Page 37 – Harmonics in 6-Pulse & 12-Pulse Converters
Subject: Power Electronics
Topic: Harmonic Analysis of Line Current
Level: GATE / PSU High Importance
🔹 Why Harmonics Matter?
- Cause heating in transformers
- Increase losses
- Reduce power factor
- Create EMI problems
🔹 Harmonics in 6-Pulse Converter
Harmonic order formula:
h = 6k ± 1
Where k = 1,2,3...- 5th harmonic
- 7th harmonic
- 11th harmonic
- 13th harmonic
🔹 Harmonics in 12-Pulse Converter
h = 12k ± 1
- 11th harmonic
- 13th harmonic
- 23rd harmonic
- 25th harmonic
5th and 7th harmonics are cancelled due to 30° phase shift.
🔹 Total Harmonic Distortion (THD)
THD = √(I₂² + I₃² + I₄² + ...)/I₁
Lower THD → Better waveform quality🔹 GATE Important Observations
- Higher pulse number → Lower harmonics
- 12-pulse reduces lower order harmonics
- Used in HVDC systems
- Filters still required but smaller
📌 Quick Comparison
| Converter | Harmonic Order | Ripple Frequency |
|---|---|---|
| 6-Pulse | 6k ± 1 | 6f |
| 12-Pulse | 12k ± 1 | 12f |
Advanced Harmonic Analysis – Shaktimatha Learning
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