Electrical Engineering ⇒ Topic : Construction of synchronous motor

CONSTRUCTION

A three-phase synchronous motor consists of the following essential parts :

• Laminated stator core with three-phase armature winding.
• Revolving field complete with amortisseur winding and slip rings.
• Brushes and brush holders.
  Two end shields to house the bearings that support the shaft.

The stator core and windings of a synchronous motor are similar to those of a 3-Phase squirrel-cage induction motor or a wound-rotor induction motor. The leads for the stator winding, marked T₁, T₂ and T₃, terminate in a terminal box usually mounted on the side of the motor frame.

The rotor is generally a salient pole rotor. The number of rotor field poles must equal the number of stator field poles. In order to eliminate hunting and to develop the necessary

                 Fig.(a)pole of an A.C. synchronous motor.                                Fig. (b). Damper winding

starting torque when A.C. voltage is applied to the face conductors which stator, the rotor poles contain pole- are short-circuited at their ends as shown in Fig.(a). This aniortisseur or damper winding consists of solid copper bars embedded at the surface of the pole face and short-circuited at each end by means of a shorting strip as shown in Fig.(b).

The field circuit leads are brought out to two slip rings mounted on the rotor shaft. Carbon brushes mounted in brush holders make contact with the two slip rings. The terminals of the field circuit are brought out from the brush holders to a second terminal box mounted on the motor frame. The two leads for the field circuit are marked F₁ and F₂.