Driving change in electric motors

Growing concern about carbon emissions is motivating industry to develop energy efficient motor solutions that benefit the environment but don't compromise operational requirements. Katherine Crichton writes.

THE current economic downturn, rising global costs and extreme weather conditions combined with the necessary maintenance investments to sustain increased demand, means electricity costs will continue to rise, with an increase of 20% in NSW already on the agenda.

While the price rises are set to lead to increased investment in the renewable energy sector which has obvious long term benefits, until this happens, manufacturers who still haven’t invested in energy efficient technologies will continue to pay.

However, the good news for end users is that the increased demand for high speed, high efficient products is driving an increased focus on more effective motor and drive technologies.

While the use of Variable Speed Drives (VSD) is well under way in industry, it is the move to replace traditional motor types with more advanced motor technologies that is offering exciting production cost savings for manufacturers, particularly in the domestic and commercial chilling and refrigeration sector.

Howard Lovatt, Team Leader for Scientific Devices at CSIRO told Manufacturers’ Monthly, technologies such as brushless permanent magnet and switched reluctance motors are replacing traditional motors because they can offer the same or better operational efficiencies while eliminating maintenance and reliability issues associated with older type motors.

“Brushless permanent magnet drives or brushless dc motors (BLDC) are very similar to the older dc motor, but they offer significant efficiency advantages simply due to the nature of their design,” Lovatt explained.”

With the advent of cheap computers and power transistors, it is now possible to ‘turn the motor inside out’ and eliminate the brushes.

“The permanent magnets can then be placed on the rotor and the electromagnets are moved to the stator.

“Then you use a computer (connected to high-power transistors) to charge up the electromagnets as the shaft turns,” Lovatt said.

“These motors are often called a brushless dc motor to emphasise the fact they are basically the same motor but they have improved efficiency because with the electromagnets on the stator they are very easy to cool.

“Also the elimination of the commutator means there is more room to reduce the electrical loading so this improves the efficiency compared to a traditional dc motor quite considerably.”

While these types of motors are more efficient, a distinct disadvantage of a brushless motor is its high initial cost due to using more expensive permanent magnet materials, but Lovatt says often this cost is recovered through the greater efficiency of the product over the life of the motor.

“Generally the motivation is an economical one. As the price of energy goes up, people can afford to spend more on better motors to get a better payback in a more reasonable amount of time.”

Lovatt believes that advanced motor technologies such as brushless permanent magnet motors will look to replace dc and induction motors in the small to medium-size motor applications, but says in the very high end motor market this transition will take longer simply because the payback isn’t significant enough as yet.

Commercialising the technology

While high speed, permanent magnet motors are more commonplace in industry nowadays, nearly 15 years ago when now R&D manager with Danfoss Turbocor Randolph Dietzel first looked at these types of motors, it was still a largely high cost, unproven experimental technology.

Working together with CSIRO and Lovatt, Dietzel said the initial idea of the project was to eliminate the use of ac drives which incorporated a stepper gearbox to increase compressor’s impeller tip speed hence shaft revolutions as commonly used in centrifugal compressors.

“One of our key initial objectives was to eliminate the gearbox because it presented an oil management and maintenance issue. Worse still, it was a significant system of mechanical loss.

“We replaced it with a high 45,000rpm variable speed high efficiency motor comprising only one moving part (the shaft) which would directly drive the impellers.

“We eliminated the oil management problem by developing in house, frictionless magnetic bearings, further reducing the system losses,” Dietzel explained to Manufacturers’ Monthly.

“If you think about the catalysts back in 1994 when we began the project, such as the Montreal protocol which was all about phasing out ozone-depleting refrigeration gases, that was really the impetus for designing from the ground up, a new, revolutionary compressor for cooling applications,” he said.

“The same motivations exist today in the form of climate ready programs and carbon emission trading schemes etc.

“The point is with all this technology its all about saving energy. It is about doing mechanical refrigeration in a much more efficient way.”

According to Dietzel, the fact that the company was developing the motor for HVAC applications enabled the company to incorporate certain cooling topologies into the motor design that couldn’t be used for most other applications.

“This has allowed us to create a 75kW motor for example which is physically the size of a one horsepower washing machine motor offering a large amount of power density,” Dietzel said.

The project was technically challenging and had a significant incubation period, and while a prototype was running by 1996, the technology was only commercially available much later.

Dietzel said working with CSIRO was a good stepping stone for the company but one of the key obstacles that needed to be overcome was the commercialisation of the technology.

In the end, Turbocor moved to French Canada (Montreal) in order to commercialise the technology and in 2003 formed a joint venture with European company Danfoss, to form Danfoss Turbocor which is now based in the US.

“We moved to Canada for two main reasons: one, we wanted to be on the doorstep of our key market which was north America, but two, the venture capital and all the other funds available in Canada at that time was much more prolific than what we could get in Australia.”

Since then, the company has won many awards for the technology, and its products are sold around the world, including Australia, an irony which isn’t lost on Diestzel.

“Looking back on the project, there nothing in there that we couldn’t have done equally as well or better in Australia but the key challenge at that time was the tyranny of distance – being so far away from your market.

“But we are part of a rapidly advancing global economy and things are a lot different now than they were 15 years ago,” Dietzel said.

CSIRO 02 9413 7412, www.csiro.au.

Danfoss Turbocor Compressors Inc Aust 03 9761-7433, www.turbocor.com.

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