## electrical

### Transformer MCQ Objective Questions and Answers Page - 4

1.
 The full load copper loss and iron loss of a transformer are 6,400 W and 5,000 W respectively. The copper loss and iron loss at half load will be respectively A 3,200 W and 2,500 W B 3,200 W and 5,200W C 1,600 W and 1,250W D 1,600W and 5,000w Answer : D Explanation :
2.
 If the frequency of input voltage of a transformer is increased keeping the magnitude of voltage unchanged, then A Both hysteresis loss and eddy current loss in the core will increase B Hysteresis loss will increase by eddy current loss will decrease C Hysteresis loss will decrease but eddy current loss will increase D Hysteresis loss will decrease but eddy current loss will remain unchanged Answer : D Explanation :
3.
 The total iron loss in a transformer core at normal flux density was measured at 25 Hz and at 50 Hz and was found to be 250W and 800 W respectively. The hysteresis loss at 50Hz would be A 100w B 150w C 200W D 600W Answer : C Explanation :
4.
 The hysteresis and eddy current loss of 1-phase transformer working on 200 V, 50Hz supply and Ph and Pe respectively. The percentage decrease in these losses when operated on 160 V , 40Hz supply would respectively be A 32,36 B 20,36 C 25,50 D 40,80 Answer : B Explanation :
5.
 The main purpose of performing open circuit on a transformer is to measure its A Copper loss B Core loss C Total loss D Insulation resistance Answer : B Explanation :
6.
 Open circuit test in a transformer is performed with A Rated transformer voltage B Rated transformer current C Direct current D High frequency supply Answer : A Explanation :
7.
 The open circuit test on a transformer is usually performed by exciting the low voltage winding. This is because A It draws sufficiently large no load current which can be conveniently measured B The required power input is low C It is not advisable to work on high voltage size D The voltage required is low. Answer : A Explanation :
8.
 The open circuit test on a transformer gives A Equivalent resistance and leakage reactance B Magnetizing current and core loss at rated voltage C Copper losses D Both b and c Answer : B Explanation :
9.
 In transformers, which of the following statements is valid? A In an open-circuit test, copper losses are obtained while in short-circuit test, core losses are obtained. B In an open-circuit test, current is drawn at high power factor. C In a short-circuit test, current is drawn at zero power factor. D In an open-circuit test, current is drawn at low power factor. Answer : D Explanation :
10.
 During short circuit test, the core losses are negligible. This is because A The voltage applied across the high voltage side is a fraction of its rated voltage and so is the mutual flux B The current on the Iv side is very small C The power factor is high D Iron becomes fully saturated Answer : A Explanation :
11.
 While performing the open circuit and short circuit tests on a transformer to determine parameters the status of the low voltage (LV) and high voltage (HV) windings will be such that A In OC, LV is open and in SC HV is shorted B In OC, HV is open and in SC LV is shorted C In OC, LC is open and in SC LV is shorted D in OC, HV is open and in SC HV is shorted Answer : B Explanation :
12.
 For a transformer to be tested at full load conditions but consuming only losses form the mains, we do A Load test B Open circuit and short circuit tests C Back to back test D None of the above Answer : C Explanation :
13.
 The efficiency of two identical transformers under load conditions can be determined by A Back to back test B Open circuit test C Short circuit test D Any of the above Answer : A Explanation :
14.
 The efficiency of a power transformer can be determined indirectly by A Open circuit test alone B Short circuit test alone C Open circuit and short circuit tests D Back to back test Answer : C Explanation :
15.
 The transformer efficiency at relatively light loads is quite low. This is due to A Small copper losses B Small secondary output C High fixed loss in comparison to the output D Poor power factor. Answer : C Explanation :
16.
 The transformer efficiency, under heavy loads is comparatively low doe to A Large increase in copper losses in comparison to the output B Large increase in iron losses C Drop in power factor D None of the above Answer : A Explanation :
17.
 The full load copper loss and iron loss of a transformer are 6,400 W and 500 W, respectively. The above copper loss and iron loss at half load will be A 3,200 W and 250 W respectively B 3200W and 500W respectively C 1,600 W and 125 W respectively D 1,600 W and 500 W respectively Answer : D Explanation :
18.
 The efficiency of a 100 kVA transformer is 0.98 at full as well as half load. For this transformer at full load the copper loss A Is less than core less B Is equal to core loss C Is more than corer loss D None of the above Answer : C Explanation :
19.
 Buchholz’s relay gives warning and protection against A Electrical fault inside the transformer itself B Electrical fault outside the transformer in outgoing feeder C For both outside and inside faults D None of the above Answer : A Explanation :
20.
 The magnetizing current of a transformer is usually small because it has A Small air gap B Large leakage flux C Laminated silicon steel core D Fewer rotating parts Answer : A Explanation :
21.
 Which of the following does not change in an ordinary transformer? A Frequency B Voltage C Current D Any of the above Answer : A Explanation :
22.
 Which of the following properties is not necessarily desirable for the material for transformer core? A Low hysteresis loss B High permeability C High thermal conductivity D Adequate mechanical strength Answer : C Explanation :
23.
 The leakage flux in a transformer depends upon A Load current B Load current and voltage C Load current, voltage and frequency D Load current, voltage, frequency and power factor Answer : A Explanation :
24.
 The path of magnetic flux in transformer should have A High reluctance B Low reluctance C High resistance D Low resistance Answer : B Explanation :
25.
 Noise level test in a transformer is a A Special test B Routine test C Type test D None of the above Answer : C Explanation :
26.
