Discussion
What firing angle would that bridge need to deliver 150 V?
Answer: B
Correct answer: 44 degrees
From \( V_{dc} = (2V_m/\pi)\cos\alpha \) with the 230 V supply of the preceding item, \( 2V_m/\pi \approx 207 \) V, so
\[ \cos\alpha = \frac{150}{207} = 0.724 \quad \Rightarrow \quad \alpha \approx 44^\circ \]The 136 degree answer is the supplement, which would give minus 150 V - the same magnitude but with the bridge inverting rather than rectifying, so the machine would be braking rather than motoring.
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