Torque measurement methods for very high‐speed motors

Abstract

PurposeThe purpose of this paper is to develop a contactless torque measurement methods. The need for low‐weight, high‐efficiency and high‐power density motors has led to an increased research and development activity in the field of very high speed (VHS) motors or generators. Torque measurement methods are inherently linked with the target speed and power of the motor. Therefore, new torque measurement methods compatible with VHS need to be designed in order to apprehend this new area of electrical machines. In this paper, the target speed is 200,000 rpm.Design/methodology/approachThe goal is to develop contactless torque measurement methods. Indeed, a mechanical connection between the motor shaft and the measuring device adds normal modes to the shaft. Also, if a measuring device is mechanically connected and held through bearings, then the whole design is hyperstatic. Both aspects can be critical at VHSs.FindingsAn indirect method based on the inertia of the rotor allows to measure high torques very rapidly. It is validated through a second method based on eddy currents. Also, a practical setup for measuring friction torque in VHS ball bearings is presented.Originality/valueThe presented methods are of high value for assessing a motor efficiency and useful to anybody confronted with the difficulties of torque measurements in the area of high‐speed machines.