1
GATE EE 2013
+2
-0.6
The following arrangement consists of an ideal transformer and an attenuator which attenuates by a factor of 0.8. An ac voltage VWX1 = 100V is applied across WX to get an open circuit voltage VYZ1 across YZ. Next, an ac voltage VYZ2 =100V is applied across YZ to get an open circuit voltage VWX2 across WX. Then, $$\frac{V_{YZ1}}{V_{WX1}}$$, $$\frac{V_{WX2}}{V_{YZ2}}$$ are respectively,
A
125/100 and 80/100
B
100/100 and 80/100
C
100/100 and 100/100
D
80/100 and 80/100
2
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
3
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
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.

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 $$D$$
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