501 MCQ Questions on Transformer

212. 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.
(d) secondary terminal voltage to primary applied voltage.

213. For minimum weight of a transformer, the weight of iron should be:

(a) equal to weight of copper.
(b) less than weight of copper.
(c) greater than weight of copper.
(d) zero. [ESIC JE – 2016]

214. Core of transformer is made of good quality material like CRGO steel to minimize:

(a) eddy current loss.
(b) full load copper loss.
(c) hysteresis loss.
(d) no load copper loss. [FCI – 2015]

215. The function of conservator in a transformer is to:

(a) store extra oil to be used in emergency.
(b) prevent entry of moisture.
(c) cool transformer.
(d) take care of expansion and contraction of oil due to change in temperature of oil. [FCI – 2015]

216. What is the cause of occurrence of stray load losses in transformer?

(a) Leakage flux
(b) Poor cooling
(c) Overloading
(d) Under frequency operation [FCI – 2015]

217. When the turns ratio of a transformer is 20 and the primary ac voltage is 12 V, the secondary voltage is:

(a) 12 V
(b) 120 V
(c) 240 V
(d) 2,400 V [RRB SSE 2015]

218. The nominal ratio of a current transformer is:

(a) Primary winding current/secondary winding current
(b) Number of Primary winding turns/Number of secondary winding current
(c) Rated Primary winding current/Rated secondary winding current
(d) Number of Secondary winding turns/ Number of Primary winding turns [FIC 2015]

219. When moist air passes through a bed of silica gel, the ………

(a) dry bulb temperature of air decreases.
(b) dry bulb temperature of air increases.
(c) specific humidity of air increases.
(d) it undergoes adiabatic saturation.

220. Single phase Transformer voltage is maximum when the primary and secondary coils are……..

(a) normal to each other.
(b) have a phase shift of 90° from each other.
(c) aligned along the same axis.
(d) have a phase shift of 120° from each other.

221. In a transformer, electric power is transferred from primary coil to secondary

(a) through air.
(b) by electric field.
(c) through insulating medium.
(d) by magnetic flux. [RRB JE 2015]

222. Which part of transformer is subjected to maximum heating? [RRB JE 2015]

(a) frame
(c) oil
(b) core
(d) winding

223. Which test is performed to determine core loss of a transformer?

(a) Short circuit
(b) Sumpner
(c) Open Circuit
(d) None of these [Uttarakhand AE 2013]

224. The maximum efficiency of a 200 kVA transformer having an iron loss of 1800 W and full load copper loss of 3200 W occurs at

(a) 100 kVA
(b) 150 kVA
(c) 200 kVA
(d) 125 kVA [Uttarakhand AE – 2013]

225. The emf per turn for a single phase 2200/220 V, 50 Hz transformer is approximately 12 V. The number of primary and secondary turns are

(a) 18, 183
(b) 183, 18
(c) 155, 26
(d) 172, 21 [Uttarakhand AE 2013]

226. Which type of connection is employed for current transformers for the protection of star-delta connected 3-phase transformer?

(a) Delta-Delta
(b) Star-Star
(c) Star-Delta
(d) Delta-Star [Uttarakhand AE 2013]

227. If the secondary burden of a current transformer is 15 VA and secondary current is 5A, then the impedance of the connected load will be:

(a) 0.6 Ω
(b) 5 Ω
(c) 6 Ω
 (d) 10 Ω [UPRVUNL AE – 2016]

228. A PT is a device which is:

(a) electro-statically coupled.
(b) electrically coupled.
(c) electromagnetically coupled.
(d) conductively coupled [UPRVUNL AE 2016]

229. A T-T transformer cannot be paralleled with ….. transformer.

(a) V-V
(b) Y- Δ
(c) Y-Y
 (d) Δ – Δ [BSNL TTA 2016]

230. A 200 KVA transformer has an iron loss of 1 kW and full load copper loss of 2 kW. Its load KVA corresponds to maximum efficiency is

(a) 100 kVA
(b) 70.7 kVA
(c) 200 kVA
 (d) 141.4 kVA [ J&K (JE) – 2016]

231. For Higher Voltage Ranges …….. transformers are used. [BSNL TTA 2016]

(a) core type
(b) shell type
(c) both core type and shell type
(d) none of these

232. In order to achieve high all day efficiency in a transformer:

(a) the copper losses should be less.
(b) the operating temperature should be low.
(c) the shell type construction should be used.
(d) the iron losses should be less. [BSNL TTA 2016]

233. In a step-up transformer, the turn’s ratio is 1 : 2. A Leclanche cell (emf 1.5 V) is connected across the primary. The voltage across the secondary is

(a) 3.0 V
(b) 0.75 V
(c) 0 V
 (d) 1.5 V [BSNL TTA 2016]

234. In a transformer, the ratio of primary to secondary is 9 : 4. If power input is P, what will be the ratio of power output to the power input

(a) 4 : 9
(b) 9 : 4
(c) 5 : 4
 (d) 1 : 1 [BSNL TTA 2016]

235. CT and PT are used generally to

(a) Step up the respective quantities
(b) Step down the respective quantities
(c) Both
(d) None of these [BSNL TTA 2016]

236. Current drawn by the primary of a transformer which steps down from 220 V to 22 V to operate a device having an impedance of 220 will be

(a) 1 A
(b) 0.1 A
(c) 0.01 A
(d) 10 A [BSNL TTA 2013]

237. In a transformer the resistance between the primary and secondary must be

(a) Zero
(b) 1 ΚΩ
(c) 100 ΚΩ
(d) Infinite [BSNL TTA (JE) – 2013]

238. A good transformer must have voltage regulation as high as possible. [BSNL TTA 2016]

(a) True
(b) False
(c) Cannot be said
(d) None of these

239. Calculate the regulation of transformer in which ohmic loss is 1% of the output and reactance drop is 5% of the voltage, when the power factor is 0.8 lag. [BSNL TTA 2016]

(a) 3.8%
(b) 3.5%
(c) 1%
(d) 5%

240. In an ideal transformer the no load primary current I_o

(a) is in phase with V₁
(b) Leads V₁, by 90°
(c) Lags V₁, behind 90°
(d) None of these [BSNL TTA 2016]

241. At relatively light loads, transformer efficiency is low because

(a) secondary output is low.
(b) transformer losses are high.
(c) fixed loss is high in proportion to the output.
(d) cu loss is small. [BSNL TTA 2016]

242. At low frequencies, the material used for transformer cores is

(a) copper
(b) silicon iron
(c) soft iron
(d) none of these [BSNL TTA 2016]

243. The kVA Rating of an ordinary 2-winding transformer is increased when connected as an autotransformer is due to

(a) transformation ratio is increased.
(b) secondary voltage is increased.
(c) energy is transferred both inductively and conductively.
(d) energy is transferred inductively [BSNL TTA 2016]

244. If we leave the secondary winding of current transformer open

(a) Nothing will happen
(b) ct will blast.
(c) there will be only magnetizing component of the current flowing in the primary.
(d) there will not be any current in primary.

245. The magnitude of magnetic flux in a transformer

(a) decreases with increase in load.
(b) increases with increase in load.
(c) is same at all loads.
(d) increases as load increases from zero and remain nearly constant at high loads. [BSNL TTA 2015]

246. Transformers are rated in kVA instead of kW because

(a) load power factor is often not know
(b) kVA is fixed whereas kw depends on load pf.
(c) total transformer loss depends on VA.
(d) it has become customary. [BSNL TTA – 2016]