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Inverter-optimised motors approach IE3 efficiencies

25 June, 2010

Lenze has revealed details of a range of inverter-optimised motors designed to bridge the gap between low-cost standard AC motors and more efficient, but more expensive, servomotors. The new MF motors, which made their UK debut at the recent Drives & Controls Show, are said to deliver energy savings of around 5% compared to standard AC motors, as well as being smaller and at least 20% cheaper.

They are based on standard four-pole motors optimised for use at 120Hz – equivalent to a speed of about 3,500 rpm. While this is similar to two-pole motor speeds, the motors have also been designed for long operating lives. They use components such as special high-speed shaft seals and high-temperature grease in the bearings.

In most cases, the high output speeds mean that it will not be possible to use them directly and they will generally be supplied with gearboxes (as shown above). Although there will be a slight decrease in gearbox efficiency at the high input speeds, Lenze says that this will be more than compensated for by the motors’ gains. The motors can be supplied with in-line helical, right-angle bevel, helical bevel or helical worm gearboxes.

The motor efficiencies will typically be 5–6% higher than standard four-pole motors. For example, at 0.75kW, efficiencies will be almost 80% and close to the IE3 efficiency levels that will become compulsory in 2015. Lenze points out that changing from IE1 standard to IE2 high-efficiency motors at similar power ratings will deliver savings of only about 3%.

The motors’ high speeds boost their outputs, allowing frames to be reduced by one or two sizes, thus cutting costs.

For example, a 1.5kW MF motor has a 71 frame compared to the 90 frame size of a standard 1.5kW  motor. Moreover, the smaller size means lower inertia and more dynamic operation. The performance approaches servo levels with high acceleration and deceleration. Full torque is available over a 1:24 speed range.

Lenze admits that the MF motors will not be suitable for all applications. Their strength lies in low-to-medium powers and output speeds from 60–500 rpm.

The motors are available in freestanding versions or as geared motors for use with Lenze’s new 8400 motec inverters, which can be terminal box or wall mounted. Versions up to 1.5kW have already been released and the power range will be extended later to 22kW. Options include spring-applied brakes for stopping and holding, incremental encoders, blowers to extend the operating range, and plug connectors.

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