📘 DC Motor Types – Shunt, Series & Compound
DC motors are classified based on how the field winding is connected. Each type has different torque-speed characteristics.
🔹 1. DC Shunt Motor
Field winding connected in parallel with armature.Characteristics:
- Flux approximately constant
- Torque ∝ I_a
- Speed nearly constant
- Good speed regulation
Speed Equation:
N ∝ (V − I_a R_a) / Φ
Since Φ ≈ constant → speed nearly constant. Applications:- Lathes
- Fans
- Machine tools
🔹 2. DC Series Motor
Field winding connected in series with armature.Characteristics:
- Flux ∝ I_a (before saturation)
- Torque ∝ I_a²
- Very high starting torque
- Speed varies widely
- Cranes
- Electric traction
- Hoists
🔹 3. DC Compound Motor
Combination of shunt and series fields. Types:- Cumulative compound
- Differential compound
🔹 4. Torque Comparison
| Motor Type | Starting Torque | Speed Regulation |
|---|---|---|
| Shunt | Moderate | Good |
| Series | Very High | Poor |
| Compound | High | Better than Series |
🔹 5. Example Concept Question
Which motor should never be run without load?DC Series Motor
Because at no load: I_a small → Flux small → Speed increases dangerously.🎯 GATE Important Points
- Torque in series motor ∝ I_a²
- Shunt motor has constant speed
- Series motor has high starting torque
- Never run series motor at no-load
Shunt = Constant Speed Series = High Torque Compound = Balanced Performance
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