As one of the largest consumers of electrical energy, the AC induction motor has enormous potential to demonstrate savings. A recent development brings together the technology of the AC induction motor with that of permanent magnet servo motors. It offers to contain running costs while promising to pay for itself many times over.
The performance characteristics of a new hybrid motor based upon an AC induction motor with that of permanent magnet servo makes it ideal for applications that involve continuous duty with variable load across its full speed range. Under such conditions the motor could offer savings of up to 80% on energy costs. This is the aim of manufacturer, Lafert Group who believe that key applications that could benefit significantly from the motor’s optimum performance range are pumps, compressors and fans.
What makes Lafert’s ‘HP'(High Performance)motor particularly attractive for pump, fan and compressor OEMs – in addition to the operating savings–is the fact that for simple applications where volumes are involved, the permanent magnet motor solution becomes a genuine financially viable alternative to the conventional AC induction motor and frequency converter package.
The company also believes that the enhanced performance characteristics of a new high performance motor would permit it to offer smaller frame size solutions and weight savings of around 50%
Frame size comparison between a standard AC motor and a HP motor.
Further, when combined with the special sensorless drive, the motor’s operation can be fine tuned to match an application’s specific requirements so as to maximise efficiency. Similar control can be achieved with a standard servo drive when an
Frame sizes and power outputs comparison (2 poles – 3000 min -1).
1) EFF1 Class definition value according to CEMEP voluntarty agreement
2) Average catalogue data
3) Nema Premium efficiency level according to NEMA MG-1
appropriate transducer (encoder, resolver etc.) is fitted. Lafert claims that the HP motor extends the benefits already being obtained from the use of inverter controlled motors by the pump industry. While inverters enable pumps to operate at optimum efficiency according to duty and flow requirements, instead of working on an on/off basis, the new HP motor is designed to add significantly higher efficiency to the drive package whilst delivering constant torque across all driving speeds Unlike the conventional AC induction motor, the rotor of the HP motor experiences no losses because it employs brushless, permanent magnet technology.
Also, the stator currents are lower, consequently generating lower losses due to low current demand (Joule effect), which in turn results in reduced temperature rise for both the windings and bearings. These low temperature rises can go on to eliminate the need for a cooling fan and its related losses. Ultimately, the sum of these minimised heat gains provides the options of higher running speeds or extended bearing life, extending flexibility of operation or reducing routine maintenance needs.
By combining these two motor technologies,it is expected that the HP motor has achieved substantial efficiency advantages over conventional AC induction motors, including EFF1 and even Premium Efficiency machines. This is manifested by constant and superior efficiency across the whole speed range and under variable load.
For an example of superior efficiency and size advantage, an IEC 71 frame 2.2 kW, 2-pole HP motor from Lafert offers an efficiency of 91.5% while similarly rated Premium (IE3) motor would be a 90 frame and operate at 86.5% efficiency. As an illustration, against standard EFF1 motors, a 71 frame HP motor covers conventional 80 and 90 frame size ouptputs. Further examples of motor comparisons are shown in the table above.
The motor’s dimensions and configurations are not restricted to IEC frame formats or conventional servomotor dimensions – although it is acknowledged that designs based upon these established standards will be the most commercial. However, in order to give the best possible flexibility for the OEM, the motor frames can be tailor engineered to suit specific requirements. Options include a long stator pack to achieve low-centre height similar to ‘spindle’ type motors or a short stator pack similar to ‘pancake’ type motors which can be used to provide direct drive and eliminate the need for methods of mechanical transmission and speed reducers.
The flexibility of the motor allows many alternatives to be explored with current developments including water or oil cooled options. Further, there is the option to specify if the drive unit is either mounted upon the motor, saving space and cabling, or is located remotely in a system control cabinet.
Obviously, where such specialised engineering is required a high level of involvement on the part of the OEM would be necessary as would a significant production volume. The new HP motor offers the potential of achieving significant savings on running costs from a smaller motor that has been engineered for purpose and which is cooler and quieter, reducing space demands while enhancing work environments.
Lafert specialises in engineering motors both for specific customer needs and for niche markets with some 90% of the company’s production being specials. It is from this scope of engineering expertise which embraces AC induction motors and brushless permanent magnet servo motors that the company has been able to draw upon in-house know-how to harness the strengths of the two – such as the AC induction motor’s standard stator and the surface-mounted permanent magnet rotor from the brushless servo motor.
“The new ‘HP’ motor is a product targeted particularly at the OEM whose customers are becoming increasingly concerned about energy efficiency and for applications where size is an issue,” said Luca Trevisiol, International Sales Director for Lafert. “With operating costs for the end user going up, manufacturers that can offer such energy savings that the HP makes possible will have a very attractive sales proposition.”
The new High Performance motors from Lafert are available for both single and three phase supply with ratings 0.75 – 2.2 kW, 200 – 240 V 50/60 Hz and 0.75 – 22 kW, 380 – 480 V 50/60 Hz, respectively.