electrical

Transformer MCQ Objective Questions and Answers Page - 1

1.
 The basic function of a transformer is to change A The level of the voltage B The power level C The power factor D The frequency Answer : A Explanation :
2.
 In an ordinary transformer which of the following does not change A Voltage B Current C Frequency D All of the above Answer : C Explanation : In an ordinary transformer one parameter cannot be changed that is frequency.
3.
 The efficiency of a power transformer is around A 50% B 60% C 80% D 95% Answer : D Explanation :
4.
 In a transformer, electrical power is transferred from primary to secondary A Through air, B By magnetic flux C Through insulating medium D None of these Answer : B Explanation :
5.
6.
 Transformer action requires a A Constant magnetic flux B Increasing magnetic flux C Alternating magnetic flux D Alternating electric flux Answer : C Explanation :
7.
 The  flux created by the current flowing through the primary winding induces emf in A Primary winding only B Secondary winding only C Transformer core only D Both primary and secondary windings Answer : D Explanation :
8.
 The primary and secondary  windings of a power transformer always have A A common magnetic flux B Separate magnetic circuits C Wire of same size D Same number of turns Answer : A Explanation :
9.
 The iron core in a transformer provides a _____path to the main flux A Low reluctance B High reluctance C Low resistance D High conductivity Answer : A Explanation :
10.
 If rated dc voltage is applied instead of ac to the primary of a transformer A Secondary of transformer will burn B Primary of transformer will burn C Secondary voltage will be excessively high D There will be no secondary voltage Answer : B Explanation :
11.
 A transformer transforms A Voltage B Current C Voltage and current D Frequency Answer : C Explanation :
12.
 For an ideal transformer the windings should have A Maximum resistance on primary side and least resistance on secondary side B Least resistance on primary side and maximum resistance on secondary side C Equal resistance on primary and secondary sides D No ohmic resistance on either side. Answer : D Explanation : For an ideal transformer the windings should have no ohmic resistance on either side.
13.
 The core flux in transformer depends mainly on A Supply voltage B Supply voltage and frequency C Supply voltage frequency and load D Supply voltage and load but independent of frequency Answer : B Explanation : The core flux in transformer depends mainly on Supply voltage and frequency
14.
 When voltage is transformed  from primary to secondary then it is ______ A Multiplied by K2 B Multipled by K C Divided by K2 D Divided by K Answer : B Explanation :
15.
 A transformer steps up the voltage by a factor 100. The ratio of current in the primary to that in the secondary is A 1 B 100 C 0.01 D 0.1 Answer : B Explanation :
16.
 If the applied voltage to a transformer primary is increased by keeping the V/f ratio fixed, then the magnetizing current and the core loss will, respectively : A Decrease and remain the same B Increase and decrease C Both remain the same D Remain the same and increase Answer : D Explanation :
17.
 If the applied voltage of a certain transformer is increased by 50% and the frequency is reduced to 50% (assuming that the magnetic circuit remain unsaturated), the maximum core flux density will&l A Change to three times the original value B Change to 1.5 times the original value C Change to 0.5 times the original value D Remain the same as the original value Answer : A Explanation :
18.
 The applied voltage of a certain transformer is increased by 75%; while the frequency of the applied voltage is reduced by 25%. The maximum core flux density will A Increase by seven times B Increase by three times C Reduce to one quarter D Remain the same. Answer : B Explanation :
19.
 If the supply frequency of a transformer is increased, keeping the supply voltage constant , then A Both magnetizing component and core loss component of current ill decrease B Both magnetizing component and core loss component of current will increase C Magnetizing component of current will increase while core loss component of current will decrease D Magnetizing component of current will decrease while core loss component of current will increase Answer : A Explanation :
20.
 The low voltage winding of a 400/230v single phase 50 Hz transformer is to be connected to a 25 Hz supply. In order to keep the magnetization current at the same level in both the cases the voltage A 230V B 460V C 115V D 65V Answer : C Explanation :
21.
 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 :
22.
 A transformer core is laminated to A Reduce hysteresis loss B Reduce eddy current loss C Reduce copper loss D Reduce all above losses Answer : B Explanation :
23.
 The degree of mechanical vibrations produced by the laminations of a transformer depends on A  tightness of clamping B Gauge of laminations C Size of laminations D All of the above Answer : D Explanation :
24.
 The no-load current drawn by transformer is usually what percent of the full-load current? A 0.2 to 0.5 percent B 2 to 5 percent C 12 to 15 percent D 20 to 30 percent Answer : B Explanation :
25.
 The path of magnetic flux in a transformer should have A High resistance B High reluctance C Low resistance D Low reluctance Answer : D Explanation :
26.
 No-load in a transformer is carried out to determine A Copper loss B Magnetizing current C Magnetizing current and loss D Efficiency of the transformer Answer : C Explanation :
27.
 The dielectric strength of transformer oil is expected to be A 1 kV B 33 kV C 100 kV D 330 kV Answer : B Explanation :
28.
 Sumper’s test is conducted on transformer to determine A Temperature B Stray losses C All-day efficiency D None of the above Answer : A Explanation :
29.
 The permissible flux density in case of cold rolled grain-oriented steel is around A 1.7 Wb/m² B 2.7 Wb/m² C 3.7 Wb/m² D 4.7 Wb/m² Answer : A Explanation :
30.
 The efficiency of a transformer will be maximum when A Copper losses = hysteresis losses B Hysteresis losses = eddy current losses C Eddy current losses = copper losses D Copper losses = iron losses Answer : D Explanation :
31.
32.
 The purpose of providing an iron core in a transformer is to A Provide support to winding B Reduce hysteresis loss C Decrease the reluctance of the magnetic path D Reduce eddy current losses Answer : C Explanation :
33.
 Which of the following is not a part of transformer installation? A Conservator B Breather C Buchholz relay D Exciter Answer : D Explanation :
34.
 While conducting short circuit test on a transformer the following side is short-circuited A High voltage side B Low voltage side C Primary side D Secondary side Answer : B Explanation :
35.
 In the transformer following winding has got more cross-sectional area A Low voltage winding B High voltage winding C Primary winding D Secondary winding Answer : A Explanation :
36.
 A transformer transforms A Voltage B Current C Power D Frequency Answer : C Explanation :
37.
 A transformer cannot raise or lower the voltage of a D.C supply because A There is no need to change the D.C voltage B A D.C circuit has more losses C Faraday’s law of electromagnetic induction is not valid since the rate of change of flux is zero D None of the above Answer : C Explanation :
38.
 Primary winding of a transformer A Is always a low voltage winding B Is always a high voltage winding C Could either be a low voltage or high voltage winding D None of the above Answer : C Explanation :
39.
 Which winding in a transformer has more number of turns A Low voltage winding B High voltage winding C Primary winding D Secondary winding Answer : B Explanation :
40.
 Efficiency of a power transformer is of the order of A 100% B 98% C 50% D 25% Answer : B Explanation :