Energy Efficiency of Induction Machines: A Critical Assessment

In this work, some fundamental aspects concerning the efficiency of induction machines are treated. The standards and the therein prescribed methods for the determination of the energy efficiency of induction machines are discussed. A detailed comparison of the four most relevant and recent methods identifies the differences. By means of measurement results of different machines, the differences between and the shortcomings of certain methods is confirmed. In that context, special attention is paid to the new, so-called ‘Eh-Y’ method. A concise overview of the most important points of attention for an increased efficiency of motor drives en the role of the induction motor (efficiency) in this context is completed with some examples. The difference between motor and generator mode is discussed and explained based on measurement results of machines of different size and efficiency class. Special attention is paid to the behaviour and performance of induction machines supplied by unbalanced voltages. More specifically it is investigated if and how the susceptibility to voltage asymmetry is influenced by material choice, in which the main focus lies on copper rotor technology. Therefore, the different standards for the description and quantification of voltage unbalance are studied first. The theoretical discussion is backed-up with experimental results of several machines.