Magnetic Bearings and Heat Essay

Magnetic Bearings and Heat Essay

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One of the main problems associated with the design and application of active magnetic bearings is excessive heat. Heat is generated by two primary mechanisms. The first heating source comes from eddy current loss. Eddy currents are electric currents driven within conductors by a dynamic magnetic field located in the conductor. Eddy current loss in a magnetic bearing are caused by the rate of change in the magnetic field. The relative motion creates a rotating flow of current inside the conductor, which leads to efficiency loss. The second source of heat comes from wire resistance in the coils. Because copper wires have a resistivity that increases with temperature, heating can get out of hand extremely fast if there is no way to dispose of the surplus of heat. A magnetic bearing’s excessive heat can even be caused by having no lubrication. Although a magnetic bearing’s lubrication-free operation provides for a wear-free system, there is nothing that can now cool down the bearing. Heat buildup can create many serious problems such as destroying the magnetic bearings by breaking down the coil insulation and causing short circuits. Excessive heat can also cause the inability to carry the desired load in the application.
Another important problem produced by magnetic bearings is limited fault protection. Machines with magnetic bearings always install a set of backup bearings, which are usually rolling element bearings. These backup bearings can produce their own set of problems. The placement of backup bearings can modify the machine’s rotor dynamic behavior. Backup bearings also have a very limited life. When a magnetic bearing fails, the backup bearing has to catch up in speed to the rotor in as little as a millisecond. Typically...


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...ing’s inadequate direct stiffness was also formerly mentioned. A bearing’s low direct stiffness occurs when the clearance is increased in order to contain the conventional backup bearings. This causes magnetic bearings to provide a large surface area to be able to support a moderate load. (Add innovation to low direct stiffness)
Conclusion
Magnetic bearings have provided us with new ways and innovations to run various systems such as space equipment and energy storage systems. Magnetic bearings have given people a way to run systems unlike any other bearing system. They have implemented a lubrication free and maintenance free system, which in turn provides a much cheaper and unblemished system. Although magnetic bearings are not perfect and are limited in specific areas, we believe they have the potential to revolutionize the field of mechanical power transmission.

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