceptionally constricted and constantly busy site, used by pedestrians as a cut-through and surrounded by Grade II listed buildings and protected gardens, not only did room have to be found for three 2.5MVA transformers and eight-panel DC and HV switchboards but all the work had to be carried out in ways that were sensitive to commuters, local residents and a much- loved park.


A hidden secret


completion in 2013, SSR2’s main focus is on the District and Circle lines – although the whole infrastructure will benefit from the increased power available. As with VLU, the core purpose behind the power upgrade is to increase passenger capacity by allowing newer, more sophisticated trains to be run. In all, a fleet of 191 new trains is planned; they’ll be longer with seven carriages each and together they’ll bring a 65% capacity increase on the Circle and Hammersmith & City lines, 24% on the District line and 27% on the Metropolitan line.


Behind the broad scope and ambition of the project lies a range of individual technical challenges that have to be overcome if it is to meet its 2013 completion target.


On a small scale and within the tunnels themselves, many of the existing cable routes have either reached or are very close


This London Underground station however hides a secret; located directly below in the nearby gardens and disused for over 50 years is a chamber that formed part of an earlier electrification scheme. Over time it has fallen into a state of advanced disrepair and although it had once been suggested it might re-open as a nightclub, it is now the perfect place to house the new infrastructure that SSR2 demands.


The remedial works required are significant. A new floor has to be constructed, drainage system considered, hazardous material has to be removed and disposed of, and the walkways and access points all require substantial works to meet the new proposed layout. A vent shaft in the park looked like the ideal works access point through which material and equipment could be lowered, but this is limited. The major equipment will need to be craned through a new opening to be formed in the roof, but before this can be carried out, it is necessary to negotiate with the local authority and plan for trees to be trimmed and street furniture removed.


Above right: A typical layout in a substation with limited access


And of course there will be some temporary restrictions on public access to the park whilst this work is carried out. However, through careful planning and close liaison, it’s unlikely that even one of the many thousands of people who pass by every day will be remotely aware of the major upgrade works happening beneath their feet.


That ability to carry out major works in an imaginative way whilst causing minimum disruption has typified UK Power Networks Services’ approach to both the VLU and SSR2. In many cases passenger inconvenience has been minimised by ‘piggy-backing’ work on top of already planned activities – so a line is only affected once and for the minimum amount of time.


When daytime working cannot be planned, night working is utilised. However, the tube system is only shut for a short time each night (once safety checks have been carried out, barely three hours are left for major engineering works). Despite this, and despite the significant engineering challenges associated with bringing a 150-year-old sub-surface railway system up to the standards that are expected in an international capital, the work is continuing and without most passengers noticing a thing until the new trains start running.


FOR MORE INFORMATION


T: 0207 397 7695 E: rail@ukpowernetworks.co.uk W: www.ukpowernetworks.co.uk/rail


rail technology magazine Jun/Jul 11 | 67


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