Electrical Studys

 

1➤ Efficiency of a power transformer is of the order of

1 point100 per cent98 per cent50 per cent25 per cent

2➤ In a given transformer for given applied voltage, losses which remain constant irrespective of load changes are

1 pointfriction and windage lossescopper losseshysteresis and eddy current lossesNone of the above

3➤ A common method of cooling a power transformer is

1 pointnatural air coolingair blast coolingoil coolingany of the above

4➤ The no load current in a transformer lags behind the applied voltage by an angle of about

1 point180°120°90°75°

5➤ In a transformer routine efficiency depends upon

1 pointA. supply frequencyB. load currentC. power factor of loadD. both (b) and (c)

6➤ In the transformer the function of a conservator is to

1 pointprovide fresh air for cooling the transformersupply cooling oil to transformer in time of needprotect the transformer from damage when oil expends due to heatingnone of the above

7➤ Natural oil cooling is used for transformers upto a rating of

1 point3000 kVA1000 kVA500 kVA250 KVA

8➤ Power transformers are designed to have maximum efficiency at

1 pointnearly full load70% full load50% full load no load

9➤ The maximum efficiency of a distribution transformer is

1 pointat no loadat 50% full loadat 80% full loadat full load

10➤ Transformer breaths in when

1 pointload on it increasesload on it decreasesload remains constantnone of the above

11➤ No-load current of a transformer has

1 pointhas high magnitude and low power factorhas high magnitude and high power factorhas small magnitude and high power factorhas small magnitude and low power factor

12➤ Spacers are provided between adjacent coils

1 pointA. to provide free passage to the cool¬ing oilB. to insulate the coils from each otherC. both (a) and (b)D. none of the above

13➤ Greater the secondary leakage flux

1 pointless will be the secondary induced e.m.f.less will be the primary induced e.m.f.less will be the primary terminal voltagenone of the above

14➤ The purpose of providing iron core in a step-up transformer is

1 pointto provide coupling between primary and secondaryto increase the magnitude of mutual fluxto decrease the magnitude of mag-netizing currentto provide all above features

15➤ The power transformer is a constant

1 pointvoltage devicecurrent devicePower devicemain flux device

16➤ Two transformers operating in parallel will share the load depending upon their

1 pointleakage reactanceper unit impedanceefficienciesratings

17➤ What will happen if the transformers working in parallel are not connected with regard to polarity ?

1 pointThe power factor of the two trans-formers will be different from the power factor of common loadIncorrect polarity will result in dead short circuitThe transformers will not share load in proportion to their kVA ratingsnone of the above

18➤ If the percentage impedances of the two transformers working in parallel are different, then

1 pointtransformers will be overheatedpower factors of both the trans-formers will be sameparallel operation will be not possibleparallel operation will still be possible, but the power factors at which the two transformers operate will be different from the power factor of the common load

19➤ In a transformer the tappings are generally provided on

1 pointprimary sidesecondary sidelow voltage sidehigh voltage side

20➤ The use of higher flux density in the transformer design

1 pointreduces weight per kVAreduces iron lossesreduces copper lossesincreases part load efficiency

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