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A new way to save energy

A new way to save energy
Inverter optimised motors from Lenze approach IE3 efficiency levels, at a cost that is actually lower than standard AC motors. The motors deliver additional benefits of long service and an extremely compact design.

A large gap exists between standard AC motor technology and that of servo motors. Standard AC motors have low cost, moderate efficiency and suit mains or frequency inverter operation. Servo motors with rare earth permanent magnet technology are more efficient but much more expensive. Now Lenze have introduced their MF inverter optimised motors positioned in this gap. MF motors can not only yield around 5% saving in energy, but also additional advantages of smaller dimensions and a purchase cost that is actually lower than standard AC motors. The energy saving of 5% is significant (at similar powers changing from IE1 standard to IE2 high efficiency motors will only deliver about 3%) leading to long term savings and reduction in greenhouse gas emissions.

Lenze has achieved the twin goals of higher efficiency and lower purchase costs by taking standard 4-pole motor designs and optimising them for use at 120Hz, equivalent to a speed of about 3500rev/min. Whist this is not so different from 2-pole motor speeds, Lenze have taken steps to ensure a long service life. Special shaft seals are fitted for running at the higher speeds, and high temperature grease is used in the bearings. In most cases the high output speed is not directly usable, and motors are generally supplied with a gearbox. Lenze have a full range of in-line helical and right angle bevel, helical bevel and helical worm gearboxes. There is a slight decrease in gearbox efficiency at these higher input speeds, but this is more than compensated by the motor gains. 

The efficiency of these 120Hz optimised MF motors increases by typically 5 or 6% compared to a standard 4-pole motor. For example at 0.75kW the efficiency is practically 80% and close to the IE3 efficiency level which becomes compulsory in 2015. The higher speed increases the rated power delivered by the motor. This in turn allows the size of the motor to be reduced by one or two frame sizes leading to lower purchase costs. For example a 1.5kW MF motor is 71 frame compared to a standard 1.5kW pole motor which is 90 frame. Moreover the smaller size means lower inertia and more dynamic drives. The performance takes a step towards servo levels with high acceleration and deceleration. Full torque is available over a 1:24 speed range.

Currently the MF motor is available from Lenze freestanding or as a geared motor for use with the new 8400 motec inverter which can be terminal box or wall mounted. Powers up to 1.5kW were released in the first half of 2010; this autumn the power range will extend to 22kW and use will also be possible with all cabinet mounted inverters of the Lenze 8400 range. A full range of options can be added to MF motors This includes spring applied brakes for stopping and holding, incremental encoders, blowers to extend the operating range and plug connectors. The new Lenze MF motors will not suit every application. Their strength lies in low to medium powers and where output speeds from 60 to 500rev_/min are required. Here they give nothing but benefits with reduced energy bills, reduced purchase costs and increased dynamic performance.
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