Transformer_01

FIG: Reference for the question-2

ELECTRICAL UPDATES

TRANSFORMERS

  

 

1. A 200V/100V, 50Hz T/F is to be excited at 40HZ from 100 V side. For the exciting current to be the same, the applied voltage should be
   1.   150 V
   2.   80 V
   3.   140 V
   4.   160 V
2. In 3-phase delta/star T/F shown in figure, the phase displacement of secondary line voltage from corresponding primary line voltage will be
   
   FIG shown above.
   1.   Zero
   2.   30° lead
   3.   30° lag
   4.   180°
3. In a 100KVA,1100/220 V, 50Hz 1-Phase with 2000 turns on the high voltage side, the open-circuit test result gives 200V, 91A, 5KW on low-voltage side.The core loss comonent of current is ___________
   1.   9.1A
   2.   25 A
   3.   31A
   4.   24A
4. An iron cored T/F is working at a maximum flux density of 0.8 web/sq.m. Its core is replaced by silicon steel core, working at maximum flux density of 1.2 web/sq.m. If the total flux is to remain same, what is reduction in volume expressed as a persentage of the original volume? The frquency and voltage per turn are the samein both cases.
   1.   9%
   2.   33%
   3.   22%
   4.   11%
5. Two transformers of same type, using the same grade of iron and conductor meterials, are designed to work at the same flux and current densities, but the linear dimensions of one are two times those of other in all respects.The ratio of KVA of the two transformers closely equals
   1.   8
   2.   16
   3.   4
   4.   2
6. If load powerfactor of T/F is 0.8 lagging, then its primary power factor is_______
   1.   0.9 lag
   2.   0.8 lag
   3.   0.6 lag
   4.   UPF
7. A T/F has hysterisis loss of 30W at 240 V, 60HZ supply.the hysterisis loss at 200V, 50HZ supply is ___________
   1.   30 W
   2.   60 W
   3.   25 W
   4.   100 W
8. A T/F has iron loss of 90W at 60Hz supply and 52 W at 40Hz supply. Both losses being measured at same peak flux density. The total iron in the T/F at 50Hz supply will be _________
   1.   70W
   2.   90W
   3.   50W
   4.   30W
9. At 50Hz operation, a single-phase T/F has hysterisis loss of 200W and eddy current loss of 100W. its corre loss at 60 Hz operation will be
   1.   432W
   2.   384W
   3.   408W
   4.   360W
10. A single phase T/F when supplied from 220V, 50Hz has eddy current loss of 50W. If the T/F is connected to 330V,50Hz, the eddy current loss will be_______
    1.   168.75 W
    2.   112.5 W
    3.   75 W
    4.   50W

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