Assessment of Efficiency of Low Voltage, Three Phase Motors

Abstract

Three-phase, low-voltage squirrel cage induction motors are the most commonly used electric motors in industry. They can be found from a few hundred watts up to several megawatts. The induction motors are characterised by data provided by the manufacturer at rated speed, power, voltage, current, power factor and efficiency. In the past, the efficiency value was of minor importance. Nowadays, with the growing emphasis on energy conservátion the efficiency value has become very important and even dominant for applications in industry. Efficiency data by manufacturers are measured or calculated according to certain standards. The main differences between these standards are discussed in this paper, as well as the process of making accurate measurements. Knowing the real efficiency at rated and partial load, instead of the fictional IEC efficiency, allows choosing the motor that has the highest efficiency in the actual process where it is used. Annual energy savings of up to 50% of the purchase cost can be achieved. Some practical examples of energy saving using variable speed drives are also given.