CONSTRUCTION OF DC MACHINE

The main parts of DC Machine (motor or generator) are as follows:

Yoke
pole core and pole shoes
Pole coil and field coil
Armature core
Armature winding or conductor
Commutator
Brushes and bearings

Construction of DC Machine
1. Yoke


Yoke
Function
It provide mechanical Support for poles
It also provide protection to whole machine from dust, moisture etc.
It also carries magnetic flux produced by the poles
Yoke is also called as frame.
Material used
For small M/C yoke is made of cast iron.
For large M/C it is made of cast steel or rolled steel.

2. Pole & Pole core


Pole & Pole core
Function
Pole of a generator is an electromagnet.
The field winding is winding over pale.
Pole provides magnetic flux when field winding is excited.
Material used
Pole core or pole made of cast iron or cast steel.
It built of these laminations of annealed steel. The laminations is done to reduce the power lose due to eddy currents.

3. Pole Shoe

Function
It is extended part of pole. It enlarge area of pole
Due to this enlarged area, flux is spread out in the air gap and more flux can pass through the air gap to armature.
Material used
It is made of cast iron or cast steed.
It built of this lamination of annealed steel. the lamination is done to reduce power loss due to eddy currents

4. Pole coil or field windings


Pole coil or field windings
Function
It is wound around pole core and called as field coil
it is connected in series to from field winding
When Current is passed through field winding it electro magnetize the poles which produce necessary flux.
Material used
The material used for field conductor is copper.

5. Armature Core


Armature Core
Function
It has large number of slots in its periphery
Armature conductor, are placed in this slots
It is also provide path of low reluctance to the flux produced by field winding
Material used
High permeability low reluctance materials such as cast or iron are used for armature core.
The lamination is provided so as to reduce the loss due to eddy current.

6. Armature Winding

Function
Armature conductor are inter connected to form armature Winding
When armature winding is rotated using prime mover. the magnetic flux and voltage gets induced in it
Armature winding is connected to external circuit
Material used
It is made of conducting material such as coppers.

7. Commutator


Commutator
Function
It Convert alternating current induce in the current in a unidirectional current
It collects the current form armature conductor and pass it load with the help of brushes
It also provide unidirectional torque for dc motor
Material used
It is made of a large number of edge shaped segments of hard drawn copper.
The Segments are insulated from each other by thin layer of mica.
OR
The Segment of commutator is made of copper and insulating material between segments is mica.

8. Brushes

Function
Brushes collect the current from commutator and apply it to external load.
Brushes wear with time and it is should be inspected regularly.
Material used
Brushes are made of carbon or graphite it is rectangular in shape.