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Transformer
Chapter-1
GATE-16. A single-phase 50 kVA, 250 V/500V two winding transformer has an
efficiency of 95% at full load, unity power factor. If it is reconfigured as a
500V/750V autotransformer, its efficiency at its new rated load at unity
power factor will be:
[GATE-2007]
(a) 95.752% (b) 97.851% (c) 98.276 % (d) 99.241%
Statement for Linked Answer Questions Q17 and Q18:
The figure above shows coils 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.
GATE-17. The coils are to be connected to obtain a single-phase, 400 ,
1000 V autotransformer
to drive a load of 10 kVA.Which of the options given should
be exercised to realize the required auto-transformer [GATE-2009]
(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
GATE-18. In the autotransformer obtained in Question 97, the current in each coil
is:
[GATE-2009]
(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.
Per-unit System
GATE-19. The resistance and reactance of a 100 kVA 110001400V, Δ – Y distribution
transformer are 0.02 and 0.07 pu respectively. The phase impedance of
the transformer referred to the primary is:
[GATE-2004]
(a) (0.02 + j0.07)Ω
(b) (0.55 + j 1.925)Ω
(c) (15.125 + j52.94)Ω
(d) (72.6 + j254.1)Ω
Transformer Construction
GATE-20. The equivalent circuit of a transformer has leakage reactances X, 1
X', 2
and magnetizing reactance X
M
. Their magnitudes satisfy [GATE-2005]
X X' X
(a)
1 2 M
(b) X
1
X'
2
XM
(c) X
1
≈ X'
2
X
M
(d) X
1
≈ X'
2
X
M
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