501 MCQ Questions on Transformer

176. Find the line current under measurement, if a 100 :  5 CT is used in conjuction with a (0 – 5A) ammeter reads 3A.

(a) 70 A
(b) 35 A
(c) 60 A
(d) 15 A

177. Two transformer are to be operated in parallel such that they share load in proportion to their KVA ratings. The rating of the first transformer is 500 kVA and its pu leakage is 0.05 pu. If the rating of the second transformer is 250 kVA then its pu leakage impedance is:

(a) 0.025
(b) 0.1
(c) 0.05
 (d) 0.2

178. A 3-phase transformer has its primary is delta connected and secondary in star. Secondary to primary turns ratio per phase is 5. What would be the secondary voltage for a primary voltage of 400 V?

(a) 2000 V
(b) 80 V
(c) 3464 V
(d) 138 V

179. A transformer having a turn’s ratio 1 : 5 and a resistance of 500 is connected across the secondary terminals. What is the equivalent resistance for the current flowing in the primary?

(a) 100 Ω
(b) 10 Ω
(c) 20 Ω
(d) 50 Ω

180. The percentage resistance of a 100 kVA, 5kV, 5 Ω resistance is given by:

(a) 2%
(b) 20%
(c) 40%
 (d) 4%

181. In a transformer having 1000 primary and 400 secondary turns, if the primary voltage is 250 volts, the secondary voltage will be:

(a) 400 Volts
(b) 100 Volts
(c) 625 Volts
(d) 1600 Volts

182. Which test on transformer provides information about regulation efficiency and heating under load conditions?

(a) Open circuit test
(b) Back to back test
(c) Hopkinson test
(d) Short circuit test

183. If the flux density in the core of a transformer is increased

(a) frequency on secondary windings will change.
(b) wave shape on secondary side will be distorted.
(c) size of transformer can be reduced.
(d) eddy current losses will be reduced.

184. In a transformer magnetic coupling between the primary and secondary circuit can be increased by:

(a) increasing the number of turn.
(b) using soft materials for windings.
(c) using magnetic core of low reluctance.
(d) using transformer oil of better quality.

185. For a transformer of the full load, copper losses are A and iron losses are B. Then the load at which these two losses would be equal is given by:

(a) Full load x A/B
(b) Full load x B/A
(c) Full load x √(A/B)
(d) Full load  x √(B/A)

186. Full load copper loss in a transformer is 1600 watts. At half load, the loss will be:

(a) 6400 Watt
(b) 1600 Watt
(c) 800 Watt
(d) 400 Watt

187. A Transformer has full load copper losses of 800 watt and core loss of 600 watt. Total losses at no load will be:

(a) 1400 watt
(b) 1100 watt
(c) 100 watt
(d) 600 watt

188. A 600 kVA, 1-φ, transformer when working at unity p.f. has an efficiency of 92% at full load, total losses at full load are:

(a) 104.4 kW
(b) 48 kW
(c) 52.2 kW
(d) 26.1 kW

189. Efficiency of a power-transformer under no load condition is approximately:

(a) 75%
(b) 50%
(c) 25%
(d) None of the above

190. A single phase transformer rated at 3000 kVA, 69 kV/4.16 kV, 60 Hz has a total internal impedance Z, of 127 ohm, referred to the primary side. Calculate the primary current if the secondary is accidentally short circuited. [J & K JE – 2016]

(a) 43.5 A
(b) 543 A
(c) 9006 A
(d) 721 A

200. Which test is used to determine the magnetizing impedance of a transformer? [J & K JE 2016]

(a) Short-circuit test
(b) Impulse test
(c) Load test
(d) Open-circuit test

201. Three single phase transformers are connected in delta-delta to step down a line voltage of 138 kV to 4160 V to supply power to a production plant. The plant draws 21 MW at a lagging power factor of 86%. Calculate the apparent power furnished by the HV line. [Jammu & Kashmir JE – 2016]

(a) 24.4 MVA
(b) 48.8 MVA
(c) 12.2 MVA
(d) 6.1 MVA

202. A large transformer operating at no load draws an exciting curent I_o, of 5A, when the primary is connected to a 120 V, 60 Hz source. From a wattmeter test, it is known that iron losses are equal to 180 W. Calculate the reactive power absorbed by the core. [Jammu & Kashmir JE 2016]

(a) 600 var
(b) 572 var
(c) 180 var
(d) 360 var

203. The exciting current in a single phase transformer consists of

(a) fundamental component current.
(b) odd harmonics.
(c) even harmonics.
(d) fundamental and odd harmonics.

204. For minimum weight of the transformer, the iron weight should be….. the weight of the copper. [RRB SSE 2015]

(a) more than
(b) equal to
(c) less than
(d) no relation

205. What KVA rating is required for a transformer that must handle a maximum load current of 8 A with a secondary voltage of 2 kV? [RRB SSE 2015]

(a) 4 kVA
(b) 0.25 kVA
(c) 16 kVA
(d) 8 kVA

206. When is an Auto transformer used in transmission and distribution?

(a) When operator is not available.
(b) When iron losses are to be reduced.
(c) When efficiency consideration can be ignored.
(d) When transformation ratio is small.

207. No-load on a transformer is carried out to determine:

(a) copper loss.
(b) magnetising current.
(c) magnetising current and loss.
(d) efficiency of the transformer.

208. The power transformer is a constant:

(b) current device.
(a) voltage device.
(c) power device.
(d) main flux device.

209. Which of the following is not a routine test on transformers? [ESIC JE 2016]

(a) Core insulation voltage test
(b) Impedance voltage test.
(c) Radio interference test
(d) Polarity test

210. A transformer can have zero voltage regulation at:

(a) leading power factor.
(b) lagging power factor.
(c) unity power factor.
(d) zero power factor.

211. 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. [ESIC JE 2016]