Transformers Objective Test Questions Answers

1. Which of the following will improve the mutual coupling between primary and secondary circuits:

a)  Transformer oil of high breakdown voltage

b) High reluctance magnetic core

c) Winding material of high resistivity

d) Low reluctance magnetic core

D

2. The magnetic properties of silicon steel crystal are best along the:

a) Cube diagonals

b) Cube edges

c) Surface diagnals

d) None of the above

B

3. Transformer core is mad of:

a) Silicon sheet steel

b) Chromel steel

c) Low carbon steel

d) High content silicon steel

A

4. Which of the following statements associated with the Buchholz relay is not true:

a) It is a voltage sensitive device

b) It is used only on oil cooled transformers

c) It is not provided on transformers of the rating below 500kVA

d) Its operating time is of the order of 0.1 seconds

A

5. With stepping in construction of the transformer core:

a) Core losses are reduced

b) Copper losses are saved

c) Mechanical strength of the core is improved

d) Both (a) and (b)

D

6. A distribution transformer is required to supply:

a) Variable load between no load to full load

b) Constant part full load throughout the day

c) Constant full load through out the day

d) Variable load between no load to full load at a fixed power factor

A

7. In a Delta -Delta connection, if one of the transformer winding is open, the capacity will reduce to:

a) 66.67%

b) 57.74%

c) 50%

d) 33.33%

B

8. A 3-phase transformer over a bank of 3-single phase transformers of equal rating, has the advantage of:

a) Low cost

b) Less weight

c) Occupation of less space

d) All the above

D

9. In which of the transformer, the tertiary winding is used:

a) Star-delta

b) Delta-delta

c) Star-star

d) Delta-star

C

10. The magnetizing current in a transformer is rich in:

a) 3rd harmonic

b) 5th harmonic

c) 7th harmonic

d) 11th harmonic

A

11. Scott connections are used for:

a) Single phase to three phase transformation

b) Three phase to single phase  transformation

c) Three phase to two phase transformation

d) Any of the above

C

12. For successful parallel operation of two single phase transformers, the most essential condition is that their:

a) Percentage impedances are equal

b) Polarities are properly connected

c) Turn-ratios are exactly equal

d) kVA ratings are equal

B

13. Maximum transient currents flow through the transformer winding when when it is switched on with its secondary winding ___ circuited and when the input voltage wave passing through the __ value

a) Open, zero

b) Short, zero

c) Open, maximum

d) Short, maximum

A

14. Tappings of a transformer are provided:

a) At the phase end of the LV side

b) At the phase end of the HV side

c) At the neutral end of the HV side

d) At the middle of the HV side

D

15. The excessive temperature rise in the Transformer causes maximum damage to:

a) Winding insulation

b) Core laminations

c) Copper wining

d) Dielectric strength of the oil

A