Detection of secondary current and torque of squirrel-cage induction motor using amorphous magnetic sensor

Abstract

Reports experimental results on detecting the secondary current (I/sub 2/) and the electromagnetic torque (T/sub m/) using an amorphous-core magnetic-field sensor. The output of the sensor (E/sub out/) was proportional to I/sub 2/. E/sub out/ had not only a voltage component of the exciting frequency f, but also components of a slip frequency (s*f), fn-sf, and fn+sf, where s is slip and fn is the drive frequency. The value of the component of fn-sf was proportional to T/sub m/. The component of sf was due to magnetic field through the shaft. The components of fn+or-sf were due to a precession motion of the rotor. A torque calculated using E/sub out/ closely coincided with T/sub m/ and was detected without the influence of variation of temperature in an operating induction motor. >