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11/08/2011
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With minimum motor efficiency levels having recently come into force, Paul Fanning looks at the cutting edge.
 Mandatory minimum efficiency levels for low-voltage electric motors are now in force across the European Union. Since 16 June, most general-purpose motors in the range 0.75–375kW bought for use in Europe must achieve a minimum efficiency level of IE2, according to the classification drawn up by the International Electrotechnical Commission (IEC).
The requirements cover two-, four- and six-pole motors for use on 50 and 60Hz supplies. Some motors, such as those designed for use in explosive atmospheres, are currently excluded from EU MEPS but some suppliers, including ABB, expect that these machines will eventually have to comply with IEC 60034-30 and are therefore giving them IE markings.
The second stage of the EU MEPS scheme will come into force from January 2015, when motors with output powers above 7.5kW will have to achieve IE3 efficiency levels – or IE2 if used with variable speed drives. The third stage, which applies from January 2017, will extend the scheme to include motors with outputs down to 750W. However, as is usual in such matters, the regulation lags behind the technology by some distance.
While IE2 is now the minimum that can legally be sold (with IE3 not coming into force for four more years) there are already a number of motors that have been launched that are billed as meeting the IE4 'super premium' level of efficiency. Of course, the slight difficulty with this is that the IEC has not yet even defined what IE4 means, let alone outlined any plans to make it mandatory. That aside, however, there are motors available that offer previously unimaginable levels of efficiency.
WEG beat the rest of the field in this department when it launched its WQuattro range last year. WEG's new WQuattro line of super premium efficiency motors employs a hybrid design to achieve the highest efficiency in the market, exceeding the requirements of the impending IE4 Super Premium Efficiency classification across its entire output range.
The WQuattro line has been developed for users who consider energy saving a major priority. It is an environmentally- friendly range of motors that, due to its highly efficient performance - with no energy (joule) losses from its rotor - demands less energy from the grid. For the user, this translates into lower total cost of ownership, a reduction in CO2 emissions, and a faster return on investment.
The WQuattro is a hybrid motor integrating a conventional three-phase distributed winding, and a rotor with an aluminium cage and internal high energy magnets. This combination makes the WQuattro ideal for direct- on- line starting and acceleration up to synchronous speed. With this type of operation the motor speed does not vary with load, despite overload variations, or cases of voltage drop, as long as the mains frequency is kept constant.
In addition, there is no requirement for positioning/speed sensors, or special protection relays, and the low bearing temperatures that result from synchronous operation also ensure longer life and reduced maintenance for the motors. Where the speed of the motor needs to be adjustable, the WQuattro can be used with inverters , offering an extended speed range with constant torque.
In addition inverter control also offers the key benefit of multi-motor operation: i.e. several motors can operate in synchronism fed by the same inverter. The WQuattro line offers interchangeability with existing installations. It employs the same frame size for output as standard induction motors, and so is easy to retrofit into existing applications. The WQuattro line is available in 4 and 6 pole versions, with frame sizes from 80 to 132S, and outputs of 0,37kW up to 7,5 kW.
The motors benefit from class F insulation, and are suitable for operation on 230/400, 400/690 or 525V supplies. ABB has entered the 'super premium' market with the launch of a new motor based on an innovative rotor with no windings, offering high efficiency and high power output. Using synchronous reluctance technology, the new motor is robust and has practically no losses.
The motor is offered as a complete package together with a frequency converter and dedicated software. Juha Silvennoinen, head of ABB's motors and generators business unit, says: "The new rotor is a break-through in motor technology, an achievement that makes it possible to make motors that are much more efficient and smaller than conventional induction motors."
The motor and drive package is offered in two configurations, one that maximises efficiency, the other maximising output. The high efficiency package meets the latest most stringent efficiency level specified by the IEC; class IE4, super premium efficiency. For customers, this means 40 percent less energy losses than a conventional motor.
The motor and drive package is designed specifically for variable-speed drive operation, leading to further energy savings. Thanks to these savings the pay-back time of this package is very short, in many cases less than two years. The second package is configured for maximum output. This motor-drive package offers a power density up to 40 percent higher than in a conventional induction motor. As a result the motor size can be up to two frame sizes smaller than a conventional induction motor, an important benefit for machine builders who often work with stringent space restrictions.
Customers who buy this package get the high power density of an equivalent permanent magnet motor with the robustness of an asynchronous squirrel-cage motor. Because the rotor runs cooler than other technologies, the bearings also run much cooler, making the motor much more reliable. With bearing failure accounting for around 70 percent of unplanned motor outages, customers will appreciate the longer greasing intervals and higher reliability offered by the new motor and drive packages. SEW-Eurodrive also launched an IE4 motor.
Seen at this year's Hannover Fair, it is a line-start permanent magnet motor which can either be connected directly to the power supply or operated with a frequency inverter. The DRU motors are based on AC asynchronous designs, using squirrel-cage rotors that contain permanent magnets.
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Author
Paul Fanning
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