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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

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

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

11.  The commercial efficiency of a transformer while on open-circuit is
A. zero
B. maximum
C. indeterminate
D. incalculable

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

13.  A transformer has negative voltage regulation when its load power factor is
A. zero
B. unity
C. leading

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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