As offshore wind turbines continue to grow in size and power output, UK wind farm developers and operators are preparing to switch over to 66kV technology rather than the current 33kV technology.
This is because operating at the higher voltage offers important lifecycle cost-efficiency benefits such as the possibility of reducing the number of substations required as well as reducing the length of cables that need to be installed.
From the first half of 2018 the advantages of 66kV technology have been demonstrated in three pilot projects; the Blyth Offshore Demonstrator (UK), Nissum Bredning Vind (DK) and Aberdeen Bay (UK) wind parks, which have all been successfully connected to the grid and are generating power.
French company, Nexans, has played an important role in these projects by supplying a range of products and accessories including 66kV sea cables (array and export cables), power cable accessories (equipment bushings, connectors, coupling connectors, surge arresters, dead-end receptacles, junction cabinets), GPH connection technology and pre-assembled cables.
Offshore wind parks
The Blyth Offshore Demonstrator, 6 km off the UK coast, is a pilot plant constructed by the Renewable Energies Division of the French energy group EDF.
With a total capacity of 41.5MW, produced by five V164-8.0 turbines from MHI Vestas Offshore Wind, it has produced low-carbon power for about 34,000 homes since January 2018.
The French company delivered pre-assembled cable jumpers to connect transformers and switchgear, sea cables for the array cabling and connectors to connect the array cables to the wind turbine switchgear.
The transformers were assembled with EUROMOLD bushings and surge arresters. Read more: High voltage DC makes offshore wind power transmission possible
In addition, pre-assembled junction cabinets, export cables and connectors to connect the wind park to the existing power grid were used.
The cable lengths were pre-assembled and electrically tested at Nexans Power Accessories in Hof, Germany.
The installation teams were comprehensively trained in how to use the connectors and the GPH connection technology at the company’s HV Training Centre in Hof, in order to make future projects as safe and efficient as possible.
The sea cables, with a diameter of 127 mm, were produced in Hanover and delivered in one continuous length in 2017.
The general contractor responsible for the Nissum Bredning Vind project is Siemens Wind Power A/S.
In the Danish North Sea, four Siemens Gamesa turbines of the SWT-7.0-154 type with a total capacity of 28 MW were installed.
Nexans delivered EUROMOLD connectors and three core cables for the tower cabling, equipment bushings and surge arresters to the Siemens transformer plant in Weiz/Austria and connectors to connect the array and export cabling.
Located off the Scottish North Sea coast, the Aberdeen Bay Vattenfall project, also known as the Offshore Wind Deployment Centre (EOWDC), represents the largest of the three European pilot plants with 11 V164-8.4 and V164-8.8 turbines especially engineered by MHI Vestas Offshore Wind and an installed total capacity of 92.4MW.
In addition to training in the installation of accessories, Nexans Power Accessories was also responsible for manufacturing 66kV cable jumpers to connect the transformers and switchgear.
The accessories and cable jumpers were shipped via the cable plant in Moenchengladbach, Germany.
Equipment bushings and surge arrestors were shipped to ABB Finland, the transformer manufacturer.
Nexans is currently the world's only supplier that is able to equip this new generation of wind parks with a complete in-house portfolio of state-of-the-art cables and standardised connection solutions suitable for a maximum operating voltage of 72.5kV.
The 66kV installations to date are pilot projects and the experience and results obtained will have significant impacts on future offshore wind projects.