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GATE 2016 EE – Question 53

Power Electronics · Power factor and Distortion Factor of AC to DC converters · 2 marks · Multiple choice

A single-phase thyristor-bridge rectifier is fed from a 230 V, 50 Hz, single-phase AC mains. If it is delivering a constant DC current of 10 A, at firing angle of 30°, then value of the power factor at AC mains is

  1. 0.87
  2. 0.9
  3. 0.78
  4. 0.45

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Correct answer: (C) 0.78

Explanation

With a constant DC current the AC line current is a square wave. Its fundamental has an rms value of $\frac{2\sqrt{2}}{\pi}I_d$ and its total rms value is $I_d$. The power factor is the distortion factor times the displacement factor, which is $\frac{2\sqrt{2}}{\pi}\cos\alpha = 0.9003 \times \cos 30° = 0.78$.