A thyristor string is built from SCRs in series and parallel and must handle 11 kV and 4 kA. Each available SCR is rated 1800 V and 1000 A. For a string efficiency of 90%, if a SCRs are in series and b in parallel, what are a and b?
Correct answer A. 7, 5
Explanation
Series: 11000/(0.9 × 1800) = 6.8, rounded up to 7. Parallel: 4000/(0.9 × 1000) = 4.4, rounded up to 5. So a = 7 and b = 5.
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