The GATE Grind

GATE 2019 EE – Question 19

Power Electronics · Single and three-phase configuration of uncontrolled rectifiers · 1 mark · Multiple choice

A six-pulse thyristor bridge rectifier is connected to a balanced three-phase, 50 Hz AC source. Assuming that the DC output current of the rectifier is constant, the lowest harmonic component in the AC input current is

  1. 100 Hz
  2. 150 Hz
  3. 250 Hz
  4. 300 Hz

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Correct answer: (C) 250 Hz

Explanation

The AC line current of a six-pulse bridge contains harmonics of order $6k\pm1$ only, so the lowest is the 5th, which is $5\times50=250$ Hz.