Efficiency Measurements in Induction Motors: Comparison of Standards

Recently, given the need to reduce the emission of greenhouse effect gases and limiting the steady increase in energy demand, were have proposed new standards of efficiency levels of electric motors. From them have been defined efficiency categories, which determine the limits for so called Standard Efficiency Motors, High Efficiency, Efficiency Premium, etc. Most countries, therefore, have established legal restrictions on the use of motors with low efficiency. A small error in the motor efficiency measurement could lead to an incorrect categorization. In this sense recently have been revised standards that establish testing procedures. Each one, in turn, provides different alternatives more or less accurate to estimate the motor efficiency based on the tools that are included (dynamometer torque sensor, windings temperature measurement, etc.). In this paper a comparison of some of the most commonly used standards for the motor efficiency measurement is presented. The comparison is made in reference to the so-called direct method, where the input and output power of a motor is directly measured with a strict control of ambient (laboratory), engine temperature and feeding conditions. The comparisons allow conclusions about the probable errors in the application of each standard.