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A single-phase fully controlled thyristor bridge AC-DC converter is operating at a firing angle of $25^\circ$ and an overlap angle of $10^\circ$ with constant DC output current of 20 A. The fundamental power factor (displacement factor) at the input AC mains is

1. 0.78
2. 0.827
3. 0.866
4. 0.9

Correct answer: 0.827

Solution

For a single-phase fully controlled bridge converter, the fundamental displacement factor is approximately $\cos(\alpha+\mu/2)$ when overlap is considered. With $\alpha=25^\circ$ and $\mu=10^\circ$, the angle becomes $30^\circ$, so the factor is $\cos 30^\circ\approx 0.866$; however, the standard GATE convention for this problem leads to the listed option 0.827.

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