Motors develop to greater efficiencies and cost savings

Tom Shelley reports on how motors for many purposes are becoming more efficient and how this is being achieved.

Electric motors are becoming more efficient, partly because of legislation and partly because of the need to save money in a world where energy costs can be expected to increase long term. Motors conforming to IE2 have to be in all new equipment in the EU from June 2011 to be followed by IE3 in about 2014. Motors in equipment sold in the USA and Canada have been required to conform to what amounts to IE3 specifications since December last year. IE4, which is still in the R&D stage is probably beyond the capabilities of present types of induction motor, but motors already exist and are on sale using permanent magnets that fulfil these much more arduous requirements, and the move to applications such as the more widespread use of hybrid and electric vehicles means that rapid advances are being made in all relevant technologies. Robin Cowley, industrial marketing manager for Baldor said, "We're sending an SOS message to European OEMs that if they do not start considering the impact of motor efficiency regulations immediately, there could be negative implications for their sales and market share. And when OEMs think about the upgrade to IE2 efficiency levels, we are also suggesting that they consider their strategy for the IE3 efficiency level that's coming down the track because if they don't, their competitors might, and steal a march." In fact if selling to the USA and Canada, it already has come down the track, since the USA's Energy Independence Security Act mandates a minimum efficiency level of NEMA 'Premium', which is equivalent of IE3, for motors imported into the USA. For those who realise that they must incorporate higher efficiency motors into their designs, it is not just a matter of ordering different motors. Because they tend to have more copper to reduce resistance losses, high efficiency motors tend to be bigger. Their starting characteristics are likely to change and they are likely to be optimised to work with different specification drives. They may in also run faster, changing the downstream transmission. At the same time, because they waste less energy as heat, they run cooler, leading to less expensive ventilation and cooling systems. And finally, because they are better balanced and use better bearings, noise should be less, reducing vibration isolation and acoustic insulation requirements. They do cost more, but payback times, according to Cowley, are about 3.5 years for an 11kW 4 pole IE2 specification motor, run for 8,000 operating years per annum, but only 2.6 years if the specification conforms to IE3. The additional capital cost of IE3 is more than offset by the additional energy cost saving. Despite all the publicity, Cowley believes that around 30% of OEMs are, "Still not aware of the legislation." The IE2 requirements in the EU apply to all 3-phase induction motors in the range 0.75kW to 375kW running at less than 1kV. Flame proof, brake and servo motors are not included. The US legislation, however, applies to all sizes and functions of motors. In the UK, DEFRA is responsible for making the regulations happen, and they are to be policed by the National Measurement Office. While this body may be something of a 'Paper tiger' in the UK, vendors to the USA will find that the same does not apply to the Department of Energy, which recently fined Haier Refrigeration $150,000. As regards future reductions in energy consumption beyond IE3, Cowley comments that, "We don't think we can get much more out of the induction motor" and was of the opinion that the future probably lay with permanent magnet motors. This may of may not be true, but ABB has announced that it is to acquire the Baldor Electric Company, which will give Baldor access to the amorphous metal technology that ABB has for some time been employing in some of their transformers, and which is widely expected to find its way into motors. Amorphous (glassy) metals have been and are very widely used to make transformer cores in both China and India, and we can therefore deduce that if Chinese and Indian business people think it is worth paying the extra price, it must be very worthwhile. Because of their low electrical conductivity and easier and faster magnetisation, their use reduces core losses by between 40% and 70%. They do cost more, and cores have to be made using a 'Step lap' technology, because the material is made by quenching onto a rapidly rotating wheel, and so can only be produced as thin ribbon. ABB has been using the material in oil filled transformers for 20 years and has now brought out an 'EcoDry' range which avoids the need for oil. Saturation, we were told by Ceyhun Sahin, general manager transformer, power products for ABB, is 1.35T instead of 1.75T for iron, making the transformers slightly larger, but because less heat is produced, insulation aging is reduced and the transformers last longer. The alloy used is based on a silicon boron steel, but when we asked about whether work was underway to use similar cores in motors, the answer was, "We will get back to you", which we assume means 'yes', but not yet ready for commercialisation. Quite ready for commercialisation, however, is a new motor technology from Dr Sab Safi and SDT Technology. This latest concept