DC Generator – Principle, Parts, Types, Function and EMF Equation
DC Generator – Additional Theory
Construction of a DC Generator
A DC generator consists of several important parts that work together to convert mechanical energy into electrical energy.
1. Yoke (Frame)
- The outer frame of the generator is called the yoke.
- It provides mechanical support to all internal parts.
- It provides a magnetic path for flux.
- Usually made of cast iron or steel.
2. Field Poles
- Field poles are fixed to the inner side of the yoke.
- They support the field winding.
- They produce the magnetic field.
Each pole consists of:
- Pole core
- Pole shoe
The pole shoe spreads the magnetic flux uniformly.
3. Field Winding
- Field winding is wound on the pole core.
- When current flows through the winding, it produces a magnetic field.
Types of field winding:
- Shunt winding
- Series winding
- Compound winding
4. Armature Core
- The armature core is mounted on the shaft.
- Made of laminated silicon steel.
- Laminations reduce eddy current losses.
5. Armature Winding
- Conductors placed in armature slots form the armature winding.
- These conductors cut magnetic flux and generate EMF.
6. Commutator
- Commutator converts AC into DC.
- Made of copper segments insulated by mica.
7. Brushes
- Brushes collect current from the commutator.
- Usually made of carbon or graphite.
Working of DC Generator
The DC generator works on the principle of Faraday’s Law of Electromagnetic Induction.
- The prime mover rotates the armature.
- The armature conductors cut the magnetic flux.
- An EMF is induced in the conductors.
- Current flows through commutator and brushes.
- Electrical power is supplied to the external circuit.
EMF Equation of DC Generator
E = (P × Φ × Z × N) / (60 × A)
| Symbol | Meaning |
|---|---|
| P | Number of poles |
| Φ | Flux per pole |
| Z | Total armature conductors |
| N | Speed in RPM |
| A | Parallel paths |
Types of DC Generators
1. Separately Excited Generator
The field winding is supplied from an external DC source.
2. Self Excited Generator
Three types:
- Shunt Generator – Field winding connected parallel to armature
- Series Generator – Field winding connected in series with armature
- Compound Generator – Combination of series and shunt field
Compound generator types:
- Cumulative compound
- Differential compound
Losses in DC Generator
1. Copper Loss
- Armature copper loss
- Field copper loss
2. Iron Loss
- Hysteresis loss
- Eddy current loss
3. Mechanical Loss
- Friction loss
- Windage loss
Applications of DC Generator
- Battery charging
- Electroplating
- Welding generators
- Exciters in power plants
- DC traction systems
Important Exam Points (ITI / NCVT)
- DC generator works on Faraday’s law.
- Commutator converts AC into DC.
- EMF depends on speed and magnetic flux.
- Armature core is made of laminated steel.
- Brushes are made of carbon.
