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Magnetic bearings give high-speed motors a lift

01 September, 2004

Magnetic bearings give high-speed motors a lift

A British firm has signed an agreement to design and build high-speed motors and drives for SKF. The motors, being developed by Turbo Genset, will use SKF`s magnetic bearing technology and could represent the first volume market for these low-friction, non-contact bearings, which use electromagnets to suspend the shaft.

The deal, which could be worth more than €6m to Turbo Genset, follows an earlier agreement under which the UK company is using SKF`s magnetic bearings (shown above) to support the rotors in a range of compact, high-speed gas-turbine-driven generators that it is developing.

The potential benefits of Turbo Genset`s high-speed motors include high power densities, high reliability, and low contamination of user processes. SKF`s will use them initially for spindle drives, but they could be adapted for other uses, such as electric vehicle propulsion, DC traction systems for railways, and compressors.

The agreement between Turbo Genset and SKF consists of an initial development and evaluation phase, followed by a five-year production contract. Serial production of the spindle motors is due to start next year.

Turbo Genset, which was set up in 1993 as a spin-off from London`s Imperial College, is also developing a range of high-speed turbo-generators which will develop 80kW-2MW of power for distributed generation applications. By operating at 20,000 rpm and eliminating the conventional gearbox between the engine and generator, these generators will be 50-60% smaller than conventional low-speed generators of a similar rating.

Turbo Genset has recently signed a deal to supply a 1.2MW generator to a US company for use at a landfill site, powered by gas from the site. The high-speed generators are due to enter series production next year.

Magnetic bearings have several attractions for the high-speed motor and generator applications. There are no components to wear, so maintenance is low; they are vibration-free; they do not need oil, so are environmentally friendly; they incorporate advanced condition monitoring; and they have a low energy consumption.

The bearings control the motion of a shaft in five axes and use digital controls maintain an airgap of 0.5-2mm between the shaft and the stator. Sensors monitor the position of the shaft and algorithms control the current sent to the magnetic stator to keep the shaft in the required position.

SKF acquired its magnetic bearing technology when it bought the Canadian company, Revolve, in 2000. Until now, these bearings have been limited to specialised applications. But recent developments have reduced the size and cost of their control systems, and boosted their performance.




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