advantages
1. What "Advantages" Refers To (Three-Phase Advantages)
This topic is the complement to necessity — listing advantages of three-phase over single-phase (often combined in one answer). If necessity asks "why needed", advantages list benefits realized.
2. Advantages (exam list — 6 with one-line)
| Advantage | Detail |
|---|---|
| 1. More power for same material | For same and copper weight, 3-phase delivers ~73% more power (or needs ~25% less copper for same ) |
| 2. Constant power, smooth torque | No pulsation ⇒ motors/generators less vibration, smooth rotation |
| 3. Smaller machines | For same , 3-phase generator/motor is smaller and lighter (more efficient use of windings) |
| 4. Self-starting induction motor | Rotating field inherent ⇒ no starter capacitor needed (single-phase needs) |
| 5. Efficient transmission/distribution | 3 or 4 wires carry more power with lower loss; voltage can be stepped up/down with 3-phase transformers (three cores in one) |
| 6. Two voltages available | Line-to-line (400V) for three-phase loads and phase-to-neutral (230V) for single-phase loads from same supply |
3. Quantitative Comparison
Single-phase power (2 wires): P = V·I·cosφ (pulsating)
Three-phase (3 wires) balanced: P = √3·V_L·I_L·cosφ =3·V_ph·I_ph·cosφ (constant, higher)
For same P and loss, 3-phase copper saving ≈25%.
4. Exam Points
- List 5–6 advantages with one-line — 5-7 marks, very frequent (often asked as "advantages of 3-phase system").
- Mention constant power and self-starting — 5 marks, frequent.
- Show power formula for 3-phase — 3-5 marks, frequent (next topics elaborate).