Transformers

Delta/star transformer works satisfactorily when______________?

A. load is balanced only
B. load is unbalanced only
C. on balanced as well as unbalanced loads
D. none of the above

Star/star transformers work satisfactorily when________________?

A. load is unbalanced only
B. load is balanced only
C. on balanced as well as unbalanced loads
D. none of the above

Which of the following property is not necessarily desirable in the material for transformer core ?

A. Mechanical strength
B. Low hysteresis loss
C. High thermal conductivity
D. High permeability

Distribution transformers are generally designed for maximum efficiency around________________?

A. 90% load
B. zero load
C. 25% load
D. 50% load

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

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

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

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

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

A transformer oil must be free from________________?

A. sludge
B. odour
C. gases
D. moisture