TRANSFORMERS MCQs SET 01

TRANSFORMERS MCQs SET 01

1. The majority of power transformers in use throughout the world are oil filled using a mineral oil.
a) True
b) False
 

Answer: a
 

Explanation: In majority power transformers dielectric material used is the oil, which serves the dual purpose of providing insulation and as a cooling medium to conduct away the losses which are produced in the transformer in the form of heat.
 

2. Dielectric mineral oil is used in ____________
a) Small transformers
b) Medium transformers
c) Large transformers
d) In all transformers
 

Answer: c
 

Explanation: Because of the fire hazard associated with mineral oil, it has been the practice to use designs for smaller transformers which do not contain oil. It is usual, therefore, to locate transformers with mineral oil, out of doors where a fire is more easily dealt with and consequentially the risks are fewer.
 

3. The purpose of the transformer core is to provide ____________
a) High reluctance path
b) Low reluctance path
c) High inductive path
d) High capacitive path
 

Answer: b
 

Explanation: The purpose of a transformer core is to provide a low-reluctance path for the magnetic flux linking primary and secondary windings. In doing so, the core experiences iron losses due to hysteresis and eddy currents flowing within it which, in turn, show themselves as heating of the core material.
 

4. Transformer core is designed to reduce ______________
a) Hysteresis loss
b) Eddy current loss
c) Hysteresis loss and Eddy current loss
d) Cannot be determined
 

Answer: c
 

Explanation: Hysteresis loss and eddy current loss are the losses which take place in core of the transformer thus they are also termed as core losses. While other losses take place in winding or in air gap which can’t be dealt with core design.
 

5. Transformers windings are generally made of __________
a) Steel
b) Iron
c) Copper
d) Steel iron alloy
 

Answer: c
 

Explanation: In order to avoid losses due to loading current, winding materials must be chosen wisely. Winding conductors are thus made of copper or more precisely saying they are made of high conductivity copper by some industrial processes.
 

6. Before using oil in transformers, insulation material was _________
a) Asbestos
b) Cotton
c) Low grade pressboard in air
d) Kraft paper
 

Answer: d
 

Explanation: At the time of discovery of transformer, people were using asbestos, cotton, low grade pressboard in air for insulation purpose. Further, Kraft paper was invented which became much popular insulation material.
 

7. Which transformer insulation material is best compare to Kraft paper?
a) Oil
b) Asbestos
c) Low grade pressboard
d) Cotton
 

Answer: a
 

Explanation: Newly developed oil-filled transformers have capabilities much greater than those transformers which used Kraft paper as dielectric material. Also, electrical properties of Kraft paper depend on physical and chemical properties of paper.
 

8. Which of the following is not the property of oil that should be fulfilled before using in transformer?
a) Low viscosity
b) High flash point
c) Low electrical strength
d) High chemical stability
 

Answer: c
 

Explanation: There are various important parameters that oil must follow for its use in oil cooled transformer. These parameters include low viscosity, high stability, high flash point, high electrical strength, low pour point.
 

9. Transformer ratings are given in _____________
a) kW
b) kVAR
c) HP
d) kVA
 

Answer: d
 

Explanation: There are two types of losses in a transformer, Copper Losses and Iron Losses or Core Losses or Insulation Losses. Copper losses (I2R) depends on current passing through transformer winding while Iron losses or Core Losses or Insulation Losses depends on Voltage. That’s why the rating of Transformer is in kVA.
 

10. Function of transformer is to _________________
a) Convert AC to DC
b) Convert DC to AC
c) Step down or up the DC voltages and currents
d) Step down or up the AC voltages and currents
 

Answer: d
 

Explanation: A Transformer does not work on DC and operates only on AC, therefore it Step up of Step down the level of AC Voltage or Current, by keeping frequency of the supply unaltered on the secondary side.