Synchronous Motor: Construction and Working Principle

Synchronous Motors: Unveiling the Magnetic Precision

Construction of Synchronous Motors

A synchronous motor comprises two essential components: the stator (stationary part) and the rotor (rotating part). Here’s a breakdown of each:

1. Stator:

   • The stator houses the armature winding, similar to that of a synchronous generator.
   • It consists of a core and slots to hold the armature winding.
   • The three-phase winding is wound in these slots.
   • A three-phase AC supply is connected to the stator winding.

2. Rotor:

   • The rotor can be either salient pole type or non-salient pole type.
   • It is wound with the field winding, which is excited by a DC supply.

Features of Synchronous Motors

1. Constant Speed:

   • Synchronous motors maintain a constant speed, determined by the supply frequency.
   • Speed variation occurs only when the supply frequency changes, regardless of the load.

2. Not Self-Starting:

   • Synchronous motors are inherently not self-starting.
   • External means (such as initial rotation) are required to bring them close to synchronous speed before synchronization with the supply.

3. Power Factor Correction:

   • These motors can operate under a wide range of power factors.
   • They are commonly used for electrical power factor correction.

Working Principle

• The synchronous motor operates based on the principle of magnetic locking.
• When a three-phase supply is fed to the stator winding, a rotating magnetic field (RMF) is produced.
• The RMF rotates at synchronous speed, determined by the supply frequency.
• The rotor winding, excited by a DC supply, sets up a magnetic field in the rotor.
• The rotor poles interact with the stator poles, resulting in magnetic locking.
• The synchronous motor’s speed is given by:

  Ns​=120⋅f/P​

  where:
  • (N_s) is the synchronous speed of the RMF.
  • (f) is the frequency of the supply voltage.
  • (P) is the number of poles in the rotor.

Applications

• Synchronous motors find use in:
  • Large industrial applications (e.g., pumps, compressors, conveyors).
  • Power plants (for power factor correction).
  • High-precision applications (due to constant speed).

Remember, synchronous motors play a crucial role in our modern world, ensuring efficient and reliable operation across various industries. 🌟