A three-phase induction motor cannot run at synchronous speed due to the following reasons:
- Rotor and Stator Interaction:
In an induction motor, the rotor is not connected to any external power supply. Instead, it is powered by the magnetic field produced by the stator (the stationary part of the motor). This magnetic field rotates at a speed called the
synchronous speed.
- Relative Speed:
For the rotor to experience a torque (force), it must always lag behind the rotating magnetic field of the stator. If the rotor were to catch up with the synchronous speed of the rotating magnetic field, the relative speed between the stator's magnetic field and the rotor would become zero. In that case, no
induced current would be generated in the rotor, and no torque would be produced.
- Slip Concept:
The difference between the synchronous speed and the actual speed of the rotor is called
slip. The slip is essential for torque generation in the motor. A motor operates with a certain amount of slip, meaning the rotor speed is always slightly less than the synchronous speed. Without slip, the motor would not be able to generate any torque, and thus, it wouldn't be able to run.
- Magnetic Induction:
The rotor needs to "cut" the magnetic field lines to induce current in its windings. If the rotor were moving at synchronous speed, the field lines wouldn't be cut, and no current would be induced. This current is what creates the electromagnetic force that causes the motor to turn.
In summary, a three-phase induction motor cannot run at synchronous speed because the rotor must always lag behind the stator's magnetic field to induce current and produce torque. If it were to run at synchronous speed, no relative motion would exist, and no torque could be generated.
