High or premium efficiency motors
By J van Niekerk and E Cristofolini, Zest Automation and Drives
Electricity+Control, January 2014 (pages 14 - 19)
Download the full article on High or premium effciency motors in PDF format.
Motor efficiency is basically the ratio between the output power available at the motor shaft, and the electrical input power or absorbed power. The difference between Pout and Pin are the losses. In order to improve motor efficiency, it is necessary to reduce the losses on the motor.
The most reliable way to determine additional load losses is from measurement, where you find the actual value. Manufacturers are allowed to select the method they want to use to determine the additional load losses, but the standard defines that they must state their option on the motor documentation since motors tested using different methods are not comparable.
For an end user to make a sensible comparison, motors of the same efficiency level and tested by the same standard method should be compared. It is not possible to predict the efficiency of the same motor based on different test methods.
Although manufacturers are allowed to specify their product lines with different terminology, such as ‘Top Premium Efficiency’ or ‘Ultra Energy Saver Range’ they must include the IE classification on the motor nameplate and test method selected must be stipulated on the motor datasheet.
The effort and extra capital spent when purchasing high efficiency motors may be lost if motor selection is not properly done. Efficiency on motors decreases when operated below nominal operating point at 100% load. Some motors are designed to deliver equivalent efficiency down to 75% load. If one considers less than 75% load, there is a definite decrease in efficiency.
Efficiency levels are defined by IEC60034-30:2008 and tested according to IEC60034-2-1:2007
- A premium efficiency motor can save costs.
- Motors must be selected to match the application for which they are intended.
- Loading on a motor is key when considering the effectiveness of premium efficiency motors.