machine building & automation - Industrial Technology Magazine

DRIVES, MOTORS & CONTROLSElectric MotorsA new way to save energyInverter optimised motors from Lenze approach IE3efficiency levels, at a cost that is actually lower thanstandard AC motors. The motors deliver additional benefitsof long service and an extremely compact designAlarge gap exists between standard AC motortechnology and that of servo motors. StandardAC motors have low cost, moderate efficiencyand suit mains or frequency inverter operation.Servo motors with rare earth permanent magnettechnology are more efficient but much more expensive.Now Lenze have introduced their MF inverter optimisedmotors positioned in this gap. MF motors can not onlyyield around 5% saving in energy, but also additionaladvantages of smaller dimensions and a purchase costthat is actually lower than standard AC motors. Theenergy saving of 5% is significant (at similarpowers changing from IE1 standard toIE2 high efficiency motors will onlydeliver about 3%) leading to long termsavings and reduction in greenhousegas emissions.Lenze has achieved the twin goals ofhigher efficiency and lowerpurchase costs by takingstandard 4-pole motordesigns and optimising them for use at120Hz, equivalent to a speed of about3500rev/min. Whist this is not sodifferent from 2-pole motor speeds,Lenze have taken steps to ensure along service life. Special shaft sealsare fitted for running at the higherspeeds, and high temperature greaseis used in the bearings. In most casesthe high output speed is not directlyusable, and motors are generally suppliedwith a gearbox.Lenze have a full range of inlinehelical and right angle bevel, helicalbevel and helical worm gearboxes. There is aslight decrease in gearbox efficiency at thesehigher input speeds, but this is more than compensatedby the motor gains.The efficiency of these 120Hz optimisedMF motors increases by typically 5 or 6%compared to a standard 4-pole motor. Forexample at 0.75kW the efficiency ispractically 80% and close to the IE3efficiency level which becomes compulsory in2015. The higher speed increases the rated powerdelivered by the motor. This in turn allows the size of themotor to be reduced by one or two frame sizes leadingto lower purchase costs. For example a 1.5kW MF motoris 71 frame compared to a standard 1.5kW pole motorwhich is 90 frame. Moreover the smaller size meanslower inertia and more dynamic drives. The performancetakes a step towards servo levels with high accelerationand deceleration. Full torque is available over a 1:24speed range.Freestanding or geared motorsCurrently the MF motor is available from Lenzefreestanding or as a geared motor for use with the new8400 motec inverter which can be terminal box or wallmounted. Powers up to 1.5kW were released in the firsthalf of 2010; this autumn the power range will extendto 22kW and use will also be possible with all cabinetmounted inverters of the Lenze 8400 range. A full rangeof options can be added to MF motors This includesspring applied brakes for stopping and holding,incremental encoders, blowers to extend the operatingrange and plug connectors. The new Lenze MF motorswill not suit every application. Their strength lies in lowto medium powers and where output speeds from 60 to500rev/min are required. Here theygive nothing but benefits withreduced energy bills, reducedpurchase costs and increaseddynamic performance.www.lenze.co.ukFor the very latestproduct information, most up todate industry news, plus usefulcompany profile information,visit the pages of IndustrialTechnology online atwww.industrialtechnology.co.uk36INDUSTRIAL TECHNOLOGY • November 2010