Question

What is the principle of the synchronous motor?

Answer 1

The principle of a synchronous motor is based on the interaction between the magnetic fields of the stator (the stationary part) and the rotor (the rotating part). Here's how it works in simple terms:

1. **Magnetic Fields:** The stator of a synchronous motor produces a rotating magnetic field when connected to an alternating current (AC) power supply. The rotor, on the other hand, has a magnetic field (either produced by a DC supply or permanent magnets).

2. **Synchronization:** The rotor starts to rotate in sync with the rotating magnetic field produced by the stator. This means the rotor tries to "lock in" with the stator's magnetic field and rotates at the same speed as the field. This speed is called the **synchronous speed**.

3. **No Slip:** Unlike induction motors, where the rotor lags behind the rotating magnetic field (called "slip"), a synchronous motor runs at exactly the same speed as the field. There is no slip; the rotor speed and the stator's magnetic field speed are always equal.

4. **Constant Speed:** Because of this synchronization, the motor runs at a constant speed, regardless of the load, as long as the frequency of the AC supply remains constant.

### Key Points:
- The rotor's speed is synchronized with the stator's magnetic field.
- The motor operates at a fixed speed, known as synchronous speed.
- It requires an external DC power supply to excite the rotor, creating its magnetic field (or it can use permanent magnets).

So, in summary, the synchronous motor works by aligning the rotor's magnetic field with the stator's rotating magnetic field, making it rotate at a constant speed.