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Electrical Engineering Objective Questions { Transformers }

155.  When a given transformer is run at its rated voltage but reduced frequency, its
A. flux density remains unaffected
B. iron losses are reduced
C. core flux density is reduced
D. core flux density is increased
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156.  In an actural transformer the iron loss remains practically constant from no-load to full-load because
A. value of transformation ratio remains constant
B. permeability of transformer core remains constant
C. core flux remains practically constant
D. primary voltage remains constant
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157.  An ideal transformer will have maximum efficiency at a load such that
A. copper loss = iron loss
B. copper loss < iron loss
C. copper loss > iron loss
D. none of the above
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158.  If the supply frequency to the transformer is increased, the iron loss will
A. not change
B. decrease
C. increase
D. any of the above
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159. Negative voltage regulation is indicative that the load is
A. capacitive only
B. inductive only
C. inductive or resistive
D. none of the above
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160. Iron loss of a transformer can bemeasured by
A. low power factor wattmeter
B. unity power factor wattmeter
C. frequency meter
D. any type of wattmeter
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161.  When secondary of a current transformer is open-circuted its iron core will be
A. hot because of heavy iron losses taking place in the due to high flux density
B. hot because primary will carry heavy current
C. cool as there is no secondary current
D. none of above will happen
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