Ørsted's Walney Extension Offshore Wind Farm, located off England's north west coastline, will become the world's largest wind farm when it is completed later this year. A high-performance heat-conducting concrete is being used to maximise the transmission of wind turbine generated electricity via the onshore substation at Heysham, Lancashire. Terry Balmer, technical services manager at Hanson Concrete, explains.
The last turbines at the Walney Extension Offshore Wind Farm, located in the Irish Sea around 19 kilometres off the coast of Cumbria, were installed in April. The extension is situated next to the existing wind farm and comprises of 87 new turbines, spread across 145km2, which will be capable of generating 659MW of energy a year when fully operational: enough to power more than half a million homes.
Wind farms rely on underground cables to take the turbine-generated electricity to a substation so it can be safely and effectively transferred to the National Grid. It is vital that as much of this electricity as possible is delivered to the grid but this can be a challenge, as running high voltage (HV) and ultra-high voltage (UHV) power cables underground generates heat and, as the temperature increases, so does the resistance, resulting in capacity loss.
Powercrete has been specifically developed for use in the energy sector as a bedding and infill material to overcome these issues. It provides low thermal resistance so the heat generated by HV and UHV electrical cables is dissipated effectively and the conductor temperature is reduced, preventing the underground cables from overheating. As a result, the power capability of the cable run is increased.
The specialist concrete has been developed by Hanson's parent company, HeidelbergCement, and has the same ease of placement as normal concrete. Its consistency can also be adjusted to suit the application.
More than 750 cubic metres of Powercrete were supplied from Hanson's Westhoughton and Blackburn plants in Lancashire to contractor Murphy Group for the onshore substation at Heysham over a strict timeframe. The concrete was used for a heavily congested connection point to the transformer, known as a hot spot, where the underground cables come together within the substation to transfer the electricity generated by the wind turbines to the grid.
The project presented a number of challenges with regards to the safe delivery of the concrete as HV overhead powerlines are close by and the electricity passing through the substation itself created a magnetic charge. These were addressed by the instigation of a stringent safety regime, including the earthing of the concrete mixer trucks and on-site safety zoning. The use of Hanson's latest fleet addition, an articulated 12 cubic metre ready-mixed concrete truck, also reduced the number of vehicle movements. The truck has a 50 per cent bigger capacity than a standard vehicle.
Using Powercrete increases power capacity, reduces conductor cross-sectioning and allows a switch to more efficient, cost-effective aluminium conductors. It also serves to reduce magnetic field strength for alternating current and mitigate hotspots. This allows the harvesting of natural energies to be maximised.
Scott Marsden, project manager at Murphy Group, added: "Hanson's level of customer service and technical expertise throughout the project meant the supply, delivery and installation was safe, smooth and successful. Ørsted was also delighted that Powercrete met all its technical requirements for effective heat dissipation on the cable system."