As turbines become more complex, they call for more advanced materials. Furthermore, the financial crisis has altered the trajectory of wind-farm projects by tightening developers’ budgets with a need to control costs, an increasing priority even as the industry expands. Like other complex products, wind turbines are made of a range of materials. Composites, for one, are dealt with in Section 1:18 and Coatings in Section 1:17. A few others are dealt with here.
Rare earths: The neodymium used in permanent magnets deserves attention. The rare earth and others have been supplied from mines in China but that country has restricted their exports, driving up generator costs. As a result, other sources of rare earth materials will enter world supply in the next year or two, which should keep material costs on the recent downward trend.
Metals: The most used metal in a wind turbine is steel in the tower and other components. But a few more recent material formulations deserve mention. For instance, one solution to the climbing cost of all copper wire is in copperclad steel. It is said to be reliable, cost effective, and can provide the wind industry with a smarter alternative to copper-based grounding systems.
A good grounding system plays a critical role guarding against catastrophic damage to blades, electronics, transformers, nacelles, and collector systems out to substations.
Until recently, copper has been the predominant material in wire and cable used to ground of electrical systems. But the cost of copper fluctuates substantially. This is bad news for wind-farm developers, and electrical and construction contractors under increasing pressure to control costs.
Given the cost sensitivity of any wind-farm project, the idea of burying a precious metal (copper) underground makes little economic sense when less expensive alternatives are readily available. Copper-clad steel has been around for decades and is a practical option to consider in grounding applications. It offers an alternative to copper by combining the strength of steel with the conductivity of copper through a cladding that delivers comparable performance.
Polymer adhesives: Because of a large spectrum of possible polymer architectures, polyurethane adhesives have been used as bonding agents in many different industrial sectors for more than 30 years. Construction, automotive, transportation, and shipping vessels have all benefited from the use of polyurethanes.
A recent polyurethane (PUR) adhesive satisfies particular mechanical requirements for use in the wind industry while improving the long-term reliability of rotor blades. It also makes rotor-blade production faster and less expensive. The adhesive is said to provide superior dynamic fatigue strength and increased resistance to crack propagation, while making the production of rotor blades more efficient than with epoxy technology. For instance, says the supplier, the PUR adhesive requires fewer curing steps than epoxies, resulting in reduced production costs and production cycles 15 to 30% shorter.
In addition to blade bonding, the two-component polyurethane adhesive is also used in other structural bonding applications on turbines including bonding components to the rotor blade, performing field repairs of blades, and securing various components inside the tower assembly.
GL’s requirements for the adhesive primarily relate to its tensile-shear strength, long-term durability, creep behavior, and glass transition. The adhesive’s physical properties are temperature-dependent. Within a temperature range known as glass transition (Tg), the change in the adhesive’s mechanical properties is considerable. The glass-transition temperature separates the lower, brittle, or glass range from the upper, flexible, or rubbery-elastic range.
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