Concept Notes
1. Construction of a DC Generator
A DC generator converts mechanical energy into DC electrical energy. The main parts are:
- Yoke (Frame):
- Provides mechanical support.
- Protects internal parts.
- Made of cast iron or steel.
- Poles:
- Mounted on the yoke.
- Carry field windings to produce magnetic flux.
- Types: Salient pole (large, low-speed) & Cylindrical pole (high-speed).
- Armature Core:
- Cylindrical iron core on which armature winding is wound.
- Laminated to reduce eddy current losses.
- Armature Winding:
- Wound on armature core.
- Conductors cut by magnetic flux → induced EMF.
- Commutator:
- Converts AC induced in armature to unidirectional DC at terminals.
- Made of copper segments insulated from each other.
- Brushes:
- Carbon/graphite blocks.
- Slide over commutator to extract current.
- Flux / Field Winding:
- Provides magnetic field.
- Can be shunt, series, or compound connected.
Working Principle:
- Based on Faraday’s Law of Electromagnetic Induction: EMF induced in a conductor moving in a magnetic field is proportional to the rate of change of flux linkage.
2. EMF Equation of a DC Generator
The generated EMF is given by:
Where:
→ Generated EMF (Volts)
→ Number of poles
→ Flux per pole (Weber)
→ Total number of armature conductors
→ Speed in RPM
→ Number of parallel paths (2 for wave winding, P for lap winding)
Example:
A 4-pole wave-wound generator has:
conductors- Flux per pole
- Speed
3. Types of DC Generators
- Separately Excited: Field winding powered externally.
- Self-Excited: Field winding powered by its own generated EMF.
- Shunt: Field winding in parallel.
- Series: Field winding in series.
- Compound: Combination of series and shunt.
Applications:
- Shunt generators → battery charging.
- Series generators → arc welding.
- Compound generators → industrial DC supply.
⚙️ Formulas
- EMF Equation:
- Parallel paths:
- Wave winding:
- Lap winding:
- Wave winding:
🔟 10 MCQs
Q1. The main function of the commutator is:
a) Reduce losses
b) Convert AC to DC
c) Increase flux
d) Provide mechanical support
Q2. In a wave winding, number of parallel paths:
a) P
b) 2
c) 1
d) Depends on speed
Q3. EMF of DC generator is directly proportional to:
a) Speed and flux
b) Resistance
c) Current
d) Load
Q4. Shunt generator has:
a) Field in series
b) Field in parallel
c) No field
d) Both series and parallel
Q5. Flux per pole is denoted by:
a) Z
b) Φ
c) P
d) n
Q6. A 4-pole generator with 500 conductors and 0.01 Wb flux/pole running at 1500 rpm wave wound generates:
a) 250V
b) 500V
c) 5000V
d) 25V
Q7. Series generator is mainly used for:
a) Battery charging
b) Arc welding
c) Low voltage supply
d) Lighting
Q8. Laminated armature is used to:
a) Reduce copper loss
b) Reduce eddy current loss
c) Increase flux
d) Reduce resistance
Q9. Faraday’s Law states:
a) Current produces flux
b) Flux induces EMF
c) Power = VI
d) Flux = IR
Q10. In a DC generator, increasing speed will:
a) Increase EMF
b) Decrease EMF
c) No effect
d) Only affects current
✅ Answer Key
| Q.No | Answer |
|---|---|
| 1 | b |
| 2 | b |
| 3 | a |
| 4 | b |
| 5 | b |
| 6 | b |
| 7 | b |
| 8 | b |
| 9 | b |
| 10 | a |
🧠 Explanations
- Q1: Commutator converts AC induced in armature to DC → (b).
- Q2: Wave winding always has 2 parallel paths → (b).
- Q3: EMF ∝ flux × speed → (a).
- Q4: Shunt → field in parallel → (b).
- Q5: Flux per pole → Φ → (b).
- Q6:
→ (b). - Q7: Series generator → arc welding → (b).
- Q8: Laminations reduce eddy current loss → (b).
- Q9: Faraday’s Law: changing flux induces EMF → (b).
- Q10: EMF ∝ speed → increase speed → increase EMF → (a).
🎯 Motivation / Why Practice Matters
DC generator EMF equation and construction is crucial for understanding all DC machines. ECET 2026 EEE expects conceptual + numerical questions on EMF, parallel paths, speed, and flux. Mastering this ensures you can solve machine design & problem-based questions quickly.
📲 CTA
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