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SarkariResultOutBMS · 2024

Previous Year Question

In power electronics circuit, commutation is the process of
  1. Turning off an electronic switch, which usually involves transferring the load current from one switch to another.
  2. Reversal of current in commutator of dc motor.
  3. Increasing the switching frequency of a power electronic device.
  4. Amplification of gate signals in a thyristor circuit.

Correct answer: A

Explanation

Commutation is the process of transferring current away from a conducting power semiconductor so that its current falls below the required holding value and the device turns off. In line-commutated circuits the AC source provides this naturally; in forced commutation an auxiliary network produces the required current/voltage condition.

Formula

SCR turn-off condition: iA < IH for at least the turn-off time tq

Step-by-step solution

Turn-Off of Conducting Device explanatory diagram

Correct Answer

A — Turning off an electronic switch, which usually involves transferring the load current from one switch to another.

Concept and Reasoning

Commutation is the process of transferring current away from a conducting power semiconductor so that its current falls below the required holding value and the device turns off. In line-commutated circuits the AC source provides this naturally; in forced commutation an auxiliary network produces the required current/voltage condition.

Calculation / Key Relation

SCR turn-off condition: iA < IH for at least the turn-off time tq

Exam Takeaway

Commutation is fundamentally a current-transfer/turn-off process.

Common Mistake

Do not confuse commutation with gate triggering, which initiates conduction.

Common mistake

Do not confuse commutation with gate triggering, which initiates conduction.

Exam tip

Commutation is fundamentally a current-transfer/turn-off process.

Quick method

Commutation is fundamentally a current-transfer/turn-off process.