Construction of DC Machine

Overview

DC Machine: Can be a DC motor or DC generator
Common Components: Rotor, armature, commutator, and brushes
Operation:
- As a generator: Converts mechanical rotation into electrical energy
- As a motor: Converts electrical energy into mechanical rotation
Constructional Similarity: Both motors and generators share the same constructional features

Main Parts of a DC Machine

Field System
- Objective: Create a uniform magnetic field for the armature to rotate in
- Types: Permanent magnet or electromagnet (electromagnets preferred)
- Components:
  - Yoke (Frame)
    - Acts as cover/frame; carries magnetic flux
    - Made of cylindrical shape, can be cast or fabricated steel
    - For small machines: cast iron due to cheapness
    - For large machines: fabricated steel for high permeability
    - Split yoke for large machines; halves bolted together
  - Pole Cores
    - Circular section; carries coils of insulated wires with field current
    - Generally made of cast steel; sometimes laminated
  - Pole Shoes
    - Supports field coils; spreads flux over armature
    - Larger cross-section reduces magnetic path reluctance
    - Always laminated to avoid heating and eddy current losses
Armature
- Purpose: Rotate conductors in uniform magnetic field
- Components:
  - Coils of insulated wires: Bound around iron core
  - Iron Core:
    - Provides support and low reluctance path for magnetic flux
    - Made of thin laminations of silicon steel
    - Laminations insulated with thin paper or varnish
    - Slots: Die-cut or punched, usually open-type
    - Ventilation: Longitudinal ducts for air cooling
  - Construction:
    - Laminations sometimes built from segments attached by dovetail joints
Commutator
- Role: Acts as a rotating switch, reverses current in armature coil
- Structure:
  - Cylindrical; made of hard-drawn or drop-forged copper
  - Segments insulated by mica; held by V-shaped rings
Brushes
- Function: Collect current from commutator
  - DC Generator: Supply current to external load circuit
  - DC Motor: Supply current to commutator
- Construction:
  - Rectangular in shape; rest on commutator

Conclusion

Basics of construction of a rotating DC machine covered