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MCQOPTIONS
This section includes 293 Mcqs, each offering curated multiple-choice questions to sharpen your Transformers knowledge and support exam preparation. Choose a topic below to get started.
| 201. |
In which type of windings extra insulation between layer is required in addition to the insulation of conductors. |
| A. | Cross over windings |
| B. | Continuous disc windings |
| C. | sandwich windings |
| D. | Helical windings |
| Answer» E. | |
| 202. |
Addition of a small per cent of silicon 3% to iron will increase the ________ significantly; by that ________ will be reduced. |
| A. | eddy current loss, resistivity |
| B. | resistivity, eddy current loss |
| C. | conductivity, eddy current loss |
| D. | conductivity, hysteresis loss |
| Answer» C. conductivity, eddy current loss | |
| 203. |
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 |
| Answer» C. Interleaved primary and secondary windings | |
| 204. |
A magnetic circuit has 150 turns-coil, the cross-sectional area 5 × 10-4 m2 and the length of the magnetic circuit 25 × 10-2 m. What are the values of magnetic field intensity and relative permeability when the current is 2 A and total flux is 0.3 × 10-3 Wb? |
| A. | 1200 AT/m and 397.9 |
| B. | 300 AT/m and 500 × 10-6 |
| C. | 300 AT/m and 397.9 |
| D. | 1200 AT/m and 500 × 10-6 |
| Answer» B. 300 AT/m and 500 × 10-6 | |
| 205. |
Hysteresis loss at constant v/f ratio in a transformer depends upon: |
| A. | Frequency |
| B. | Supply voltage |
| C. | Square of the frequency alone |
| D. | Square of the voltage alone |
| Answer» B. Supply voltage | |
| 206. |
______ is a device of the transformer which takes up expansion and contraction of oil. |
| A. | Buchholz's relay |
| B. | Bushing |
| C. | Conservator |
| D. | Breather |
| Answer» D. Breather | |
| 207. |
No winding resistance means |
| A. | Primary winding have constant resistance |
| B. | Secondary winding have infinite resistance |
| C. | No ohmic power loss |
| D. | Infinite resistive voltage drop |
| Answer» D. Infinite resistive voltage drop | |
| 208. |
A good transformer must have voltage regulation as high as possible |
| A. | TRUE |
| B. | FALSE |
| C. | Cannot be said |
| D. | None of these |
| Answer» C. Cannot be said | |
| 209. |
An open circuit test on a transformer gives _______. |
| A. | friction losses |
| B. | iron losses |
| C. | total losses |
| D. | copper losses |
| Answer» C. total losses | |
| 210. |
A 2000 kVA, single-phase transformer is in circuit continuously. For 8 hours in a day, the load is 160 kW at 0.8 pf. For 6 hours, the load is 80 kW at unity pf and for the period remaining out of 24 hours, it runs on no-load. If the full-load copper losses are 3.02 kW, the total copper losses in 24 hours are: |
| A. | 35.02 W |
| B. | 24.16 W |
| C. | 11.46 W |
| D. | 38.40 W |
| Answer» B. 24.16 W | |
| 211. |
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 |
| Answer» C. kVARh at particular instant | |
| 212. |
A 40 kVA, 100/400 V, 1-ϕ, 50 Hz transformer has iron loss of 400 W and copper loss of 1600 W at full load. What is the efficiency of the transformer at half load with 0.8 power factor lagging? |
| A. | 95.2 % |
| B. | 86.6 % |
| C. | 99.1 % |
| D. | 90.8 % |
| Answer» B. 86.6 % | |
| 213. |
If primary and secondary windings of core type single-phase transformer are wound on the non-magnetic core, then the1. efficiency of the transformer will decrease2. efficiency of the transformer will increase3. transformer regulation will increase4. transformer regulation will decrease |
| A. | 1 and 4 |
| B. | 1 and 3 |
| C. | 2 and 3 |
| D. | 2 and 4 |
| Answer» C. 2 and 3 | |
| 214. |
At any power factor of the load, the efficiency of transformer will be maximum when: |
