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Electrical Engineering Objective Questions { Transformers }

15. Two transformers A and B having equal outputs and voltage ratios but unequal percentage impedances of a 4 and 2 are operating in parallel. Transformer A will be running overload by ?percent.

16. Which of the following parallel combination is not possible for three-tothree phase transformer connection?
A. Y ? Y to ? A
B. Y ? to ? A
C. Y ? to ? Y
D. Y ? Y to Y ? Y

17.  Which of the following three-to-three phase transformer connections are possible for parallel operation?
A. Y ? Y to ? Y
B. ? Y to Y ? A
C. A ? Y to ? Y
D. A ? to ? Y

18. If three transformers in A ? A are delivering rated load and one trans former is removed, then overload on each of the remaining transformers is ? precent.

19.  A T-T connection has higher ratio of utilization than a V-V connection only when
A. identical transformers are used
B. load power factor is leading
C. load power factor is unity
D. non-identical transformers are used

20.  For 3-to-3 phase conversion, which of the following given polyphase connections would you select?
A. delta/double-delta
B. star/double-star
C. delta/interconnected-star
D. delta/double-star

21. When two identical transformers are available, then the best method to find their efficiency under load conditions is the test.
A. short-circuit
B. back-to-back
C. open-circuit
D. phase-sequence

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