Changing gears: A look at wind turbines

As countries around the world seek to reduce their carbon emissions and transition towards a sustainable future, wind power has become a pivotal component of their renewable energy strategy. The UK, in particular, has seen the amount of power generated by wind grow significantly in recent years. In fact, in early 2023, wind be-came the country’s leading source of power for the first time ever, producing more electricity than gas and imports.

Driving the growth of wind power in the UK and around the globe are a host of technologies, one of which is wind turbine gearboxes.

All about gears

Modern wind turbines are complex pieces of equipment, with many moving parts. To ensure their efficient operation, some gearing is necessary.

A gearbox is typically used in wind turbines to transform low-speed, high-torque wind turbine rotation to a higher speed required by the generator. In wind energy conversion systems, the gearbox is one of the most critical components of the powertrain system. Generally, for wind turbine gearboxes, operational conditions are challenging, and expectations are high – these gearboxes are subject to severe loads and are often in locations where it is extremely expensive to replace or repair a failed gearbox.

Traditionally, mechanical gears are used inside of these energy-conversion systems to connect a high-speed electric machine to a low-speed physical energy source. However, over time, gearbox failures have accounted for a vast amount of downtime, maintenance, and loss of power generation. In fact, reports indicate that there is one gearbox failure in every 145 wind turbines in service annually, leading to significant downtime and high costs for owners. These issues have led to the emergence of magnetic gears as an alternative to mechanical gears.

Just like mechanical gears, magnetic gears transform rotational power between different speeds and torques, but instead of physically interlocking teeth, they use magnetic fields. By using magnets to transmit torque between the input and output shafts of the gear, they avoid mechanical contact. This provides several advantages, such as high torque density, reduced acoustic noise and vibration, lower maintenance and improved reliability, inherent overload protection, and contactless power transfer.

Moreover, if too much torque is applied to mechanical gears, they may break. If the same happens to magnetic gears, they simply slip past each other without causing any damage to themselves or other parts of the system.

Innovative and efficient technology

To ensure efficiency, reliable motors – in particular innovative magnetically geared motors – are a key enabling technology for the renewable energy sector. Magnomatics offers revolutionary magnetic gears which have been implemented in a range of innovative industry solutions, including offshore wind.

The company’s patented Pseudo Direct Drive (PDD), which is designed to overcome the torque limitations of conventional direct drive electrical machines, consists of a magnetic gear mounted inside a stator. The outer magnetics of the magnetic gear are attached to the inner bore of the stator, and copper windings in the stator are used to drive the inner rotor of the magnetic gear.

This is a relatively high-speed electric motor with a relatively low load, which results in low currents and hence, low temperatures. This in turn brings great efficiency, long life, and prevents demagnetisation of the outer magnet array. The torque in the inner rotor is then geared up in the novel polepiece rotor, typically by between 5 and 10:1.

Simulations have shown that the PDD is less than two-thirds the size of an equivalent permanent magnet motor and half the length of an induction motor. Furthermore, it can be designed to be 2 – 3% more efficient without compromising torque density.

The result is a very compact and highly-efficient motor; perfect for wind turbines, as they have excellent efficiency even at part load due to wind inconsistency, which is where the bulk of operations take place. In fact, the efficiency of the PDD excels in these conditions because it continues working nearly to nominal values.

The technology is also becoming increasingly recognised across the world, not only for offshore wind but for a multitude of applications including marine propulsion, automotive and wider industrial.

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