Sensing of Secondary Current and Torque of 3-Phase Squirrel Cage Induction Motors

Abstract

In this paper, new experimental results for detecting, I₂ and T_e are reported using a magnetic-field sensor which is constituted with some amorphous microcores operating in a stake multivibrator followed by a low-pass filter.
The output of the Sensor with eight pair of micro cores (E_out) is proportional to I₂. The E_out has not only a voltage component of the frequency f but also components of frequency sf, fn-sf, fn+sf and others when a sensing with only one pair of microcores, where sf is a slip frequency, fn is a rotor speed requency, f (1-s)/2. It causes the components fn±sf that the rotor performs a precession motion. The voltage component of the fn-sf was proportional to T_e.
A calculated torque (T_m) using the measured value of I₂ almost coincieds to a measured torque (T_e) using a DC generator which is a load of IM.