| A. | Copper loss is equal to core loss |
| B. | Copper loss is equal to eddy current loss |
| C. | Copper loss is less than core loss |
| D. | Copper loss is greater than core loss |
| Answer» B. Copper loss is equal to eddy current loss | |
| 215. |
Hysteresis loss in electrical machine is typically given as |
| A. | \( Kf^2B_m^{η}\) |
| B. | \( K f^{-2} B_m^{η}\) |
| C. | \( Kf^{-1}B_m^{η}\) |
| D. | \( KfB_m^{η}\) |
| Answer» E. | |
| 216. |
Eddy current loss in the transformer depends on: |
| A. | The frequency |
| B. | The flux density |
| C. | The thickness of the core |
| D. | All of the above |
| Answer» E. | |
| 217. |
A transformer transforms: |
| A. | Frequency |
| B. | Voltage |
| C. | Current |
| D. | Both current and voltage |
| Answer» E. | |
| 218. |
Directions: It consists of two statements, one labeled as the ‘Statement (I)’ and the other as ‘Statement (II)’. Examine these two statements carefully and select the answer using the codes given below:Statement (I): In the construction of a core-type power transformer, the high-voltage winding is placed around the low-voltage winding in each limb.Statement (II): When the high-voltage winding is placed around the low-voltage winding in a core-type transformer, only one layer of high-voltage insulation is required between the two coils. |
| A. | Statement (I) and Statement (II) are individually true and statement (II) is the correct explanation of statement (II) |
| B. | Statement (I) and Statement (II) are individually true but statement (II) is not the correct explanation of statement (I) |
| C. | Statement (I) is true but statement (II) is false |
| D. | Statement (I) is false but statement (II) is true |
| Answer» B. Statement (I) and Statement (II) are individually true but statement (II) is not the correct explanation of statement (I) | |
| 219. |
A 25-kVA transformer has 500 turns on the primary and 50 turns on the secondary winding. The primary is connected to a 3000-V, 50 Hz supply. Find the full-load primary and secondary currents. |
| A. | Ip = 83.3 A, Is = 83.3 A |
| B. | Ip = 83.3A, Is = 8.33 A |
| C. | Ip = 833 A, Is = 83.3 A |
| D. | Ip = 8.33 A, Is = 83.3 A |
| Answer» E. | |
| 220. |
At 50 Hz operation, a single – phase transformer has hysteresis loss of 200 W and eddy current loss of 100 W. Its core loss at 60 Hz operation will be |
| A. | 432 W |
| B. | 408 W |
| C. | 384 W |
| D. | 360 W |
| Answer» D. 360 W | |
| 221. |
A transformer can have regulation closer to zero on __________. |
| A. | full load |
| B. | over load |
| C. | leading power factor |
| D. | zero power factor |
| Answer» D. zero power factor | |
| 222. |
A single-phase transformer is switched on to an AC supply. In order to have minimum inrush current switch should be closed at? |
| A. | Maximum supply voltage |
| B. | Zero supply voltage |
| C. | \(\frac{1}{{\sqrt 2 }}\) times of the maximum supply voltage |
| D. | \(\frac{1}{2}\) times of the maximum supply voltage |
| Answer» B. Zero supply voltage | |
| 223. |
Non-loading heat run test on transformers is performed by means of |
| A. | SC test |
| B. | OC test |
| C. | Core balance test |
| D. | Sumpner’s test |
| Answer» E. | |
| 224. |
In a 400/320 V single-phase 50 Hz transformer, the primary winding is connected to 400 V. Then the value of (EMF per turn in the primary winding)/(EMF per turn in the secondary winding) is: |
| A. | 0.5 |
| B. | 1.73 |
| C. | 1 |
| D. | 0 |
| Answer» D. 0 | |
| 225. |
A 3-phase transformer has 420 and 36 turns on the primary and secondary windings respectively. The supply voltage is 3300 V. The secondary line voltage on no-load when the windings are connected in star-delta is nearly |
| A. | 22260 V |
| B. | 1908 V |
| C. | 164 V |
| D. | 490 V |
