MULTIPLE CHOICE QUESTIONS
Q.1 In operating a 400 Hz transformer at 50 Hz
(A) only voltage is reduced in the same proportion as
the frequency
(B) only kVA rating is reduced in the same proportion
as the frequency
(C) both voltage and kVA rating are reduced in the
same proportion as the frequency
(D) none of the above.
Q.2 The voltage applied to the h.v. side of a transformer
during short-circuit test is 2% of its rated voltage. The core loss will
be.......percent of the rated core loss.
(A) 4
(B) 0.4
(C) 0.25
(D) 0.04
Q.3 Transformers are rated in kVA instead of kW
because
(A) load power factor is often not known
(B) kVA is fixed whereas kW depends on load p.f.
(C) total transformer loss depends on voltampere
(D) it has become customary.
Q.4 When a 400-Hz transformer is operated at 50 Hz its
kVA rating is
(A) reduced to 1/8
(B) increased 8 times
(C) unaffected
(D) increased 64 times.
Q.5 At relatively light loads, transformer efficiency
is low because
(A) secondary output is low
(B) transformer losses are high
(C) fixed loss is high in proportion to the output
(D) Cu loss is small.
Q.6 A 200 kVA transformer has an iron loss of 1 kW and
full-load Cu loss of 2kW. Its load kVA corresponding to maximum efficiency is
....... kVA.
(A) 100
(B) 141.4
(C) 50
(D) 200
Q.7 If Cu loss of a transformer at 7/8th full load is
4900 W, then its full-load Cu loss would be
.......watt.
(A) 5600
(B) 6400
(C) 375
(D) 429
Q.8 The ordinary efficiency of a given transformer is
maximum when
(A) it runs at half full-load
(B) it runs at full-load
(C) its Cu loss equals iron loss
(D) it runs slightly overload.
Q.9 The output current corresponding to maximum
efficiency for a transformer having core loss of 100 W and equivalent
resistance referred to secondary of 0.25 Ω is ....... ampere.
(A) 20
(B) 25
(C) 5
(D) 400
Q.10 The maximum efficiency of a 100-kVA transformer
having iron loss of 900 kW and F.L. Cu loss of 1600 W occurs at ....... kVA.
(A) 56.3
(B) 133.3
(C) 75
(D) 177.7
