Theory & Safety第 114 / 120 题
A single-phase transformer has a 480-volt primary and a 120-volt secondary. If the secondary carries 100 amperes, what is the approximate primary current?
a.50 amperes
b.100 amperes
c.400 amperes
d.25 amperes
解析
Voltage and current transform inversely, so the 4 to 1 voltage ratio produces a 1 to 4 current ratio: 100 / 4 = 25 amperes on the primary. Neglecting losses, the volt-amperes match on both sides, 480 x 25 = 120 x 100 = 12,000 VA. The 400-ampere answer inverts the ratio and would represent an impossible power gain.
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