Carrying the power

Thibaut Zumsteeg asks: how are cables powering us to a renewable future?

It is clear that there is an increasing global demand for energy. The population is only set to increase; meaning the amount of energy available also needs to follow this trend. The more the growing demand is met with renewable energy, the better, as carbon emissions will be reduced. Hence, pressure is mounting on power supply companies to increase the number of wind farms and the amount of power generated on each site. One way to do this is by creating higher capacity wind farms in more extreme environments and at a lower cost.

National grid data shows that 2015 was a record-breaking year for the British wind industry, with 11 per cent of all the UK’s energy generated by wind. Due to wind energy becoming more prevalent, developers are looking for ways to develop wind farm technology, ensuring turbines are operating as efficiently as possible.

Looking into different cabling innovations can be a good place to start. Cabling is a key feature in the success of wind farms. It is used within turbines, between turbines, and between the wind farm and grid. Between 50 and 100 different cables make up the nacelle, tower and base. Much like a variety of different neurons make up a nervous system, a variety of different cables make up a wind turbine. It is vital that cables work together (like neurons do) to create a functioning system, as without this operational system, wind farms would cease to work. This reinforces why it is so important that cables are of the highest quality.

The cables found in wind farms consist of a variety of medium voltage (MV) and low voltage (LV) power cables, and control cables. There are many developments in cable technologies, which are allowing higher capacity wind farms to be built in more extreme environments, and at lower costs.

Three main types of cabling innovations will be focused on in this article: lighter aluminum cables (which make installing cables in wind farms easier), higher voltage intraarray cables (that carry extra capacity) and pre-assembled wind turbine sections (which are easily constructed on site).

The advantages of Aluminium cables
Aluminium cables are a recent development in loop cables and allow the nacelle to turn freely in the wind. At 40 per cent lighter than traditional copper cables, they are cheaper and easier to install within wind turbines.

To ensure that these cables function properly they are tested before being installed, guaranteeing that they are resilient and flexible enough to resist torsional effects. Wind turbines are expected to last up to and maybe more than 20 years so it is really important that these tests are carried out. Under torsional tests, the chosen aluminium cables are able to withstand a torsion of ±100 degrees/meter during at least 2000 cycles.

High voltage helps harness wind power Higher voltage intra-array cables are also helping to meet the growing demand for renewable energy. They are allowing for higher capacity wind farms to be built using higher capacity turbines, in comparison to the more expensive option of building wind farms with more turbines. For example, if a typical 500 MW wind farm was built using 3.6 MW turbines, 138 would be needed. However, if 5 MW turbines were used, only 100 would be needed and if 10 MW turbines were used only 50 turbines would be needed.

These higher voltage intra-array cables are helping to transform wind energy production by allowing for greater power capacity with a smaller cross section and lower current. Normally, 33 kV intra-array cables are used to connect wind turbines to each other. However, if these cables were used to connect higher capacity wind turbines, a larger cable cross-section would be needed to carry the extra current. This in turn would need more metal, making the cables more expensive. Increased current would also lead to greater losses due to electrical resistance. However, by doubling the voltage to 66 kV a smaller cross section can be used resulting in cheaper cables, with an increased efficiency.

Offshore wind farms located in deep, rough seas can really benefit from 66 kV cables as a new ring configuration can be used, rather than the traditional radial one, to increase redundancy. As a result, opportunities for renewable energy production are expanding.

Powering on with pre-assembly
Pre-assembled wind turbine sections can be supplied with cables already wired inside. Split into four or five sections, up to 25 m in length, they can be used for the tower to make construction easier. The average wind turbine stands at 140m high so building them on site is an immense challenge. To make this easier, many OEMs are offering cable kits to further simplify the process. Cable kits have cables, which are cut to the correct lengths in the tower and are already pre-stripped. They also include relevant connectors thus making construction at site significantly easier.

In summary, the way wind farms are being built and developed is being revolutionised by innovative cable technologies. Cables are now lighter and cost effective, able to cope with higher voltages and available in pre-assembled sections. This is allowing wind farms to generate more power by contending with harsher environments, opening up a wider range of opportunities for wind energy. Therefore, as wind farms move further and further from the shore, the need for reliable cabling to carry energy to the grid is only going to keep increasing.

Thibaut Zumsteeg, Global Marketing Manager for Wind Energy, Nexans. Nexans brings energy to life through an extensive range of cables and cabling solutions that deliver increased performance for customers worldwide. Nexans’ teams are committed to a partnership approach that supports customers in four main business areas: Power transmission and distribution, Energy resources, Transportation, and Building.

For further information please visit: