## electrical

### Transformer MCQ Objective Questions and Answers Page - 3

1.
 Power transformed from primary to secondary depends upon A Number of primary turns B Number of secondary turns C Current transformation ratio D Magnetic coupling between primary and secondary windings Answer : D Explanation :
2.
3.
 In a transformer supplying inductive load A The secondary current results in equivalent primary current in phase opposition B The secondary terminal voltage is less than the secondary induced emf. C The power factor on primary side will be lower than that of load D All of the above Answer : D Explanation :
4.
 The phasor diagram of transformer on load can be drawn only if we know A Equivalent circuit parameters of the transformer B Load current C Load pf D All of the above Answer : D Explanation :
5.
 When a transformer is operating on no load, the primary applied voltage is approximately balanced by A Primary induced emf B Secondary induced emf C Terminal voltage across the secondary D Voltage drop across the resistance and reactance Answer : A Explanation :
6.
 In the transformer circuit mode, the core loss is represented as a A Series resistance B Series inductance C Shunt resistance D Shunt inductance Answer : C Explanation :
7.
 Full load voltage regulation of a power transformer is zero when power factor of the load is near A Unity and leading B Zero and leading C Zero and lagging D Unity and lagging Answer : A Explanation :
8.
 In a transformer, zero voltage regulation at full load is A Not possible B Possible at leading power factor load C Possible at lagging power factor load D Possible at unity power factor load Answer : B Explanation :
9.
 Positive voltage regulation is an indication of ____load A Inductive B capacitive C Either inductive or capacitive D Pure resistive Answer : C Explanation :
10.
 A 4 kVA, 400/200V single-phase transformer has resistance of 0.02 pu and reactance of 0.06 pu. Its actual resistance and reactance referred to hv side, are respectively A 0.2 ohm and 0.6 ohm B 0.8 ohm and 2.4 ohm C 0.08 ohm and 0.24 ohm D 2 ohm and 6 ohm Answer : B Explanation :
11.
 If the percentage resistance of a power transformer for secondary side si 2.5 percent and turn ratio is 1:10 , the percentage secondary resistance referred to primary will be A 25 B 2.5 C 0.25 D 0.025 Answer : B Explanation :
12.
 In a 3-phase, 5kV, 5MVA system, what is the base impedance? A 5 ohms B 50 ohms C 500 ohms D 0.5 ohms Answer : A Explanation :
13.
 In a power transformer iron loss remain practically constant from no load ot full load. This is because A Core flux remains constant B Leakage flux remains constant C Both a and B D Neither a nor b Answer : A Explanation :
14.
 In a power transformer, if in place of sinusoidal wave, a peaked wave voltage is fed to the primary A Copper losses will be loess B Noise level will be reduced C Iron losses will be more D Iron losses will be less Answer : D Explanation :
15.
 The use of higher flux density in the transformer design A Reduce weight per kVA B Reduces iron losses C Reduces copper losses D Increases part load efficiency Answer : A Explanation :
16.
 The chemical used in breather for transformer should have the quality of A Ionizing air B Absorbing moisture C Cleansing the transformer oil D Cooling the transformer oil Answer : B Explanation :
17.
 The chemical used in breather is A Asbestos fibre B Silica sand C Sodium chloride D Silica gel Answer : D Explanation :
18.
 The transformer rating are usually expressed in terms of A Volts B Amperes C kW D KVA Answer : D Explanation :
19.
 The noise resulting from vibrations of laminations set by magnetic forces is termed as A magnetostriction B boo C hum D zoom Answer : C Explanation :
20.
 Hysteresis loss in a transformer varies as (Bmax = max. flux density) A Bmax B Bmax1.6 C Bmax1.85 D Bmax2.4 Answer : B Explanation :
21.
 Material used for construction of transformer core is usually A Wood B Copper C Aluminium D Silicon steel Answer : D Explanation :
22.
 The thickness of laminations used in a transformer is usually A 0.4 mm to 0.5 mm B 4mm to 5mm C 14 mm to 15 mm D 25 mm to 40 mm Answer : A Explanation :
23.
 The function of conservator in a transformer is A  to project against internal flux B To reduce copper as well as core losses C To cool the transformer oil D To take care of the expansion and contraction of transformer oil due to variation of temperature of surroundings Answer : D Explanation :
24.
 The highest voltage for transmitting electrical power in India is A 33 kV B 66 kV C 132 kV D 400 kV Answer : D Explanation :
25.
 In a transformer the resistance between its primary and secondary is A Zero B 1 ohm C 1000 ohms D Infinite Answer : D Explanation :
26.
 A transformer oil must be free from A Sludge B Odour C Gases D Moisture Answer : D Explanation :
27.
