The Instrumentation Influence on the Motor Loss Determination Uncertainty

Abstract

The input-output method is the most frequently used and, in practice, the only viable alternative to determine the losses of all electrical machines regardless of the supply type or motor technology. However, the losses obtained with the input-output method are sensitive to power measurement uncertainties of the input and output powers. The power measurement uncertainty is formed by two parts: type A uncertainty is related to the variations in the measurement data and type B uncertainty is related to measurement instruments. The variations in the data can be controlled using data processing techniques and the type B uncertainty can be controlled using accurate measurement devices and choosing correctly rated measurement instruments for each task. In practice, the range of the instruments is limited and it is not always possible to perfectly match the instruments to the measured values. In here, the effect of the ratings of the instruments on the loss measurement uncertainty when using the input-output method is studied using a set of induction motors with rated powers from 7.5 kW to 355 kW. The specifications of the measurement instruments available at Electric Drives laboratory at LUT-University are used to derive the theoretical loss measurement uncertainty for the motors. The detailed uncertainty analysis includes the electric and mechanical powers, and as a result, loss measurement uncertainty is given. The results can be used to get an overview about the level of the expected measurement uncertainty for motors with different power ratings and its effect on the determination of efficiency.