Leading cable manufacturer JDR Cable Systems says 66 kV cables of the type now being introduced in the offshore wind industry are not the end of the road in terms of development
Leading cable manufacturer JDR Cable Systems says 66-kV cables of the type now being introduced in the offshore wind industry are not the end of the road in terms of development.
Stepping up the voltage of array cable systems in offshore windfarms to 66 kV is having a significant effect in the sector, enabling increased offshore power density, reduced operational losses and fewer offshore substations. It is also helping to reduce the levelised cost of energy.
Ultimately, this is essential for developing larger offshore wind turbines, but even as 66-kV cables begin to be adopted on projects in Europe, cable system manufacturer JDR Cables believes that another step up in voltage is already technically feasible and has the potential to be developed when required.
Speaking exclusively to OWJ at the Global Offshore Wind 2019 conference in London on 25 June, JDR Cable Systems’ chief technology officer James Young said the company believes that 90-kV cables are “technically feasible.”
The company is not actively developing 90-kV cables but anticipates that as the size of offshore wind turbines continues to grow, so a further step up in voltage could one day be advantageous. “The need for higher voltage is primarily driven by the increase in the size of turbines,” Mr Young said.
From 6-8-MW units, the size of offshore wind turbines has grown quickly to the point where 9-10-MW units are becoming the norm. Larger turbines such as GE Renewable Energy’s 12-MW Haliade-X are being developed, with Haliade-X due to begin testing later this year. New, larger turbines such as the Haliade-X have growth potential too and, in the longer term, even larger units are expected to be introduced.
By doubling the voltage of industry-standard 33-kV inter-array cables, technology developed by JDR and other manufacturers enables increased transmission between turbines at larger, higher-capacity windfarms, helping to reduce costs.
“With wind turbines becoming larger and larger and offshore wind projects growing in size, use of 33 kV had become a limiting factor,” Mr Young explained. A large number of cable strings were required to enter each offshore transformer, which meant that the total length of cable required for projects was greater than was optimum.
More cabling means higher costs and the longer the cable and lower the voltage, the greater the potential for electrical system losses, making the system as a whole less efficient. In contrast, 66 kV provides the potential to connect windfarms with fewer cable strings, reducing costs and electrical system losses. 66-kV cabling can also transmit twice as much power as 33 kV with only a relatively small increase in upfront costs.
Among the first applications of the 66-kV technology was Vattenfall’s European Offshore Wind Deployment Centre off Aberdeen in the UK, for which JDR was awarded a contract for the inter array and export cables. Here, power is exported through two strings of 4-km export cable with a capacity of 66 kV.
In 2017, JDR was selected by WindPlus as the preferred cable supplier for the Windfloat Atlantic 25-MW floating offshore windfarm. Windfloat Atlantic thus brings together two developments in array cables: dynamic cable design for floating offshore wind and high-voltage power transmission, through 66-kV cable technology. JDR was also recently awarded the world’s first large-scale commercial 66-kV project, for the East Anglia One windfarm in the UK.
“As the offshore wind industry demands greater power, so 66-kV technology will enable our clients to transmit more power,” said Mr Young, noting that, as turbines grow in size, so a further step up in voltage could one day make array cables even more cost-effective.