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NETWORK / 27 / MARCH 2017 The unprecedented increase in onshore wind development in south-west Scotland has led to SP Energy Networks (SPEN) in particular feeling the pinch on capacity. Unlike National Grid, its connection forecasts have been smashed, with more than 4.9GW already connected – far exceeding the initial prediction of 2.5GW for the entire eight-year regulatory period. DNOs have a range of options at their disposal when they have to connect generation in places where it traditionally would not be possible without reinforcement. But for SPEN – with an offshore windfarm waiting to connect to the transmission network – reinforcement was the only option. The traditional reinforcement option – the mammoth task of constructing an entirely new tower route – comes at vast expense and with long build times. Instead, SPEN chose to test a new conductor technology on Scottish shores for the first time. It would let the company maintain its existing tower infrastructure while doubling its capacity so the windfarm could connect. SPEN says: "This ground- breaking trial is an exceptional example of engineering, and represents a step-change for the Scottish renewable energy industry, achieving more effective and efficient network reinforcement which will result in less environmental impact and more cost-effective grid connections for generators – plus transmission and distribution owners." The problem SPEN had to increase capacity on the Coylton to Mark Hill route in South Ayrshire. The route lies on some of the most inaccessible terrain. The only traditional option available would have been to build 194 new towers because the increase in heat caused by installing larger conductors would have been inadvisable and uneconomical on the existing towers. The technology SPEN formed a partnership with technology company 3M to use its aluminium conductor composite reinforced (ACCR) technology. The project represents the first time the technology has been used in Scotland, but ašer the commercial introduction of ACCR in 2005, it has been successfully installed in countries such as China, Germany and France. The technology is particularly useful in situations where tower replacement is difficult or uneconomical, including crowded urban areas and environmentally sensitive places such as river crossings and estuaries. The patented technology consists of a core composed of multi-strand aluminium oxide (alumina) fibres embedded in high-purity aluminium. The manufacturing process is highly specialised and proprietary to 3M. The conductor's unusual structure allows it to withstand high temperatures without any appreciable loss in strength. Extensive testing has demonstrated that the conductor retains its integrity ašer exposure to temperatures even higher than the rated continuous operating temperature of 210°C and the emergency operating temperature of 240°C, giving it the durability and longevity of traditional steel core conductors. The conductor is based on aluminium, so it has the corrosion resistance typically associated with all-aluminium conductors, but the composite core design gives it the strength and stiffness of steel- core conductors, with half the weight. 3M calls ACCR "one of the most significant breakthrough technologies" it has delivered to the energy market for infrastructure upgrades. It is designed as a "drop-in" replacement for existing electrical conductors. 3M says ACCR lets transmission operators avoid building new substations or reinforcing old ones, and existing pylons do not have to be made taller to increase clearance heights. This means there is minimal impact on the environment and helps overcome the delays frequently caused by planning objections from pressure groups and land owners. The project Working closely with both 3M and Balfour Beatty, SPEN re- conductored two 275kV routes between Kilmarnock South, Coylton (15.5km) and Mark Hill (49.5km). The two routes make up the largest circuit sections in the UK. The initial eight-month schedule for the project was cut to just 15 weeks despite the remote, difficult terrain and a particularly wet Scottish summer. Collaboration between SPEN, Balfour Beatty and 3M was critical to the project's success, says Richard Wylie, lead design engineer for overhead lines. "Advance planning contributed to on-site efficiency and speed of project completion, including making sure that the installers were familiar with the technology long before they were on site. So they were not learning on the job and any concerns had already been addressed." During the project it became clear that some aspects of the installation process would have to be amended to suit SPEN's specifications. For example, longer installation platforms would have to be designed. This was done in advance of site work. Preparation work also included a week-long course hosted by 3M, with guest speakers from 3M in Key points • The conductors' aluminium conductor composite reinforced (ACCR) technology has the strength and stiffness of steel core conductors, but only half the weight. • The ACCR technology has doubled the capacity on the existing route without the need for any extra infrastructure. • SPEN saved £60 million simply because it did not have to build new towers on difficult terrain. • The new technology meant the installation time was eight years shorter than that of traditional reinforcement techniques. the US and input from existing ACCR customers. The benefits The benefits of the project are wide ranging, and include a saving of £60 million simply because 194 towers did not have to be built. This also meant SPEN did not have to use 4,000 tonnes of steel and 8,500 tonnes of concrete – preventing the emission of greenhouse and other gases associated with manufacturing and construction – and avoiding the need for new access roads. The approach also resulted in reduced impact on the local community and removed the delays that civil engineering permissions and rights of way would traditionally involve. The project has been delivered eight years ahead of the standard industry method, with one route now complete and another approaching completion. The technology has also allowed SPEN to meet its baseline shared use infrastructure target of 1,073MVA by the end of 2016. n