Transformers

11. The dielectric strength of transformer oil is expected to be

lkV
33 kV
100 kV
330 kV

Detailed SolutionThe dielectric strength of transformer oil is expected to be

12. The use of higher flux density in the transformer design

reduces weight per kVA
reduces iron losses
reduces copper losses
increases part load efficiency

Detailed SolutionThe use of higher flux density in the transformer design

13. Sumpner’s test is conducted on transformers to determine

temperature
stray losses
all-day efficiency
none of the above

Detailed SolutionSumpner’s test is conducted on transformers to determine

14. Which motor is preferred for use in mines where explosive gases exist?

Air motor
Induction motor
Shunt motor
Synchronous motor

Detailed SolutionWhich motor is preferred for use in mines where explosive gases exist?

15. Auto-transformer makes effective saving on copper and copper losses, when its transformation ratio is

approximately equal to one
less than one
great than one
none of the above

Detailed SolutionAuto-transformer makes effective saving on copper and copper losses, when its transformation ratio is

16. The maximum efficiency of a distribution transformer is

at no load
at 50% full load
at 80% full load
at full load

Detailed SolutionThe maximum efficiency of a distribution transformer is

17. An ideal transformer has infinite values of primary and secondary inductances. The statement is

TRUE
nan
nan
nan

Detailed SolutionAn ideal transformer has infinite values of primary and secondary inductances. The statement is

18. The path of a magnetic flux in a transformer should have

high resistance
high reluctance
low resistance
low reluctance

Detailed SolutionThe path of a magnetic flux in a transformer should have

19. For a transformer, operating at constant load current, maximum efficiency will occur at

0.8 leading power factor
0.8 lagging power factor
zero power factor
unity power factor

Detailed SolutionFor a transformer, operating at constant load current, maximum efficiency will occur at

20. In a step-down transformer, there is a change of 15 A in the load current. This results in change of supply current of

less than 15 A
more than 15 A
15 A
none of the above

Detailed SolutionIn a step-down transformer, there is a change of 15 A in the load current. This results in change of supply current of

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