FIELDS OF APPLICATION:
1) AEROSPACE APPLICATION :
The only commercial application in this are today are momentum wheel
for satellites and turbo molecular vacuum pumps.
The main reasons for using active magnetic bearings on momentum
wheels for satellite are their capability to operate in vacuum and that
there is no friction and so very limited power consumption, and at last
and unlimited life.
The turbo molecular vacuum pumps such as the one installed on the
European space laboratory are very similar to the regular industry ones
we will talk about.
The major development work going on is related to the application of
the AMB technology to rocket engine turbo pumps and aircraft engines.
The main reason for applying AMB to rocket engine turbopumps are
their better capability to withstand high temperature(liquid hydrogen)
and temperature (steam) and low temperature gradients, their higher
speed of rotation, so better performances of the machine, a as no wear,
no lubrication, and a better reliability.
As far as aircraft engines are concerned, the AMB will allow the concept
of the “all electric engine” and mainly for its higher speed of rotation, so
better performances of the engine, modtly because of their better
control of the rotor dynamics enabling more sophisticated shaft design,
no wear, no lubrication, better reliability, and the cancellation of all
auxiliaries (pumps, filters, pipings) of the actual lube oil system.
For both the applications there is still a lot of development to perform
before commercial products can be offered on the market.
This development is engaged, it mostly concerns the compatibility of the
AMB materials with the environment. Magnetic materials with improved
characteristics in order to lower the bearings size and weight.
Demonstration models are being built. The road is opened.
2) MACHINE TOOL APPLICATION :
The AMB applications to the machine tool industry are mostly related to
electrospindles. These electrospindles ranging from 25 kW 30,000 rpm to 1
kW - 180,000 rpm, are used in milling and grinding (internal grinding and
creep feed grinding). The main reasons for using AMB on machine tool
spindles are: high speed (so higher metal removal rate), no wear and thus
better reliability, no vibrations and so better accuracy, and a permanent
monitoring of the operating conditions (adaptive control). These products
are now standard products manufactured on an industrial basis.
IV-3. Light industry applications
The light industry is a puzzled family of applications. It includes many
different types of machines which common characteristic is to have a light
rotor (less than 50 kg) and not to be a machine tool spindle. Some of the
applications are under development such as the X-ray tube applications,
others are commercial products but manufactured in limited quantities and
on a customized design basis such as the pumps for liquid helium, others
are standard products, manufactured on a large scale basis such as the
turbomolecular vacuum pumps.
The major reasons to use AMB for the suspension of the rotating anode of
X-ray tubes are their higher speed of rotation, so capability to accept higher
flux of X-rays enabling better image, an unlimited life, the capability to
move axially the rotor and to adjust the focusing point of the electron beam
on the anode, and at last no vibration, no noise.
For liquid helium pumps, it is obvious that the major advantage of the AMB
is its capability to operate in a 4 K environment.
Some of the numerous reasons to use AMB for this application are the very
limited heat input (less than 1 W) in the liquid helium, the very high speed
involving a better efficiency, and that there is no thermal barrier, so
possibility of shorter shaft.
For turbomolecular vacuum pumps the main reasons for using AMB are the
fact that there is no pollution of the vacuum by any lube oil or grease (the
auxiliary bearings are dry lubricated) and that they offer a high speed and
so a better level of vacuum, and above all no vibration.
There are many other light industry applications of the AMB such as:
neutron chopper, liquid metal centrifuges, medical centrifuges, rotating
mirrors, textile electrospindle, but today they are either at the
development stage or represent a very limite market. But this may change
in the future.
IV-4. Heavy industry applications
The heavy industry applications are those related to turbomachines and
electrical machines where the rotor mass exceeds 50 kg and for ground (or
sea) based applications.
These machines are mainly compressors and related drivers, and turbo
expanders, as shown on the table hereafter.
MACHINE TYPE QUANTITY POWER RANGE NOMINAL SPEEI) APPLICATION
kW / HP RANGE
TEST COMPRESSORS 7 20 kW to 10,000 rpm to - TEST STAND 4,200 kW
16,000 rpm
INDUSTRIAL 3,100 kW to 3,000 rpm to - PIPELINE COMPRESSORS 31 26,100
kW 15,700 rpm - REFINING - CHEMISTRY
IIFITMEIIC 1 6,000 kW 10,000 rpm - PIPELINE MAT UCUMPRESSORS MIT
IORIZFU 4 5 kW to 3,600 rpm to - TEST STANDS BLOWERS 200 kW 12,000
rpm - HOT HELIUM LOOP
GAS TURBINES 1 12,000 kW / 5,250 rpm - COMPRESSOR DRIVE 16,300 FIP
STEAM TURBINES 1 3,000 kW / 15,000 rpm - COMPRESSOR DRIVE 4,100 HP
IIIRISGENERAIORS 1 5,000 kW / 3,000 rpm - ENERGY RECOVERY 6,800 HP
(BLAST FURNACE GAS) TURBO EXPANDERS 31 200 kW to 18,000 rpm to -
AIR LIQUEFACTION 3,500 kW / 47,000 rpm - DEW POINT 275 HP to 4,700 HP
This domain is the largest one for the application of the active magnetic
bearings and is also the one which has grown the most drastically over the
last three years. About 10 equipment only were delivered by the end of
1986, more than 50 were delivered by the end of 1989. The accumulated
operating hours on 28 machines by the end of 1989 exceeded 200,000
hours. For all these machines the major reasons for utilizing AMB are that
they allow the design of completely oil-free machines (elimination of the
lube oil system), the capability to operate at speeds higher than the third
critical speed (first shaft bending mode). There is no process gas pollution
by lube oil and elimination of fire hazard. It results vibration-free equipment
and permanent monitoring of the operating conditions (preventive
maintenance capability), reduced operating cost (lower losses, reduced
maintenance),and finally better reliability and availability (immediate start
up capability).
a) Compressors and drivers : The major world OEMs have compressors
equipped with active magnetic bearings. The main users are in the field of
pipelines, refineries and chemical plants. The application concerns both
new machines and retrofit of existing machines.
