Electrical Machines Questions and Answers – Autotransformers

This set of Electrical Machines Multiple Choice Questions & Answers (MCQs) focuses on “Autotransformers”.

1. While comparing potential transformer to an auto transformer, a potential transformer transfers power ________
a) conductively
b) inductively
c) both conductively as well as inductively
d) electromagnetic induction
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2. The statements which support the points that auto transformers are advantageous?

I. Weight of conductor reduces
II. Ohmic losses reduces
III. Leakage reactance reduces
IV. Lower short-circuit current

a) I, II, III
b) II, III, IV
c) I, II, III, IV
d) I, IV
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3. The statements which support the points that auto transformers are advantageous?

I. Weight of conductor reduces
II. Direct electrical contacts
III. Leakage reactance reduces
IV. Lower short-circuit current

a) I, III
b) II, III
c) I, II, III, IV
d) I, IV
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4. The statements which support the points that auto transformers are disadvantageous as compared to 2-winding transformer?

I. Weight of conductor reduces
II. Direct electrical contacts
III. Leakage reactance reduces
IV. Lower short-circuit current

a) I, III
b) II, III
c) II, IV
d) I, II, IV
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5. Which of the above are correct for an auto transformer when compared to the identical rating two winding transformer?

I. KVA rating : 1/(1-k)
II. Losses : (1-k)
III. Impedance drop = 1/(1-k)

a) I, II
b) II, III
c) 1, III
d) I, II, III, IV
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6. The voltage regulation of a transformer at full-load 0.8 p.f leading is -2%. Its voltage regulation at full load 0.8 p.f lagging _____________
a) will be positive
b) will be negative
c) may be positive
d) may be negative
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7. The voltage regulation of a transformer depends on its __________

(A) Equivalent reactance  
(B) Equivalent resistance 
(C) Load power factor     
(D) Transformer size 
(E) Load current 

a) A, B, C, E
b) A, B, C, D, E
c) A, B, D, E
d) A, B, C, D
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8. Three transformers having identical dimensions but with core of iron, aluminium and wood are wound with same number of turns and have same supply. Then choose the order for hysteresis losses.
a) wood > aluminium > iron
b) aluminium > iron > wood
c) iron > wood > aluminium
d) iron > aluminium > wood
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9. Three transformers having identical dimensions but with core of iron, aluminium and wood are wound with same number of turns and have same supply. Then choose the order for eddy current losses.
a) wood > aluminium > iron
b) aluminium > iron > wood
c) iron > wood > aluminium
d) iron > aluminium > wood
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10. Maximum efficiency of a transformer for a constant load current, occurs at __________
a) at any p.f
b) zero p.f leading
c) zero p.f lagging
d) unity p.f
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11. A 1-phase tranformer has a leakage impedance of 1+ j4 Ω for primary and 3+ j11 Ω for secondary windings. This transformer has __________
a) H.V primary
b) Medium voltage primary
c) L.V primary
d) L.V secondary
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12. If a transformer is at no load, then it will act like __________
a) a resistor at p.f = 0
b) an inductive reactor at 0.2 lagging
c) a capacitive reactor at0.2 leading
d) an inductive reactor at 0.8 lagging
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13. The tappings on the transformers is provided on __________
a) h.v side at one end of the winding
b) l.v. side at one end of the winding
c) h.v side at middle
d) l.v side at middle
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14. In a transformer, we place the tapping windings at the middle because __________
a) of radial forces on the windings
b) axial forces on the windings
c) insulation level of the winding
d) to provide a mechanical balance to the windings
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15. When a transformer winding suffers a short circuit, then inter turns of the same winding experience ______ forces.
a) an attractive
b) a repulsive
c) no force
d) may be attractive or repulsive type
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16. Two tranformer having same voltage but different KVA are operating in parallel. For a good load sharing __________
a) impedance must be equal
b) pu impedances must be equal
c) pu impedance and X/R ratios must be equal
d) impedance and X/R ratios must be equal
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Sanfoundry Global Education & Learning Series – Electrical Machines.

To practice all areas of Electrical Machines, here is complete set of 1000+ Multiple Choice Questions and Answers.