Permanent Magnet Couplings & Adjustable Speed Drives
EP Editorial Staff | July 16, 2012
Perhaps it’s time to expand your motor-control horizons.
Power is expensive. It really doesn’t matter what you do: refine crude oil, make paper, produce electricity or mine and process ore, a significant portion of your total cost-of-goods-sold is tied up in the power you need to run your operation. Add to this the recent unrest in the world’s oil-producing regions, and the result is clear: Power is expensive!
A recent study showed that approximately 23% of the electricity consumed in industry is used to run fans, pumps, and blowers. The industrial world has known for years that the use of motor-speed control can reduce the power required by such equipment by up to 60%. Unfortunately, only a fraction of possible applications have leveraged this technology. And, in applications where adjustable speed is called for, the process industry has basically had few options to call on…
The introduction of Permanent Magnet Couplings and Adjustable Speed Drives manufactured by MagnaDrive, a U.S. corporation based in Bellevue, WA, has given the process industry the option it needs to significantly reduce energy consumption while, at the same time, greatly improving the reliability and performance of the process itself.
Rare earth magnets are more common than many end-users may think—they’re found in many consumer products including computers and automobiles. When originally discovered, scientists called certain elements “rare earths” because they believed they were extremely rare. Over time, however, it became apparent that these rare earths were often plentiful. First introduced to the market during the 1980s, rare earth magnets made of neodymium/iron/boron (NdFeB) create the highest magnetic energy of all permanent magnets, permitting a small size coupled with high torque transmission capability. NdFeB magnets can operate in extreme conditions up to 300 F and have a half-life of more than 20,000 years.
MagnaDrive’s Permanent Magnet Couplings consist of two parts. The first piece, a set of copper conductor plates, is connected to the motor shaft; the second piece of the coupling is a rigid assembly of NeFeB magnets, which is connected to the load. During operation, the magnet assembly is held at a constant 0.125 in. (≈3mm) distance from the conductor plates. Relative motion between the parts creates currents in the conductor that transmit torque across the air gap.
In adjustable-speed applications, the same principle is used. The torque that the motor transmits to its load is controlled by changing the distance between the conductor plates and the magnet assembly. Again, with this technology, no connection exists between the motor and the load.
ASDH 16.5, 75 hp Pump,
Proving the value proposition
In a test-site evaluation, MagnaDrive’s concept for speed control was applied to a 500 hp draft fan model. Compared to available baseline energy information, this technology resulted in a savings of over a million kilowatt hours per year—about one-third of the motor’s annual electricity consumption. In the study, this amounted to about $55,000 annually in energy savings. Over a 10-year period, this would be equivalent to about 24,000 barrels of oil or 7600 tons of coal.
The product’s cushioned-start feature also sets it apart from other speed-control devices. Because the coupling has the unique characteristic of physically disconnecting the load from its prime mover, the motor is able to come up to full speed almost instantly. The load is able to gradually come up to synchronous speed. The advantages of this feature include: reduced wear on motor windings, reduced energy use due to lower in-rush current draw, and reduced wear on the driven components of the system without the added complexity of an electronic soft-start circuit. In addition, some customers found that they were able to reduce the size of the motor being used as a result of not having to overcome the inertia of a stationary load. MT
Note: MagnaDrive welcomes distributor inquiries.
According to MagnaDrive, its products help save energy by releasing the stress and friction in the system due to misalignment, thermal expansion and vibration. The MagnaDrive air gap accommodates some misalignment and system thermal growth. The motor wastes no energy deforming the shaft or adding load to bearings and seals. Energy lost due to friction in traditional couplings and in bearings, seals and other rotating equipment systems is minimized because the air gap prevents vibration transfer.