Three-phase induction motors

We can describe the operation of a three-phase induction motor when the magnetic field formed in the rotor circuit will chase the rotating field of the stator. This type of electric motor has in its rotor, which we call ‘squirrel cage’, the action of the force exerted by the rotating field that will induce a current that will provoke its impulsion. When the motor is energized, it acts as a transformer with the secondary being shorted, which will require a much larger current than the rated current from the mains, which can reach about 8 times its value.

Depending on the shape of the rotor cage will be the characteristics of the three-phase induction motor and can be various configurations and conductivity.

The high starting currents are an inconvenience, as it will require the dimensioning of cables with diameters much larger than normal. In addition, there may be momentary drops in the power factor, and this is monitored by the utility, causing the power bills to rise. To avoid these high starting currents, there are motor drive methods that provide a reduction in starting current value, such as: star-delta start; serial-parallel start; departure by self-compensator.