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

Reports experimental results on detecting the secondary current ( I₂) and the electromagnetic torque (T_m ) using an amorphous-core magnetic-field sensor. The output of the sensor (E_out) was proportional to I₂ . E_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_m. The component of sf was due to magnetic field through the shaft. The components of fn±sf were due to a precession motion of the rotor. A torque calculated using E_out closely coincided with T_m and was detected without the influence of variation of temperature in an operating induction motor