As stated earlier, the construction of a dc machine whether a generator or a motor remains the same. It consists of the following parts.
YOKE
It is the outer most part of the d.c machine. So that the insulating materials get protected from moisture dust and gases like SiO₂, acidic fumes etc. It provides a path of low reluctance and high permeability since it forms a part of magnetic circuit. The choice of material will be cast iron for small machines and cast steel, silicon steel for large machines.
POLES
Each pole is divided in two parts.
i. Pole core
ii. Pole shoe
The pole core basically carries the field winding which is necessary to produce the flux. It directs the flux produced through air gap to the next pole. The pole shoe enlarges the area of armature core to come across the flux which is necessary to produce larger induced emf The choice of material will be cast iron or cost steel. As it requires a definite shape and size, laminated construction is used.
FIELD WINDING
The field winding is wound on pole core with definite direction. It is a conducting material which carries the current due to which the pole core behaves as an electromagnet producing the necessary flux. As it helps in producing the magnetic field it is called field winding or exciting winding. The choice of material will be aluminum or copper Since field coils are required to take any type of shape copper is I because of good liability.
ARMATURE
It is divided into two parts
i. Armature core and
ii. Armature winding
i. Armature core
Armature core is cylindrical in shape mounted on the shaft. It consists of slots on its periphery and air ducts for air flow in armature which serves for cooling purpose. Armature core provides house for armature winding. It provides a path of low reluctance to the magnetic flux produced by field winding. The choice of material is cast iron or cast steel. It is made of laminations to reduce eddy current loss.
A single circular lamination used for the construction of armature core.
(ii) Armature winding
Armature winding is the inter connection of the armature conductors placed in the slots provided on the armature core. Generation of e.m.f takes place in the armature winding in case of generators. In case of motors it carries the current from the supply. There are two types of connections in armature winding
a. a. Lap winding
b. b. Wave winding
a. Lap winding
In this case, the connection is started from a conductor in slot 1 then the connections overlap each other as winding proceeds till the starting point is reached again. The armature winding in lap type.
b. Wave winding
In this type of connection winding always travels ahead, avoiding overlapping. It travels like a progressive wave hence called wave winding. Two coils starting from slot 1 and slot 2 are progressing in wave type.
Since it carries current the choice of material is copper.
COMMUTATOR
The basic nature of e.m.f induced in armature conductors is alternating. This needs rectification in case of d.c generators, which is possible by commutator..
It is used to collect the current from armature conductors and converts alternating e.m.f to unidirectional e.m.f. In case of motors, it produces unidirectional torque. The choice of material is copper and insulated from each other by thin layer of mica.
BRUSHES
Brushes are stationary and resting on the surface of the commutator. It collects current from commutator and provides to the stationary external circuit. The brushes are normally made up of soft material like Carbon, to avoid wear and tear of commutator.
See More: Working Principle of D.C Generator
See More: Working Principle of D.C Motor
See More: Three Point Starter
