Posted to News on 7th Sep 2010, 22:36
Inverter-optimised motors save energy and are cheaper to buy
Traditionally there has been a large gap 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 is introducing the MF inverter-optimised motors to fill this gap. MF motors not only yield around 5 per cent saving in energy, but also additional advantages of smaller dimensions and a pricing structure that makes them cheaper than standard AC motors. The energy saving of 5 per cent is significant (at similar powers changing from IE1 standard to IE2 high efficiency motors will only deliver about 3 per cent), leading to long-term savings and reductions in greenhouse gas emissions.
Lenze has achieved the twin goals of higher efficiency and lower purchase costs by taking standard four-pole motor designs and optimising them for use at 120Hz, which is equivalent to a speed of about 3500rpm. While this is not so different from two-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. Lenze has 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 for by the motor gains.
The efficiency of these 120Hz optimised MF motors increases by typically five or six per cent compared with a standard four-pole motor. For example, at 0.75kW the efficiency is around 80 per cent 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 a lower purchase costs. For example, a 1.5kW MF motor is a 71 frame compared to a standard 1.5kW pole motor which is 90 frame. Moreover, the smaller size means lower inertia and more dynamic performance. Indded, Lenze says the performance takes a step towards servo levels, with high acceleration and deceleration possible. 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; in the autumn the power range will extend to 22kW and use will also be possible with all cabinet-mounted inverters from 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 500rpm are required. Here they are claimed to give nothing but benefits, with reduced energy bills, reduced purchase costs and increased dynamic performance.
Follow the link for more information and a brochure describing the L-force MF inverter-optimised motors.
