Q61GATE 2001MCQ

A 3-phase transformer has rating of 20 MVA, 220 kV (star) - 33 kV (delta) with leakage reactance of 12%. The transformer reactance (in ohms) referred to each phase of the L.V. delta-connected side is

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📖 Explanation

\begin{aligned} [(Z)_{base}]_{per\; phase}&=\frac{(V_{phase})^2}{(S_{base})_{phase}} \\ &=\frac{(33kV)^2}{\frac{20}{3}MVA} \\ Z_{actual}&=Z_{base} \times Z_{pu} \\ &= \frac{3 \times (33)^2}{20} \times \frac{12}{100}\\ &= 19.6\Omega \end{aligned}

Q62GATE 2001MCQ

A single-phase transformer is to be switched to the supply to have minimum inrush current. The switch should be closed at

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📖 Explanation

When the value of input voltage is maximum, rate of change of core flux is minimum, as both are $90^{\circ}$ out of phase in case of sinusoidal input.

Q63GATE 2001MCQ

A 50 Hz balanced three-phase, Y-connected supply is connected to a balanced three phase Y-connected load. If the instantaneous phase-a of the supply voltage is $Vcos(\omega t)$ and the phase-a of the load current is $Icos(\omega t-\phi)$ , the instantaneous three-phase power is

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Q64GATE 2001MCQ

The core flux of a practical transformer with a resistive load

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Q65GATE 2001MCQ

In the protection of transformers, harmonic restraint is used to guard aainst

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