How induction motor works?

This post’s subject is the induction motor. I will talk how it works and where is applied. 50% of electrical power consumption come from induction motors.

3 phase induction motor

The stator has 3 coil winding and the coils are positioned in a way that coils from same phase stay in opposite directions.

This is the stator’s appearance.

The rotor is formed by aluminum bars linked by aluminum rings and has iron blades inside, this rotor is called squirrel cage. Can use copper instead of aluminum.

Both the stator and the rotor have bladed iron core to strengthen the magnetic field and reduce parasite currents, like in transformers.

To turn on this type of motor, it is necessary use three AC signals delayed 120° between themselves.

The three AC signals create a rotating magnetic field.

If you put a closed conductor inside this field, the conductor will produce a induced voltage due to Faraday`s law of induction. Since it is in short circuit will be generated an electrical current. This current in the presence of a magnetic field will receive a Lorentz`s force. In this way the squirrel cage rotor rotate. The magnetic field speed is called synchronous speed and it always bigger than the rotor speed.

1 phase induction motor

The 1 phase induction motor has two coil winding: the main and the auxiliar. The winding are perpendicular between themselves.

When the coil is supplied by an AC source, it is produced a pulsing magnetic field constantly changing the direction.

How the motor is turned on with this magnetic field? A capacitor in series with the auxiliar winding make the auxiliar winding have a delay of 90°, allowing the motor to start. After the start, the key is opened shutting down the auxiliar winding.

Some monophasic motors have copper rings instead of an auxiliar winding and a capacitor to produce a rotating magnetic field.

The copper ring delay the field formation where it stays, generating a result field which rotate.

Some applications

The induction motor don’t have brushes, therefore do not generate electromagnetic interference. Also don’t have permanent magnets, neither commutator rings simplifying the construction and are controlled only by the input frequency. The 3-phase motor is self-starting. The 1-phase motor is used in lower power applications. These motors are used in:

• Electrical car;
• Elevators;
• Cranes;
• Industrial applications;
• Fans;
• Refrigerators;
• Domestic low power applications.