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Electrical Engineering Objective Questions { Transformers }

8. Iron loss in an actual transformer remains practically constant from no-load to full load because
A. core flux remains practically constant
B. primary voltage remains constant
C. value of transformation ratio remains constant
D. premeability of transformer core remains constant
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9. The primary reason why open-circuit test is performed on the lowest-voltage winding of the transformer is that it
A. draws sufficiently large no-load current for convenient reading
B. requires least voltage to perform the test
C. needs minimum power input
D. has become a universal custom
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10. During short-circuit test, the iron loss of a transformer is negligible because
A. the entire input is just sufficient to meet Cu losses only
B. voltage applied across the h.v. side is a small fraction of the rated voltage and so is the flux.
C. iron core becomes fully saturated
D. supply frequency is held constant
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11.  The commercial efficiency of a transformer while on open-circuit is
A. zero
B. maximum
C. indeterminate
D. incalculable
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12.  The ordinary efficiency of a given transformer is maximum when
A. it runs at half full-load
B. it runs at full-load
C. its Cu loss equals iron loss
D. it runs overload
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13.  A transformer has negative voltage regulation when its load power factor is
A. zero
B. unity
C. leading
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14. The saving in Cu achieved by convert ing 2-winding transformer into an autotransformer is determined by
A. voltage transformation ratio
B. load on the secondary
C. magnetic quality of core material
D. size of the transformer core
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