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All questions of Three Phase Transformers and Autotransformers for Electrical Engineering (EE) Exam
The primary and secondary of a transformer are ________ coupled but _______ connected.- a)magnetically, not electrically
- b)electrically, not magnetically
- c)magnetically, also magnetically
- d)electrically, also electrically
Correct answer is option 'A'. Can you explain this answer?
The primary and secondary of a transformer are ________ coupled but _______ connected.
a)
magnetically, not electrically
b)
electrically, not magnetically
c)
magnetically, also magnetically
d)
electrically, also electrically
|
Aniket Choudhury answered |
Transformer is the machine which has physical spacing and has magnetic circuit to exchange the voltage.
Hence Option (A) is correct
To access short notes on Single-phase Transformers click on the link given below
It was needed that to isolate dc noise coming from the transmitted signal, to attain the same which machine can be used without suffering significant loss- a)transformer
- b)dc machine
- c)induction machine
- d)stepper motor
Correct answer is option 'A'. Can you explain this answer?
It was needed that to isolate dc noise coming from the transmitted signal, to attain the same which machine can be used without suffering significant loss
a)
transformer
b)
dc machine
c)
induction machine
d)
stepper motor
|
Samridhi Bose answered |
We should use transformer to achive the isolation of dc.
A transformer has comparitively much higher efficiency than a similar induction machine due to- a)small air gaps
- b)no moving parts
- c)strong coupling
- d)all of the mentioned
Correct answer is option 'D'. Can you explain this answer?
A transformer has comparitively much higher efficiency than a similar induction machine due to
a)
small air gaps
b)
no moving parts
c)
strong coupling
d)
all of the mentioned
|
Rajesh Saha answered |
Transformer does not has any moving components so losses are anyway reduced and also the coupling is very strong between two sides.
The delta-delta connections are used in applications of- a)large l.v. transformers
- b)small h.v. transformers
- c)large h.v. transformers
- d)small l.v. transformers
Correct answer is option 'A'. Can you explain this answer?
The delta-delta connections are used in applications of
a)
large l.v. transformers
b)
small h.v. transformers
c)
large h.v. transformers
d)
small l.v. transformers
|
Divya Singh answered |
Delta connected winding handle line voltages so it needs more turns in the winding but thin wires.
Consider two transformers X and Y having exact ratings, but have flux densities of 1.5T and 2T respectively. The weight of the transformer A per KVA will be- a)more than that of B
- b)lesser than that of B
- c)equal to that of B
- d)can not be said from the given data
Correct answer is option 'A'. Can you explain this answer?
Consider two transformers X and Y having exact ratings, but have flux densities of 1.5T and 2T respectively. The weight of the transformer A per KVA will be
a)
more than that of B
b)
lesser than that of B
c)
equal to that of B
d)
can not be said from the given data
|
Shivam Das answered |
Flux density = flux/Area.
Hence A has more area than B and so weight of A will be more than that of B.
Hence A has more area than B and so weight of A will be more than that of B.
The leakage flux is the flux in side the transformer which- a)links either of the windings
- b)links both of the windings
- c)yoke of the core
- d)windows of the core
Correct answer is option 'A'. Can you explain this answer?
The leakage flux is the flux in side the transformer which
a)
links either of the windings
b)
links both of the windings
c)
yoke of the core
d)
windows of the core
|
|
Rajat Kumar answered |
Leakage flux is meant to to be loss as it does not link two windings.
Maximum efficiency of a transformer for a constant load current , occurs at- a)at any p.f
- b)zero p.f leading
- c)zero p.f lagging
- d)unity p.f
Correct answer is option 'D'. Can you explain this answer?
Maximum efficiency of a transformer for a constant load current , occurs at
a)
at any p.f
b)
zero p.f leading
c)
zero p.f lagging
d)
unity p.f
|
|
Bijoy Mehta answered |
Efficiency = KVA*p.f/(KVA*p.f + Losses); So the efficiency is maximum at unity power factor.
The transformer which is more feasible to use in the distribution ends should be- a)star-delta
- b)delta-star
- c)scott
- d)delta-delta
Correct answer is option 'A'. Can you explain this answer?
The transformer which is more feasible to use in the distribution ends should be
a)
star-delta
b)
delta-star
c)
scott
d)
delta-delta
|
|
Bijoy Mehta answered |
Star-delta will have lower voltage at delta end.
