Measurement Accuracy Requirements for the Efficiency Classification of Converters and Motors

Electrical machines play a major role in the electrical energy consumption in the modern world; therefore, the efficiency of electrical machines has been regulated for a long time by different authorities. Recently, the international efficiency classes for converters and converter-fed machine packages were introduced by IEC. The increased efficiency of the devices creates a challenge for accurate loss and efficiency determination of these devices. This paper examines the measurement accuracy of the direct-on-line and converter-fed electrical machines, frequency converters, and converter-fed machine packages from a theoretical basis. The measurement uncertainty is presented as a function of the rated powers of the devices and as a function of the efficiency classes.