501 MCQ Questions on Transformer

106. Open circuit test on a transformer is used to find

(a) no load current.
(b) full load copper loss.
(c) equivalent resistance referred to metering side.
(d) equivalent resistance referred to metering side and no load current both.

107. Which of the following part of a transformer consists of a small vessel which contains a drying agent?

(a) Conservator
(b) Breather
(c) Oil tank
(d) Windings

108. If the reciprocal of transformation ratio of a transformer is 11. The ratio of current in the secondary to primary is

(a) 1/11
(b) 11
(c) 11/2
(d) 2/11

109. The voltage regulation of a transformer having 4% resistance and 5% reactance at full load, 0.8 pf lagging is:

(a) 4.60%
(b) -4.6%
(c) -6.2%
 (d) 6.20%

110. A 2 kVA transformer has iron-loss of 100 W and full load copper loss of 200 W. The full load efficiency at unity power factor will be

(a) 90.90%
(b) 85.60%
(c) 80.60%
(d) 86.95%

111. Two transformers are connected in parallel. These transformers do not have equal percentage impedance which results

(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 proportional to their kva ratings.

112. The function of oil in a transformer is to provide

(a) insulation and cooling.
(b) protection against lighting.
(c) protection against short circuit.
(d) lubrication.

113. The transformer laminations are insulated from each other by:

(a) mica strip.
(b) thin coat of varnish.
(c) paper.
(d) copper sheets.

114. Eddy current loss in a transformer is proportional to:

(a) frequency.
(b) supply voltage.
(c) square of the frequency.
(d) square of the voltage.

115. What does the Eddy current loss depend on? [UPPCL JE 2018]

(a) Flux density
(b) Frequency
(c) Thickness
(d) All of these

116. A 20,000 KVA transformer with 10% reactance will have a reactance of ………. at 10,000 kVA base.

(a) 10%
(b) 20%
(c) 15%
(d) 5%

117. What can we reduce by using thin laminations in a machine? [UPPCL JE 2018]

(a) Hysteresis losses
(b) Iron losses
(c) Eddy current losses
(d) Copper losses

118. Which law states that an e.m.f is induced in a conductor whenever it cuts the flux?

(a) Gauss’s law for magnetism
(b) Lenz’s law of electromagnetic induction
(c) Faraday’s law of electromagnetic induction
(d) Lorentz force law

119. A property of a transformer which makes it ideal is.

(a) CRGO core for its primary and secondary windings
(b) No losses and magnetic leakage
(c) Interleaved primary and secondary windings
(d) None of these [UPPCL JE 2018]

120. Reason for using silicon steel in electrical machines?

(a) High retentivity
(b) High coercivity
(c) Low hysteresis loss
(d) Low coercivity [UPPCL JE 2018]

121. A 25 kVA, 3300 /230 V, single phase transformer has iron and copper losses of 350 W and 400 W. The efficiency at 0.8 p.f is …..

(a) 96.39%
(b) 97.09%
(c) 98.43%
(d) 98.04%

122. To minimise loss due to hysteresis, the magnetic material should have?

(a) High resistivity
(b) High retentivity
(c) Low hysteresis coefficient
(d) Large B-H loop area [UPPCL JE – 2018]

123. The most common method of cooling employed in power transformer is:

(a) oil natural.
(b) natural cooling.
(c) air cooling.
(d) air-blast cooling. [RRB SSE – 2015]

124. Laminations of core are generally made of

(a) case iron
(b) carbon
(c) silicon steel
(d) stainless steel

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

(a) through cooling coil.
(b) through air.
(c) by the flux.
(d) none of the above.

126. A transformer core is laminated to

(a) reduce hysteresis loss.
(b) reduce eddy current losses.
(c) reduce copper losses.
(d) reduce all above losses.

127. Major insulation in a transformer is the insulation between the

(a) LV winding and core.
(b) LV winding and HV winding.
(c) turns of the windings.
(d) Both (a) and (b) [RRB SSE – 2015]

128. Delta/star transformer works satisfactorily when

(a) load is balanced only.
(b) load is unbalanced only.
(c) on balanced as well as unbalanced loads.
(d) none of the above.

129. Transformer breaths in when

(a) load on it increase.
(b) load on it decreases.
(c) load remains constant.
(d) none of the above.

130. No-load current of a transformer

(a) has high magnitude and low power factor.
(b) has high magnitude and high power factor.
(c) has small magnitude and high power factor.
(d) has small magnitude and low power factor .

131. The purpose of providing iron core in a step-up transformer is

(a) to provide coupling between primary and secondary.
(b) to increase the magnitude of mutual flux.
(c) to decrease the magnitude of magnetizing current.
(d) to provide all above features.

132. Two transformers operating in parallel will share the load depending upon their

(a) leakage reactance.
(b) per unit impedance.
(c) efficiencies.
(d) ratings.

133. Which winding of the transformer has less cross-sectional area?

(a) Primary winding
(b) Secondary winding
(c) Low voltage winding
(d) High voltage winding

134. Power transformers are generally designed to have maximum efficiency around

(a) No-load
(b) Half-load
(c) Near full-load
(d) 10% overload

135. Which of the following is the main advantage of an auto-transformer over a two winding transformer?

(a) Hysteresis losses are reduced
(b) Saving in winding material
(c) Copper losses are negligible
(d) Eddy losses are totally eliminated

136. When a given transformer is run at its rated voltage but reduced frequency, its

(a) flux density remains unaffected.
(b) iron losses are reduced.
(c) core flux density is reduced.
(d) core flux density is increased.

137. An ideal transformer will have maximum efficiency at a load such that

(a) copper loss = iron loss.
(b) copper loss < iron loss.
(c) copper loss > iron loss.
(d) none of the above.

138. If the supply frequency to the transformer is increased, the iron loss will

(a) not change.
(b) decrease.
(c) increase.
(d) any of the above.

139. The no load primary input is approximately equal to the

(a) iron loss of transformer.
(b) sum of iron loss and copper loss of transformer.
(c) neither iron loss of transformer nor copper loss.
(d) copper loss of transformer.