transformers MCQs – Page 3

Practise focused transformers questions with marked answers for exam preparation and subject revision.

transformers Mcqs
101. The secondary of a current transformer is always short-circuited under operating conditions because it____________________?
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A. protects the primary circuit

B. is safe to human beings

C. none of the above

D. avoids core saturation and high voltage induction
102. A transformer cannot raise or lower the voltage of a D.C. supply because_______________?
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A. a D.C. circuit has more losses

B. none of the above

C. Faradays laws of electromagnetic induction are not valid since the rate of change of flux is zero

D. there is no need to change the D.C. voltage

103. Auto-transformer makes effective saving on copper and copper losses, when its transformation ratio is_________________?
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A. approximately equal to one

B. less than one

C. none of the above

D. great than one

104. Which of the following protection is normally not provided on small distribution transformers ?
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A. Buchholz relay

B. Overfluxing protection

C. Overcurrent protection

D. All of the above

105. Minimum voltage regulation occurs when the power factor of the load is_____________?
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A. leading

B. zero

C. unity

D. lagging

106. Short circuit test on transformers is conducted to determine____________?
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A. core losses

B. hysteresis losses

C. eddy current losses

D. copper losses
107. Negative voltage regulation is indicative that the load is___________?
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A. capacitive only

B. none of the above

C. inductive only

D. inductive or resistive

108. A Transformer transforms____________?
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A. current and voltage

B. power

C. voltage

D. current

109. A transformer can have regulation closer to zero___________?
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A. on zero power factor

B. on overload

C. on full-load

D. on leading power factor
110. The secondary winding of which of the following transformers is always kept closed?
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A. Potential transformer

B. Step-down transformer

C. Step-up transformer

D. Current transformer
111. Helical coils can be used on___________?
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A. low voltage side of high kVA transformers

B. high voltage side of small capacity transformers

C. high frequency transformers

D. high voltage side of high kVA rating transformers

112. The efficiencies of transformers compared with that of electric motors of the same power are____________?
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A. much higher

B. much smaller

C. about the same

D. somewhat smaller

E. none of the above

113. The thickness of laminations used in a transformer is usually____________?
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A. 4 mm to 5 mm

B. 14 mm to 15 mm

C. 0.4 mm to 0.5 mm

D. 25 mm to 40 mm

114. The core used in high frequency transformer is usually___________?
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A. copper core

B. cost iron core

C. air core

D. mild steel core

115. Noise level test in a transformer is a______________?
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A. none of the above

B. type test

C. special test

D. routine test

116. Which of the following is not a part of transformer installation ?
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A. Exciter

B. Conservator

C. Buchholz relay

D. Breather

117. Which of the following does not change in a transformer ?
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A. Voltage

B. All of the above

C. Current

D. Frequency
118. The efficiency of a transformer will be maximum when_____________?
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A. hysteresis losses = eddy current losses

B. copper losses = hysteresis losses

C. eddy current losses = copper losses

D. copper losses = iron losses
119. The hum in a transformer is mainly attributed to______________?
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A. load changes

B. magnetostriction

C. oil in the transformer

D. mechanical vibrations

120. Power transformers are designed to have maximum efficiency at___________?
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A. 50% full load

B. nearly full load

C. 70% full load

D. no load

121. If the supply frequency to the transformer is increased,the iron loss will__________?
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A. increase

B. not change

C. any of the above

D. decrease

122. The value of flux involved m the e.m.f. equation of a transformer is____________?
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A. maximum value

B. average value

C. instantaneous value

D. r.m.s. value

123. Which of the following statements regarding an idel 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?
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A. Its secondary voltage is 400 V

B. Its rating is 2 kVA

C. Its secondary current is 5 A

D. It is a step-up transformer

E. Its secondary current is 20 A
124. If a transformer is switched on to a voltage more than the rated voltage______________?
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A. its power factor will be zero

B. its power factor will remain unaffected

C. its power factor will deteriorate

D. its power factor will increase

125. The function of breather in a transformer is___________?
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A. to cool the transformer oil

B. to arrest flow of moisture when outside air enters the transformer

C. to provide oxygen inside the tank

D. to cool the coils during reduced load

126. Part of the transformer which is most subject to damage from overheating is_____________?
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A. copper winding

B. transformer tank

C. winding insulation

D. frame or case

E. iron core

127. The transformer ratings are usually expressed in terms of______________?
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A. kW

B. volts

C. amperes

D. kVA
128. Open circuit test on transformers is conducted to determine____________?
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A. core losses

B. hysteresis losses

C. copper losses

D. eddy current losses

129. In a transformer the energy is conveyed from primary to secondary_________?
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A. none of the above

B. by the flux

C. through cooling coil

D. through air

130. The chemical used in breather is_______________?
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A. asbestos fiber

B. silica sand

C. silica gel

D. sodium chloride

131. When a given transformer is run at its rated voltage but reduced frequency, its____________?
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A. core flux density is reduced

B. core flux density is increased

C. iron losses are reduced

D. flux density remains unaffected

132. The purpose of providing an iron core in a transformer is to_____________?
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A. provide support to windings

B. decrease the reluctance of the magnetic path

C. reduce eddy current losses

D. reduce hysteresis loss

133. Buchholzs relay gives warning and protection against_________________?
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A. electrical fault inside the transformer itself

B. electrical fault outside the transformer in outgoing feeder

C. for both outside and inside faults

D. none of the above

134. What will happen if the transformers working in parallel are not connected with regard to polarity ?
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A. none of the above

B. The power factor of the two trans-formers will be different from the power factor of common load

C. The transformers will not share load in proportion to their kVA ratings

D. Incorrect polarity will result in dead short circuit