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GATE 2019: Electrical Machines Quiz 6

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Question 1

A 500 kVA, 3-phase transformer has iron loses of 300 W and full load copper losses of 600 W. The percentage load at which the transformer is expected to have maximum efficiency is

Question 2

A 3-phase delta/star transformer is supplied at 6000 V on the delta-connected side. The terminal voltage on the secondary side when supplying full load as 0.8 lagging power factor is 415 V. The equivalent resistance and reactance drops for the transformer are 1% and 5% respectively.
The turn’s ratio of the transformer is:

Question 3

Figure shows an ideal three–winding transformer. The three windings 1, 2, 3 of the transformer are wound on the same core as shown. The turn’s ratio N₁:N₂:N₃ is 4:2:1. A resistor of 10W is connected across winding–2. A capacitor of reactance 2.5W is connected across winding–3. Winding–1 is connected across a 400 V, ac supply. If the supply voltage phasor V₁ = 400∠0 °, the supply current phasor I₁ is given by

Question 4

A 400V/200V/200V, 50 Hz three winding transformer is connected as shown in the following figure. The reading of the voltmeter, V, will be
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Question 5

Three single-phase transformers are connected to form a 3-phase transformer bank. The transformers are connected in the following manner:

The transformer connection will be represented by

Question 6

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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ESE & GATE EE Electrical Machines

Jun 18ESE & GATE EE