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GATE 2014 EE (EE2) – Question 64

Power Electronics · Static V-I characteristics and firing/gating circuits for Thyristor, MOSFET, IGBT · 2 marks · Multiple choice

A single-phase SCR AC regulator supplies R = 5 Ω and L = 16 mH from 230 V, 50 Hz. Find the maximum firing angle at which device voltage remains zero throughout, and rms current through one SCR under this condition.

  1. 30° and 46 A
  2. 30° and 23 A
  3. 45° and 23 A
  4. 45° and 32 A

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Correct answer: (C) 45° and 23 A

Explanation

The load phase angle isatan(ωL/R)=atan(2π×50×0.016/5)≈45.153°. The nearest listed maximum firing angle for continuous full-wave conduction is45°. With full sinusoidal load conduction,Irms=230/√(5²+(2π×50×0.016)²)≈32.44A. Each antiparallelSCRcarries one half-cycle,so its rms current is32.44/√2≈22.94A. Thus **45°,23A,C**.