SKF magnetic bearings and permanent magnet high speed motors assists technology shift in air and chiller compressors, increasing efficiency from 75 to 85 per cent

SKF’s magnetic bearing technology is part of the new variable speed drive solutions that are seeing screw compressors replaced by centrifugal turbo-machines in air and chiller compressor applications and give a typical efficiency increase from 75 per cent to 85 per cent.





This technology shift delivers lower operating costs in applications such as air conditioning, industrial refrigeration and the oil and gas industry, from these additional benefits: lower energy consumption; higher reliability; no bearing component wear, thus longer service life; virtually maintenance free; smaller machine footprint.

The new technology is based on high speed direct drives, coupling the compressor impeller to the drive-shaft, and using magnetic bearings as the support bearings. Because there is no metal to metal contact when magnetic bearings are in operation, there is almost no bearing friction generated and no bearing wear. Magnetic bearings are oil-free and thus very environmentally friendly. And they can operate safely at very high speeds thanks to sophisticated control systems developed by SKF.




In the past magnetic bearings were used in very unique or high-speed applications, but are now suitable for a wider usage thanks to SKF developments that have seen a reduction in size of the control systems, yet an increase in the performance beyond that originally considered possible.

A magnetic bearing system has three main elements: bearing stator and rotor to apply electro magnetic forces to levitate the shaft; position sensors to identify the position of the shaft in five axes; controller and control algorithms to control the current sent to the magnetic bearing stator to keep the shaft at a pre-defined position.

The magnetic bearing stator consists of a stack of laminations with copper coils wound around it to form a series of north and south poles. A current is supplied to each coil to produce an attractive force that levitates the shaft inside the bearing. The controller controls the current applied to the coils by monitoring the position signal from the positioning sensors in order to keep the shaft at the desired position through out the operating range of the machine. Usually there is 0.2 to 0.5 mm air gap between the rotor and stator depending on the application. The shaft is typically driven by another source such as a turbine, or a motor integrated to the shaft design.

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