391. Harmonics in transformer result in___________?
A. increased core losses
B. increased I2R losses
C. magnetic interference with communication circuits
D. all of the above

392. In a transformer the resistance between its primary and secondary is____________?
A. zero
B. 1 ohm
C. 1000 ohms
D. infinite

393. The core used in high frequency transformer is usually___________?
A. copper core
B. cost iron core
C. air core
D. mild steel core

394. A transformer oil must be free from________________?
A. sludge
B. odour
C. gases
D. moisture

395. A Buchholz relay can be installed on______________?
A Buchholz relay can be installed on
A. auto-transformers
B. air-cooled transformers
C. welding transformers
D. oil cooled transformers

396. The full-load copper loss of a trans¬former is 1600 W. At half-load, the copper loss will be___________?
A. 6400 W
B. 1600 W
C. 800 W
D. 400 W

397. Gas is usually not liberated due to dissociation of transformer oil unless the oil temperature exceeds?
A. 50°C
B. 80°C
C. 100°C
D. 150°C

398. The main reason for generation of harmonics in a transformer could be_______________?
A. fluctuating load
B. poor insulation
C. mechanical vibrations
D. saturation of core

399. The value of flux involved m the e.m.f. equation of a transformer is____________?
A. average value
B. r.m.s. value
C. maximum value
D. instantaneous value

400. Distribution transformers are generally designed for maximum efficiency around________________?
A. 90% load
B. zero load
C. 25% load
D. 50% load

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