Magnetic Bearing Technology For High Power Machines

A magnetic bearing is a bearing that balances a load using magnetic flotation. Magnetic bearings support moving parts without any physical contact. Hence magnetic bearings have been utilized by a variety of industrial sectors for over a decade with benefits that include non-contact rotor support, no lubrication and even no friction.

Conventional mechanical bearings physically interface with the shaft and require some form of greasiness, can be replaced by a technology that suspends a rotor in a magnetic field, which eliminates all friction losses.

Today there are two types of magnetic bearing technologies in use. They are Passive and Active. Now the passive bearings are similar to mechanical bearings and don’t need any active control for operation. In active systems, with no contact position sensors can continually monitor shaft position and feed this information to the control system. This in turn is based on the response commanded by the system, flows to the actuator via current amplifiers. These currents are then converted to magnetic forces by the actuator and act on the rotor to adjust position and provide some damping.

Additional advantages of magnetic bearings:

• Frictionless

• No need of lubrication

• No oil contamination

• Low energy consumption

• Able to operate within a wider temperature range

• No need for seals, pumps,filters, piping, coolers or tanks

• Eco friendly workplace

• cost savings

In practice, these attractions are balanced in order to maintain a gap between the shaft i.e. rotor and static parts i.e. stator. The function of the magnetic bearing is to locate the shaft’s rotation axis i.e. in the center, reacting to any load variation or any external disturbing forces.

Floating rotors can boost compressor efficiencies

Conventional centrifugal compressors are based on mechanical gears, low-speed drives and oil-film bearings yielding in high running costs because of their high losses, wear and need to maintain.

The new compressor drive uses a permanent magnet motor, operating at an efficiency of around 97%, to drive a rotor "floating" on magnetic bearings, which spins the compressor impeller at speeds of around 60,000 rpm. These drives experience almost no friction or wear, and need very little maintenance. They also minimize the risk of oil contamination, and result in compressors that are about half the size of conventional designs.

Working

Magnetic bearings are basically a system of bearings which provide non-contact operation, virtually removing friction from rotating mechanical systems. Now magnetic bearing systems have many components. The components consist of the electromagnets, rotors and position sensors. The electronics consist of a set of power amplifiers that supplies current to electromagnets. A controller works with the position sensors which provide feedback to control the position of the rotor within the gap.

The position sensor registers a change in position of the shaft i.e. rotor. This change in position is communicated back to the processor where the signal is processed and the controller decides what the necessary response should be, then initiates a response to the amplifier. This response should increase the magnetic force in the corresponding electromagnet in order to bring the shaft back to center. In a representative system, the radial clearance can range from 0.5 to 1 mm. This process repeats itself over and over again. The rotor on getting closer to the magnet, the force increases. The system needs to continuously adjust the magnetic strength that is being recieved from the electromagnets in order to hold the rotor in the desired position.

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