Lead-free cables as the solution of the future for offshore wind farms

Operators of offshore plants are increasingly upgrading their systems to higher voltages because, on the one hand, the demand for power is constantly increasing and, on the other, the energy generated can be transmitted much more efficiently from the wind turbine to land. Offshore parks are currently operating at a 66 kV voltage level, with an upgrade to 132 kV in preparation. These conditions place high demands on the systems and the cable connections and connection fittings used.

In addition, systems on the open sea must be as easy to maintain as possible and as robust as possible against salt water and harsh sea climates. Last but not least, health and safety aspects must also be taken into account in addition to the technical specifications. From a technical point of view, offshore systems follow the standard of the International Electrotechnical Commission (IEC). Prysmian Group provides a large portfolio of innovative cable solutions that are specified for these requirements. Prysmian continuously invests in the development of cable technologies to reduce lead content with the aim of creating innovative and more efficient solutions.

For the most adverse conditions: optimised cable solutions for offshore use

With the registered brands Feltoflex® and Windflex®, the Prysmian Group has cable solutions that meet the adverse conditions on the high seas and the special technical specifications of the wind energy industry. Due to the low bending radius, Feltoflex cables from Prysmian qualify themselves in comparison to conventional cable applications on the market thanks to their space-optimised cable routing. Feltoflex cables are also suitable for connecting offshore platforms. This area of application demands a high degree of flexibility from the product, as the platforms can move relative to each other.

The Feltoflex solution is primarily used in cases where the submarine cable cannot be attached directly to the switchgear that connects it to the tower. In this case, the Feltoflex cable acts as a dropper cable to connect the machine to the grid. More precisely, it docks onto the so-called array cable, which connects the individual turbines of the offshore wind farm so that the wind energy generated can be transported ashore. The dropper cable therefore establishes the connection between the wind turbine and the grid. The technical advantages of the Feltoflex solution over conventional high-voltage cables include, in particular, the small bending radii, which make it possible to lay the cable in the smallest possible installation space. As a result, the design and construction costs can be significantly reduced.

As the gondolas of the wind power plants are known to rotate with the wind, the energy pipelines, which are meant to transport the obtained wind energy downwards, must also rotate. Where the wires are conducted in a cable hole, the windflex and feltoflex wires will be used. Flexibility is crucial here in order to counteract possible mechanical damage and breakage. To ensure the highest possible flexibility of the windflex cables, various factors must be reconciled. These are in particular the coat strengths, the construction of the energy conductors, the stretchability, and the fire stability of the material.

Among the great advantages of the Windflex and Feltoflex series are the mechanical resistance and in particular the excellent torsion ability. Tests include whether the gondola in the tower can be rotated several times up to 100 degrees per meter in one direction without causing damage to the cable. The resistance of the pipelines is also tested by variable wind and temperature conditions. Windflex and Feltoflex pipes can withstand temperatures ranging from -40 to +80° C. Environmental requirements can vary greatly and require project-specific adjustments. Windflex cables are maintenance-free and mainly without material wear.

The Windflex product family was first installed in 2005 and since then it has been operating 100% fault-free in the respective plants. The Windflex family is designed for the entire life cycle of a platform, i.e. for at least 25 years. Extensive tests, such as on Prysmian's own torsions test stand, form the basis for high product quality and contribute to a constant expansion of the digital database.

On the way to lead-free solutions

The industry is facing new challenges, for example, with increased declaration obligations for hazardous substances. So far, lead-containing solutions have been used for the insulation of cables in order to lower wall thickness. Lead is known to be harmful to health. The development of lead-free solutions in this field is crucial mainly because the metal is considered to be toxic for reproduction and any health risks resulting from it are to be avoided. According to the European Chemicals Agency, lead in humans can lead to cardiovascular disease, decreased fertility, neurological developmental problems in infants and children, and repeated exposure to organ damage and cancer. In addition to human health risks, public pressure on the lead processing industry is increasing, as the substance is also harmful to the further environment and can lead to poisoning in birds, for example.[1]

The abandonment of lead-containing wires means for industry – and therefore also for Prysmian – the search for substances that can replace the positive properties of previous products. In this case, good mechanical properties, such as the abrasion resistance of the coat, thermal properties such as heat resistance, short-circuit thermal safety, as well as flexibility and removability, are crucial. Alternatives include advanced solutions with calcium and zinc stabilizers.

Prysmian has been manufacturing medium- and high-voltage wires with lead-free insulation mixtures for almost ten years and is thus one of the pioneers in lead-less cable solutions. Even in the area of medium voltage, lead-free insulation mixtures are not yet the standard for every supplier. In this context, the Prysmian Group passed the type test with 66 kV – an innovation in the field of high voltage lines, as lead-free solutions were previously designed only for medium voltages. The use of lead-free insulations is beneficial for clothing. Because when processing lead-containing cables, employees can be exposed to toxic substances such as dust particles during grinding.

Prysmian will soon implement the first projects with 100% lead-free cable solutions in the high voltage area. The individual components are produced at different locations, consistently under very high standards and "Made in Germany".

Prysmian will soon implement the first projects with 100% lead-free cable solutions in the high voltage area. The individual components are produced at different locations, consistently under very high standards and "Made in Germany".

With regard to the cable and cable industry, it is expected that lead-free solutions will become a industry-wide standard, promoted both by increased requirements for health protection and by reduced administrative burdens with regard to declaration obligations on the part of customers and manufacturers. However, it is important to bring the mechanical properties of the substances into line with health specifications and economic aspects – a challenge that Prysmian brings in its decades of experience.

[1] https://echa.europa.eu/de/hot-topics/lead-in-shot-bullets-and-fishing-weights