A coupling magnetic field inside a rotating machine or static machine like transformers must involve withI. electrical system to extract energy from electrical system.II. mechanical system to extract energy from electrical system.- a)Only I is true
- b)Only II is true
- c)I and II are true
- d)I and II are false
Correct answer is option 'B'. Can you explain this answer?
A coupling magnetic field inside a rotating machine or static machine like transformers must involve with
I. electrical system to extract energy from electrical system.
II. mechanical system to extract energy from electrical system.
a)
Only I is true
b)
Only II is true
c)
I and II are true
d)
I and II are false
|
Puja Shah answered |
The energy conversion which involves both electrical as well as mechanical systems must have mutual field.
A coupling magnetic field inside a rotating machine or static machine like transformers must involve with- a)both electrical and mechanical
- b)electrical parts
- c)mechanical parts
- d)either of the electrical or mechanical parts
Correct answer is option 'A'. Can you explain this answer?
A coupling magnetic field inside a rotating machine or static machine like transformers must involve with
a)
both electrical and mechanical
b)
electrical parts
c)
mechanical parts
d)
either of the electrical or mechanical parts
|
|
Prasad Verma answered |
The coupling field should interact with both the electrical as well as mechanical parts in order to achieve electromechanical energy conversion.
Three transformers having identical dimensions but with core of iron, aluminium and wood are wound with same number of turns and have same supply.Then choose the order for hysteresis losses.- a)wood > aluminium > iron
- b)aluminium > iron > wood
- c)iron > wood > aluminium
- d)iron > aluminium > wood
Correct answer is option 'D'. Can you explain this answer?
Three transformers having identical dimensions but with core of iron, aluminium and wood are wound with same number of turns and have same supply.Then choose the order for hysteresis losses.
a)
wood > aluminium > iron
b)
aluminium > iron > wood
c)
iron > wood > aluminium
d)
iron > aluminium > wood
|
Aarya Basu answered |
Hysteresis losses occur maximum in the ferromagnetic material.
While comparing potential transformer to an auto transformer, a potential transformer transfers power ________- a)inductively
- b)conductively
- c)both conductively as well as inductively
- d)electromagnetic induction
Correct answer is option 'A'. Can you explain this answer?
While comparing potential transformer to an auto transformer, a potential transformer transfers power ________
a)
inductively
b)
conductively
c)
both conductively as well as inductively
d)
electromagnetic induction
|
EduRev GATE answered |
A potential transformer is a device that transfers electrical power through inductive coupling. This means it uses electromagnetic fields to transfer energy from one circuit to another without direct electrical connection.
- A potential transformer is primarily used for measurement and protection in power systems.
- It provides isolation between the high-voltage circuit and the measuring instruments.
- Power transfer occurs inductively rather than conductively.
In contrast, an auto transformer can transfer power both conductively and inductively, as it has common windings between the input and output.
A V-V connected transformer can be connected in parallel to delta-delta connected transformer but not to- a)delta-star
- b)star-delta
- c)star-V
- d)all of the mentioned
Correct answer is option 'A'. Can you explain this answer?
A V-V connected transformer can be connected in parallel to delta-delta connected transformer but not to
a)
delta-star
b)
star-delta
c)
star-V
d)
all of the mentioned
|
|
Arpita Banerjee answered |
The V-V connected transformer and D-D connected transformers have same phase displacement, so they only can be connected in parallel to each other.
Three units of single phase transformers and one single three-phase transformer rating- a)will be same for one rating
- b)can never be made same
- c)may be same
- d)none of the mentioned
Correct answer is option 'A'. Can you explain this answer?
Three units of single phase transformers and one single three-phase transformer rating
a)
will be same for one rating
b)
can never be made same
c)
may be same
d)
none of the mentioned
|
Baishali Bajaj answered |
It is found that generation, transmission and distribution of electrical power are more economical in three phase system than single phase system. For three phase system three single phase transformers are required. Three phase transformation can be done in two ways, by using single three phase transformer or by using a bank of three single phase transformers. Both are having some advantages over other. Single 3 phase transformer costs around 15 % less than bank of three single phase transformers. Again former occupies less space than later. For very big transformer, it is impossible to transport large three phase transformer to the site and it is easier to transport three single phase transformers which is erected separately to form a three phase unit.
If para magnetic core is used in the place of the ferromagnetic core of the transformer, then magnetostriction will- a)be vanished
- b)reduce
- c)increase
- d)not be affected
Correct answer is option 'A'. Can you explain this answer?
