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GATE 2026 EE – Question 31

Electrical Machines · Single phase transformer: equivalent circuit, phasor diagram, open circuit and short circuit tests, regulation and efficiency · 1 mark · Multiple select

A 220 V/12 V single-phase transformer is designed for use in India and rated 100 VA at 50 Hz. Later, this unit is shipped to the USA where it is used as a 110 V/6 V transformer at 60 Hz.

Which of the following statements is/are correct?

  1. No-load current drawn would be smaller for operation in the USA compared to that in India
  2. For the same load current, the losses would be higher in the USA compared to that in India
  3. The peak magnetic flux density in the core would be higher while operating in the USA compared to that in India
  4. The eddy current losses in the core would be approximately 44% higher while operating in the USA compared to that in India

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Show answer and explanation

Correct answer: (A) No-load current drawn would be smaller for operation in the USA compared to that in India

Explanation

The peak flux is $\phi_m\propto V/f$: $\dfrac{110/60}{220/50}=0.417$, i.e. it drops to about 42% (C is false). A lower flux means a smaller magnetising (no-load) current: A is true. Copper losses depend on the load current, which is the same, so the losses are not higher (B false). Eddy-current loss scales as $B_m^2f^2\propto V^2$, so it is $(110/220)^2=0.25$ of the original, not 44% higher (D false).