A 45 kVA single-phase transformer is served at 240 V. Ignoring losses, what primary current is drawn at full load?
Correct Answer
A) 187.5 A
Single-phase current is VA divided by volts: 45,000 / 240 = 187.5 A. Other choices divide by 416 V, multiply by a power factor assumption, or divide by 120 V.
Why This Is the Correct Answer
Single-phase current is VA divided by volts: 45,000 / 240 = 187.5 A. Other choices divide by 416 V, multiply by a power factor assumption, or divide by 120 V.
Why the Other Options Are Wrong
Option B: 108.3 A
single-phase transformer current, choice a: 108.3 A backs into 0.58 when divided by 45000 / 240; the accepted setup gives 1 on that same base.
Option C: 216.0 A
single-phase transformer current, choice c: 216.0 A backs into 1.15 when divided by 45000 / 240; the accepted setup gives 1 on that same base.
Option D: 375.0 A
single-phase transformer current, choice d: 375.0 A backs into 2 when divided by 45000 / 240; the accepted setup gives 1 on that same base.
Memory Technique
Store single-phase transformer current with its last math move; nearby answers are usually unfinished versions of 187.5 A.
Reference Hint
Open Mechanical and Electrical Systems for Construction Managers, 4th Ed., 2024; use the index entry or section for "Single-phase power calculation" to confirm that Single-phase current is VA divided by volts: 45,000 / 240 = 187.5 A.
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