Magnetic Bearings
Magnetic bearings are a good match with high-speed permanent magnet (PM) motors. These devices offer a non-contact rotor support system with extremely low friction and wear. While conventional mechanical bearings physically interface with the shaft and require some form of lubrication, magnetic bearings are an electromagnetic technology that suspends the target rotor in a magnetic field.
Advantages of magnetic bearings in PM rotating machinery include:
- Elimination of physical contact between rotating and stationary components
- Elimination of lubrication system and possible contamination
- Reduction of operating costs
- Simplified maintenance
- Improved reliability
- Enhanced machine operating parameters (such as speed and operating temperature)
- Environmentally friendly operation
- Real time monitoring of your system performance for predictive maintenance
- Optimization of the entire installation
Two basic types of magnetic bearing technologies are in use today – active and passive.
In active magnetic bearings, non-contact position sensors monitor shaft position and feed this information to the control system, which in turn controls the required current flow to an actuator to maintain proper rotor position. Active bearing systems, while more complex than passive types, provide much higher support stiffness and are tunable for optimizing system response. Both configurations provide very low stiffness and minimal damping.
Passive magnetic bearings are similar to mechanical bearings in that no active control is necessary for operation. One passive bearing approach utilizes repulsive effects of permanent magnets, which is essentially two magnets repelling each other. Another involves reluctance centering, which is essentially two magnets, or magnetic pole faces, attracting to align poles. In both cases, the developed forces act to cause the rotor to remain in the desired position. This type of bearing system is suited for very lightly loaded systems, or ones with any significant load in only one axis and very limited response necessary from the remaining axes. For a horizontal motor coupled to another machine that has a thrust bearing, it can be a good choice to use two active radial magnetic bearings and a passive axial magnetic bearing.
The image below shows Calnetix’s permanent magnet generator rotor with integral expander and magnetic bearing on a single shaft.
Calnetix Technologies specializes in active magnetic bearings and offers Powerflux™ Magnetic Bearings in radial and combination configurations and Xcelflux™ High Performance Magnetic Bearings in a side by side combination configuration. Calnetix’s in-house experts can help you select the proper magnetic bearing type for your application and help you integrate it into your solution.