| Answer» D. 490 V | |
| 226. |
For the parallel operation of single-phase transformers, it is necessary that they should have |
| A. | same efficiency |
| B. | same polarity |
| C. | same kVA rating |
| D. | same number of turns on the secondary side |
| Answer» C. same kVA rating | |
| 227. |
For higher voltage ranges __________ transformers are used. |
| A. | Core type |
| B. | Shell type |
| C. | Both core type & shell type |
| D. | None of these |
| Answer» B. Shell type | |
| 228. |
A one-phase, 50 Hz, 40 kVA transformer with a ratio of 2000 V/250 V has a primary resistance of 1.15 Ω and a secondary resistance of 0.0155 Ω. Calculate total copper loss on half of the full load. |
| A. | 856.8 W |
| B. | 214.2 W |
| C. | 642.6 W |
| D. | 428.4 W |
| Answer» C. 642.6 W | |
| 229. |
An electrical transformer can work on: |
| A. | d.c. supply |
| B. | a.c. supply |
| C. | d.c. and a.c. both |
| D. | none of these |
| Answer» C. d.c. and a.c. both | |
| 230. |
Full load copper loss in a transformer is 1600 watts. At half load the copper loss will be: |
| A. | 6400 W |
| B. | 1600 W |
| C. | 800 W |
| D. | 400 W |
| Answer» E. | |
| 231. |
A single-phase 50 kVA, 250 V/500 V two winding transformer has an efficiency of 95% at full load, unity power factor. If it is reconfigured as a 500 V/750 V autotransformer, its efficiency at its new rated load at unity power factor will be |
| A. | 95.752% |
| B. | 97.851% |
| C. | 98.276% |
| D. | 99.241% |
| Answer» D. 99.241% | |
| 232. |
In a 3 – ϕ, delta / star connected transformer, the ratio of phase voltages (primary to secondary) is 3 : 1. Find the ratio of their line voltages? |
| A. | 1 : 2 |
| B. | √3 : 1 |
| C. | 3 : 1 |
| D. | 3 : 2 |
| Answer» C. 3 : 1 | |
| 233. |
A transformer possesses a percentage resistance and percentage reactance of 1% and 4% respectively. Its voltage regulation and power factor 0.8 lagging and 0.8 leading would be |
| A. | 2.4% and -0.8% |
| B. | 3.2% and -1.6% |
| C. | 3.2% and -3.2% |
| D. | 4.8% and -1.6% |
| Answer» C. 3.2% and -3.2% | |
| 234. |
Directions: It consists of two statements one labeled as statement I and the other as statement II. Examine these two statements carefully and select the correct answer using the code given below.Statement I: When a transformer is loaded there is a change in its secondary voltage expressed as a percentage of secondary voltage on no-load, and this change is called its regulation.Statement II: The change in secondary voltage is due to the transformer impedance and the load current. The regulation could be zero for leading load conditions. |
| A. | Both statements I and statement II are individually true and statement II is the correct explanation of statement I |
| B. | Both statement I and statement II are individually true but statement II is not the correct explanation of statement I |
| C. | Statements I is true but statement II is false |
| D. | Statement I is false but statement II is true |
| Answer» B. Both statement I and statement II are individually true but statement II is not the correct explanation of statement I | |
| 235. |
Hysteresis loss is given by: |
| A. | We = K B2maxf2 t2 W |
| B. | Wh = η Bm1.6 f V W |
| C. | Wcu = (I12 R1 + I22 R2) W |
| D. | Wcu = (I12 R1) W |
| Answer» C. Wcu = (I12 R1 + I22 R2) W | |
| 236. |
If the star side of the star-delta transformer shown in the figure is excited by a negative sequence voltage, then |
| A. | \({V_{AB}}\;leads\;{V_{ab}}\;by\;{60^o}\) |
| B. | \({V_{AB}}\;lags\;{V_{ab}}\;by\;{60^o}\) |
| C. | \({V_{AB}}\;leads\;{V_{ab}}\;by\;{30^o}\) |
| D. | \({V_{AB}}\;lags\;{V_{ab}}\;by\;{30^o}\) |
| Answer» E. | |
| 237. |
A transformer is working at its maximum efficiency. Its iron loss is 1 kW. Its copper loss will be |
| A. | 0.2 kW |
