Precise Efficiency Data for Electric Motors – an Illusion?

Abstract

Significant differences can exist between

• test results from various determination methods

• the designated nominal efficiency η_N, and

• the actual efficiency under practical operation

Pragmatic, clear and easy to handle rules, covering the overall context, are needed. The expenditure for a “precise” determination method appears only to be justified, if it is ensured that the improvements which are achieved are not lost within the scope of accuracy, reproducibility and existing tolerances. The full load efficiency of a 4 kW-Motor can change by + 2 to - 4 percentage points due to the field operating conditions. Until now, no information has been provided on this issue. On the other hand, considerable effort is being made to come up with “more accurate” methods, whose results frequently only differ by less than 1 percentage point. In this case, the question must be asked whether the priorities have really been set correctly.

Committees of IEC and CENELEC are responsible in creating appropriate specifications. At the end of 1996, the EC gave CENELEC a clearly formulted mandate. Unfortunately the presented Draft IEC 61972 CDV is not sufficient and it has been rejected at the voting procedure. Therefore the introduction of the European high efficiency motors will be realized on the basis of the existing IEC 60034-2.