501 MCQ Questions on Transformer

140. An exact equivalent circuit of a transformer is given by:

(a) conductance and susceptance for mutual flux.
(b) resistance and inductance for primary and secondary windings and conductance and susceptance to represent the mutual flux.
(c) resistance and inductance for primary and secondary windings respectively.
(d) resistance and inductance for primary, secondary and mutual flux linkages respectively.

141. The short circuit test in a transformer is carried out

(a) at full load current.
(b) at half load current.
(c) at very small load current.
(d) at greater than full load current.

142. Regulation of a transformer is defined by rise in primary voltage required to maintain rated output voltage at a given power factor for a lagging power factor load

(a) from no load to 50% of full load.
(b) from no load to full load.
(c) from no load to 25% of full load.
(d) from no load to 75% of full load.

143. Booster transformers are used to

(a) change the voltage magnitude and phase angle.
(b) reduce the voltage magnitude.
(c) increase the voltage magnitude.
(d) change the voltage phase angle.

144. Two 3- ɸ   transformers can be operated in parallel if the ………….. condition is satisfied.

1. Same voltage ratio and same voltage refering to the primary and secondary of the transformer to be connected in parallel.
2. The phase displacement between primary and secondary must be the same for all transformers connected in parallel.
3. The phase sequence must be same.

(a) Only 3 is correct
(b) Only 1 is correct
(c) Only 2 is correct
(d) All 1, 2 and 3 conditions are satisfied simulataneously.

145. The sheet steel material used in transformer core has :

(a) high core loss and low permeability.
(b) low core loss and low permeability.
(c) low core loss and high permeability.
(d) high core loss and high permability.

146. Auto transformer has:

(a) one winding.
(b) multiple windings.
(c) two windings.
(d) does not have any winding.

147. The Δ connection has the advantage of restricting the third harmonic components currents to:

(a) within star connection.
(b) within delta connection.
(c) within both star and delta connections.
(d) neither star nor delta connections.

148. In a transformer the leakage flux:

(a) contributes to transfer of energy from primary to secondary.
(b) does not contribute to transfer of energy from primary to secondary.
(c) contributes to transfer of energy from secondary to primary.
(d) contributes to transfer of energy between both coils simultaneously.

149. A transformer is equivalent to an ideal transformer

(a) with inductive coil connected in the secondary circuit.
(b) when no coils are connected to primary and secondary.
(c) with inductive coil connected in only the primary circuit.
(d) with inductive coils connected in both the primary and secondary circuits.

150. The current transformer’s used in differential protection of a star/delta transformer will be connected in the configuration of:

(a) Delta connection on both sides of transformer.
(b) Star connection on both sides of transformer.
(c) Star connection on star side and delta connection on delta side of transformer.
(d) Delta connection on star side and star connection on delta side of transformer.

151. The flux density affects:

(a) neither hysteresis nor eddy current loss.
(b) only eddy current loss.
(c) only core loss.
(d) only hysteresis loss.

152. The frequency affects

(a) both hysteresis and eddy current loss.
(b) only eddy current loss.
(c) neither hysteresis nor eddy current loss.
(d) only hysteresis loss.

153. In electrical power transmission the …….. configuration of transformers are extensively used.

(a) Neither Y/Δ and Δ/Y
(b) Y/Δ
(c) Both Y/Δ and Δ/Y
(d) ΔY

154. The short circuit test in a transformer is carried out by solidly shorting:

(a) only high voltage windings.
(b) only low voltage windings.
(c) either high voltage and low voltage windings.
(d) both high voltage and low voltage windings.

155. Transformers…………. reactive power.

(a) generate
(b) neither generate nor absorb
(c) absorb
(d) absorb as well as generate

156. The no load primary current will be approximately in the range of ….. time the rated load current in a transformer.

(a) 0.8
(b) 0.1
(c) 0.9
 (d) 0.5

157. The efficiency of a transformer depends:

(a) on both load power factor and load magnitude.
(b) on load power factor.
(c) on load magnitude.
(d) neither on load power factor nor on load magnitude.

158. In a transformer on load the total primary current is given by

(a) load component of secondary current.
(b) sum of magnetising current and reflected load current on primary side.
(c) reflected load current on primary side.
(d) magnetising current.

159. The per unit quantity for voltage is defined by:

(a) V_pu = V_b
(b) V_pu = V
(c) V_pu = V_b/V
(d) V_pu = V/V_b

160. Transformers can be connected in:

(a) both series and parallel.
(b) series.
(c) parallel.
(d) neither series nor parallel.

161. Open Circuit Test on 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.

162. Dissolve gas analysis of transformer oil is carried out to determine:

(a) condition of transformer oil.
(b) condition of transformer.
(c) condition of bushings.
(d) condition of bushing stud.

163. The steel used in transformer core is high silicon content to:

(a) produce low permeability and low hysterisis loss.
(b) produce high permeability and low hysteresis loss.
(c) produce low permeability and low eddy. current loss.
(d) produce high permeability and low eddy current loss.

164. A 1 φ, 10 kVA, 220/110V, 50Hz transformer is connected to a 220V supply. It draws rated current at 0.8 p.f. leading. The transformer may be considered ideal. What is the KVA rating of the load?

(a) 10
(b) 20
(c) 15
(d) 8

165. How the leakage flux is minimized in an actual transformer?

(a) Interleaving and sectionalizing both primary and secondary windings.
(b) Sectionalizing primary windings only.
(c) Interleaving and Sectionalizing secondary windings only.
(d) Sectionalizing secondary windings only.

166. Which machine is protected by Buchholz relay?

(a) Generators
(c) Motors
(b) Transformers
(d) Transmission lines

167. If the voltage ratio of the transformer is 1 : 30 then the ratio of primary and secondary turns will be

(a) 2 : 30
(b) 1 : 30
(c) 1 : 3
(d) 2 : 10

168. Which quantity is preferred as a reference vector to draw a Phasor diagram in a series circuit?

(a) Phase angle
(b) Current
(c) Power
(d) Voltage

169. Which type of “Current Transformer Arrangmenet (CT) is preferred in protection of star-star power transformer?

(a) Star/delta connections
(b) Star/star connections
(c) Delta/delta connections
(d) Delta/star connections

170. The current and potential transformers are used to measure

(a) high current and high voltage.
(b) low current and low voltage.
(c) high voltage and low current.
(d) high current and low voltage.

171. All day efficiency of a transformer is defined as the ratio of output to input in

(a) kVA at particular instant.
(b) kWh during 24 hours.
(c) kVARh at particular instant.
(d) kW during 24 hours.

172. An electric transformer is

(a) a magnetic device that consists of two or more multi turn coils wound on a common core.
(b) a magnetic device that consists of only two coils wound on a common core.
(c) an electric device that consists of two or more multi turn coils wound on a common core.
(d) an electric device that consists of only two coils wound on a common core.

173. A 2000/200 V, 20 kVA transformer has 66 turns in the secondary. The number of primary of turns are:

(a) 660
(b) 440
(c) 770
 (d) 330

174. A transformer has efficiency of 80% and works at 100V and 4 kW. If the secondary voltage is 240V, find the primary current.

(a) 16.67 A
(b) 40 A
(c) 30 A
(d) 10 A

175. The full load efficiency at unity power factor of a 230/115 V, 2 kVA single phase transformer having a Cu loss of 60W at half load and iron loss of 50 W is:

(a) 92%
(b) 87%
(c) 90%
(d) 98%