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SarkariResultOutAdditional Assistant Engineer (Electrical) · 2026

Previous Year Question

After a thyristor in a power electronic converter of a wind turbine system is triggered into conduction, under which condition does it stop conducting current?
  1. It stops conducting when the reverse leakage current increases
  2. It stops conducting when the anode current falls below the holding current
  3. It stops conducting when the gate signal is removed
  4. It stops conducting when the forward voltage across it increases

Correct answer: B

Explanation

Once an SCR is latched ON, removing the gate signal does not turn it OFF. It turns OFF when its anode current is forced below the holding current (and sufficient recovery conditions are provided).

Formula

Turn-off condition: IA < IH

Step-by-step solution

Holding Current explanatory diagram

Correct Answer

B — It stops conducting when the anode current falls below the holding current

Explanation

Once an SCR is latched ON, removing the gate signal does not turn it OFF. It turns OFF when its anode current is forced below the holding current (and sufficient recovery conditions are provided).

Key Concept

Holding Current

Formula

Turn-off condition: IA < IH

Exam Point

Gate turns an SCR ON; current below holding current turns it OFF.

Common Mistake

Do not assume gate removal turns off a conventional SCR.

Common mistake

Do not assume gate removal turns off a conventional SCR.

Exam tip

Gate turns an SCR ON; current below holding current turns it OFF.

Quick method

Gate turns an SCR ON; current below holding current turns it OFF.