MOTORS AND DRIVES 65
Interior permanent magnets promise ultra high efficiency
Robin Cowley looks at the advantages of permanent magnet motors driven by electronic adjustable speed drives.
T
he International Electrotechnical Commission (IEC) recently set new motor efficiency standard levels under the specification IEC 60034-30. This new standard that has four
levels: IE1 = Standard Efficiency, IE2 = High Efficiency, IE3 = Premium Efficiency, and IE4 which has yet to be named. IE1, 2 and 3 have defined efficiency values for low voltage, three-phase motors from 0.75 to 375kW in 2-, 4- and 6-pole speed ratings. The standard stipulates IEC 60034-2 2007 to
measure these levels. For comparison purposes, the older
standards set by CEMEP (European body of electrical manufacturers), which is now superseded by the new IEC standards, were as follows: CEMEP Eff2 = IEC IE1; CEMEP Eff1= IEC IE2. There was no CEMEP equivalent to the Premium Efficiency IE3 rating. The IEC has yet to formally name and set actual
efficiency levels for the future IE4 level of Industrial low voltage motor efficiency. However, the very high efficiency levels of IE3 are
such that it is unlikely current technology will allow us to build an induction motor to reach significantly higher levels.
Therefore the use of motors with electronic drives is
widely seen as the most likely future to higher efficiency levels that may be called ‘IE4’. Permanent magnet (PM) motors driven by electronic
adjustable speed drives are such a solution. Baldor’s state of the art technology has the magnets embedded within the rotor, called interior or integrated PM (IPM) and achieve efficiency levels well in excess of IE3.
T
he salient-pole, IPM design buries flux-producing permanent magnets within the rotor structure whereas conventional PM motors simply mount the magnets on the
rotor surface. This results in greater torque and power density, lower temperature rise and greater efficiency in the IPM design. IPM motors have actually been in use for some time
on high performance machine tool type applications, but for dynamic response reasons and smaller, lighter package size rather than efficiency. The Baldor design also utilises cooling frame fins
actually formed on the stator laminations to provide optimum cooling, yet still looks like a cast-iron frame motor (picture). As an example a 300kW, 4-pole machine would have
an IE3 motor at ~96.2 per cent efficiency, whereas the Baldor IPM motor is testing up to 98.3 per cent efficient. Other benefits of IPM machines include frame sizes
that are up to five times smaller for the same power ratings, cooler operation, higher speed ratings and lower noise and vibration. n
Enter 65 or ✔ at
www.engineerlive.com/ede
Fig. 1. Baldor's IPM motors utilise cooling fins formed on the stator laminations for optimum cooling.
Robin Cowley is with Baldor UK Ltd, Bristol, UK.
www.baldoreurope.com For Baldor RPM AC motor site, visit
www.reliance.com/products/motors/rpmac/index.html
www.engineerlive.com
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