Auto Transformer MCQ

1. Auto transformer has

  1. One winding
  2. Multiple windings
  3. Two windings
  4. Does not have any winding

Answer. a

2. The essential feature of an auto-transformer is that it

  1. is more suited for single-phase supply
  2. is completely automatic in its operation
  3. uses only one winding
  4. is particularly suited for situations where voltage transformation ratio exceeds unity

Answer. c

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

  1. Hysteresis losses are reduced
  2. Saving in winding material
  3. Copper losses are negligible
  4. Eddy losses are totally eliminated

Answer. b

4. A 100/10 V, 50 VA transformer is converted to 100V/110V auto transformer, the rating of the auto transformer will be

  1. 550 VA
  2. 500 VA
  3. 110 VA
  4. 100 VA

Answer. a

5. In an auto-transformer, the number of turns in primary winding is 210 and in secondary winding is 140. If the input current is 60A, the currents in output and in common winding are respectively.

  1. 40 A, 20 A
  2. 40A, 100 A
  3. 90 A, 30 A
  4. 90A, 150A

Answer. c

6. The kVA Rating of an ordinary 2-winding transformer is increased when connected as an auto transformer is due to

  1. transformation ratio is increased
  2. secondary voltage is increased
  3. energy is transferred both inductively and conductively
  4. energy is transferred inductively

Answer. c

7. A 400 V/100 V, 10 KVA two winding is reconnected as an auto transformer across a suitable voltage source. What could be the maximum rating of such an arrangement?

  1. 50 KVA
  2. 15 KVA
  3. 10.5 KVA
  4. 8.75 KVA

Answer. a

8. A 2000 V/200 V, 20 KVA, two winding single-phase transformer is reconnected as a step up auto-transformer having 20O V/2200V ratings. Then the power rating for the auto transformer will be

  1. 18 kVA
  2. 16 kVA
  3. 22 kVA
  4. 20 kVA

Answer. c

9. A 240 V/120 V, 12 kVA auto-transformer has 96.2% efficiency at full-load and unity power factor. The full-load efficiency at 0.85 pf lagging when connected to a load across 360 V would be

  1. 89.5%
  2. 92.8%
  3. 88.9%
  4. 98.5%

Answer. d

10. The ratio of primary/secondary voltages is 2 : 1. The saving in terms of weight of copper required if an autotransformer is used instead of a two-winding transformer will be

  1. 95%
  2. 66.7%
  3. 50%
  4. 33.3%

Answer. c

11. A 2 V/1 V two winding transformer is connected as an autotransformer. Its voltage regulation as an auto transfornmer compared to the two winding transformer is

  1. 1.5 times
  2. The same
  3. 3 times
  4. 2 times

Answer. c

12. A two winding 220 V/110 V, 1.5 kVA transformer is reconnected as a 220/330V autotransformer. It is re-rated as

  1. 3.88 KVA
  2. 4.488 kVA
  3. 1.58 kVA
  4. 2.258 kVA

Answer. b

13. It is advisable to use auto-transformer if the transformation ratio is

  1. Greater than 1
  2. Near to 1
  3. 0.25
  4. 0.5

Answer. b

14. In an auto-transformer, power is transferred, through

  1. Conduction process only
  2. Induction process only
  3. Both conduction and induction processes
  4. Mutual coupling

Answer. c

15. Neglecting losses, if the power transformed inductively is equal to power transformed conductively in an auto-transformer, then the secondary to primary ratio of the transformer is

  1. 2
  2. 0.5
  3. 1.25
  4. 1.5

Answer. b

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