Electrical Engineering ⇒ Topic : Parts of a D.C. machine

A D.C. machine consists of two main parts :

Stationary part : designed mainly for producing magnetic flux.

Rotating part : called armature, where mechanical energy is converted into electrical (electric generator) or, conversely, electrical energy into mechanical (electric motor).

Fig. (a) shows the sectional view of a four pole D.C. machine

                                               Fig. (a) Sectional view of a four pole D.C. machine.

The various parts of a D.C. machine are enumerated below :

(i) Frame (ii) Field poles

(iii) Commutating poles (iv) Armature

(v) Commutator (vi) Brush gear

(vii) Armature shaft bearings (viii) Armature windings

According to the degree of closure produced by winding, armature windings are of the following two types

• Open coil winding.
• Closed coil winding.

The closed armature windings are of two types

(i) Ring winding. (ii) Drum winding.

In general there are two types of drum armature windings :

(i) Lap winding. (ii) Wave winding.

`Lap winding' is suitable for comparatively low voltage but high current generators where as 'Wave winding' is used for high voltage, low current machines.

In the 'lap winding' the finish of each coil is connected to the start of the next coil so that winding or commutator pitch is unity. In the 'wave winding' the finish of coil is connected to the start of another coil well away from the first coil