As considered earlier, EN 50598 is a standard that defines two new energy efficiency classifications for variable-speed drives. Here, ABB Drives UK Ltd explain in more depth how these efficiencies will be calculated.

New methodology

One of the helpful feature of EN 50598 is that it provides a methodology for measuring the efficiency of the complete drive module (CDM) and power drive system (PDS), where previously it was a case of guesswork based on combining the efficiency ratings of the individual components. The measurements also take account of variable-speed drives (VSD) running at different capacities, giving a more accurate reflection of the drive’s efficiency in practice.

IE classification

The IE classification for motors is ordinarily taken at 100 percent motor speed and 100 percent motor torque; however, this is not the case for CDM, for which the IE classification is taken at 90 percent frequency and 100 percent current. EN 50598-2 also defines eight operating points of various frequency and current loads from which the CDM losses can be determined to establish the efficiency based on the CDM running at different capacities.

IES classification

As considered in the earlier article, EN 50598-2 also introduces a new IES for the motor and VSD combination, or PDS for motors and drives from 100 to 1,000 volts, with power up to 1,000 kW. IES classifications range from IE0, the lowest efficiency, up to IE2, although higher efficiency classes will be introduced in the future to keep pace with evolving technologies. Like the CDM, the standard defines different operating points from which a more accurate efficiency rating can be determined based on typical operating levels, as many VSDs are often run at partial loads.

Benefits in combination

Clearly there are advantages for companies such as ABB, who manufacturer both motors and VSDs and can advise machine builders and end-users on how best to meet the new European regulations resulting from Ecodesign.

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