Magnetic Bearing – Working , Advantages and Applications
Introduction to Magnetic Bearing
A magnetic bearing is a type of bearing that supports a load using magnetic levitation. Magnetic bearings support moving parts without physical contact. For instance, they are able to levitate a rotating shaft and permit relative motion with very low friction and no mechanical wear. Magnetic bearings support the highest speeds of all kinds of bearing and have no maximum relative speed.
Magnetic bearings are used in several industrial applications such as electrical power generation, petroleum refinement, machine tool operation and natural gas handling. They are also used in the Zippe-type centrifuge,for uranium enrichment and in turbomolecular pumps, where oil-lubricated bearings would be a source of contamination.
Construction Of Magnetic Bearing :
The Hardware consists of an electromagnet assembly, a set of power amplifiers which supply current to the electromagnets, a controller, and gap sensors with associated electronics to provide the feedback required to control the position of the rotor within the gap. The power amplifier supplies equal bias current to two pairs of electromagnets on opposite sides of a rotor. This constant tug-of-war is mediated by the controller, which offsets the bias current by equal and opposite perturbations of current as the rotor deviates from its center position.
Working of Magnetic Bearing :
An active magnetic bearing works on the principle of electromagnetic suspension based on the induction of eddy currents in a rotating conductor. When an electrically conducting material is moving in a magnetic field, a current will be generated in the material that counters the change in the magnetic field (known as Lenz’ Law). This generates a current that will result in a magnetic field that is oriented opposite to the one from the magnet. The electrically conducting material is thus acting as a magnetic mirror.
Advantages of Magnetic Bearings
• Magnetic Bearings are free of contact and can be utilized in vacuum techniques, clean and sterile rooms, transportation of aggressive media or pure media
• Highest speeds are possible even till the ultimate strength of the rotor
• Absence of lubrication seals allows the larger and stiffer rotor shafts
• Absence of mechanical wear results in lower maintenance costs and longer life of the system
• Adaptable stiffness can be used in vibration isolation, passing critical speeds, robust to external disturbances
Classification of Magnetic Bearings
- According to control action
- According to Forcing action
- According to Sensing action
– Sensor sensing
– Self sensing
- According to Load supported
– Axial or Thrust
– Radial or Journal
- According to Magnetic effect
– Electro magnetic
– Electro dynamic
- According to Application
– Precision flotors
– Linear motors
– Levitated rotors
– Bearingless motors
– Contactless Gear trains
Applications of Magnetic Bearings
•Turbo molecular pumps
•Molecular beam choppers
•Contact free linear guides
•Variable speed spindles
•Elastic rotor control
•Test rig for high speed tires
•Magnarails and maglev systems
•Gears, Chains, Conveyors, etc
•Energy Storage Flywheels
•High precision position stages
•Active magnetic dampers
•Smart Aero Engines
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