What is a Synchronous Machine? Synchronous Speed / Advantages

What is a Synchronous Machine?

Synchronous Machine constitutes of both synchronous motors as well as synchronous generators. An AC system has some advantages over a DC system. Therefore, the AC system is exclusively used for the generation, transmission, and distribution of electric power. The machine which converts mechanical power into AC electrical power is called a Synchronous Generator or Alternator. However, if the same machine can be operated as a motor is known as Synchronous Motor.


Synchronous machine is an AC machine whose satisfactory operation depends upon the maintenance of the following relationship.


  • Ns is the synchronous speed in revolution per minute (r.p.m)
  • f is the supply frequency
  • P is the number of poles of the machine.


  1. Stationary Armature can be easily insulated for higher voltages.
  2. Since the armature windings are stationary, they are not subjected to vibrations and centrifugal forces.
  3. Output Current can be easily taken as terminals are fixed on the stationary armature. No need of using slip rings and brushes.
  4. Only 2 slip rings are required for providing direct current to the rotating field, while at least 3 slip rings would be required for the rotating armature ( that too of higher voltages).
  5. Size of the machine is reduced.
  6. Rotating field is comparatively light and can be constructed for high speed rotations.
  7. Cooling becomes more easier in the case of stationary armature.
    Functionally, Synchronous Machine are of two types – Synchronous Motor and Synchronous Generator (Alternator).

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