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SarkariResultOutBMS · 2024

Previous Year Question

In a 12-pulse line commutated converter, the first dominant ac (pair) harmonic at ac-side and dc harmonic at dc-side are respectively
  1. (5th, 7th) and 12th
  2. (9th, 11th) and 11th
  3. (11th, 13th) and 12th
  4. (13th, 15th) and 13th

Correct answer: C

Explanation

For a 12-pulse converter the characteristic AC-side harmonics are h=12k±1, so the lowest pair is 11th and 13th. On the DC side, ripple harmonics occur at multiples of 12 times the fundamental frequency, making the first characteristic DC ripple the 12th. This combination corresponds to option C.

Formula

AC: h=12k±1; DC ripple: h=12k

Step-by-step solution

Characteristic Harmonics explanatory diagram

Correct Answer

C — (11th, 13th) and 12th

Concept and Reasoning

For a 12-pulse converter the characteristic AC-side harmonics are h=12k±1, so the lowest pair is 11th and 13th. On the DC side, ripple harmonics occur at multiples of 12 times the fundamental frequency, making the first characteristic DC ripple the 12th. This combination corresponds to option C.

Calculation / Key Relation

AC: h=12k±1

DC ripple: h=12k

Exam Takeaway

12-pulse → 11th/13th on AC side and 12th ripple on DC side.

Common Mistake

Do not use six-pulse 5th/7th characteristic harmonics for a 12-pulse bridge.

Common mistake

Do not use six-pulse 5th/7th characteristic harmonics for a 12-pulse bridge.

Exam tip

12-pulse → 11th/13th on AC side and 12th ripple on DC side.

Quick method

12-pulse → 11th/13th on AC side and 12th ripple on DC side.