Question 36Electricity/Electronics - Assistant Engineer70% to pass
A 4160/480Y-277 VAC three phase power transformer bank as configured in figure "3" of the illustration produces the following voltages when 4160 VAC is applied across A1 to B1, B1 to C1, and C1 to A1. What condition is indicated? Illustration EL-0084 • A2 to B2: 480 VAC • B2 to C2: 0 VAC • C2 to A2: 0 VAC • A2 to N2: 277 VAC • B2 to N2: 277 VAC • C2 to N2: 0 VAC
AI Explanation
The correct answer is D) A few shorted turns in the secondary winding of transformer #3 (T3).
The voltages provided indicate that transformer #3 (T3) has a few shorted turns in its secondary winding. This would result in the observed secondary voltages - 480 VAC between A2 and B2, 0 VAC between B2 and C2 and C2 to A2, and 277 VAC between A2 and N2 and B2 and N2, but 0 VAC between C2 and N2. This pattern is consistent with a partially shorted secondary winding in one of the transformers.
The other answer choices are incorrect because an open secondary winding (option A) would result in 0 VAC across all secondary terminals, and a balanced transformer bank (option B) would produce the expected 480/277 VAC secondary voltages across all phases.
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