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ABB helps Marks & Spencer store complete a seamless switch from copper busbars to cables

ABB Limited (Group Headquarters) : 04 July, 2006  (New Product)
ABB has helped Marks & Spencer
At the same time, ABB’s innovative approach to materials handling enabled the work to be completed with a minimum of scaffolding and without the need for cranes.

Power for the retail store is provided by two roof-mounted 11kV/415V transformers. Previously, these transformers fed two independent 2300A resin-encapsulated copper busbar circuits that took a complex route to the Main Essential and Non-Essential LV distribution boards. A second pair of circuits from the Main LV distribution boards followed a route from the roof down to basement level, on through a tunnel under the road, and then up into the store offices and warehouse on the other side of Argyle Street. Although the busbars were only around five years old, one had already failed. So Dunwoody Maintenance Management, who manage the electrical maintenance at the site on behalf of Marks & Spencer, invited ABB to propose a solution that would restore the LV distribution network to the required level of robustness and reliability.

After carrying out a detailed site survey and reviewing the busbar replacement options, ABB suggested that the solution that would create the minimum disruption to the store operation would be to completely remove the existing busbars and to replace them with XLPE (cross-linked polyethylene cables).

Four single-core ABB copper cables, with a 630 mm cross-section, have been installed for each transformer phase, a total of 16 cables per transformer, each with a length of around 30 m. The cables have been laid in steel trays (galvanised ladder racking) with a lid to prevent degradation by UV light. ABB also replaced the busbar terminations with new transformer switches capable of handling loads of 700A per phase.

Sunday shutdowns
The main transition activities were carried out during the store’s Sunday shutdown periods, a window of just two and a half hours. In the first phase, ABB isolated the Essential Services of the transformer circuits and then linked the LV switchboards via a switchboard link so that both switchboards were fed by the Non-Essential transformer. A typical example of the attention to detail during this project was that a mains engineer was kept on call during this operation, ready to bring the permanent site back-up generators on line should there be a problem with the main supply.

On completion of the first phase, and after a week-long soak period to confirm the correct operation of the cable, the second phase was carried out by transferring all load onto the Essential Services transformer to allow replacement of the second busbar circuit. Once completed the switchboard link was removed and the second cable circuit re-energised so that the two transformers now feed two independent cable circuits.

Busbar removal
Removing the encapsulated copper busbars was a particular challenge as their weight (69 kg per metre) required them to be cut out in individual one metre lengths, while ensuring that they were held carefully to avoid them dropping from height. In fact, thanks to the great care taken with all aspects of the project ABB received a glowing health and safety report.

Initially, it was thought that heavy lifting equipment might be required. This would of course have required a great deal of planning and notice of road closures to bring a crane into a busy part of Glasgow’s City Centre. However, during the site survey, ABB established that it was possible to use the existing service lift, by spreading the load to prevent point loadings that would exceed the safe loading limit, avoiding the extra cost and disruption of using a crane.
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