A race to the finish line

A £6 million project that involves laying 14km of cable close to Silverstone racetrack is approaching the finish line.

Now you see it…

Unlike the Roman road that runs alongside the works, the two-year project to install the new 33kV circuit, which runs from Towcester to Wicken, has been far from straightforward.

The work was triggered by a new connection for a large housing development; when the works are complete, the capacity of Towcester 33/11kV substation will increase from 15 MVA to 28 MVA and will benefit 6,000 customers. 

…Now you don’t. More than 5km of overhead lines close to Towcester have been moved underground.

Restrictions that apply to the A5 Roman road prevented engineers from taking down overhead line and laying it in the road, meaning the work had to be done in painstaking sections. While much of the work has been in rural and remote locations, it has still called for a number of road closures and the need for traffic management. 
Rob Woodhall, Project Coordinator, explained: “The single biggest engineering obstacle caused by the rural location of the cable was its planned route over a bridge. The shallow road profile made this route impossible, so we considered drilling but were forced to rule this out because of hard rock and a fragile water main. The cable was eventually re-routed by creating a new stream crossing.”

When determining network strategy, engineers had to take into account the distance of the Towcester substation from both Brackley and Stony Stratford 132/33kV substations. This meant ensuring sufficient capacity while keeping the voltage within legal limits. The solution was to add a third 33kV to 11kV transformer. This decision brought complications of its own, as the existing layout of the compound made it virtually impossible for designers to accommodate the new £200,000, 24 MVA transformer.

Rob continued: “The only way around the issue was to re-arrange the existing structures, which included cable connectors and supports, neutral earthing resistors and civil structures. 

Project Engineer Mark Shenton (left) and Engineering Specialist Darren Impey discuss commissioning work on the transformer temperature monitoring and control system at Towcester substation.

“The existing substation building was extended to create space for an eight-panel 11kV switchboard to be connected to the original switchgear. This enabled the connection of the new transformer and circuits feeding the development and wider local area. Following these largescale changes, modifications were needed to the existing protection to prevent failure of the transformers and circuit breakers.”
Further complications arose when developers asked for an existing 33kV overhead line to be removed so they could begin building. “Because there were no roads in place, we had to create a raised verge to lay the displaced cables, along with 11kV and LV cables,” said Rob. “Negotiations with developers to plan the phased dismantling of the overhead line ran into trouble because of the need to keep the circuit live to feed the substation.” 

Alongside the new Towcester to Wicken circuit, engineers are also undergrounding 5.5km of overhead lines on an existing 33kV circuit from Towcester to Roade, where an automated switching point was also installed, as well as replacing 700m of 33kV underground cable on the Towcester to Silverstone circuit.

Engineering Specialist Darren Impey has overseen cable and circuit work.

Rob said: “As part of this project, we not only want to meet demand now; we have deliberately chosen specifications of plant and cable to accommodate the requirements of future connections, so we are ready to deliver future capacity.”
Following initial planning by Primary System Design, the project has been a partnership between the Northamptonshire district team, Northampton-based Engineering Specialist Darren Impey, who has overseen cable and circuit work, and Mark Shenton in Major Projects, who is responsible for the substations.