Auto Transformers - MCQs with Answers

Auto Transformers - MCQs with Answers

Q1. For the same excitation voltage and winding currents, the autotransformer gives

a. Less output than two winding transformer
b. Equal to the output of two winding transformer
c. Half of the output of two winding transformer
d. More than the output of the two winding transformer

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Q2. If K is the transformation ratio of step up autotransformer and W_tw is the total weight of copper in two winding transformer. Then the saving of copper is given by

a. K W_tw
b. W_tw/ K
c. W_tw/ K ∧ 2
d. K² W_tw

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Q3. In a step down autotransformer, if the transformation ratio increases then the saving of copper

a. Increases
b. Decreases
c. Remains same
d. Either increases or decreases

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Q4. If the transformation ratio of an autotransformer is given by V2 / V1 then the ratio of power transferred to that of input power is given by

a. (V2-V1) / V1
b. (V2+V1) / V1
c. (V1-V2) / V1
d. V2 / V1

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Q5. Use of an autotransformer is economical when its transformation ratio is

a. Near unity
b. Much greater than unity
c. Much lesser than unity
d. None of these

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Q6. If an autotransformer having transformation ratio equal to 0.6 is supplying a load of 8kw then its power transferred from primary to secondary is given by

a. 3 kW
b. 3.2 kW
c. 3.4 kW
d. 3.5 kW

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Q7. In an autotransformer if the power transferred inductively is equal to the power conducted through, then transformation ratio is given by

a. 1
b. 0.5
c. 2
d. 0

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Q8. For a two winding transformer if VA rating is given by (VA)_tw and K is the transformation ratio of an autotransformer then the VA rating of the autotransformer is given by

a. (K/(K-1)) * (VA)_tw
b. (K/(1-K)) * (VA)_tw
c. ((1-K)/K) * (VA)_tw
d. ((K-1)/K) * (VA)_tw

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Q9. Whether the given autotransformer is step up or step down, its VA rating is always

a. Greater than the two winding transformer
b. Equal to the two winding transformer
c. lesser than the two winding transformer
d. cannot say

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Q10. Compared to the two winding transformer, in an autotransformer the leakage reactance and copper losses is

a. less, more
b. less, less
c. more, more
d. more, less

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Q11. If a two winding transformer is converted into an autotransformer by applying additive polarity and subtractive polarity which results in the secondary voltages of 1840 and 1810 volts. Then the primary and secondary voltages of transformer are

a. 1800V, 50V
b. 1810V, 40V
c. 1820V, 30V
d. 1825V, 15V

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Q12. A star connected three phase transformer is provided with tertiary delta connected winding which allows the flow of

a. Second harmonic of exciting current
b. Third harmonic of exciting current
c. Fifth harmonic of exciting current
d. Seventh harmonic of exciting current

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