The Partial-Load Efficiency of Induction Motors

This paper presents result of a project that enabled older operating motors to be removed from service and tested for efficiency under laboratory conditions, with the displaced motors being replaced by new National Electrical Manufacturers Association premium motors. The objective of the project is to determine the efficiency of a population of motors in operation before the Energy Policy Act of 1992 and to investigate if there was economic justification in replacing such motors with new ones. The economic benefit of repair/replace is computed at the tested partial-load efficiency of the motors. In addition, results are presented that show the load point at which maximum efficiency occurs for each motor. The differences in the partial-load characteristics of the old and new motors are also discussed.