A more accurate measure of motor efficiency

An ABB Automation Tech (Drives and Motors) product story

Edited by the Engineeringtalk editorial team Mar 28, 2008

ABB has already started retesting its motor range to the new IEC/EN60034-2-1 standard, and will publish the new efficiency values in its catalogues during 2008.

Leading power and automation technology company ABB is welcoming a new IEC international testing standard for low-voltage electric motors that will make it easier for users to save energy by selecting the right high-efficiency motors.

The company has already started retesting its motor range according to the new standard, IEC/EN60034-2-1, and will publish the new efficiency values in its catalogues during 2008, as soon as tests are completed.

"We welcome the fact that the efficiency measurement standards for electric motors are becoming more harmonised worldwide", says Steve Ruddell, for ABB.

"We have waited a long time for a level playing field to be introduced".

The new standard will tighten up testing procedures and gives manufacturers the opportunity to publish more accurate efficiency values.

Unlike the old standard, which was partly based on estimated values, the new one is based on actual measured values of losses in the motor, giving more accurate efficiency values.

The measuring of winding, rotor and additional load losses are all affected by the new standard.

Winding and rotor losses will now be based on actual measured temperature rises.

The new standard significantly tightens up the calculations of the additional load losses.

These losses are the result of magnetic flux created as the motor is running.

Under the old efficiency testing standard, additional load losses were estimated at 0.5% of the input power at rated load.

The new standard allows for measurement of these losses.

ABB will be using this method, the most onerous, which requires highly accurate measuring equipment.

Motor manufacturers must, under the new standard, state in their motor documentation how the efficiency values have been measured.

The method used under the old standard with estimated additional losses resulted in total losses being estimated too low.

The new efficiency value calculated using measured losses will, therefore, be a slightly lower figure.

The new efficiency figure does not mean that the motor's design or performance has changed, only that the efficiency is now measured much more accurately.

Compared with other machines, electric motors are very efficient, typically 95% for a 90kW high-efficiency motor.

But the large number of motors installed means that even small changes in efficiency can make a big difference to industry as a whole.

Two-thirds of the electricity used in industry is used by electric motors.

While high-efficiency motors (EFF1) normally cost 10-15% more than standard motors (EFF2), this price premium is quickly repaid by energy savings.

The purchase cost of a motor is only about 1% of its total life cycle cost, electricity being by far the greatest part of the cost.