If para magnetic core is used in the place of the ferromagnetic core of the transformer, then magnetostriction will
a)
be vanished
b)
reduce
c)
increase
d)
not be affected
|
|
Prasad Saini answered |
If the core is not ferromagnetic then the transformer will not operate at all so no humming sound.
The voltage regulation of a transformer depends on its
- a)transformer size
- b)equivalent resistance
- c)load power factor
- d)equivalent reactance
- e)load current
Correct answer is option 'A'. Can you explain this answer?
The voltage regulation of a transformer depends on its
a)
transformer size
b)
equivalent resistance
c)
load power factor
d)
equivalent reactance
e)
load current
|
Debanshi Basak answered |
The voltage regulation of a transformer depends on its transformer size.
The voltage regulation of a transformer refers to the ability of the transformer to maintain a constant voltage output even when there are variations in the load or input voltage. It is an important parameter that determines the performance and efficiency of a transformer.
Explanation:
The transformer size, or its kVA rating, has a direct impact on its voltage regulation. The size of a transformer determines its power handling capacity and its ability to handle varying load conditions.
When a transformer is operating at full load, its voltage regulation is typically at its highest. This is because the transformer has to supply the maximum amount of power to the load, and any losses or impedance in the transformer windings will result in a drop in the output voltage.
As the load on the transformer decreases, the voltage regulation improves. This is because there is less current flowing through the windings, resulting in fewer losses and a smaller voltage drop. Therefore, the size of the transformer plays a crucial role in determining its voltage regulation.
Other Factors:
While transformer size is the primary factor that determines voltage regulation, there are other factors that can also influence it to some extent. These factors include:
- Equivalent Resistance: The equivalent resistance of a transformer represents the resistive losses in the windings. Higher resistance can lead to higher voltage drop and poorer voltage regulation.
- Load Power Factor: The power factor of the load connected to the transformer affects the reactive power requirements and can impact the voltage regulation. Loads with low power factors (such as motors) can increase the reactive power demand and result in a voltage drop.
- Equivalent Reactance: The equivalent reactance of a transformer represents the inductive and capacitive reactance in the windings. Higher reactance can lead to more voltage drop and poorer voltage regulation.
- Load Current: The magnitude of the load current can also affect the voltage regulation. Higher load currents can result in higher losses and voltage drops.
While these factors do have an impact on voltage regulation, the transformer size remains the primary determinant. A properly sized transformer will have a lower voltage drop and better voltage regulation compared to an undersized transformer.
The voltage regulation of a transformer refers to the ability of the transformer to maintain a constant voltage output even when there are variations in the load or input voltage. It is an important parameter that determines the performance and efficiency of a transformer.
Explanation:
The transformer size, or its kVA rating, has a direct impact on its voltage regulation. The size of a transformer determines its power handling capacity and its ability to handle varying load conditions.
When a transformer is operating at full load, its voltage regulation is typically at its highest. This is because the transformer has to supply the maximum amount of power to the load, and any losses or impedance in the transformer windings will result in a drop in the output voltage.
As the load on the transformer decreases, the voltage regulation improves. This is because there is less current flowing through the windings, resulting in fewer losses and a smaller voltage drop. Therefore, the size of the transformer plays a crucial role in determining its voltage regulation.
Other Factors:
While transformer size is the primary factor that determines voltage regulation, there are other factors that can also influence it to some extent. These factors include:
- Equivalent Resistance: The equivalent resistance of a transformer represents the resistive losses in the windings. Higher resistance can lead to higher voltage drop and poorer voltage regulation.
- Load Power Factor: The power factor of the load connected to the transformer affects the reactive power requirements and can impact the voltage regulation. Loads with low power factors (such as motors) can increase the reactive power demand and result in a voltage drop.
- Equivalent Reactance: The equivalent reactance of a transformer represents the inductive and capacitive reactance in the windings. Higher reactance can lead to more voltage drop and poorer voltage regulation.
- Load Current: The magnitude of the load current can also affect the voltage regulation. Higher load currents can result in higher losses and voltage drops.
While these factors do have an impact on voltage regulation, the transformer size remains the primary determinant. A properly sized transformer will have a lower voltage drop and better voltage regulation compared to an undersized transformer.
