Assessment of nonintrusive motor efficiency estimators

Three instruments have been evaluated for their ability to estimate the load conditions and efficiency of operating motors based solely on measurements of terminal voltage and current. Laboratory tests, compared to a high-accuracy dynamometer system were used to assess the instruments' accuracy. Field tests were conducted in a paper mill to determine the ease of use and lack of intrusion. In both laboratory and field tests the instruments were applied to 50-hp, 100-hp, and 200-hp 460-V induction motors. Data of the relative accuracies of the three instruments, as functions of motor load and supply voltage, are presented together with observations of ease and lack of intrusion in use.