Torque X Speed

An induction electric motor operates first in a vacuum, very close to the synchronous speed. Relative motion is small, and consequently, the induced voltage in the rotor rod and the flow of the current in the rotor are also small. Since the rotor frequency is much lower, its reactance is approximately zero and the rotor current is almost in phase with the rotor voltage. In this type of motor the resulting spinning field is produced by the magnetizing current. In this state the slip and the relative movement between the rotor and the magnetic fields are low, even so, the rotor frequency is also reduced.

The rotor current then produces a low magnetic field and an angle a little more than 90 ° behind the resulting magnetic field. We note that the stator current must be very high, still unladen, as it will supply most of the resulting rotating field. For this reason the induction motors have high unladen currents compared to other types of motors and the induced torque keeps the motor running. As the rotor’s magnetic field is low, the induced torque is also small, but large enough to oppose the rotational losses of the motor.