Electrical Studys

 

1] The magnetising current of a transformer is usually small because it has .....

1 pointA. small air gapB. large leakage fluxC. laminated silicon steel coreD. fewer rotating parts

2] Which of the following does not change in an ordinary transformer ?

1 pointA. Frequency B. VoltageC. CurrentD. Any of the above

3] Which of the following properties is not necessarily desirable for the material for transformer core ?

1 pointA. Low hysteresis lossB. High permeabilityC. High thermal conductivityD. Adequate mechanical strength

4] The leakage flux in a transformer depends upon

1 pointA. load current B. load current and voltageC. load current, voltage and frequencyD. load current, voltage, frequency and power factor

5] The path of the magnetic flux in transformer should have .....

1 pointA. high reluctance B. low reactanceC. high resistanceD. low resistance

6] Noise level test in a transformer is a ......

1 pointA. special test B. routine testC. type testD. none of the above

7] Which of the following is not a routine test on transformers ?

1 pointA. Core insulation voltage testB. Impedance testC. Radio interference test D. Polarity test

8] A transformer can have zero voltage regulation at .....

1 pointA. leading power factor B. lagging power factorC. unity power factorD. zero power factor

9] Helical coils can be used on .....

1 pointA. low voltage side of high kVA trans¬formersB. high frequency transformersC. high voltage side of small capacity transformersD. high voltage side of high kVA rating transformers

10] Harmonics in transformer result in .......

1 pointA. increased core losses B. increased I2R lossesC. magnetic interference with communication circuitsD. all of the above

11] The core used in high frequency transformer is usually .......

1 pointA. copper core B. cost iron coreC. air coreD. mild steel core

12] The full-load copper loss of a transformer is 1600 W. At half-load, the copper loss will be ......

1 pointA. 6400 W B. 1600 WC. 800 WD. 400 W

13] The value of flux involved m the e.m.f. equation of a transformer is .......

1 pointA. average value B. r.m.s. valueC. maximum valueD. instantaneous value

14] Silicon steel used in laminations mainly reduces ......

1 pointA. hysteresis loss B. eddy current lossesC. copper lossesD. all of the above

15] Which winding of the transformer has less cross-sectional area ?

1 pointA. Primary windingB. Secondary windingC. Low voltage windingD. High voltage winding

16] Power transformers are generally designed to have maximum efficiency around

1 pointA. no-load B. half-loadC. near full-loadD. 10% overload

17] Which of the following is the main advantage of an auto-transformer over a two winding transformer ?

1 pointA. Hysteresis losses are reduced B. Saving in winding materialC. Copper losses are negligibleD. Eddy losses are totally eliminated

18] During short circuit test iron losses are negligible because ........

1 pointA. the current on secondary side is negligibleB. the voltage on secondary side does not varyC. the voltage applied on primary side is lowD. full-load current is not supplied to the transformer

19] Two transformers are connected in parallel. These transformers do not have equal percentage impedance. This is likely to result in .....

1 pointA. short-circuiting of the secondariesB. power factor of one of the transformers is leading while that of the other laggingC. transformers having higher copper losses will have negligible core lossesD. loading of the transformers not in proportion to their kVA ratings

20] The changes in volume of transformer cooling oil due to variation of atmospheric temperature during day and night is taken care of by which part of transformer.......

1 pointA. ConservatorB. BreatherC. BushingsD. Buchholz relay

You Got