Construction of Synchronous Motor

Construction of Synchronous Motor

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The stator and the rotor are the two main parts of construction of synchronous motor. The stator becomes stationary, and it carries the armature winding of the motor. The armature winding is the main winding because of which the EMF induces in the motor. The rotator carry the field windings. The main field flux induces in the rotor. The rotor is designed in two ways, i.e., the salient pole rotor and the non-salient pole rotor.

The synchronous motor uses the salient pole rotor. The word salient means the poles of the rotor projected towards the armature windings. The rotor of the synchronous motor is made with the laminations of the steel. The laminations reduce the eddy current loss occurs on the winding of the transformer. The salient pole rotor is mostly used for designing the medium and low-speed motor. For obtaining the high-speed cylindrical rotor is used in the motor.

Construction of Synchronous Motor

Synchronous motors run at synchronous speed. The synchronous speed is given by:


  • Ns = synchronous speed,
  • f = supply frequency and
  • p = number of poles.

As we can see from the equation, the synchronous speed depends on the frequency of the supply and the number of poles.

The construction of a synchronous motor is very similar to the construction of an alternator. Both are synchronous machines where one we use as a motor and the other as a generator.

Just like any other motor, the synchronous motor also has a stator and a rotor. We will look into the construction details of the various parts one by one in detail.

Stator of Synchronous Motor

The main stationary part of construction of synchronous motor is stator. The stator consists of the following parts.

Stator Frame

The stator frame is the outer part of the machine and is made up of cast iron. It protects the enter inner parts of the machine.

Stator Frame of Synchronous Motor

Stator Core

The stator core is made up of thin silicon laminations. It is insulated by a surface coating to minimize hysteresis and eddy current losses. Its main purpose is to provide a path of low reluctance for the magnetic lines of force and accommodate the stator windings.

Stator Core of Synchronous Motor

Stator Winding

The stator core has cuts on the inner periphery to accommodate the stator windings. The stator windings could be either three-phase windings or single phase windings.

Stator Winding of Synchronous Motor

Enamelled copper is used as the winding material. In the case of 3 phase windings, the windings are distributed over several slots. This is done to produce a sinusoidal distribution of EMF.

Rotor of Synchronous Motor

The rotor is the moving part of construction of synchronous motor. Rotors are available in two types:

  • Salient Pole Type
  • Cylindrical Rotor Type

The salient pole type rotor consists of poles projecting out from the rotor surface. It is made up of steel laminations to reduce eddy current losses.

Salient Pole Type Rotor of Synchronous Motor

A salient pole machine has a non-uniform air gap. The gap is maximum between the poles and is minimum at the pole centres. They are generally used for medium and low-speed operations as they have a large number of poles. They contain damper windings which are used for starting the motor.

A cylindrical rotor is made from solid forgings of high-grade nickel chrome molybdenum steel forgings of high-grade nickel chrome molybdenum steel. The poles are created by the current flowing through the windings.

They are used for high-speed applications as they have less number of poles. They also produce less noise and windage losses as they have a uniform air gap. DC supply is given to the rotor windings via slip-rings. Once the rotor windings are excited, they act like poles.

Cylindrical Rotor

Construction of Synchronous Motor Conclusion

After going through the above portion of synchronous motor we can now establish construction of synchronous motor. I hope you enjoy when reading this article, thank you.