GATE 2021 IN – Question 61
A bar-primary current transformer rated 1000/1 A, 5 VA, UPF has 995 secondary turns. At 1000 A and rated burden, its ratio error is zero and phase error 30 minutes. The watt-loss component of primary excitation current is ______ A (one decimal place).
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Correct answer: 4.9 to 5.1
Explanation
Zero ratio error at rated 1000 A and nominal ratio 1000/1 implies Is=1 A. With actual turns ratio 995, the secondary ampere-turn component referred to the single-turn primary is 995 A. The first-order in-phase excitation component is Ip−995Is=**5 A**. The small phase error mainly sets the quadrature magnetizing component; retaining its cosine correction still rounds to 5.0 A.