Cambridge Arbury Grid

With 70,000 new homes planned in the north of Cambridge, EDF Energy was committed to doubling the city's energy capacity to provide them with power. In 2004, VolkerInfra (formerly Visser & Smit Hanab (UK) Ltd) was called in to assist.

Facts and figures

Delivery this extra electricity required the laying of cables to bring it from three existing city centre substations and an entirely new feed from the grid.

"There were six circuits, two to each substation," says VolkerInfra's Fred Mastop, who managed the project. In all the distance spanned was 7km, which required the use of 98 drums carrying 1,000m of copper cable.

This quantity of copper was a formidable physical burden, with each drum weighing 6 tonnes, and also presented a serious security risk.

With copper prices at a premium, each was worth £20,000, putting the total value of the copper cable used at nearly £2m. Despite the enormous bulk, it was still a potentially attractive prize for thieves. "There was substantial unwelcome interest in stealing materials from the local community. The police even warned us about organised crime," says Mastop.

There were also some significant physical obstacles to overcome or, more accurately, go under. Most of the cable could be installed by laying ducts in a trench, back filling and then pulling and pushing the cable through using a special roller system. But in some places it could only be done by directional drilling, where long lengths of ducting and cables can be installed from access points at either end without disturbance to the land in between.

For obvious reasons, drilling was the only way for the cables to cross the river Cam. But, for conservation reasons, the technique also had to be used when crossing the historic public areas of Jesus Green and Stourbridge Common. "There was concern about damage to ancient trees, some are over 300 years old," says Mastop.

The same technique was needed also to get around the more recently created Newmarket roundabout. The project was split into three phases, the first being the directional drilling at Stourbridge Common in autumn 2004. A longer phase of duct installation, lasting two months starting in May 2006, enabled VolkerInfra to install the remaining duct work and leave the site without a trace of their presence.

The cable itself was installed in early 2007, with the team returning to excavate 1.5m deep pits by hand at intervals of around 400m along the course of the ducting, allowing operatives to install the cables, using both pull and push rollers to minimise the strain.

Great attention was paid to choosing the location of the pits to minimise the disruption to traffic, local residents and businesses. The same pits could later be used to join the lengths of cable before being filled back in again.

VolkerInfra worked very closely with the police and brought in the services of a private security company," says Mastop, of the installation phase when great emphasis was put on minimising the risk of the copper cables being stolen.

Each pit was guarded and surrounded by security fencing and the hole covered with a steel plate for safety and the safekeeping of materials.  Each of the drums had a security tag and a private security company was used to guard them.  But more fundamental was minimising the quantity of cable kept on site.  "We devised a very tight schedule with just two to six drums on site at any one time," says Mastop.

The entire installation process was successfully completed in February 2007.

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