1
GATE EE 2012
+2
-0.6
A single phase 10 kVA, 50 Hz transformer with 1 kV primary winding draws 0.5 A and 55 W, at rated voltage and frequency, on no load. A second transformer has a core with all its linear dimensions $$\sqrt2$$ times the corresponding dimensions of the first transformer. The core material and lamination thickness are the same in both transformers. The primary windings of both the transformers have the same number of turns. If a rated voltage of 2 kV at 50 Hz is applied to the primary of the second transformer, then the no load current and power, respectively, are
A
0.7 A, 77.8 W
B
0.7 A, 155.6 W
C
1 A, 110 W
D
1 A, 220 W
2
GATE EE 2010
+2
-0.6
A balanced star-connected and purely resistive load is connected at the secondary of a star-delta transformer as shown in the figure. The line-to-line voltage rating of the transformer is 110 V/220 V. Neglecting the non-idealities of the transformer, the impedance 'Z' of the equivalent star-connected load, referred to the primary side of the transformer, is
A
(3 + j0) Ω
B
(0.866 − j0.5) Ω
C
(0.866 + j0.5) Ω
D
(1 + j0) Ω
3
GATE EE 2009
+2
-0.6

The figure above shows coil $$1$$ and $$2,$$ with dot markings as shown, having $$4000$$ and $$6000$$ turns respectively. Both the coils have a rated current of $$25$$ $$A.$$ Coil $$1$$ is excited with single phase, $$400$$ $$V,$$ $$50$$ $$Hz$$ supply.

The coils are to be connected to obtain a single-phase, $${{400} \over {1000}}\,\,V,$$ auto-transformer to drive a load of $$10$$ $$kVA.$$ Which of the options given should be exercised to realize the required auto-transformer?

A
Connect $$A$$ and $$D;$$ Common $$B$$
B
Connect $$B$$ and $$D;$$ Common $$C$$
C
Connect $$A$$ and $$C;$$ Common $$B$$
D
Connect $$A$$ and $$C;$$ Common $$D$$
4
GATE EE 2009
+2
-0.6

The figure above shows coil $$1$$ and $$2,$$ with dot markings as shown, having $$4000$$ and $$6000$$ turns respectively. Both the coils have a rated current of $$25$$ $$A.$$ Coil $$1$$ is excited with single phase, $$400$$ $$V,$$ $$50$$ $$Hz$$ supply.

In the auto-transformer obtained in Question $$30,$$ the current in each coil is

A
Coil -$$1$$ is $$25$$ $$A$$ and Coil - $$2$$ is $$10$$ $$A$$
B
Coil -$$1$$ is $$10$$ $$A$$ and Coil - $$2$$ is $$25$$ $$A$$
C
Coil -$$1$$ is $$10$$ $$A$$ and Coil - $$2$$ is $$15$$ $$A$$
D
Coil -$$1$$ is $$15$$ $$A$$ and Coil - $$2$$ is $$10$$ $$A$$
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