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A magnetic bearing consists of two concentric ring shaped permanent magnets (rotor and stator). The rotor is made
to suspend over the stator without direct contact each other by using special magnetism. The advantage of the
bearing is apparently no mechanical friction between rotor and stator. Therefore, magnetic bearings are widely
used in industries, for instance, the aerospace technology, ultra high speed rotation machine and inductive
(mechanical) energy meter.
    The rotating part of inductive (mechanical) energy meter needs a bearing. Traditionally, this bearing is made of jewel. Initially, the mechanical friction of new jewel bearing is very small. As a result, the start electrical current is also very small. But the fatal shortage of jewel bearing is that it cannot resist abrasion. After 2-3 years of working, the friction retardation of the bearing makes the energy meter lose the measuring accuracy of of electricity. In order to overcome the weakness of jewel bearing, scientists thought of using magnetic bearing to replace it. The practice has proved the magnetic bearing can extend the life of energy meter to 20-30 years without influencing its measurement accuracy. The magnetic bearing can be divided into two categories as per the arrangement of magnets in the bearing. The first is Magnetic Thrust Bearing (MTB), the second Magnetic Suspension Bearing (MSB). MTB is installed under the rotating part of energy meter. The stator of MTB pushes the rotor which is connected with the shaft of rotating disk in the air. However, MSB is installed over the rotating part of energy meter. The stator of MSB attracts the rotor which is connected with the shaft of rotating disk in the air. Axially there is no mechanical friction between the stator and rotor for either MSB or MTB. The starting performance of MSB is better than MTB. But there is much more magnetic material needed for MSB than for MTB. The MSB is practically less adopted in order to reduce cost. Therefore, the widely used type is MTB. According to whether the stator and rotor are paired and encapsulated before delivery, magnetic bearings can be further divided into three types: encapsulated type, open type (no pairing and encapsulation before delivery) and detachable type. Whether the bearing is paired and encapsulated or not is not the decisive factor of its performance. The encapsulated bearings may have a little difficulty when installation. The detachable bearings have the advantage of the other two types. |
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