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Inverter optimised motor range delivers higher efficiency

15 September 2010

Lenze has introduced the MF inverter optimised motor range that is able to yield around 5 per cent saving in energy, despite the fact that it is smaller and less expensive than standard ac motors. This energy saving is significant as, power for power, changing from IE1 standard to IE2 high efficiency motors will only deliver about 3 per cent savings.

The twin benefits of higher efficiency and lower purchase cost were achieved by taking standard 4 pole motor designs and optimising them for use at 120Hz, equivalent to a speed of about 3,500rpm. Whist this is not so different from 2 pole motor speeds, Lenze has 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.

The efficiency of these 120Hz optimised MF motors increases by typically 5 or 6 per cent compared with 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.

A 1.5kW MF motor is 71 frame compared with a standard 1.5kW 4-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 be extended to 22kW.

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