## electrical

### Transformer MCQ Objective Questions and Answers Page - 2

1.
 A single phase transformer rated for 220/240V,  50Hz operates at no load at 220 V , 40 Hz. This frequency operation at rated voltage  results in which one of the following A Increase of both eddy current and hysteresis losses. B Reduction of both eddy current and hysteresis losses C Reduction of hysteresis loss and increase in eddy current loss. D Increase of hysteresis loss and no change in the eddy current loss. Answer : D Explanation :
2.
 A 50 Hz transformer having equal hysteresis and eddy current losses at rated excitation is operated at 45Hz at 90% of its rated voltage . Compared to rated operating point, the core loses under thi A Reduce by 10% B Reduce by 19% C Reduce by 14.5% D Remain unchanged Answer : C Explanation :
3.
 A single phase transformer when supplied form 220V , 50 Hz has eddy current loss of 50W. If the transformer is connected to a voltage of 330V, 50Hz the eddy current loss will be A 168.75W B 112.5W C 75W D 50W Answer : B Explanation :
4.
 1 kVA, 230V, 50Hz single phase transformer has an eddy  current loss of 30 watts. The eddy current loss when the transformer is excited by a dc source of same voltage will be A 30 watt B More than 30 W C Less than 30 watts D Zero will Answer : D Explanation :
5.
 At 50 Hz operation, a single phase transformer has hysteresis loss of  200 W and eddy current loss of 100 W. Its core loss at 60 Hz operation will be A 432W B 408W C 384W D 360W Answer : C Explanation :
6.
 Can a 50Hz transformer be used for 25Hz, if the input voltage is maintained constant at the rated value corresponding to 50H A Yes, since the voltage is constant current level will not change B No, flux will be doubled which will drive the core to excessive saturation C No, owing to decreased resistance of transformer, input current will be doubled at the load D Yes, at constant voltage , insulation will not be overstressed. Answer : B Explanation :
7.
 On no load phasor diagram of transformer, the core loss component of the current remains in phase with A No load current B Primary supply voltage C Core flux D Primary induced voltage Answer : B Explanation :
8.
 In a transformer core, third and fifth harmonic components of fluxes are respectively 10% and 4% of the fundamental flux. The third and fith harmonic induced emfs in the winding in terms of the fun A 30%, 20% B 10%, 12% C 50%,  20% D 50%,  12% Answer : A Explanation :
9.
 If a sinusoidal voltage source is connected to a power transformer, its no load current would be A Sinusoidal and lagging the voltage by 900 B Sinusoidal and lagging the  voltage by less than 900 C Rich in third harmonic and its fundamental would lag the voltage by 900 D Rich in third harmonic and its fundamental would lag the voltage by less than 900 Answer : D Explanation :
10.
 In a transformer , the exciting current will be in phase quadrature with the impressed voltage provided A Only the leakage impedance drop is ignored B Only the core loss is ignored C Both the leakage impedance drop and the core loss are ignored D Only the no load copper loss is ignored Answer : C Explanation :
11.
 The power factor of a power transformer on no load will bne about A Unity B 0.75 C 0.5 D 0.35 Answer : D Explanation :
12.
 The power factor of a transformer on no loadis poor due to A Magnetizing reactance of the transformer B Open circuited secondary C Low primary winding resistance D Low no load current Answer : A Explanation :
13.
 If in a transformer core a material having high reluctance path but having same hystersis loop is employed A Ie will increase B Im will increase C Im will decrease D Both Im and Ie will increase Answer : B Explanation :
14.
 Primary winding of a transformer comprises of two identical windings in parallel. If one winding is removed, magnetizing current will b A Halved B The same C Doubled D Increased four times Answer : C Explanation :
15.
 The core flux of a practical transformer  with a resistance load A Is strictly constant with load changes B Increases linearly with load C Increases as the square root of the load D Decreases with increase of load Answer : A Explanation :
16.
