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

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

Correct answer: 0.78

Solution

For a single-phase fully controlled bridge with continuous current, the power factor is approximately \(\frac{2\sqrt{2}}{\pi}\cos\alpha\). With \(\alpha = 30^\circ\), this gives about 0.78. Hence the correct option is 0.78.

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