TRANFORMER MCQ PSCPL UPSC GOVT EXAM
(PART-I)
1. Transformer is a _____________ Electric Device?
a) Static
b) Dynamic
c) Both
d) None of These
View Answer
Explanation: A Transformer is a Static electrical device . because transformer has no any moving or rotary part.
2. What is Transformer?
a) Transformer is a device used to convert low alternating voltage to a high alternating voltage
b) Transformer is a device used to convert alternating current to direct current
c) Transformer is a device used to convert low alternating current to a high alternating current
d) Transformers are used only for low alternating voltage
View Answer
Explanation: A Transformer is static device which convert low into high voltage and vice-versa.
3. What is the function of a transformer?
a) Transformer is used to step down or up the AC voltages and currents
b) Transformer is used to step down or up the DC voltages and currents
c) Transformer converts DC to AC voltages
d) Transformer converts AC to DC voltages
View Answer
Explanation: A Transformer does not work on DC and operates only on AC, therefore it Step up or Step down the level of AC Voltage or Current, by keeping frequency of the supply unaltered on the secondary side.
4. What is the working principle of a Transformer?
a) Transformer works on the principle of self induction
b) Transformer works on the principle of mutual induction
c) Transformer works on the principle of ampere law
d) Transformer works on the principle of coulomb law
View Answer
Explanation: A transformer is an electrical device used to vary the input voltage. Transformer works on the principle of mutual induction.
5. Transformer can work on ____________
a) ac supply only
b) dc supply only
c) Both ac and dc
d) None of These
View Answer
ac supply only
Explanation: A transformer is an electrical device which the used to step up and step down the ac voltage only .
6. A transformer cannot work on the DC supply because __________________
a) There is no need to change the DC voltage
b) A DC circuit has more losses
c) Faraday’s laws of electromagnetic induction are not valid since the rate of change of flux is zero
d) Cannot be determined
View Answer
Faraday’s laws of electromagnetic induction are not valid since the rate of change of flux is zero
Explanation: For DC supply the direction and the magnitude of the supply remains constant, produced flux will be constant. Thus, rate of change of flux through the windings will be equal to zero. As a result, voltage at secondary will always be equal to 0.
7. A winding which ac supply is connected is known as ______________
a) Primary Winding
b) Secondary Wing
c) Low voltage winding
d) High voltage winding
View Answer
Explanation:ac supply is always connected to Primary winding of a Transformer.
8. A winding which load is connected is known as ______________
a) Primary Winding
b) Secondary Wing
c) Low voltage winding
d) High voltage winding
View Answer
Explanation:load is always connected to Secondary winding of a Transformer.
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
View Answer
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.Transformers windings are generally made of __________
a) Steel
b) Iron
c) Copper
d) Steel iron alloy
View Answer
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.
a) Infinite
b) 100 ohm
c) Zero
d) 1000 ohm
View Answer
Explanation: The primary and secondary windings of Transformers are magnetically coupled and electrically isolated; ideally, the resistance between the two windings should be infinity, but practically the insulation resistance is in the order of megaohms.
12. If secondary number of turns are higher then primary number of turns in transformer is called _________
a) Step-down
b) Step-up
c) One-one
d) Autotransformer
View Answer
Explanation: When secondary number of turns are higher compare to primary, voltage induced in secondary windings will obviously high. Thus, this transformer is used for stepping up the output voltage by keeping frequency constant.
13. If primary number of turns are higher then secondary number of turns, transformer is called _________
a) Step-down
b) Step-up
c) One-one
d) Auto transformer
View Answer
Explanation: When primary number of turns are higher compare to secondary, voltage induced in secondary windings will obviously low compare to primary. Thus, this transformer is used for stepping down the output voltage by keeping frequency constant.
14. If a transformer is having equal number of turns at primary and secondary then transformer is called as _______________
a) Step-down
b) Step-up
c) isolation
d) Autotransformer
View Answer
Explanation: A transformer is having equal number of turns at primary and secondary then transformer is called as one-one transformer. This transformer have turns ratio equal to 1, so is the voltage ratio for the one-one transformer.
15. Isolation transformers are used because ______________
a) To isolate any part of circuit electrically
b) To get more voltage at secondary
c) To get less voltage at secondary
d) To reduce losses, present in circuit
View Answer
Explanation: In one to one transformers is called isolation transfomer, we have same number of turns in primary and in secondary. So, increasing/ reducing voltage is not possible. They are generally used to isolate one part of circuit from another part of circuit, electrically.
16. 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
View Answer
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.
17. Which winding has more number of turns?
a) Low voltage winding
b) High voltage winding
c) Primary winding
d) Secondary winding
View Answer
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. 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.
18. When Transformation Ratio (K) is More then unity ______________. (PSPCL 2021 Exam)
a) Step-up Transformer
b) Step-down Transformer
c) Isolation Transformer
d) Auto Transformer
View Answer
Explanation: 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.
K=E2/E1 =N2/N1. So K>1 then Transformer is called Step-up Transformer
19. When Transformation Ratio (K) is Less then unity ______________. (PSPCL 2021 Exam)
a) Step-up Transformer
b) Step-down Transformer
c) Isolation Transformer
d) Auto Transformer
Explanation: voltage is directly proportional to the number of turns.If K<1, then Transformer is called Step-down Transfomer.
