Deck 5: Transformers: Voltage Regulation, Efficiency, and Protection

Question 1

A transformer can have regulation closer to zero

A)on full-load
B)on overload
C)on leading power factor
D)on zero power factor

Answer 1

on leading power factor

Question 2

A transformer transforms

A)voltage
B)current
C)current and voltage
D)power

Answer 2

power

Question 3

Which of the following is not the standard voltage for power supply in India ?

A)llkV
B)33kV
C)66 kV
D)122 kV

Answer 3

122 kV

Question 4

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

Question 5

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 fromdamage
C)to reflect the line surge and save the winding of a transformer from damage
D)none of the above

Question 6

For given applied voltage, with the increase in frequency of the applied voltage

A)eddy current loss will decrease
B)eddy current loss will increase
C)eddy current loss will remain unchanged
D)none of the above

Question 7

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

Question 8

In a given transformer for a given applied voltage, losses which remainconstant irrespective of load changes are

A)hysteresis and eddy current losses
B)friction and windage losses
C)copper losses
D)none of the above

Question 9

Which of the following statements regarding an idel single-phase transformerhaving 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

Question 10

The secondary of a current transformer is always short-circuited underoperating 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

Question 11

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

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

Question 12

A good voltage regulation of a transformer means

A)output voltage fluctuation from no load to full load is least
B)output voltage fluctuation with power factor is least
C)difference between primary and secondary voltage is least
D)difference between primary and secondary voltage ismaximum

Question 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

Question 14

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

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

Question 15

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

Question 16

The efficiency of two identical transformers under load conditionscan be determined by

A)short-circuit test
B)back-to-back test
C)open circuit test
D)All of the above

Question 17

Which of the following insulating materials can withstand the highest temperature safely ?

A)Cellulose
B)Asbestos
C)Mica
D)Glass fibre

Question 18

Which of the following parts of a transformer is visible from outside ?

A)Bushings
B)Core
C)Primary winding
D)Secondary winding

Question 19

The noise produced by a transformer is termed as

A)zoom
B)hum
C)ringing
D)buzz

Question 20

Which of the following loss in a transformer is zero even at full load ?

A)Core loss
B)Friction loss
C)Eddy current loss
D)Hysteresis loss

Question 21

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

Question 22

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

A)core
B)windings
C)tank
D)All of the above

Question 23

The hum in a transformer is mainly attributed to

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

Question 24

The maximum load that a power transformer can carry is limited by its

A)temperature rise
B)dielectric strength of oil
C)voltage ratio
D)copper loss

Question 25

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