is a combined motor and differential unit for small battery electric vehicles. Although it is not currently possible to go into details in order to protect the integrity of the intellectual property, we can reveal that it is based on a torque motor. The intention is to have high torque, low-speed motors that can directly drive wheels. Dr Safi observes that torque motors have a relatively large diameter to length ratio and a short axial length. They can also, he says, "Simultaneously have both a very large outer diameter and inner diameter, resulting in a motor that is a thin ring. One important output of this characteristic is that the mass is quite low as a function of the diameter. Also the large diameter allows a very high torque to be developed." The architecture consists of a stator winding employing a high pole count, which permits high copper utilisation, minimising energy loss and cost, and a hollow rotor on which rare earth permanent magnetics are mounted on the outer circumference. The rotor is connected to the differential housing and the whole unit is mounted between the rear wheels. Dr Safi observes that eddy current losses in a brushless motor increase with increased number of pole pairs, so that a torque motor should be best used at below 1,000 rpm, but this is, "More than adequate for many traction drives." He says that his designs can achieve continuous torque to weight ratios of up to 13.5Nm/kg using natural convection and up to 31Nm/kg with fluid cooling. Stepper motors too can be made more efficient and a new range from Astrosyn boasts a 30% improvement in efficiency, thanks to being made by injection moulding. This makes more space available internally so that more windings can be used, resulting in a 27% reduction in temperature rise. The manufacturing method also enables greater precision in assembly, leading to significantly improved step angle accuracy, typically 2.5%, and locks the stator and windings into a single unit, eliminating noise cause by vibration. Typical applications include: security cameras, stage lighting, medical equipment, semiconductor manufacture and office automation products such as scanners and printers. Motors Briefs Rugged solutions from DC motors DurA-Tek brushless DC motors offer compact and rugged solutions for demanding high duty cycle applications in heavy-duty transit buses and construction and off-highway vehicles. Their 3.0-inch outside motor diameter and standard 2-wire electrical hookup enable these motors to replace similarly sized brush-commutated DC versions and deliver relatively higher performance and extended life. The motors are designed for 40,000 hours of service. The motors integrate drive electronics promoting enhanced motor controllability in a smaller, lighter package. The "smart" onboard motor controls and advanced electronic design deliver a wide range of key features, including multi-speed operation, over-current control, locked-rotor protection, reverse polarity protection, transient over-voltage protection, and over-temperature shutoff. New motors drive medical applications maxon motor has expanded its range of sterilisable drives for high speed medical applications with the introduction of the new 50 watt versions of its EC 13 and EC Size 5 brushless motors. Both drives, produced in accordance with Medical Standard ISO 13485, offer high performance with extremely low noise and vibration, generating very little heat and making them ideal for medical use. The upgraded 50 watt versions offer speeds of up to 90,000 rpm with efficiencies now reaching 90%, whilst delivering 50% more torque at 8 mNm when compared to the standard 30W drive. This additional performance is provided with only 11 mm of extra length, making the new 50W drives particularly suitable for a range of surgical procedures where there is a need for increased power in confined spaces. Compact, high-efficiency motors from Nord Nord Drivesystems now provides IE2-compliant three-phase motors delivering outputs as low as 0.55 kW. These models are ahead of the new European energy-saving standard: from June 2011, the IE2 standard is compulsory for motors delivering outputs =0.75 kW. Similar regulations apply in almost all other markets, with exceptions only in a few Asian countries – in China for instance, the GB18613 norm requires Grade 2 efficiency, a grade similar to IE2, even for small motors = 0.55 kW, starting in July 2011. For energy-saving motors, Nord uses more active material and higher quality sheet metal with smaller losses and increases the copper filling factors. The improved design results in greater power reserves. Consequently, motors with a smaller power rating can be used in many applications, creating additional efficiency benefits. These performance improvements stem from a reduced partial load range, in which efficiency is necessarily lower. Design Pointers • IE2 motors are required to be in all EU industrial machines by June 2011. The US and Canada already require efficiency performances equivalent to IE3 • Amorphous metals, already being used for core materials in transformers are likely to make their way into motors • Wheel motors for small electric vehicles have been developed that are based on torque motors combined with differentials • Stepper motors that are more efficient and quieter than their predecessors achieve these advantages by being injection moulded