Transformer MCQS Part -07

 


1. An open-circuit test on a transformer is conducted primarily to measure

A. insulation resistance
B. copper loss
C. core loss
D. total loss


Answer:  C

 
2. In a transformer the energy is conveyed from primary to secondary

A. through cooling coil
B. through air
C. by the flux
D. none of the above

Answer:  C

 
3. The voltage transformation ratio of a transformer is equal to the ratio of

A. primary turns to secondary turns
B. secondary current to primary current
C. secondary induced e.m.f. to primary induced e.m.f.
D. secondary terminal voltage to primary applied voltage

Answer:  C

 
4. Iron loss of a transformer can be measured by

A. low power factor wattmeter
B. unity power factor wattmeter
C. frequency meter
D. any type of wattmeter

Answer:  A

 
5. The efficiency of a power transformer is of the order of

A. 100 per cent
B. 98 per cent
C. 50 per cent
D. 25 per cent

Answer:  B

 
6. 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

 
7. Which of the following properties is not necessarily desirable for the material for transformer core?

A. Low hysteresis loss
B. High permeability
C. High thermal conductivity
D. Adequate mechanical strength

Answer:  C


8. Natural air cooling is generally restricted for transformers up to

A. 1.5 MVA
B. 5 MVA
C. 15 MVA
D. 50 MVA

Answer:  A

 
9. 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

 
10. In a transformer the resistance between its primary and secondary is

A.zero
B.1 ohm
C.1000 ohms
D.infinite


Answer:  D


11. 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


12. 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 above


Answer: B


13. 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



14. Helical coils can be used on

A.low voltage side of high kVA transformers
B.high frequency transformers
C.high voltage side of small capacity transformers
D.high voltage side of high kVA rating transformers


Answer: A



15. 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


16. Auto-transformer is recommended for the transformation ratio:

A. 1
B. 5
C. 1.1
D. 5

Answer: C


17. From no load to full load condition, the Iron losses in real transformer:

A. Remain constant
B. Increase upto 25% of orginal losses
C. Decrease by 13% of original losses
D. None of these

Answer: A


18. The Eddy losses depends on:

A. Frequency
B. Flux density
C. Thickness
D. All of these

Answer: D


19. Scott connection in transformers are used when:

A. Three-phase to two-phase transformation is required
B. Single-phase to two-phase transformation is required
C. Three-phase to two and three-phase transformation is required
D. For all of these

Answer: B


20. The PF of the transformer:

A. Unity
B. Leading
C. Lagging
D. Depends on load

Answer: D


21. The transformer oil should have:

A. Low viscosity and Low volatility
B. Low viscosity and High volatility
C. High viscosity and Low volatility
D. High viscosity and High volatility

Answer: A


22. Which of following will be the smallest transformer
Figure the smallest transformer:

A. 5 kVA, 1000 Hz
B. 5 kVA, 2000 Hz
C. 5 kVA, 3000 Hz
D. 5 kVA, 4000 Hz

Answer: D

Explanation: Size of transformer is inversely proportional to the frequency.


23. Which one of following is a step-up transformer dealing with high frequency:

A. CT
B. PT
C. Tesla coil
D. None of these

Answer: C


24. The primary winding of a transformer can be considered as:

A. A powered inductor
B. A powered capacitor
C. Both of these
D. None of these

Answer: A

25. Transformer windings are tapped in the middle because

A. It eliminates axial forces on the windings
B. It eliminates radial forces on the windings
C. It reduces insulation requirement
D. None of these

Answer: A

26. Which of the following materials is used to absorb moisture from air entering the transformer ?

A. Silica sand
B. Silical gel
C. Felt pad
D. Sodium chloride

Answer: B

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

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

Answer: A

28. A tap changer is used on a trans-former for

A. Adjustment in power factor
B. Adjustment in secondary voltage
C. Adjustment in primary voltage
D. Adjustments in both primary and secondary voltage

Answer: B

29. Overcurrents in a transformer affect

A. Insulation life
B. Temperature rise
C. Mechanical stress
D. All of these

Answer: D

30. Highest rating transformers are likely to find application in

A. Generation
B.  Transmission
C.  Distribution
D.  Substation

Answer: A





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