141. When 2 transformer of different kVA rating are connected in parallel they share the load in proportion to their respective kVA rating only when their

1. Efficiencies are equal
2. kVA rating are identical
3. Equivalent impedance are equal
4. Per unit impedance are equal

142. 2 transformers with identical voltage ratings are working in parallel to supply a common load. The percentage impedance of one transformer is higher compared to that of another transformer. The load sharing between the two transformers will

1. be inversely proportional to their respective impedance
2. be proportional to their percentage impedance
3. depend on the resistance to leakage reactance ratio of each transformer
4. be independent of their percentage impedance

143. Which of the following are constant losses in transformers?

1. Winding losses
2. Core losses
3. Both winding core losses
4. None of these

144. The maximum efficiency of the power transformer is generally near

145. Which test helps in determining the efficiency of two identical transformers under load conditions?

1. Back to Back test
2. Short circuit test
3. No such test exists
4. Open circuit test

146. A transformer is working at its maximum efficiency. The magnitude of copper losses is 0.5 kW. The iron losses will be

1. 1 kW
2. 2 kW
3. 0.5 kW
4. 0.25 kW

147. The magnitude of mutual flux in a transformer

1. Is same at all loads

148. Vibration produced by laminations of a transformer primarily depends on

1. tightness of clamping
2. size of lamination

Which of these is/are correct?

1. Only 2
2. 1 and 2
3. Neither 1 nor 2
4. Only 1

149. Which of the following is/are the requirements of good transformer oil?

1. Low viscosity
2. Low volatility
3. High viscosity
4. High volatility
1. Only 1 and 2
2. Only 3 and 4
3. Only 1 and 4
4. Only 2 and 3

150. The number of secondary turns of a coil in a transformer is 4 times the number of turns in the primary coil. If the voltage in the primary coil is 200 V, the secondary voltage would be

1. 800 V
2. 50 V
3. 200 V
4. 2000 V

151. In a transformer, the applied voltage leads the no-load current by an angle of

1. 75 degree
2. 90 degree
3. 180 degree
4. 45 degree

152. The essential condition for parallel operation of two single-phase transformers is that they should have the same

1. Polarity
2. kVA rating
3. voltage ratio
4. percentage impedance

153. At light load, the efficiency of a transformer is low. It is because

1. Copper loss is small
2. Copper loss is high
3. Secondary output is low
4. Fixed loss is high with respect to output

154. A 10 kVA, 220 V/220 V, 50 Hz transformer shows 340 W in short circuit test and 168 W in open circuit test. Its efficiency at full load and 0.8 power factor lagging is approximately

1. 92 %
2. 94 %
3. 96 %
4. 98 %

155. The reason why open circuit test is performed on the low voltage of the winding is that it

1. Needs minimum power input
2. Draws large current to facilitate reading
3. Requires less voltage to perform the test
4. Involves less core losses

156. In a welding transformer, which type of reactor has greater reactance, it is obtained due to greater core insertion and hence the output current is less?

1. Continuously variable reactor
2. Saturable reactor
3. Moving shunt reactor
4. Moving coil reactor

157. In which type of immersed transformer, the oil is pumped through windings to extract heat from the oil

1. Oil-immersed water-cooled transformer
2. Oil-immersed forced air-cooled transformer
3. Oil-immersed forced oil-cooled transformer
4. Oil-immersed self-cooled transformer

158. Which type of transformer is used to conduct an assessment at high and ultra-high voltages?

1. Power transformer
2. Testing transformer
4. Auto transformer

159. Which type of connection is used for both large voltage and low voltage rating transformer?

1. Delta-Delta connection
2. Delta-Wye connection
3. Wye-Wye connection
4. Wye-delta connection

160. Which part of the transformer is constructed by the L, I and E type of laminated steel?

1. Coils
2. Insulating material
3. Magnetic core
4. Tank and cooling system

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