20. When Transformation Ratio (K) is Equal to unity ______________. (PSPCL 2021 Exam)
a) Step-down Transformer
b) Step-down Transformer
c) Isolation Transformer
d) Auto Transformer
Explanation: 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.K=E2/E1 =N2/N1. So K=1 means N1=N2 then Transformer is called Isolation Transformer
21. Transformer ratings are given in _____________
a) kVA
b) HP
c) kVAR
d) kW
View Answer
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
22. 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
View Answer
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.
23. Transformer core is designed to reduce ______________
a) Hysteresis loss
b) Eddy current loss
c) Hysteresis loss and Eddy current loss
d) Cannot be determined
View Answer
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.
24. Dielectric mineral oil is used in ____________
a) Small transformers
b) Medium transformers
c) Large transformers
d) In all transformers
View Answer
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.
25.Before using oil in transformers, insulation material was _________
a) Asbestos
b) Cotton
c) Low grade pressboard in air
d) Kraft paper
View Answer
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.
26.Which transformer insulation material is best compare to Kraft paper?
a) Oil
b) Asbestos
c) Low grade pressboard
d) Cotton
View Answer
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.
27.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
View Answer
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.
28.What is the dielectric strength of a transformer oil?
a) 1 kV
b) 35 kV
c) 100 kV
d) 330 kV
View Answer
Explanation: For mineral oil, an accepted minimum dielectric strength is 30 kV for transformers with a high-voltage rating of 230 kV and above and 27 kV for transformers with a high-voltage rating below 230 kV. New oil should pass the condition of a minimum dielectric strength of 35 kV by ASTM methods of testing.
29.The insulating material that can withstand the highest temperature safely is _______________
a) Cellulose
b) Asbestos
c) Mica
d) Glass fibre
View Answer
Explanation: Mica is extremely stable when it is exposed to moisture and extreme temperatures to maintain superior electrical properties as an insulator. The mechanical properties of mica allow it to be cut, punched, stamped and machined to close tolerances along with maintenance of a high thermal conductivity.
a) Low voltage winding
b) High voltage winding
c) Primary winding
d) Secondary winding
View Answer
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.
31. If a transformer is continuously operated the maximum temperature rise will occur in ___________
a) Core
b) Windings
c) Tank
d) Cannot be determined
View Answer
Explanation: Copper windings carry currents in a transformer. The loss in form of heat in copper winding carrying current is proportional to the square of the current passing through them multiplied by the resistance of the winding. This loss is dissipated in heat and corresponding temperature rise.
32. Ideal transformer core has permeability equal to _____
a) Zero
b) Non-zero finite
c) Negative
d) Infinite
View Answer
Explanation: The core has infinite permeability so that zero magnetizing current is needed to establish the requisite amount of flux in the core. The core-loss (hysteresis as well as eddy-current loss) is considered zero.
33. Turns ratio of the transformer is directly proportional to ____________
a) Resistance ratio
b) Currents ratio
c) Voltage ratio
d) Not proportional to any terms
View Answer
Explanation: According to the voltage expression, emf induced in the primary is directly proportional to the change in the flux with respect to the time and number of turns of the primary winding. Similarly, for secondary winding.
34. The size of a transformer core will depend on ________________
a) frequency
b) area of the core
c) flux density of the core material
d) frequency and area of the core
View Answer
Explanation: According to the frequency of transformer size of the core of transformer changes. While area of core also depends upon many parameters like operating voltage, capacity of transformer, hence all these contribute to the size of the core.
35. The frictional loss in a transformer is ________________
a) 10 %
b) 50 %
c) 0 %
d) More than 50 %
View Answer
Explanation: As we know, the transformer is a static device based on the principle of mutual induction with no rotating part, so there is no frictional loss.
36. Which of the given losses changes with the load in the transformer?
a) Copper loss
b) Iron loss
c) Core loss
d) None of these
View Answer
Explanation: As we know, the transformer has primarily two types of losses Iron loss and copper loss. Iron loss is always constant, whereas copper losses are varying with a load.
Iron loss = Hysteresis loss + Eddy current loss
Both hysteresis loss and eddy current loss do not depend upon load current, which means iron losses are constant with varying load.
Copper loss = Conduction losses in conductor winding, which are directly proportional to the current square.
37. Lamination of the transformer core is made up of ________
a) Aluminum
b) Iron
c) Steel
d) Silicon steel
View Answer
Explanation: A high permeable material made up of thin silicon steel laminations are used for lamination of transformer core and other electrical devices for the given reasons:
High resistance.
38. The direction of magnetic flux in a transformer must have _______
a) No reluctance
b) Low reluctance
c) High Impedance
d) Low resistance
View Answer
Explanation: Reluctance refers to analogous resistance. As we know, resistance opposes the flow of electric current in an electric circuit that same work does by a reluctance in a magnetic circuit.
Reluctance opposes the flow of magnetic flux in the magnetic circuit. It stores magnetic energy in the magnetic circuit. If the reluctance is low, less the opposite of the magnetic flux in the circuit; therefore, more flux can flow through the transformer core.
39.What is the current transformer?
a) transformer used with an A.C. voltmeter
b) transformer used with an A.C. ammeter
c) transformer used with an D.C. voltmeter
d) transformer used with an D.C. ammeter
View Answer
Explanation: A transformer used to extend the range of an A.C. ammeter is known as a current transformer. A current transformer is also abbreviated as C.T.