Lenze has introduced its MF inverter optimised motors to fill a gap between standard AC motor technology and servo motors. MF motors are claimed to yield around five per cent saving in energy, are smaller and cost less to purchase than standard AC motors.
The energy saving of five per cent is significant (at similar powers changing from IE1 standard to IE2 high efficiency motors will only deliver about three) 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 3500 r/min.
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 higher speeds, and high temperature grease is used in the bearings. In most cases high output speed is not directly usable, and motors are generally supplied with a gearbox.
The efficiency of these 120Hz optimised MF motors is said to increase by five or six per cent compared with a standard four pole motor. For example at 0.75kW the efficiency is practically 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 allows the size of the motor to be reduced by one or two frame sizes leading to lower purchase costs. The smaller size is said to mean lower inertia and more dynamic drives. The performance takes a step towards servo levels with high acceleration and deceleration.
Currently the MF motor is available from Lenze freestanding or as a geared motor for use with the new 8400 motec inverter. The new MF motors will not suit every application. Their strength is in low to medium powers and where output speeds from 60 to 500 rpm are required.