Viability of Highly Efficient Multi-Horsepower Line-Start Permanent-Magnet Motors

The incremental efficiency improvements achieved with induction motors have been mostly accomplished by adding material to the designs of the prior efficiency level. In order to achieve levels beyond NEMA Premium (or beyond IE3), it has been recognized that a different technology must be employed. The working groups for International Electrotechnical Committee efficiency levels have stated that inverter-fed permanent-magnet motors are the likely technology to reach IE4 levels. Other motor technologies (such as synchronous reluctance) which also require inverters for operation have also been proposed for higher motor efficiency. This paper will discuss a technology which can be utilized without requiring an inverter and that can achieve beyond-IE4 levels of efficiency while using less active material in the motor. This discussion is based on testing of technology demonstration prototypes in the range of 30-250 hp. Capabilities as well as limitations of this technology will be discussed.