Transformers Objective Questions Answers

1. The rating of the Transformer __ when the supply frequency is increased:

a) Remains unchanged

b) Increases

c) Decreases

d) None of the above

B

2. Distortion of the whole core and subsequent damage to the coil insulation due to intense eddy currents may be caused due to the failure of:

a) Insulation of the winding

b) Insulation between the laminations

c) Insulation between the core and damping bolts

d) Both (a) and (b)

D

3. Booster transformer should never:

a) Have fuse in the HV winding

b) Be left open circuited

c) Be left closed circuited

d) None of the above

C

4. In a transformer, with closed magnetic coupling between primary and secondary __ will improve:

a) Efficiency

b) All day efficiency

c) Regulation

d) None of the above

C

5. Zero sequence currents can flow from a line into a transformer bank if the windings are:

a) Grounded star/delta

b) Delta/star

c) Star/Star grounded

d) Delta/Delta

C

6. An auto transformer is preferred over an ordinary two winding transformer due to:

a) Safety of operation

b) Availability of taps on secondary

c) Copper savings

d) All the above

C

7. The harmonic currents in a power transformer does not cause increase in:

a) Secondary voltage

b) Core loss

c) Copper loss

d) Magnetic interference with protective relays

A

8. In conversion of 3-phase to 2-phase supply with T connection, the transformation ratio of the teaser will be__ times to that of main transformer:

a) 1.732

b) 1.15

c) 0.866

d) Unity

C

9. Two transformers of identical voltages but different capacities are operated in parallel, for satisfactory load sharing:

a) Impedances should be equal

b) Per unit impedance must be equal

c) per unit impedance and X/R ratio must be equal

d) Impedance and X/R ratio must be equal

C

10. A shell type transformer is commonly used as it has:

a) Two magnetic paths

b) Reduced magnetic flux leakage

c) Reduced copper loss

d) Both (a) and (b)

D

11. The color of fresh dielectric oil used in the transformer is:

a) Dark brown

b) Pale yellow

c) Pale pink

d) White grey

B

12. The thickness of transformer core laminations is:

a) 3mm to 5mm

b) 0.35mm to 0.5mm

c) 30mm to 50 mm

d) 0.035mm to 0.05mm

B

13. For transformers employing CRGO, the area of the yoke is taken __ of the core:

a) 80 to 85%

b) 115 to 125%

c) Equal to

d) Half of b

B

14. The core used in high frequency transformer is __ core:

a) Aluminium

b) Ferrite

c) Carbon

d) Iron

B

15. In order to reduce the hysteresis loss:

a) Core may be laminated

b) Silica steel may be  used as the core

c) Core may be constructed with magnetic materials such as ALNICO

d) Core may be impregnated with varnish

D