Unit 2 : Transformers MCQ's

Updated on 2017/10/11 18:22

[1] High frequency transformers sometimes make use of ferrite cores because it has
A. High specific gravity
B. High resistance
C. High hysteresis
D. low permeability

[2] Harmonics in transformer result in
A. Increased core losses
B. Increased I2R losses
C. Magnetic interference with communication circuits
D. All of the above

[3] The full load copper loss of a transformer is 1600W. At half-load the copper loss will be
A. 6400W
B. 1600W
C. 800W
D. 400W

[4] Power transformers are generally designed to have maximum efficiency around
A. No load
B. Half load
C.Near full load
D. 10% overload

[5] Two transformers are connected in parallel. These transformers do not have equal percentage impedance which results
A. Short-circuiting of the secondaries
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.

[6] The changes in volume of transformer cooling oil due to variation of atmospheric temperature during day and night is taken care of by which part of transformer?
A. Conservator
B. Breather
C. Bushings
D. Buchholz relay

[7] The transformer laminations are insulated from each other by
A. Mica strip
B. Thin coat of varnish
C. Paper
D. Any of the above

[8] Which type of winding is used in 3 phase shell type transformer?
A. Circular type
B. Sandwich type
C. Cylindrical type
D. Rectangular type

[9] During open circuit test of a transformer
A. Primary is supplied rated voltage
B. Primary is supplied full load current
C. Primary is supplied current at reduced voltage
D. Primary is supplied rated kVA

[10] Which of the following is not standard voltage for power supply in India
A. 11kV
B. 33kV
C. 66 kV
D. 122 kV

[11] The low voltage winding of a 400/230 volt, 1-phase, 50Hz transformer is to be connected to a 25Hz supply in order to keep the magnetization current at the same level as that for normal 50Hz supply at 25Hz the voltage should be [Gate 1997]
a) 230V
b) 460V
c) 115V
d) 65V

[12] The primary current in the current transformer is dictated by [Gate 1997]
a) The secondary burden
b) The core of the transformer
c) The load current
d) None of the above

13. In Single Phase Transformer, The Primary Current and Primary Voltage is 4.55 and 11kV respectively. The Rating of the transformer would be________?
a) 86kVA
b) 100kVA
c) 150kVA
d) 50kVA

14. A Transformer______________.

a) Steps up or down DC Voltages & Current
b) Changes DC to AC
c) Changes ac to DC
d) Steps up or down AC Voltages & Current

15. What would happen if a power transformer designed for operation on 50 Hz (frequency) were connected to a 5 Hz (frequency) source of the same voltage?
a) Eddy Current and Hysteresis loss will be excessive
b) Current will be too much low
c) Transformer may start to smoke
d) No effect

16. In Three Phase Transformer, The load Current is 139.1A, and Secondary Voltage is 415V. The Rating of the Transformer would be ___________.
a) 173 KVA
b) 50 KVA
c) 100KVA
d) 57.72 KVA

17. If the primary power of an ideal transformer having a 2:1 voltage ratio is 100 W, the secondary power is
a) 50W
b) 100 W
c) 75 W
d) 200 W

18. Increasing the number of turns of wire on the secondary of a transformer will
a) decrease the secondary current
b) have no effect on the secondary current
c) increase the primary current
d) increase the secondary current

19. Laminated insulations coated with varnish are normally used in the transformer
a) To reduce the effect of eddy current
b) To reduce reluctance of magnetic path
c) To reduce the hysteresis effect
d) To increase the reluctance of magnetic path

20. Laminated insulations coated with varnish are normally used in the transformer
a) To reduce the effect of eddy current
b) To reduce reluctance of magnetic path
c) To reduce the hysteresis effect
d) To increase the reluctance of magnetic path

21. The transformer turns ratio determines
a) the reflected impedance
b) the ratio of primary and secondary voltages
c) the ratio of primary and secondary currents
d) all

22. An Isolation Transformer Has Primary to Secondary turns ratio of __________.
a) 1 : 2
b) 1 : 1
c) 2 : 1
d) Can be any ratio

23. The coefficient of coupling between two coils is 0.45. The first coil has an inductance of 75 mH and the second coil has an inductance of 105 mH. What is the mutual inductance between the coils?
a) 7.88 mH
b) 3.54 mH
c) 39.9 mH
d) 189.3 mH

24. In an Auto Transformer, The Primary and Secondary are__________Coupled.
a) Magnetically as well as Electrically
b) Only Magnetically
c) Only Electrically
d) None of the above

25. When does maximum power transfer happen from the source to the load?
a) When the source resistance is less than the load resistance
b) When there is negligible source resistance
c) When the source resistance is greater than the load resistance
d) When the source resistance equals the load resistance

26. A special transformer used to convert unbalanced signals to balanced signals is the
a) autotransformer
b) step-across transformer
c) balun
d) center-tapped transformer

27. Under what condition is D.C supply applied safely to the primary of a transformer?
a) We can't connect to DC Supply
b) We can connect directly to DC. No condition required
c) A High resistance should be connect in series with primary, but circuit will be useless.
d) The above statement is wrong

28. Which of the following 3-phase connection of a transformer causes interference with the neighboring communication lines:
a) Star-delta
b) Delta-star
c) Star-star
d) Delta-star

29. An Auto-transformer (which has only one winding) may be used as a ______?
a) Step-Up Transformer
b) Step-Down Transformer
c) Both Step-Up and Step-Down transformer
d) None of these

30. The friction losses in Real Transformers are _________?
a) 5%
b) 25%
c) 50%
d) 0%


Created by Sujit Wagh on 2017/09/20 12:18