TRANSFORMERS MCQs SET 03

TRANSFORMERS MCQs SET 03

1. Different core construction is required for core type and shell type transformer.
a) True
b) False
 

Answer: a
 

Explanation: In the “closed-core” type transformer, the primary and secondary windings are wound outside and surround the core ring. In the “shell type” transformer, the primary and secondary windings pass inside the steel magnetic circuit (core) which forms a shell around the windings.
 

2. There is only one magnetic flux path in the circuit. The transformer is definitely ________________
a) Core type
b) Shell type
c) Can be any of the above
d) Depends on other parameters
 

Answer: a
 

Explanation: In core type transformer, winding is placed on two core limbs, while in case of shell type transformer, winding is placed on mid arm of the core. Other limbs will be used as mechanical support. Core type transformers have only one magnetic flux path.
 

3. Which of the following is correct statement?
a) Core type transformer has more output than shell type
b) Core type transformer has higher efficiency compare to shell type
c) Core type transformer has lower efficiency than shell type
d) Can’t predict
 

Answer: c
 

Explanation: In core type winding is surrounded with considerable part of core whereas in shell type core is surrounded with considerable part of winding of transformer. In core type output is less, because of losses. In shell type transformer output is high because of less loss, thus efficiency will be more in case of shell transformer.
 

4. Core type transformer is with ____________________
a) Large size
b) Small size
c) High voltage
d) Everywhere
 

Answer: a
 

Explanation: Core type is very useful when we need large size of the transformer with operation at low voltage. While shell type transformer is very useful when we need small size high voltage. Cooling is more in core type.
 

5. Which of the following is the correct statement?
a) Shell type has more mechanical protection
b) Cooling is more in shell type
c) In core type sandwiched wiring is used
d) In core type concentric winding is used
 

Answer: d
 

Explanation: Shell type has less mechanical protection to coil while Core type has better mechanical protection to coil. Core type is easy to repair and maintain. In core type transformer concentric cylindrical winding are used. In shell type transformer sandwiched winding are used.
 

6. What is the purpose of providing an iron core in a transformer?
a) Provide support to windings
b) Reduce hysteresis loss
c) Decrease the reluctance of the magnetic path
d) Reduce eddy current losses
 

Answer: c
 

Explanation: Iron core is used in a transformer to carry flux from one winding to another winding, so there should be minimum opposition to flux passing through iron core. Hence, transformer function is to decrease the reluctance of magnetic path.
 

7. What is the thickness of laminations used in a transformer?
a) 0.1 mm to 0.5 mm
b) 4 mm to 5 mm
c) 14 mm to 15 mm
d) 25 mm to 40 mm
 

Answer: a
 

Explanation: Laminations are made to reduce the eddy currents and is made of thin strips. Generally, the steel transformer lamination range for 50 Hz varies from 0.25mm to 0.5mm, if it is a 60 Hz transformer then it ranges from 0.17–0.27mm.
 

8. In the transformer which of the following winding has got more cross-sectional area?
a) Copper winding
b) Steel winding
c) Aluminium winding
d) Iron winding
 

Answer: a
 

Explanation: The wire used for carrying current in a transformer winding is either copper or aluminium. While aluminium wire is lighter and less expensive than copper wire, a larger cross-sectional area of conductor must be used to carry the same amount of current as with copper.
 

9. Primary winding of a transformer ______________
a) Is always a high voltage winding
b) Is always a low voltage winding
c) Could either be a low voltage or high voltage winding
d) Cannot be determined
 

Answer: c
 

Explanation: Primary winding used in a transformer, can be at higher or lower voltage potential, depending on the number of turns with secondary winding. For step up and step-down transformers primary winding will be at lower and higher potential respectively.
 

10. Which winding has more number of turns?
a) Low voltage winding
b) High voltage winding
c) Primary winding
d) Secondary winding
 

Answer: b
 

Explanation: High voltage winding always has a large number of turns, as voltage is directly proportional to the number of turns. If large numbered winding is present on primary side then the transformer is step down transformer.