Cable with aluminium core can help reduce costs
August 2014 saw JDR in the UK secure the first contract for its innovative aluminium core inter-array cable
A breakthrough for a new type of inter-array cable has seen JDR’s newly developed aluminium core cabling selected by Siem Offshore Contractors for the Nordsee One offshore windfarm, as currently being developed by RWE Innogy. JDR will provide more than 70km of aluminium core inter-array cable, cable accessories and post-delivery offshore services under the contract with Siem Offshore Contractors for the Nordsee One windfarm, which is located some 40km north of the German island of Juist in a water depth of up to 34m. The Nordsee One windfarm will have 54 turbines, and the project will utilise two JDR-designed inter-array cables: a 240 mm2 aluminium conductor cable and an 800 mm2 aluminium conductor cable. Both will be XLPE insulated and type tested to IEC 60502-2 and CIGRE standards. The cables will be designed by JDR’s in-house engineering team and manufactured at JDR’s Hartlepool facility. Alongside the inter- array cables, JDR will supply a range of accessories including cable pulling grips and hang-offs, cable cleats, power core termination connectors and fibre-optic splice boxes. To complete the project, JDR’s Global Services will provide field service teams to install the hang-off as well as to route, terminate and test each inter-array cable.
Speaking at the time that the deal was announced, Paul Gahm, JDR’s executive vice president responsible for sales and marketing, said the cost-efficient aluminium core inter-array cables that have been selected for the project are the latest in a growing JDR range of products and accessories designed to support the long-term development of offshore wind energy production. As a raw material, aluminium is approximately one-third the cost of copper by weight, and it has one-third the density of copper. It is not such an efficient conductor as copper; however, having around 60 per cent
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of the conductivity, larger conductors are required to carry the same current. Larger conductors require more material for insulation and armour protection and a larger overall cable.
Another issue is that aluminium has limited corrosion resistance, and field experience has shown that aluminium cables can be too light to jet bury successfully, so they may require additional ballast, but JDR has overcome these challenges and has successfully developed and tested 3 x 800 mm2 33kV power cable using aluminium conductors. The new inter-array cable was launched only a matter of weeks earlier at the Global Offshore Wind conference and exhibition in Glasgow in June and is one of a number of potential approaches to array cables that the company is investigating with the primary goal of helping the offshore wind industry achieve cost-reduction targets. As part of this initiative, the company is also investigating opportunities to transfer its experience in offshore oil and gas markets to offshore wind applications. One of the options currently under review is the introduction of pre- terminated inter-array cables. This technology is standard in JDR’s subsea production umbilical products and could be used to reduce offshore termination costs for offshore wind operators. Speaking at the Global Offshore
Wind event, JDR’s product development director, Jeremy Featherstone, described some of the company’s cost-reduction work. As he noted, JDR continues its Department of Energy and Climate Change-supported work on high voltage inter-array cables that, it is anticipated, will improve power capacity by increasing array cable voltage ratings from 33kV to 66kV.
As he also explained, JDR’s engineering team is also investigating issues such as how dynamic ratings could reduce cable conductor sizes and subsequent material costs and how
JDR has successfully developed and can manufacture 33kV power cable for offshore windfarms using low cost aluminium conductors
strain-sensing fibre-optics can be used to minimise installation issues. In his presentation at Global Offshore
Wind, Mr Featherstone looked at five potential approaches to cost reduction. These included using aluminium rather than copper conductors, as selected for the Nordsee One project; 66kV array cables rather than 33kV; dynamic cable ratings rather than continuous ratings; the concept of realtime cable monitoring using fibre-optics to enhance installation assurance; and the pre-termination option, the main benefit of which is to reduce the amount of work that needs to be undertaken off shore. Andrew Norman, JDR’s chief executive officer, said the company was committed to working with developers, installers and throughout the supply chain to create the products and services that can help the industry achieve its cost-reduction targets. “The launch of our aluminium conductor core products and our work on high voltage 66kV inter- array cables are important steps forwards in providing the tools and choices our industry needs to enable the long-term development of successful windfarm projects,” he said. Talking about applying experience in oil and gas markets for renewable developments, Mr Norman said the company’s expertise with dynamic cable in deepwater offshore environments would be invaluable as operators look to develop floating turbines further off shore.” The company recently opened an offshore engineering technology centre in Cambridge in the UK. The focus there will be on technology development. OWJ
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