Expected Eagerly: 66 KV Is Better Than 33 KV

The wind industry is driven by constant pressure to improve efficiency. The aim is to lower the costs per kilowatt hour generated in the long term below the level of conventionally obtained energy. Stronger wind turbines with outputs of up to 8 MW, more efficient turbines and larger wind farms with total outputs of up to 1200 MW are just a few of the many answers.

Wind farm operators are therefore increasingly relying on an increased voltage level of 66 kV instead of the previous 33 kV. As one of the first cable and wire producers, the Prysmian Group can now support this new voltage level with products for the connections between the systems (inter-array) as well as in the wind turbines themselves - a decisive step towards increasing the efficiency of wind energy.

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The previously prevailing voltage level of 33 kV in the networks and lines means that the energy generated must first be converted to high voltage in transformer platforms on the high seas (usually 155 kV) and then again onshore to 380 kV, for example in Germany. If the entire voltage level of wind farms is raised to 66 kV, a large part of the costs for the energy infrastructure can be saved. This is because the size and number of transformer platforms on the high seas can be significantly reduced, which also reduces the amount of cables required. In addition, there are lower maintenance and repair costs. Reduced voltage losses at higher voltage levels included,the change from 33 kV to 66 kV over the entire lifetime can save up to 15% of the total costs of a wind farm depending on the distance to the mainland. In addition, significantly larger parks can be realized with a higher number of wind turbines.

Development of 66 kV products accelerated

As an independent foundation that pursues the development of a sustainable economy, the British Carbon Trust also recognized the great potential of an increased voltage level in wind farms. With the "Offshore Wind Accelerator" program (OWA), the organization launched a flagship project together with nine offshore wind developers to reduce the costs of offshore wind energy through new concepts in commercial solutions. Electrical arrays are among the components that offer one of the greatest savings potential in the construction of wind farms. Together with selected cable manufacturers, the OWA program initially pushed ahead with the development of a competitive 66 kV cable system and accelerated the testing and certification of the cables.

From the infrastructure to the turbine

As the world market leader for energy and telecommunications cables, the Prysmian Group has been involved since the beginning of the OWA program. After an extensive test and certification process, the company has been able to offer inter-array cables for the increased voltage level of 66 kV since the beginning of the year. The three-core cable system has EPR insulation in the so-called wet design with aluminum conductor and integrated optical element. Copper conductors are also available. The EPR insulation shows excellent material properties, even in direct contact with water. The type test of the 66 kV inter-array cable was successfully carried out in accordance with CIGRE and IEC standards - a milestone on the way to the development of innovative and cost-effective cable solutions for industry.

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Make technology easy to understand

Another logical step was the expansion of the product portfolio to include highly flexible cables for a voltage level of 66 kV within the individual wind turbines - a novelty in the industry. Technically, the cables are based on the company's existing products, but have been adapted for the voltage level of 66 kV. With the Feltoflex cable, the Prysmian Group offers a single-core connection from the inter-array cable to the switchgear of the wind turbine. Finally, a three-wire Windflex (HV) cable reliably establishes the connection to the wind turbine. In practice, the highest demands are placed on both lines. Because in order to withstand the strong vibrations and movements within the wind turbine, the best torsional properties have to be fulfilled.The cables must be easy to lay and highly flexible because there is little space.

Additional information on the challenge of offshore

What is easy to do on land often turns out to be an enormous challenge on the high seas. This also includes laying and installing the energy network of an offshore wind farm. The lines from the Prysmian Group are factory-equipped with field-mountable socket connections and pluggable connections using so-called Click-Fit-TM technology in order to save time and effort on site. The Prysmian Group also supports the laying with two company-owned laying ships. The Cable Enterprise, for example, is one of the most modern work ships in its class. The ship was only technically refurbished last year and converted to a self-propelled DP2 ship, so that it can now operate in very shallow waters.Seven independent positioning systems enable the Cable Enterprise to meet all operational requirements even under the harshest weather conditions.

Bendable even at low temperatures

Thanks to their special material properties, the Feltoflex and Windflex (HV) cables meet these high requirements. They are extremely flexible, even in cold environments, and have a greatly reduced bending radius. Inside there are flexible class 5 conductors encased in a semiconducting extruded layer. The insulation consists of a resistant and high-purity HEPR material that has excellent material properties. The Feltoflex cables are also halogen-free, flame-retardant and oil, heat and ozone resistant. By using special rubber compounds in the insulation, these properties can be achieved over a service life of around 20 years. (br) Windenergy 2016: Hall B6, Stand 562