MCQs on transformer 121-140

121. 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

122. 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✔

123. If a transformer is continuously operated the maximum temperature rise will occur in
(a) core
(b) windings✔
(c) tank
(d) any of the above

124. The hum in a transformer is mainly attributed to
(a) load changes
(b) oil in the transformer
(c) magnetostriction✔
(d) mechanical vibrations

125. 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

126. 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

127. An open-circuit test on a transformer is conducted primarily to measure
(a) insulation resistance
(b) copper loss
(c) core loss✔
(d) total loss

128. A no-load test is performed on a transformer to determine
(a) core loss
(b) copper loss
(c) efficiency
(d) magnetising current and loss✔

129. 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

130. 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

136. 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

137. 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

138. Minimum voltage regulation occurs when the power factor of the load is
(a) unity
(b) lagging
(c) leading
(d) zero✔

139. 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

140. The efficiencies of transformers compared with that of electric motors of the same power are
(a) about the same
(6) much smaller
(c) much higher✔
(d) somewhat smaller