Magnetic Bearings And Heat Essay

2098 words - 9 pages

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 ...view middle of the document...

This limited life creates higher maintenance costs, which can potentially offset the original goal of eliminating the costs for lubrication.
The next problem focused on by magnetic bearings is its relatively low direct stiffness. Because the magnetic force is a function of the air gap, the problem aggregates when clearance is raised in order to contain the backup bearings. Surface area of magnetic bearings must be large in order to support the carrying load, which makes them poor choices for applications including high radial or thrust loads.
The last substantial problem of magnetic bearings includes energy consumption. Look at fluid and magnetic bearings. Although fluid bearings require more energy to overcome mechanical losses because of friction, this can be greatly reduced by the use of a well designed externally pressurized bearing. Therefore, a more proper comparison between the two’s energy consumption would be between the additional electrical energy need for magnetic bearings against the energy created by pumps that administers the fluid to the externally pressurized bearing.

General Applications
Although the basis of this paper covers AMBs used in flywheel energy storage systems, there are still other opportunities to use this technology in other industrial settings. The main emphasis is on turbo-machinery; however, there are other applications that active magnetic bearings can be used. These include: machine tools, high-speed motors and generators, momentum wheels, and centrifuges. More specifically, AMBs can be used in a cooling gas compressor for a power laser that cuts metal sheets up to 25 mm. Because the laser needs uncontaminated gas, an AMB is the preferred alternative for this application. AMBs are also used in high speed and high temperature applications such as space equipment, jet engines, and deep sea equipment. Magnetic bearings are chosen not only for their high speed and power density, but also because of the absence of contamination by lubrication or mechanical wear, low energy consumption, and low maintenance costs.
Application
Flywheels seem to have a distinctive appeal as a substitute to traditional energy storage. This is due to the high density of power output, long life-span, and its environmentally friendly nature. These flywheel energy storage systems can be used in cases where large power is needed in a short time, such as in a city bus, shipyard cranes, braking power regenerating, and even for wind power and smart grid energy storage.
Let’s take a closer look at one specific application of the Flywheel Energy Storage System in a locomotive system.The flywheel offers acceleration and power to the entire system to assist in the overall speed and acceleration of the train itself. This takes pressure off of the alternator, allowing increased efficiency and maximum reliability. When the train activates its brakes, energy is conserved in the flywheel through electrical cables, where it is saved inside a...

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