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.
2. lA 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.
lConventional 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.
lToday 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.
3.
4. Additional advantages of
magnetic bearings
lFrictionless
lNo need of lubrication
lNo oil contamination
lLow energy consumption
lAble to operate within a wider temperature range
lNo need for seals, pumps,filters, piping, coolers or tanks
lEco friendly workplace
lCost savings
5.
6. lIn 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.
lConventional 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.
lThe 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.
7.
8. Working
lMagnetic 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.
lThe 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.