 A Buchholz relay can be installed on A Auto-transformers B Air-cooled transformers C Welding transformers D Oil cooled transformers Answer : D Explanation :
28.
 Gas is usually not liberated due to dissociations of transformer oil unless the oil temperature exceeds A 50°c B 80°c C 100°c D 150°c Answer : D Explanation :
29.
 The main reason for generation of harmonics in a transformer could be A Fluctuating load B Poor insulation C Mechanical vibration D Saturation of core Answer : D Explanation :
30.
31.
 Which of the following property is not necessarily desirable in the material for transformer core? A Mechanical strength B Low hysteresis loss C High thermal conductivity D High permeability Answer : C Explanation :
32.
 Star/star transformers work satisfactorily when A Load is unbalanced only B Load is balanced only C On balanced as well as unbalanced load D None of the above Answer : B Explanation :
33.
 Delta/star transformers work satisfactorily when A Load is balanced only B Load is unbalanced only C On balanced as well as unbalanced loads D None of the above Answer : C Explanation :
34.
 The yoke sections of transformers employing hot rolled laminations is made 15 percentage more than that of core in order to A Reduce the copper losses B Reduce the magnetizing current and iron loss in yoke C Provide better cooling D All of the above Answer : B Explanation :
35.
 The joints in the transformer core lamination are staggered so as to A Avoid continuous gap causing increase in magnetizing current B Increase the mechanical strength of the assembled core C Avoid under humming noise D All of the above Answer : D Explanation :
36.
 The degree of mechanical vibration caused by core lamination in a transformer depends on A Size of laminations B Gauge of laminations C Tightness of clamping D All of the above Answer : D Explanation :
37.
 The noise, in a transformer, caused by vibrations of laminations set by magnetic forces, is termed as A Zoom B Hum C Buzz D None of these Answer : B Explanation :
38.
 The primary and secondary windings are interlaced for A Easiness of coil making B Reduced leakage reactance C Reduced cost D Uniform heating Answer : B Explanation :
39.
 The leakage flux of primary and secondary windings can be reduced to the minimum by A Winding primary and secondary coils on separate limbs. B Winding primary and secondary coils one upon the other coaxially C Increasing the number of turns D Employing low permeability magnetic material core Answer : B Explanation :
40.
 The concentric windings are used in core type transformers with _____winding placed next to the core A LV B Primary C HV D Secondary Answer : A Explanation :
41.
 Low voltage windings are placed next to the core in the case of concentric windings as in this case _____is/are reduced A hysteresis loss B leakage fluxes C eddy current loss D insulation requirement Answer : D Explanation :
42.
 in a power transformer A primary winding is always wound with many turns of thin wire. B Secondary winding is always wound with lesser number of turns of thin wire C Low voltage winding is always wound with lesser number of turns of thicker wire D High voltage winding is always wound with larger number of turns of thicker wire. Answer : C Explanation :
43.
 In transformers, the primary and secondary are interlaced so that A There may be maximum flux linkage between the two windings B Copper is saved C Both (a) and (b) D Statements is false Answer : A Explanation :
44.
 The secondary of a current transformer is always short-circuited under operating conditions because it A Avoids core saturation and high voltage induction B Is safe to human beings C Protects the primary circuit D None of the above Answer : A Explanation :
45.
 In a transformer the resistance between its primary and secondary should be A Zero B 10Ω C 1000Ω D Infinity Answer : D Explanation :
46.
 A good voltage regulation of a transformer means A Output voltage fluctuation from no load to full load is least B Output voltage fluctuation with power factor is least C Difference between primary and secondary voltage is least D Difference between primary and secondary voltage is maximum Answer : A Explanation :
47.
 For a transformer, operating at constant load current, maximum efficiency will occur at A 0.8 leading power factor B 0.8 lagging power factor C Zero power factor D Unity power factor Answer : D Explanation :
48.
 Which of the following protection is normally not provided on small distribution transformers? A Over fluxing protection B Buchholz relay C Overcurrent protection D All of the above Answer : B Explanation :
49.
 Which of the following act as a protection against high voltage surges due to lighting and switching? A Horn gaps B Thermal overload relay C Breather D Conservator Answer : A Explanation :
50.
 The efficiency of two identical transformers under load conditions can be determined by A Short-circuit test B Back to back test C Open circuit test D Any of the a above Answer : B Explanation :
51.
 Which of the following insulating materials can be withstand the highest temperature safely? A Cellulose B Asbestos C Mica D Glass fibre Answer : C Explanation :
52.
 Which of the following parts of a transformer is visible from outside? A Bushings B Core C Primary winding D Secondary winding Answer : A Explanation :