Electrical Studys

1➤ Which of the following does not change in a transformer ?

A. CurrentB. VoltageC. FrequencyD. All of the above

2➤ In a transformer the energy is conveyed from primary to secondary

A. through cooling coilB. through airC. by the fluxD. none of the above

3➤ A transformer core is laminated to

A. reduce hysteresis lossB. reduce eddy current lossesC. reduce copper lossesD. reduce all above losses

4➤ The degree of mechanical vibrations produced by the laminations of a transformer depends on

A. tightness of clampingB. gauge of laminationsC. size of laminationsD. All of the above

5➤ The no-load current drawn by transformer is usually what per cent of the full-load current ?

A. 0.2 to 0.5 per centB. 2 to 5 per centC. 12 to 15 per centD. 20 to 30 per cent

6➤ The path of a magnetic flux in a transformer should have

A. high resistanceB. high reluctanceC. low resistanceD. low reluctance

7➤ No-load on a transformer is carried out to determine

A. copper lossB. magnetising currentC. magnetising current and lossD. efficiency of the transformer

8➤ The dielectric strength of transformer oil is expected to be

A. 11 kvB. 33 kv C. 100 kv D. 330 kv

9➤ Sumpner's test is conducted on trans-formers to determine

A. temperatureB. stray lossesC. all-day efficiencyD. none of the above

10➤ The permissible flux density in case of cold rolled grain oriented steel is around

A. 1.7 Wb/m2B. 2.7 Wb/m2C. 3.7 Wb/m2D. 4.7 Wb/m2

11➤ The efficiency of a transformer will be maximum when

A. copper losses = hysteresis lossesB. hysteresis losses = eddy current lossesC. eddy current losses = copper lossesD. copper losses = iron losses

12➤ No-load current in a transformer

A. lags behind the voltage by about 75°B. leads the voltage by about 75°C. lags behind the voltage by about 15°D. leads the voltage by about 15°

13➤ The purpose of providing an iron core in a transformer is to

A. provide support to windingsB. reduce hysteresis lossC. decrease the reluctance of the magnetic pathD. reduce eddy current losses

14➤ Which of the following is not a part of transformer installation ?

A. ConservatorB. BreatherC. Buchholz relayD. Exciter

15➤ While conducting short-circuit test on a transformer the following side is short circuited

A. High voltage sideB. Low voltage side C. Primary side D. Secondary side

16➤ In the transformer following winding has got more cross-sectional area

A. Low voltage windingB. High voltage windingC. Primary windingD. Secondary winding

17➤ A transformer transforms

A. voltageB. current C. power D. frequency

18➤ A transformer cannot raise or lower the voltage of a D.C. supply because

A. there is no need to change the D.C. voltageB. a D.C. circuit has more lossesC. Faraday's laws of electromagnetic induction are not valid since the rate of change of flux is zeroD. none of the above

19➤ Primary winding of a transformer

A. is always a low voltage windingB. is always a high voltage windingC. could either be a low voltage or high voltage windingD. None of the above

20➤ Which winding in a transformer has more number of turns ?

A. Low voltage windingB. High voltage windingC. Primary windingD. Secondary winding

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