 The inductive reactance of a transformer depends on A Electromotive force B Magneto motive force C Magnetic flux D Leakage flux Answer : D Explanation :
17.
 The flux in transformer core A Increases with load B Decreases with load C Remains constant irrespective of load D None of the above Answer : C Explanation :
18.
 The mutual flux in a loaded transformer can be varied by varying A Primary current B Load impedance C Secondary current D Reluctance of he magnetic path Answer : D Explanation :
19.
 The primary ampere turns are counter balanced by A Secondary ampere turns B Primary flux C Increase in mutual flux D Increase in secondary current Answer : A Explanation :
20.
 In a transformer_____ decreases with the increase in leakage flux A Primary induced emf B Secondary induced emf C Secondary terminal voltage D None of the above Answer : C Explanation :
21.
 In a given transformer for given applied voltage, losses which remain constant irrespective of load changes are A Friction and windage losses B Copper losses C Hysteresis and eddy current losses D None of the above Answer : C Explanation :
22.
 A common method of cooling a power transformer is A Natural air cooling B Air blast cooling C Oil cooling D Any of the above Answer : C Explanation :
23.
 The no-load current in a transformer lags behind the applied voltage by an angle of about A 180° B 120° C 90° D 75° Answer : D Explanation :
24.
 In a transformer routine efficiency depends upon A Supply efficiency B Load current C Power factor of load D Both (b) and (c) Answer : D Explanation :
25.
 In the transformer the function of a conservator is to A Provide fresh air for cooling the transformer B Supply cooling oil to transformer in time of need C Protect the transformer from damage when oil expends due to heating D None of the above Answer : C Explanation :
26.
 Natural oil cooling is used for transformer upto a rating of A 3000 kVA B 1000 kVA C 500 kVA D 250 kVA Answer : A Explanation :
27.
 Power transformers are designed to have maximum efficiency at A Nearly full load B 70% full load C 50% full load D No load Answer : A Explanation :
28.
 The maximum efficiency of a distribution transformer is A At no load B At 50% full load C At 80% full load D At full load Answer : B Explanation :
29.
 Transformer breathes in when A Load on it increases B Load on it decreases C Load remains constant D None of the above Answer : B Explanation :
30.
 No-load current of a transformer has A Has high magnitude and low power factor B Has high magnitude and high-power factor C Has small magnitude and high-power factor D Has small magnitude and low power factor Answer : D Explanation :
31.
 Spacer are provided between adjacent coils A To provide free passage to the cooling coil B To insulate the coils from the each other C Bot (a) and (b) D None of the above Answer : A Explanation :
32.
 Greater the secondary leakage flux A Less will be the secondary induced e.m.f B Less will be the primary induced e.m.f C Less will be the primary terminal voltage D None of the above Answer : A Explanation :
33.
 The purpose of providing iron core in a step-up transformer is A To provide coupling between primary and secondary B To increase the magnitude of mutual flux C To decrease the magnitude of magnetizing current D To provide all of the above features Answer : C Explanation :
34.
 The power transformer is a constant A Voltage device B Current device C Power device D Main flux device Answer : D Explanation :
35.
 Two transformers operating in parallel will share the load depending upon their A Leakage reactance B Per unit impedance C Efficiencies D Ratings Answer : B Explanation :
36.
 What will happen if the transformers working in parallel are not connected with regard to polarity? A The power factor of the two transformers will be different from the power factor of common load B Incorrect polarity will result in dead short circuit C The transformers will not share load in proportion to their kVA ratings D None of the above Answer : B Explanation :
37.
 If the percentage impedances of the two transformers working in parallel is different, then A Transformer will be overheated B Power factor of both the transformers will be same C Parallel operation will be not possible D Parallel operation will still be possible, but the power factor at which the two transformers operates will be different from the power factor of the common load Answer : D Explanation :
38.
 In a transformer the tapings are generally provided on A Primary side B Secondary side C Low voltage side D High voltage side Answer : C Explanation :
39.
