Measurement of the torque-speed characteristics of induction motors using an improved new digital approach

A measurement technique for determining the torque-speed characteristics of induction motors is presented. This technique is in compliance with the IEEE standard test procedure for polyphase induction motors and generators. It is based on the acceleration method which is performed under no-load conditions. A fast data-acquisition system is used to record the speed and other signals of interest. The data is processed digitally with the objective of removing undesired extraneous signals while preserving the accuracy of the machine characteristics over the complete range of speed. To achieve this objective, algorithms for performing adaptive window-size average filtering and numerical differentiation are developed. Experimental tests performed on 1 HP and 600 HP induction motors confirm that this approach has several advantages over other methods. It produces very accurate results over the full dynamic speed range of the machine and permits precise correlation between the switching transients on the line with the variation of the speed signal