Transformers Questions With Answers: Transformers MCQs

Transformers Questions With Answers. Multiple Choice Questions and Answers related to Transformers in Electrical and Electronics Engineering.

 

Transformers Questions With Answers

 

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 200 V A.C. supply is incorrect ?

A. Its secondary current is 5 A
B. Its secondary voltage is 400 V
C. Its rating is 2 kVA
D. Its secondary current is 20 A

View Answer

D. Its secondary current is 20 A

 

Losses which occur in rotating electric machines and do not occur in transformers are ?

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

View Answer

A. friction and windage losses

 

Which of the following protection is normally not provided on small distribution transformers ?

A. Overfluxing protection
B. Buchholz relay
C. Overcurrent protection
D. All of the above

View Answer

B. Buchholz relay

 

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

View Answer

D. unity power factor

 

In a power or distribution transformer about 10 per cent 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 absorb 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

View Answer

A. to withstand the high voltage drop due to line surge produced by the shunting capacitance of the end turns

 

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

View Answer

A. core built-up of laminations of cold rolled grain oriented steel

 

In a transformer the resistance between its primary and secondary should be ?

A. zero
B. 10 Q
C. 1000 Q
D. infinity

View Answer

D. infinity

 

The secondary of a current transformer is always short-circuited under operating conditions because it ?

A. avoids core saturation and high voltage induction
B. is safe to human beings
C. protects the primary circuit
D. none of the above

View Answer

A. avoids core saturation and high voltage induction

 

Natural air coo ling is generally restricted for transformers up to ?

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

View Answer

A. 1.5 MVA

 

If a transformer is switched on to a voltage more than the rated voltage ?

A. its power factor will deteriorate
B. its power factor will increase
C. its power factor will remain unaffected
D. its power factor will be zero

View Answer

A. its power factor will deteriorate

 

MCQs On Transformers

 

Open circuit test on transformers is conducted to determine ?

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

View Answer

C. core losses

 

The secondary winding of which of the following transformers is always kept closed ?

A. Step-up transformer
B. Step-down transformer
C. Potential transformer
D. Current transformer

View Answer

D. Current transformer

 

Part of the transformer which is most subject to damage from overheating is ?

A. iron core
B. copper winding
C. winding insulation
D. frame or case

View Answer

C. winding insulation

 

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

View Answer

C. much higher

 

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

View Answer

A. less than 15 A

 

The transformer lamination’s are insulated from each other by ?

A. mica strip
B. thin coat of varnish
C. paper
D. any of the above

View Answer

B. thin coat of varnish

 

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

View Answer

A. approximately equal to one

 

The efficiency of a transformer, under heavy loads, is comparatively low because ?

A. copper loss becomes high in proportion to the output
B. iron loss is increased considerably
C. voltage drop both in primary and secondary becomes large
D. secondary output is much less as compared to primary input

View Answer

A. copper loss becomes high in proportion to the output

 

Which of the following is the most likely source of harmonics in a transformer ?

A. poor insulation
B. Overload
C. loose connections
D. Core saturation

View Answer

D. Core saturation

 

In an actual transformer the iron loss remains practically constant from no load to full load because ?

A. value of transformation ratio remains constant
B. permeability of transformer core remains constant
C. core flux remains practically constant
D. primary voltage remains constant

View Answer

C. core flux remains practically constant

 

Transformers Questions With Answers

 

If a transformer is continuously operated the maximum temperature rise will occur in ?

A. core
B. windings
C. tank
D. any of the above

View Answer

B. windings

 

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

View Answer

A. Conservator

 

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

View Answer

C. High thermal conductivity

 

The value of flux involved m the e.m.f. equation of a transformer is ?

A. average value
B. r.m.s. value
C. maximum value
D. instantaneous value

View Answer

C. maximum value

 

Two transformers are connected in parallel. These transformers do not have equal percentage impedance. This is likely to result in ?

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

View Answer

D. loading of the transformers not in proportion to their kVA ratings

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