 Which of the following is not a routine test on transformers? A Core insulation voltage test B Impedance test C Radio interference test D Polarity test Answer : C Explanation :
27.
 A transformer can have zero voltage regulation at A Leading power factor B Lagging power factor C Unity power factor D Zero power factor Answer : A Explanation :
28.
 Helical coils can be used on A Low voltage side of high kVA transformers B High frequency transformer C High voltage side of small capacity transformers D High voltage side of high kVA rating transformers Answer : A Explanation :
29.
 Harmonics in transformer result in A Increased core losses B Increased I²R losses C Magnetic interference with communication circuits D All of the above Answer : D Explanation :
30.
 The core used in high frequency transformer is usually A Copper core B Cost iron core C Air core D Mild steel core Answer : C Explanation :
31.
 The full-load copper loss of a transformer is 1600 W.at the full-load, the copper loss will be A 6400 W B 1600 W C 800 W D 400 W Answer : D Explanation :
32.
 The value of flux involved in the e.m.f equation of a transformer is A Average value B R.M.S value C Maximum value D Instantaneous value Answer : C Explanation :
33.
 Silicon steel used in lamination mainly reduce A Hysteresis loss B Eddy current loss C Copper loss D All of the above Answer : A Explanation :
34.
 Which winding of the transformer has less cross-sectional area? A Primary winding B Secondary winding C Low voltage winding D High voltage winding Answer : D Explanation :
35.
36.
 Which of the following is the main advantage of an auto-transformer over a two-winding transformer? A Hysteresis losses are reduced B Saving in winding material C Copper losses are negligible D Eddy losses are totally eliminated Answer : B Explanation :
37.
 During short-circuit test iron losses are negligible because A The current on secondary side is negligible B The voltage on secondary side does not vary C The voltage applied on primary side is low D Full-load current is not supplied to the transformer Answer : C Explanation :
38.
 The transformers are connected in parallel. These transformers do not have equal percentage impedance. This is likely to result in A Short-circuited of the secondary B Power factor of one of the transformers is leading while that of the other lagging C Transformers having higher copper losses will have negligible core losses D Loading of the transformers not in proportion to their kVA ratings Answer : D Explanation :
39.
 In a large capacity transformer, 5% of the turns at the end of hv winding are provided with extra insulation so as to provide protection. A Against corona B Against lightening C Due to surges occurring during switching operations D All of the above Answer : C Explanation :
40.
 When a transformer winding suffers a short circuit, the adjoining turns of the same winding experience A An attractive force B A repulsive force C Above Two Force D No force Answer : A Explanation :
41.
 Under short circuit condition, the windings of transformer having 5% impedance will experience a radial force A 5 times of full load value B 20 times of full load value C 25 times of full load value D 400 times of full load value Answer : D Explanation :
42.
 Major insulation in a transformer is the insulation between the A Iv winding and core B Iv winding and hv winding C Turns of the winding turns D Both (a) and (b) Answer : D Explanation :
43.
 Minor insulation in a transformer is the insulation between the A Iv and hv windings B Turns of the windings C Layers of the windings D Both (b) and (c) Answer : D Explanation :
44.
 In a transformer an insulating material may fail due to A Moisture B Dust C Voids in the winding D Any one or more of the above Answer : D Explanation :
45.
 The function of oil in a transformer is A To provide insulation and cooling B To provide protection against lightning C To provide protection against short circuit D To provide lubrication Answer : A Explanation :
46.
 The color of fresh dielectric oil used in transformers is A Dark brown B Pale yellow C Pale pink D White grey Answer : B Explanation :
47.
 The transformer oil should have A High dielectric strength B Low viscosity to provide good heat transfer C Low volatility D All of the above Answer : D Explanation :
48.
 Transformer oil must be free from A Moisture B Sludges C Gases D Sulphur Answer : A Explanation :
49.
 Which of the following loss in a transformer is zero even at full load? A Core loss B Friction loss C Eddy current loss D Hysteresis loss Answer : B Explanation :
50.
 Which of the following is the most likely source of harmonic in transformer? A Poor insulation B Overload C Loose connections D Core saturations Answer : D Explanation :
51.
 If a transformer is continuously operated the maximum temperature rise will occur A Core B Winding C Tank D Any of the above Answer : B Explanation :
52.
 The hum in a transformer is mainly attributed to A Load changes B Oil in the transformer C Magnetostriction D Mechanical vibrations Answer : C Explanation :
53.
 The maximum load that power transformer can carry is limited by its A Temperature rise B Dielectric strength of the coil C Voltage ratio D Copper loss Answer : C Explanation :
54.
 The efficiency of a transformer, under heavy loads, is comparatively low because A Copper loss becomes high in proportion to the output B Iron loss is increased considerably C Voltage drop both in primary and secondary becomes large D Secondary output is much less as compared to primary input Answer : A Explanation :
55.
 An open-circuit test on a transformer is conducted primarily to measure A Insulation resistance B Copper loss C Core loss D Total loss Answer : C Explanation :
56.
 A no-load test is performed on a transformer to determine A Core loss B Efficiency C Magnetising current D Magnetising current and loss Answer : D Explanation :
57.
 The voltage transformation ratio of a transformer is equal to the ratio of A Primary turns to secondary turns B Secondary current to primary current C Secondary induced e.m.f to primary induced e.m.f D Secondary terminal voltage to primary applied voltage Answer : C Explanation :
58.
 Part of the transformer which is most subject to damage from overheating is A Iron core B Copper winding C Frame of case D Transformer tank Answer : C Explanation :