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Choosing the Right Cabling Option

Tue, 04/22/2014 - 1:14pm
Uwe Schenk, Global Segment Manager – Wind, Helukabel USA

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Wind cable performance can be reduced in part by exposure to extreme temperatures, oils and other lubricants, and mechanical stress. It’s important to work with your cable manufacturer to select cables that can withstand these challenges.Renewable energy industry reports suggest that more than 60% of all future power capacity will come from renewable technologies, only 25% will be in the form of gas or oil, with the remainder being nuclear. Furthermore, experts estimate in the next 10 to 15 years, the market share of renewables will increase by more than 35% worldwide.

To meet these lofty expectations, turbine manufacturers and sub-component suppliers are being tasked with designing and building state-of-the-art technologies that are efficient, yet cost effective. To be competitive under the high-price pressures of the wind industry, even the most elementary of components will be under close scrutiny. This tight oversight will allow opportunities for new technologies to be developed using alternative materials in order to make the wind turbine more efficient and economical, while also being environmentally friendly.

Efficiency vs. Cost

The balance between high-quality, efficient products and cost effectiveness requires R&D departments of companies in the wind industry supply chain to think outside the box. One area in particular, is the conductor material itself, which is often the cable’s largest expense. Cable and wire manufacturers have traditionally used copper as the conductor material of choice for cables in wind turbines. However, copper prices are extremely volatile due to its varying degree of demand. Therefore, cable R&D engineers are looking at alternative conductor materials or copper alloys that perform comparably to pure copper, but have far less price volatility.

One such material is aluminum, which has been used as a conductor material in wind turbines, but has always been stiff and not easy to use. Some manufacturers, however, have developed a cable with flexible-aluminum conductors that are safer, up to 60% lighter, and easier to install or replace.

Flexible-aluminum cables are diesel locomotive (DLO)-like cables, best used in the tower area of the turbine (second photo, right), with performance characteristics comparable to standard copper cable, but at a fraction of the cost.

The cost savings go beyond just switching the conductor material from copper to aluminum. Installation and maintenance costs are significantly reduced since the complete power cabling system, from generator to inverter, is only interrupted in the loop. This maximizes cable safety and reliability compared to the conventional installation method, which interrupts the cable at every tower section. Furthermore, installation time is reduced from days to hours.

Additionally, cable connection technology is also seeing a shift to alternative or hybrid metals, such as lugs being made completely of aluminum or aluminum-copper hybrids.

Is the Enhancement Worth the Cost?

As R&D discovers new advancements to further product growth, this usually entails a product price increase to cover associated expenses, and therein lies the challenge for suppliers – filtering out what features are essential from those that aren’t. In cables for wind turbines specifically, features that are added or eliminated depend on where the cables are used within the turbine.

Cable specifications are created based on the current state of technology. New insulating and conductive materials for cables and wires are constantly being evaluated for their compatibility. New generations of highly flexible aluminum cable up to 34 kV could further change the kind of installation in the towers. Insulation material suitable for higher temperature ranges have a positive effect on such conversion factors as deviating ambient temperatures, grouping, and at the very least, the laying method in which cables are installed.

In various wind tower applications the down tower area, the generator, and the cable loop are areas with the highest potential for cost savings. Some manufacturers are using special constructions to separate the cables found in the cable loop with a spacer. It is mandatory to separate the cable if the outer insulation is not abrasion resistant; using cable with an abrasion resistant outer jacket, like polyurethane (PUR), could be a better option depending on electrical factors like the current carrying capacity of the system.

Making recommendations about features to include/exclude is challenging as the use of wind turbines is not a one-size-fits-all situation. There are many characteristics to consider before selecting the appropriate cable to install in the turbine. In order to provide the most cutting-edge, cost-effective solution, it’s recommended to work closely with your cable manufacturer’s R&D department. 

Regulation

Regardless of the changes that are made to components to enhance their capabilities, if they do not meet certain standards they can’t be put into production. Some of the most recent developments are the changing of UL standards with regards to cable and wire requirements in wind turbines. The latest standards are UL 6141 (large wind turbine equipment), 6142 (small wind turbine electrical systems), and 6171 (wind turbine tower converters and connections). These standards specifically describe the individual components acceptable for use in wind turbines. They go further than NFPA 79 edition 2012, which provides only the basic requirements for cable installation in turbines.

Once these new UL standards are put into full effect, wind turbine operators in North America will be required to use cables that meet the approvals.

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