advances in magnetic bearing technology, including controls miniaturization,
higher levels of simplicity and integrated product solutions, plus the overall
machinery trend to more directly drive machines without gearboxes, are
overcoming past limitations inherent to magnetic bearings. As a result,
magnetic bearings are replacing oil-lubricated bearings for many new types of
machines in a variety of industries.
you look at the megatrends in the marketplace, the focus is energy efficiency
and cleaner, more reliable systems," says Troy Jamison, senior vice president
for business development at Synchrony Inc. "Magnetic bearing
technology aligns with both of those trends and provides unique solutions."
limiting frictional losses, systems become more efficient and the need for
toxic lubricants is eliminated. For example, in large oil and gas machines such
as gas compressors, oil-lubricated bearings (which require a high-pressure
lubrication system) can be eliminated.
Old Tech Finds New
says the concept of magnetic bearings has been around 40 years, but recent
improvements have overcome historical issues and changed how these bearings are
perceived by engineers. The traditional view has been that magnetic bearings
are very large and used primarily in niche applications. This has historically
meant that, though they may be suitable for labs, they were not a very good
solution for real-world applications because of size, cost and complexity of
key factor driving magnetic bearing applications is interest in directly driven
machines where there is a high-speed motor coupled to the fluid machine," says
Jamison. "Instead of needing gearboxes and oil lubrication systems, you can use
a more efficient system that incorporates a high speed, permanent magnet motor
and magnetic bearings."
Users are adopting the bearings into refrigeration
compressors for chillers and HVAC, for example. Energy recovery applications
are another growing area using high speed generators that run waste heat
through an organic Rankine cycle to generate electrical power (The Rankine
heat into work. The heat is supplied externally to a closed loop, which usually
uses water). In addition, magnetic bearings are increasingly used in
general industry pump applications to help reduce maintenance costs.
says the typical life of a magnetic bearing is about 10 years. So if a pump is
rebuilt every three years, typically the first thing to replace is the bearings
which can be costly if the application is in environments where it is difficult
to remove the bearings, such as nuclear applications, oil and gas or subsea
A Mechatronic Design Solution
bearings are really the confluence of both mechanical and electrical devices.
Traditionally systems have used a large electrical enclosure to house the
analog sensor electronics, A to D converters, digital processor, D to A
converters and power amplifiers.
advancements have digitized the whole drive train, and the digital controllers
have become much smaller. The control cabinet has been dramatically reduced in
size, and magnetic bearings are being applied in applications other than for
very large machines, expensive compressors or turbines.
2009, Synchrony introduced its Fusion magnetic bearing, where the controller is
integrated directly into the bearing housing. No external controller is
required, just a 48V input into the bearing itself for providing electrical
power to levitate the shaft.
an older system designed for a compressor, the application would use a 3,600
rpm motor running at 300 or 400 hp gearing to run the compressor wheel at
20,000 rpm. To achieve those speeds, the compressor would also need oil-lubricated
bearings help remove components, and the train now looks like a direct machine
with a high-speed, permanent magnet motor that uses magnetic bearings," says
Jamison. "The application doesn't need the gearbox, the oil lubrication system
and the compressor wheel mount directly on the shaft of the motor."
a complete drive train viewpoint, that is where you really begin to reduce
components in the system and it becomes a more simplified, more efficient machine,"
at these developments from a design engineering point of view, the real
solution is in lower costs and the elimination of oil lubrication systems'
maintenance cycles. The overall smaller size of the system makes magnetic
bearings more suitable for a wider range of applications.
magnetic bearing controller uses electromagnetic coils around the stator (which
is the fixed component of the magnetic bearing). For a radial bearing configuration,
laminations on the shaft itself are attracted by the magnetic field induced by
the electromagnetic coils. Position sensors also monitor the shaft, and
clearances are measured in thousandths of an inch.
the magnetic bearing levitates the shaft, and it starts to spin driven by the
motor and VFD (if one is used in the application). The shaft is levitated and
running up to speed, but the load is varying.
may have side loads or other forces acting on the shaft depending on the driven
equipment; regardless the position sensors check to determine if the shaft has
moved from the center position 15,000 times per second," says Jamison. "When
there is movement, the controller readjusts the fields in the electromagnets
using currents flowing from the power amplifier and into the electromagnets to
restore the shaft position."
reason behind increased interest in magnetic bearings is the availability of
information from them. This means that users can now monitor what forces are acting
on the shaft. Over time, an application may experience higher degrees of
vibration, high side loads and be able to determine what forces are acting on
the shaft, temperatures and the position of the shaft.
these products are Ethernet-enabled, engineers can use Ethernet communications
and direct the data into preventive maintenance models. By monitoring real-time
data based on what is happening at the shaft itself - not a sensor on the
casing of the motor on the machine, users can monitor the forces acting on the
shaft. For instance, changes to an impeller due to mechanical failure or
build-up of process material are the kinds of things that can be viewed by the
magnetic bearing using the Ethernet connection.
says this kind of health monitoring is the added benefit of using a magnetic
bearing over other methods of high-speed bearings.
Fusion line of magnetic bearings is Synchrony's most integrated product, says
Jamison, because of its merging of mechanical and electrical components. "This
product (Fusion) is similar to VFDs that used to be mounted in a control room,
but now they are mounted directly on the motor, or integrated with the motor,"
he says. "It's the same advantage as moving a controller closer to a machine; in
this case the controller is right on the bearing housing itself."
type of integrated, mechatronic solution is increasingly becoming the reality
for industrial equipment design. After all, any solution that allows OEM
machine builders to do away with the need for feed-throughs or cabling to make
connections to the controller, because it is now resident on the bearing
housing, is a major design improvement.