Transformer MCQS Part -04



1. The efficiencies of transformers compared with that of electric motors of the same power are

A. about the same
B. much smaller
C. much higher
D. somewhat smaller

Answer:  C

 
2. The noise resulting from vibrations of laminations set by magnetic forces, is termed as

A. Magnetostriction
B. Boo
C. Hum
D. Zoom

Answer:  C

3. The power transformer is a constant

A. voltage device
B. current device
C. power device
D. main flux device

Answer:  D

4. Sumpner's test is conducted on transformers to determine

A. temperature
B. stray losses
C. all-day efficiency
D. none of the above

Answer:  A


5. For the parallel operation of single phase transformers it is necessary that they should have

A. same efficiency
B. same polarity
C. same kVA rating
D. same number of turns on the secondary side.

Answer: Option B

 
6. In a transformer routine efficiency depends upon

A. supply frequency
B. load current
C. power factor of load
D. both (B) and (C)

Answer:  D

 
7. No-load on a transformer is carried out to determine

A. copper loss
B. magnetising current
C. magnetising current and loss
D. efficiency of the transformer

Answer:  C

 
8. The dielectric strength of transformer oil is expected to be

A. lkV
B. 33 kV
C. 100 kV
D. 330 kV

Answer:  B

 
9. A transformer oil must be free from

A. sludge
B. odour
C. gases
D. moisture

Answer:  D

 
10. Losses which occur in rotating electric machines and do not occur in trans formers are

A. friction and windage losses
B. magnetic losses
C. hysteresis and eddy current losses
D. copper losses

Answer:  A

 
11. 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

 
12. The 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

 
13. Negative voltage regulation is indicative that the load is

A. capacitive only
B. inductive only
C. inductive or resistive
D. none of the above

Answer: A

 
14. Which motor is preferred for use in mines where explosive gases exist?

A. Air motor
B. Induction motor
C. Shunt motor
D. Synchronous motor

Answer:  A

 
15. Which type of winding is used in 3phase shell-type transformer?

A. Circular type
B. Sandwich type
C. Cylindrical type
D. Rectangular type

Answer:  B

 
16. The hum in a transformer is mainly attributed to

A. load changes
B. oil in the transformer
C. magnetostriction
D. mechanical vibrations

Answer:  C

 
17. An ideal transformer is one which has
A. no losses and magnetic leakage
B. interleaved primary and secondary windings
C. a common core for its primary and secondary windings
D. core of stainless steel and winding of pure copper meta 

Answer: Option A

 
18. Noise level test in a transformer is a

A. special test
B. routine test
C. type test
D. none of the above

Answer:  C


19. The 'crawling' in an induction motor is caused by

A. high loads
B. low voltage supply
C. improper design of machine
D. harmonics developed in the motor

Answer:  D


20. Open circuit test on transformers is conducted to determine

A. hysteresis losses
B. copper losses
C. core losses
D. eddy current losses

Answer:  C

 
21. Short circuit test on transformers is conducted to determine

A. hysteresis losses
B. copper losses
C. core losses
D. eddy current losses

Answer:  B

 
22. In a certain transformer, the input power to the primary is 120 W. If 8.5 W are lost to the winding resistance, what is the output power to the load, neglecting any other issues?

A. 0 W
B. 14.1 W
C. 111.5 W
D. 1,020 W

Answer:  C


23. Which of the following acts as a protection against high voltage surges due to lightning and switching?

A. Horn gaps
B. Thermal overload relays
C. Breather
D. Conservator

Answer:  A

 
24. The power factor of an induction motor under no-load conditions will be closer to

A. 0.2 lagging
B. 0.2 leading
C. 0.5 leading
D. unity

Answer:  A


 
25. Auto-transformer makes effective saving on copper and copper losses, when its transformation ratio is

A. approximately equal to one
B. less than one
C. great than one
D. none of the above

Answer: A

 
26. The path of a magnetic flux in a transformer should have

A. high resistance
B. high reluctance
C. low resistance
D. low reluctance

Answer:  D


27. The path of the magnetic flux in the transformer should have

A. high reluctance
B. low reactance
C. high resistance
D. low resistance

Answer:  B

 
28. 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


29. 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


30. In a step-down transformer, there is a change of 15 A in the load current. This results in change of supply current of

A. less than 15 A
B. more than 15 A
C. 15 A
D. none of the above

Answer: A


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