An AC motor is commonly referred to as an induction motor due to the principle of electromagnetic induction that underlies its operation. The induction motor is a type of asynchronous motor, meaning it operates without the need for a direct electrical connection between the stator (the stationary part) and the rotor (the rotating part). Let’s explore why an AC motor is called an induction motor and how it works:
1. Electromagnetic Induction:
- Faraday’s Law: The fundamental principle behind the operation of an induction motor is Faraday’s law of electromagnetic induction. According to this law, a changing magnetic field induces an electromotive force (EMF) or voltage in a coil or conductor within the field.
2. Motor Components:
- Stator and Rotor: The induction motor consists of two main parts: the stator and the rotor. The stator is the stationary part, typically made up of laminated iron cores with three-phase windings. The rotor is the rotating part, typically a squirrel-cage rotor made of conducting bars.
3. AC Power Supply:
- Three-Phase AC Supply: Induction motors are designed to work with three-phase alternating current (AC) power. Three-phase AC provides a rotating magnetic field in the stator, which is crucial for the motor’s operation.
- Creation of Rotating Magnetic Field: When three-phase AC power is applied to the stator windings, it produces a rotating magnetic field. The magnetic field rotates at the frequency of the AC power supply.
- Induction in the Rotor: As the magnetic field in the stator rotates, it induces a voltage in the rotor conductors according to Faraday’s law of electromagnetic induction. This induced voltage causes current to flow in the rotor conductors.
- Production of Rotor Magnetic Field: The current flowing in the rotor conductors generates a magnetic field in the rotor. This rotor magnetic field interacts with the rotating magnetic field in the stator, causing the rotor to experience a torque.
- Rotor Rotation: The interaction between the rotating magnetic field in the stator and the induced magnetic field in the rotor results in the generation of torque. This torque causes the rotor to rotate, and the motor begins to turn.
5. Asynchronous Operation:
- Slip: The induction motor is asynchronous because the rotor speed is always less than the speed of the rotating magnetic field in the stator. The difference in speed is known as slip. The rotor needs this slip to generate the necessary induced voltage and current for the motor to operate.
- Simplicity and Robustness: Induction motors are known for their simplicity, robustness, and reliability. They have no brushes or commutators, reducing maintenance requirements.
- Wide Usage: Induction motors are widely used in various applications, including industrial machinery, HVAC systems, household appliances, and more, due to their efficiency and versatility.
In summary, an AC motor is called an induction motor because of its reliance on the principle of electromagnetic induction. The induction motor’s operation is based on the induction of voltage in the rotor conductors by the rotating magnetic field in the stator, resulting in the generation of torque and the rotation of the motor.