 Cores of large power transformers are made from which one of the followings? A Hot rolled steel B Cold rolled non grain-oriented steel C Cold rolled grain-oriented steel D Ferrite Answer : C Explanation :
40.
 Grain oriented laminated sheet steel in transformer reduces A Copper loss B Eddy current loss C Hysteresis loss D None of eh above Answer : C Explanation :
41.
 Silicon content in iron laminations is kept within 5% as it A Increases hysteresis loss B Increases cost C Makes the material brittle D Reduces the curie point Answer : C Explanation :
42.
 The permissible flux density in cold rolled grain-oriented steel is about A 1.8T B 2.5T C 3.5T D 4.5T Answer : A Explanation :
43.
 If the iron core of a transformer is replaced by an air core, then the hysteresis losses in the transformer will A Increase B Decrease C Remain unchanged D Become zero Answer : D Explanation :
44.
 Which of the following will improve the mutual coupling between primary and secondary circuits? A Transformed oil of high breakdown voltage B High reluctance magnetic core C Winding material of high resistivity D Low reluctance magnetic core. Answer : D Explanation :
45.
 In order to reduce the hysteresis loss A Core may be laminated B Silicon steel may be used as the core material C Core may be constructed with any permanent magnet material such as Alnico D Core may be impregnated with varnish Answer : B Explanation :
46.
 Why is the core of the transformer built up of laminations? A To reduce eddy current loss B For convenience of fabrication C No specific advantage D For increasing the permeability Answer : A Explanation :
47.
 When are eddy current losses in a transformer reduced? A If laminations are thick B If the number of turns in primary winding is reduced C If the number of turns in secondary winding is reduced D If laminations are thin. Answer : D Explanation :
48.
 Transformer core laminations are coated with an enamel layer in order to A Reduce hum B Attain adhesion between laminations C Insulate laminations from each other D Prevent corrosion of the lamination Answer : C Explanation :
49.
 A shell-type transformer has A High eddy current losses B Reduced magnetic losses C Negligibly hysteresis losses D None of the above Answer : B Explanation :
50.
 A transformer can have regulation closer to zero A On full-load B On overload C On leading power factor D On zero power factor Answer : C Explanation :
51.
 A transformer transforms A Voltage B Current C Current and voltage D Power Answer : D Explanation :
52.
 Which of the following is not the standard voltage for power supply in India? A 11 KV B 33 kV C 66 KV D 122 kV Answer : D Explanation :
53.
 Reduction in core losses and increase in permeability are obtained with transformer employing A Core built-up of laminations of cold rolled grain-oriented steel B Core built-up of laminations of hot rolled sheet C Either of the above D None of the above Answer : A Explanation :
54.
 In a power or distribution transformer about 10% end turns are heavily insulated A To withstand the high voltage, drop due to line surge produced by the shunting capacitance of the end turns B To absorbs the line surge voltage and save the winding of transformer from damage C To reflect the line surge and save the winding of a transformer from damage D None of the above Answer : A Explanation :
55.
 For a given applied voltage, with the increase in frequency of the applied voltage A Eddy current loss will decrease B Eddy current loss will increase C Eddy current loss will remain unchanged D None of the above Answer : C Explanation :
56.
 Losses which occurs in rotating electric machines and do not occurs in transformers are A Friction and windage losses B Magnetic losses C Hysteresis and eddy current losses D Copper losses Answer : A Explanation :
57.
 In a given transformer for a given applied voltage, losses which remain constant irrespective of load changes are A Hysteresis and eddy current losses B Friction and windage losses C Copper losses D None of the above Answer : A Explanation :
58.
 Which of the following statements regarding an ideal single-phase transformer having a turn ratio of 1:2 and drawing a current of 10 A from 200V A.C supply is incorrect? A Its secondary current is 5 A B Its secondary voltage is 400V C Its rating is 2 kVA D Its secondary current is 20 A Answer : D Explanation :