Magnetic drive cuts compressor energy use by 10%
SKF has developed an oil- and contact-free magnetic drive system for centrifugal compressors used in chillers that, it claims, can deliver energy savings of at least 10% compared to conventional compressors.
The system combines a high-speed PM (permanent magnet) motor and active magnetic bearings with integrated controls. Electromagnets levitate the compressor shaft, allowing it to rotate at speeds faster than 40,000 rpm, without making contact. The system is vibration-free and nearly friction-free, resulting in extremely quiet operation.
By eliminating the mechanical contact and the losses that occur in oil-lubricated bearings, the magnetic system cuts energy use and costs significantly. And, by eliminating the need for oil lubrication, it also improves heat transfer efficiency in the evaporator and condenser.
The PM motor at the heart of the system is more energy-efficient than induction motors at both full and partial loads, and offers a higher power factor and a lower current draw. It also operates with a smaller VSD than would be needed for an induction motor. It can be used with VSDs from various suppliers.
The active magnetic bearings can accommodate instant and frequent start-ups, as well as transient surge forces. Active controls track and maintain the rotor position to within microns up to 15,000 times per second, eliminating vibration.
The new drive system uses technology developed by the French magnetic bearing and motors specialist S2M, which SKF bought from BOC Edwards in 2007.