Transformers topics include: Transformer construction and phasor diagram, open circuit and short circuit test, voltage regulation of transformer, transformer losses and its efficiency, autotransformers, single phase transformer, three phase transformer and ideal two winding transformer. Transformers are electrical machines that convert electrical energy from one voltage level to another. They are static machines, while motors and generators are dynamic machines.  Here are some types of transformers: Ideal transformer: A static transformer that has no losses, magnetic leakage, core loss,... Show more

Transformers topics include: Transformer construction and phasor diagram, open circuit and short circuit test, voltage regulation of transformer, transformer losses and its efficiency, autotransformers, single phase transformer, three phase transformer and ideal two winding transformer.

Transformers are electrical machines that convert electrical energy from one voltage level to another. They are static machines, while motors and generators are dynamic machines. 

Here are some types of transformers:
Ideal transformer: A static transformer that has no losses, magnetic leakage, core loss, ohmic resistance, or leakage.
Polyphase transformer: Contains three or more conductors, up to 15 phases, and multiple windings on the primary and secondary cores.
Distribution transformer: Converts the primary voltage produced by a power station for distribution to customers.
Power transformer: Converts electrical power at different voltage levels. Faults in power transformers can inhibit electrical power distribution to consumers.
Three-phase transformer: An electromagnetic device that uses Faraday's electromagnetic induction phenomenon to transfer energy or send electrical signals between circuits.
Toroidal transformer: Uses a torus or donut-shaped core made of ferromagnetic material. The primary and secondary windings are wound around the core, separated by an insulating material.

Show less

Electrical Machines Practice Test: Transformers

Time left 00:00

25 Questions

1. The transformer which is more feasible to use in the distribution ends should be ___________

scottdelta-deltadelta-starstar-delta

2. If the pu impedance of a single phase transformer is 0.01+j0.05, then its regulation at p.f. of 0.8 lagging will be?

-3.8%3.8%-2.2%2.2%

3. Two single phase transformers A and B are operating in parallel having different impedance and identical x/r ratio. Then?

B has poorer pf than Blesser power factor angleA has poorer pf than Bboth operate at same power factor

4. Transformer action requires a ___________

constant magnetic fluxalternating magnetic fluxalternating electric fluxincreasing magnetic flux

5. A single phase transformer of 2200/220 V having rated l.v. current of 150 A has to undergo open circuit test on h.v side. The instruments used are voltmeter of 200V and ammeter of 1A. Then the results ___________

will be accurateof ammeter will burnwill be wrongnone of the mentioned

6. A single phase transformer has emf per turn having 2310/220 V, 50Hz transformer as 13 V. Then the estimated primary turns will be?

189 turns190 turns179 turns176 turns

7. There is a 10 KVA, 2000/200 V, single phase transformer having below following parameters are r1=10Ω, r2=0.1Ω, l1 = 40mH, l2=0.4 mH, M = 10H. Then the expected secondary self inductance will be?

100.04H1.0004H99.06H10.04H

8. Consider two transformers X and Y having identical ratings, but have flux densities of 1.5T and 2T respectively. The weight of the transformer B per KVA will be _________

can not be said from the given datamore than that of Aequal to that of Alesser than that of A

9. There are two identical transformers A and B such that flux density applied to B is doubled. Then magnetizing current of B is?

double of Ahalf of Asame as that of A.larger than A

10. It was needed that to isolate dc noise coming from the transmitted signal, to attain the same which machine can be used without suffering significant loss?

stepper motortransformerdc machineinduction machine

11. Power required during the open circuit and short circuit test is?

executing the power requirements by measuring instrumentspower for the core losses onlylosses incurring in the transformerall of the mentioned

12. Three units of single phase transformers and one single three-phase transformer rating ___________

can never be made samenone of the mentionedmay be samewill be same for one rating

13. To conduct the short circuit test, test is conducted on the ___________

h.v. sidesecondaryl.v. sideprimary

14. A coupling magnetic field inside a rotating machine or static machine like transformers must involve with _________

electrical partsmechanical partsboth electrical and mechanicaleither of the electrical or mechanical parts

15. If a transformer is fed from a dc rather than a 1-phase ac supply, then the transformer will __________

burn its windingsoperate normalwill not operatewill give very small leakage flux

16. From the above graph of the core losses per cycle is, the hysteresis losses per phase for a transformer at a operating frequency of 40 Hz is?

30W32W80W20W

17. Which of the below estimations require results of both open circuit test and short circuit test?

All of the mentionedEquivalent impedance of one side of the windingEfficiencyVoltage regulation for exact circuit

18. A single phase transformer of 2000/200 V having rated l.v. current of 100 A has to undergo short circuit test on l.v. side. Which of the below instruments range should be used?

200V,50A300V,100A20V, 10A200V,10A

19. Identify the correct order for the voltage transformation for the three-phase transformers.

D-Y > D-D < Y-Y < Y-DD-Y > D-D > Y-Y > Y-DD-Y > D-D = Y-Y < Y-DD-Y > D-D = Y-Y > Y-D

20. Energising the transformer primary from a triangular wave flux makes the output voltage as __________

a square wavea triangular wavea sine wavesquare wave shifted by 90°

21. In a transformer,eddy-current loss is 1000 watts which is half of the total core loss. If thickness of lamination and frequency are increased by 10%, What is the new core-losses?

3200W3300W2200W3100W

22. If the per unit leakage impedance for the primary of a transformer is ‘x’ on the given rated base value. If the voltage and volt-amperes are halved, then the changed per unit impedance will be ___________

x0.5x4x2x

23. If the transformer is excited with square wave voltage source then the shape of induced EMF will be __

Triangular WaveSinusoidal WaveSquare WaveImpulse Wave

24. Consider a 2-winding transformer as below. If the switch is open then the emf induced across the secondary having transformation ratio of 2 is?

V12*V1zeroV1/2

25. With the reference of the diagram below, Choose the most appropriate.
A:
B:

A-leading pf, B-leading pfB-lagging pf, A-leading pfA-lagging pf, B-lagging pfA-lagging pf, B-leading pf