The drivers concerned are steam turbine and power turbines (fed by gas
generators). Development is going on for high speed electrical motors (with
low speed electrical motors a mutliplying gear is necessary and so
reintroduces the lube oil).
b) Turbo expanders :
These machines are used in air separation plants and gas fields for dew
point.
In addition to the reasons already mentioned one major advantage of the
AMB is its capability to withstand a large range of temperatures (-150 °C on
the turbine side, +150 °C on the compressor side) and temperature
gradients. Up to now all the turbo expanders equipped with AMB are in
operation on shore but the first turbo expanders for offshore will be
operating on a North Sea platform by the end of 1990. This shows that this
industry has really become very confident in the technology.
c) Other applications:
There are many other applications of the AMB to the heavy industry. The
most spectacular one is related to 900 MW and 1,300 MW turbogenerators.
These large turbogenerators will be equipped with AMB installed on the
couplings between frames and providing a 30 tons rotating force in order to
reduce drastically the machine vibrations when crossing critical speed in
normal slow down conditions or after a blade loss.
FUTURE SCOPE OF MAGNETIC BEARINGS :
1) Super high speed rail :
Regular high-speed trains can travel at up to 180 miles per hour, but
they generate enormous amounts of friction and heat as they screech
down the rails, leading to mechanical wear and energy loss. By contrast,
maglev trains reach speeds faster than 300 miles per hour while
hovering a few inches above the rail. By eliminating friction, maglev
trains use less energy and can significantly reduce costs. For example
while every high-speed rail passenger pays one dollar for each mile
travelled, maglev passengers could pay as little as 5 cents per mile, says
James Powell, director of the company Maglev 2000 and a co-inventor of
superconducting maglev trains.
A handful of maglev trains already exist in Asia and Europe, and several
new projects may be in the works. Japan’s MLX01 clocked in at 361 mph
in 2003—but China is reportedly developing a train that will double that
speed. And by operating within airless tubes, maglev trains could
potentially reach speeds of several thousand miles per hour. Speeds like
that could make commuting effortless... that is, if the acceleration and
deceleration don’t squash you first.
2) Space launch system :
For years, NASA has been researching the possibility of using the high
speeds of maglev transportation to fling spacecraft into low Earth orbit.
“It would really open up space to human exploration and
commercialization,” Powell says. “It’s something we can’t do now
because it’s too expensive.”
Powell and his colleagues have proposed two generations of space
launching technology. The first is a cargo-only launch track that could be
built into a mountainside to reach a height of 20,000 feet. Magnets
could allow a spacecraft travelling along the track to reach speeds
around 18,000 miles per hour—enough to fly into space. Of course, such
a track would cost an astronomical $20 billion to build. That’s quite an
up-front cost, but some, like Powell, argue that it could actually save
money in the long run. It currently costs $10,000 to launch every
kilogram of payload into low Earth orbit. StarTram could do the same for
less than $50 per kilogram, he says.
And that’s just the first generation. A similar launch track for passengers
might cost $60 billion and would need to be 1000 miles long, 12 miles
high, and use magnetic levitation both to support the track and propel
the train forward at speeds of 5.6 miles per second. Where companies
like Virgin Galactic promise to take passengers into space for $200,000
per person, StarTram may charge as little as $50,000 per person.
3) FLYING CARS :
It’s not exactly what The Jetsons led us to expect, but SkyTran pods
promise to bring maglev transportation to the skies. Each private pod,
suspended from an elevated guideway, could carry three passengers and
would use maglev technology to reach speeds of up to 150 mph.
Theoretically, SkyTran could bring passengers anywhere they wanted to
go along the route of the guideway, without making unnecessary stops
for other passengers. The system could work using technology that is
already available and claims to be able to eliminate congestion while
reducing carbon-dioxide emissions and dependence on foreign oil.
NASA has shown an interest in this technology, and in 2009 it partnered
with Unimodal (the creators of SkyTRan) to evaluate advanced
transportation software.
4) EFFICIENT WIND POWER :
Standard wind turbines convert only 1 percent of wind energy into
usable power, and part of that glaring inefficiency stems from the loss of
energy due to friction as the turbine spins. Researchers at the
Guangzhou Energy Research Institute have estimated that magnetically
levitated turbines could boost wind energy generation by as much as 20
percent over traditional turbines.
The researchers proposed using a colossal turbine with vertical blades
that are suspended above the base of the turbine using neodymium
magnets. Because the moving parts wouldn’t touch, the turbines would
be virtually frictionless and could capture energy from winds as slow as
1.5 meters (5 feet) per second. Maglev turbines could lower the price of
wind energy to less than 5 cents per kilowatt-hour, which is on par with
coal generated electricity and only about half the typical cost of wind
power.
The researchers say that a 1-gigawatt maglev turbine would cost $53
million to build and may require 100 acres of land, but it could supply
electricity to 750,00 homes. In comparison, it would cost hundreds of
millions dollars to build a wind farm of similar capacity using traditional
turbines, and would require 64,000 acres of land to house the 1000
turbines.
