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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