| B. | 0.25 kW |
| C. | 0.5 kW |
| D. | 1 kW |
| Answer» E. | |
| 238. |
Identify the given circuit. |
| A. | Full wave rectifier |
| B. | Step down transformer |
| C. | Programmable logic circuit |
| D. | Step up transformer |
| Answer» C. Programmable logic circuit | |
| 239. |
A single-phase transformer has a rating of 15 kVA, 600/120 V. It is connected as an auto-transformer to supply at 720 V from 600 V primary source. The maximum source it can supply is: |
| A. | 90 kVA |
| B. | 18 kVA |
| C. | 15 kVA |
| D. | 12 kVA |
| Answer» B. 18 kVA | |
| 240. |
3 kW load is supplied by an autotransformer with 0.7 transformation ratio. Conductively transferred power from primary to secondary is |
| A. | 2.1 kW |
| B. | 0.9 kW |
| C. | 4.29 kW |
| D. | 3 kW |
| Answer» B. 0.9 kW | |
| 241. |
In transformer minimum voltage regulation occurs when the power factor of the load is |
| A. | leading |
| B. | lagging |
| C. | 0.8 |
| D. | unity |
| Answer» B. lagging | |
| 242. |
Compared to the secondary of a loaded step-up transformer, the primary has ________. |
| A. | lower voltage and higher current |
| B. | higher voltage and lower current |
| C. | lower voltage and lower current |
| D. | higher voltage and higher current |
| Answer» B. higher voltage and lower current | |
| 243. |
During a short circuit test, the iron losses are negligible, because: |
| A. | Mutual flux is small |
| B. | Current is high |
| C. | Power factor is low |
| D. | None of these |
| Answer» B. Current is high | |
| 244. |
Distribution Transformers:1. Have good voltage regulation2. Are designed for small value of currentWhich of these is / are CORRECT? |
| A. | Only 2 |
| B. | Both 1 and 2 |
| C. | Only 1 |
| D. | Neither 1 nor 2 |
| Answer» D. Neither 1 nor 2 | |
| 245. |
Core loss of single-phase, 230/115 V, 50 Hz power transformer is measured from 230 V side by feeding the primary (230 V side) from a variable voltage and variable frequency source while keeping the secondary open-circuited. The core loss is measured to be 1050 W for 230 V, 50 Hz input. The core loss is again measured to be 500 W for 138 V, 30 Hz input. The hysteresis and eddy current losses of the transformer for 230 V, 50 Hz input are, respectively |
| A. | 508 W and 542 W |
| B. | 468 W and 582 W |
| C. | 498 W and 552 W |
| D. | 488 W and 562 W |
| Answer» B. 468 W and 582 W | |
| 246. |
A 200/2000 V, 1-ϕ, 50 Hz transformer has primary and secondary resistance of 5 Ω and 20 Ω, respectively. Find the value of equivalent resistance of the transformer referred to the primary side. |
| A. | 20 Ω |
| B. | 10 Ω |
| C. | 5.2 Ω |
| D. | 12.4 Ω |
| Answer» D. 12.4 Ω | |
| 247. |
A 2400/240 V, 200 kVA, single phase transformer has a core loss of 1.8 kW at rated voltage. Its equivalent resistance is 1.1%. Then the transformer efficiency at 0.9 power factor and on full load is |
| A. | 95.60% |
| B. | 96.71% |
| C. | 97.82% |
| D. | 98.93% |
| Answer» D. 98.93% | |
| 248. |
Impulse testing of transformers is done to determine the ability of |
| A. | bushings to withstand vibrations |
| B. | insulation to withstand transient voltages |
| C. | windings to withstand voltage fluctuations |
| D. | all of the above |
| Answer» C. windings to withstand voltage fluctuations | |
| 249. |
A voltage transformer has 2500 turns of wire on its primary coil and 1500 turns of wire for its secondary coil. If 200 volts RMS is applied to the primary winding of the same transformer, what will be the resulting secondary voltage? |
| A. | 0.0083 volts |
| B. | 18750 volts |
| C. | 120 volts |
| D. | 333.33 volts |
| Answer» D. 333.33 volts | |
| 250. |
A transformer transfers which of the following parameters? |
| A. | Current |
| B. | Frequency |
| C. | Voltage |
| D. | Power |
| Answer» E. | |