The statements which support the points that auto transformers are disadvantageous as compared to 2-winding transformer
I. Weight of conductor reduces
II. Direct electrical contacts
III. Leakage reactance reduces
IV. Lower short-circuit current- a)I,III
- b)II,III
- c)II,IV
- d)I,II,IV
Correct answer is option 'C'. Can you explain this answer?
The statements which support the points that auto transformers are disadvantageous as compared to 2-winding transformer
I. Weight of conductor reduces
II. Direct electrical contacts
III. Leakage reactance reduces
IV. Lower short-circuit current
I. Weight of conductor reduces
II. Direct electrical contacts
III. Leakage reactance reduces
IV. Lower short-circuit current
a)
I,III
b)
II,III
c)
II,IV
d)
I,II,IV
|
|
Arshiya Basu answered |
Direct electrical contacts is a disadvantage to the auto transformer.
Short circuit current of the auto transformer is higher than the corresponding 2-winding transformer.
Short circuit current of the auto transformer is higher than the corresponding 2-winding transformer.
If a transformer is at no load , then it will act like- a)a resistor at p.f =0
- b)an inductive reactor at 0.2 lagging
- c)a capacitive reactor at0.2 leading
- d)an inductive reactor at 0.8 lagging
Correct answer is option 'B'. Can you explain this answer?
If a transformer is at no load , then it will act like
a)
a resistor at p.f =0
b)
an inductive reactor at 0.2 lagging
c)
a capacitive reactor at0.2 leading
d)
an inductive reactor at 0.8 lagging
|
Manoj Chaudhary answered |
Transformer is nothing but the arranged windings which are magnetically coupled. The windings will inductive predominantly with very low resistance.
When we magnetize the ferromagnetic core of the transformer, core length_______ and it ______ when demagnetized.- a)decreases, increases
- b)decreases, decreases
- c)increases,increases
- d)none of the mentioned
Correct answer is option 'A'. Can you explain this answer?
When we magnetize the ferromagnetic core of the transformer, core length_______ and it ______ when demagnetized.
a)
decreases, increases
b)
decreases, decreases
c)
increases,increases
d)
none of the mentioned
|
|
Sahana Sarkar answered |
Due to aligned magnetic dipoles in the material, the size will reduce by a small margin and vice versa while demagnetization.
The most widely used material in the core of the transformer is- a)cold rolled grain oriented sheet steel
- b)cold rolled grain steel
- c)soft iron
- d)steel
Correct answer is option 'A'. Can you explain this answer?
The most widely used material in the core of the transformer is
a)
cold rolled grain oriented sheet steel
b)
cold rolled grain steel
c)
soft iron
d)
steel
|
Swara Dasgupta answered |
CRGO has magnetization in the rolling direction and low core losses and very high permeability than present materials.
The voltage regulation of a transformer at full-load 0.8 p.f leading is -2%. Its voltage regulation at full load 0.8 p.f lagging- a)will be positive
- b)will be negative
- c)may be positive
- d)may be negative
Correct answer is option 'A'. Can you explain this answer?
The voltage regulation of a transformer at full-load 0.8 p.f leading is -2%. Its voltage regulation at full load 0.8 p.f lagging
a)
will be positive
b)
will be negative
c)
may be positive
d)
may be negative
|
|
Prasad Verma answered |
The leading p.f. has negative v.r. and lagging p.f. has major portion of positive voltage regulation.
We can employ transformers for a power range of- a)lower and higer values
- b)lower values
- c)higher values
- d)medium values
Correct answer is option 'A'. Can you explain this answer?
We can employ transformers for a power range of
a)
lower and higer values
b)
lower values
c)
higher values
d)
medium values
|
|
Mihir Khanna answered |
A transformer can be put in use upto a varying range of the power and it is usually available in readily in market.
It is advised that staggering of the butt joints- a)reduces reluctance of the path
- b)increases air gap
- c)increases mechanical strength
- d)all of the mentioned
Correct answer is option 'C'. Can you explain this answer?
It is advised that staggering of the butt joints
a)
reduces reluctance of the path
b)
increases air gap
c)
increases mechanical strength
d)
all of the mentioned
|
Pankaj Mehta answered |
Staggering is done for the steel butt joints of the transformer to gain more mechanical strength as the continuous air gap reduces the same.
A 1-phase tranformer has a leakage impedance of 1+ j4 Ω for primary and 3+ j11 Ω for secondary windings. This transformer has- a)H.V primary
- b)Medium voltage primary
- c)L.V primary
- d)L.V secondary
Correct answer is option 'C'. Can you explain this answer?
