431. The hum in a transformer is mainly attributed to______________?
A. load changes
B. oil in the transformer
C. magnetostriction
D. mechanical vibrations
432. The maximum load that a power transformer can carry is limited by its________________?
A. temperature rise
B. dielectric strength of oil
C. voltage ratio
D. copper loss
433. The efficiency of a transformer, under heavy loads, is comparatively low because_______________?
A. copper loss becomes high in proportion to the output
B. iron loss is increased considerably
C. voltage drop both in primary and secondary becomes large
D. secondary output is much less as compared to primary input
434. When secondary of a current transformer is open-circuited its iron core will be__________?
A. hot because of heavy iron losses taking place in it 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
435. The transformer lamination’s are insulated from each other by____________?
A. mica strip
B. thin coat of varnish
C. paper
D. any of the above
436. An open-circuit test on a transformer is conducted primarily to measure______________?
A. insulation resistance
B. copper loss
C. core loss
D. total loss
E. efficiency
F. none of the above
437. Which type of winding is used in 3 phase shell-type transformer?
A. Circular type
B. Sandwich type
C. Cylindrical type
D. Rectangular type
438. A no-load test is performed on a transformer to determine_______________?
A. core loss
B. copper loss
C. efficiency
D. magnetising current
E. magnetising current and loss
439. The voltage transformation ratio of a transformer is equal to the ratio of_______________?
A. primary turns to secondary turns
B. secondary current to primary current
C. secondary induced e.m.f. to primary induced e.m.f
D. secondary terminal voltage to primary applied voltage
440. During open circuit test of a transformer:
A. primary is supplied rated voltage
B. primary is supplied full-load current
C. primary is supplied current at reduced voltage
D. primary is supplied rated kVA
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