Construction of DC Machine

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

1. Yoke
2. Pole core and pole shoes
3. Pole coil and field coil
4. Armature core
5. Armature winding or conductor
6. Commutator
7. Brushes and bearings

1. 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

• 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

• 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

• 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

• 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.