A 1-phase tranformer has a leakage impedance of 1+ j4 Ω for primary and 3+ j11 Ω for secondary windings. This transformer has
a)
H.V primary
b)
Medium voltage primary
c)
L.V primary
d)
L.V secondary
|
|
Srestha Kumar answered |
The side which has lower impedance will have lower number of turns and so the low voltage side.
A recording of the output of the emf induced for star and delta are recorded.Then shape of the emf induced in Y-connected 3-phase transformer is non sinusoidal in nature due to- a)3rd harmonic component of currents is absent
- b)3rd harmonic component of currents is present
- c)negative sequence component of current is present
- d)none of the mentioned
Correct answer is option 'A'. Can you explain this answer?
A recording of the output of the emf induced for star and delta are recorded.Then shape of the emf induced in Y-connected 3-phase transformer is non sinusoidal in nature due to
a)
3rd harmonic component of currents is absent
b)
3rd harmonic component of currents is present
c)
negative sequence component of current is present
d)
none of the mentioned
|
|
Rajat Kumar answered |
In a star connected transformer, closed path to generate 3rd harmonic is not there. So the emf shape will be peaky in nature.
Open delta transformers can be obtained from- a)delta-delta
- b)star-delta
- c)delta-star
- d)any of the mentioned
Correct answer is option 'A'. Can you explain this answer?
Open delta transformers can be obtained from
a)
delta-delta
b)
star-delta
c)
delta-star
d)
any of the mentioned
|
|
Jaya Dasgupta answered |
If one of the transformers is removed from the bank of only delta-delta, then it behaves with 58% power delivery.
A 400 V, 10 KVA transformer at 50 Hz, is operated at the frequency of 40 Hz, then the humming- a)increases
- b)decreases
- c)remains same
- d)increases to very high
Correct answer is option 'A'. Can you explain this answer?
A 400 V, 10 KVA transformer at 50 Hz, is operated at the frequency of 40 Hz, then the humming
a)
increases
b)
decreases
c)
remains same
d)
increases to very high
|
Anirban Gupta answered |
If the frequency is reduced, the core flux density increases, so the noise also will increase.
I. KVA rating : 1/(1-k)
II. Losses : (1-k)
III. Impedance drop = 1/(1-k)
Which of the above are correct for an auto transformer when compared to the identical rating two winding transformer?- a)I,II
- b)II,III
- c)1,III
- d)I,II,III,IV
Correct answer is option 'A'. Can you explain this answer?
I. KVA rating : 1/(1-k)
II. Losses : (1-k)
III. Impedance drop = 1/(1-k)
Which of the above are correct for an auto transformer when compared to the identical rating two winding transformer?
II. Losses : (1-k)
III. Impedance drop = 1/(1-k)
Which of the above are correct for an auto transformer when compared to the identical rating two winding transformer?
a)
I,II
b)
II,III
c)
1,III
d)
I,II,III,IV
|
|
Shivani Saha answered |
KVA(auto)/KVA(2-W) = V2*I2/V2*(I2-I1)
= 1/(1-I1/I2)
= 1/(1-k)
Losses(auto)= (1-k) *Losses(2-W)
Impedance drop(auto)= (1-k)*Impedance drop(2-W).
= 1/(1-I1/I2)
= 1/(1-k)
Losses(auto)= (1-k) *Losses(2-W)
Impedance drop(auto)= (1-k)*Impedance drop(2-W).
Below is the circuit diagram for delta-delta transformer have a transformation ratio ‘k’. The current flowing in the windings of phase r-y in the below diagrams is
- a)k*I/1.73
- b)I/k*1.73
- c)1.73*k*I
- d)3*k*I
Correct answer is option 'A'. Can you explain this answer?
Below is the circuit diagram for delta-delta transformer have a transformation ratio ‘k’. The current flowing in the windings of phase r-y in the below diagrams is
a)
k*I/1.73
b)
I/k*1.73
c)
1.73*k*I
d)
3*k*I
|
|
Pallabi Pillai answered |
The phase current will be reduced by 1/1.73.
Chapter doubts & questions for Three Phase Transformers and Autotransformers - 6 Months Preparation for GATE Electrical 2025 is part of Electrical Engineering (EE) exam preparation. The chapters have been prepared according to the Electrical Engineering (EE) exam syllabus. The Chapter doubts & questions, notes, tests & MCQs are made for Electrical Engineering (EE) 2025 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests here.
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