1
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
2
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 $$D$$
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.

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 $$10$$ $$A$$
4
GATE EE 2009
+2
-0.6

The star-delta transformer shown above is excited on the star side with balanced, $$4$$-wire, $$3$$-phase, sinusoidal voltage supply of rated magnitude. The transformer is under no load condition.

With both $$S1$$ and $$S2$$ open, the core flux waveform will be

A
a sinusoidal at fundamental frequency
B
flat-topped with third harmonic
C
peaky with third-harmonic
D
none of these
EXAM MAP
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