Electrical
Circuits &Machines
UNIT II:
Transformer
MCQ’S
-Prof. Tushar V.
Kafare
BSIOTR Wagholi
[1] High frequency transformers sometimes make
use of ferrite cores because it has
A. High specific gravity
B. High resistance
C. High hysteresis
D. low permeability
Ans: B
[2] Harmonics in transformer result
in
A. Increased core losses
B. Increased I2R losses
C. Magnetic interference with
communication circuits
D. All of the above
Ans: D
[3] The full load copper loss of a
transformer is 1600W. At half-load the copper loss will be
A. 6400W
B. 1600W
C. 800W
D. 400W
Ans:D
[4] Power transformers are generally
designed to have maximum efficiency around
A. No load
B. Half load
C.Near full load
D. 10% overload
Ans:C
[5] Two transformers are connected
in parallel. These transformers do not have equal percentage impedance which
results
A. Short-circuiting of the
secondaries
B. Power factor of one of the
transformers is leading while that of the other lagging
C. Transformers having higher copper
losses will have negligible core losses
D. Loading of the transformers not
in proportion to their kVA ratings.
Ans:D
[6] The changes in volume of
transformer cooling oil due to variation of atmospheric temperature during
day and night is taken care of by which part of transformer?
A. Conservator
B. Breather
C. Bushings
D. Buchholz relay
Ans:A
[7] The transformer laminations
are insulated from each other by
A. Mica strip
B. Thin coat of varnish
C. Paper
D. Any of the above
Ans:B
[8] Which type of winding is used in
3 phase shell type transformer?
A. Circular type
B. Sandwich type
C. Cylindrical type
D. Rectangular type
Ans: B
[9] During open circuit test of a transformer
A. Primary is supplied rated voltage
B. Primary is supplied full load
current
C. Primary is supplied current at
reduced voltage
D. Primary is supplied rated kVA
Ans: A
[10] Which of the following is not
standard voltage for power supply in India
A. 11kV
B. 33kV
C. 66 kV
D. 122 kV
Ans: D
[11] The low voltage winding of a
400/230 volt, 1-phase, 50Hz transformer is to be connected to a 25Hz supply in
order to keep the magnetization current at the same level as that for normal
50Hz supply at 25Hz the voltage should be [Gate 1997]
a) 230V
b) 460V
c) 115V
d) 65V
Ans: C
[12] The primary current in the current
transformer is dictated by [Gate 1997]
a) The secondary burden
b) The core of the transformer
c) The load current
d) None of the above
Ans:A
13. In Single Phase
Transformer, The Primary Current and Primary Voltage is 4.55 and 11kV
respectively. The Rating of the transformer would be________?
a) 86kVA b)
100kVA c) 150kVA d) 50kVA
Ans: D
14. A
Transformer______________.
a) Steps up or down DC Voltages
& Current b) Changes DC to AC
c) Changes ac to DC d) Steps
up or down AC Voltages & Current
Ans: D
15. What would happen if a
power transformer designed for operation on 50 Hz (frequency) were connected to
a 5 Hz (frequency) source of the same voltage?
a) Eddy Current and
Hysteresis loss will be excessive
b) Current will be too
much low
c) Transformer may start
to smoke
d) No effect
Ans: C
16. In Three Phase
Transformer, The load Current is 139.1A, and Secondary Voltage is 415V. The
Rating of the Transformer would be ___________.
a) 173 KVA b) 50 KVA c) 100KVA d)
57.72 KVA
Ans: C
17. If the primary power
of an ideal transformer having a 2:1 voltage ratio is 100 W, the secondary
power is
a) 50W b) 100 W c) 75 W d) 200 W
Ans: B
18. Increasing the number
of turns of wire on the secondary of a transformer will
a) decrease the secondary
current b) have no
effect on the secondary current
c) increase the primary
current d) increase
the secondary current
Ans: A
19. Laminated insulations
coated with varnish are normally used in the transformer
a) To reduce the effect of
eddy current b) To reduce
reluctance of magnetic path
c) To reduce the
hysteresis effect d) To
increase the reluctance of magnetic path
Ans: A
20. Laminated insulations
coated with varnish are normally used in the transformer
a) To reduce the effect of
eddy current b) To reduce
reluctance of magnetic path
c) To reduce the
hysteresis effect d) To
increase the reluctance of magnetic path
Ans: A
21. The transformer turns ratio determines
a) the reflected impedance b) the ratio of
primary and secondary voltages
c) the ratio of primary
and secondary currents d) all
Ans: A
22. An Isolation
Transformer Has Primary to Secondary turns ratio of __________.
a) 1 : 2 b)
1 : 1
c) 2 : 1 d)
Can be any ratio
Ans: B
23. The coefficient of
coupling between two coils is 0.45. The first coil has an inductance of 75 mH
and the second coil has an inductance of 105 mH. What is the mutual inductance
between the coils?
a) 7.88 mH b)
3.54 mH
c) 39.9 mH d)
189.3 mH
Ans: C
24. In an Auto
Transformer, The Primary and Secondary are__________Coupled.
a) Magnetically as well as
Electrically b) Only
Magnetically
c) Only Electrically d) None
of the above
Ans: A
25. When does maximum
power transfer happen from the source to the load?
a) When the source
resistance is less than the load resistance
b) When there is
negligible source resistance
c) When the source
resistance is greater than the load resistance
d) When the source
resistance equals the load resistance
Ans: D
26. A special transformer
used to convert unbalanced signals to balanced signals is the
a) autotransformer b) step-across transformer
c) balun d) center-tapped transformer
Ans: C
27. Under what condition
is D.C supply applied safely to the primary of a transformer?
a) We can't connect to DC
Supply
b) We can connect directly
to DC. No condition required
c) A High resistance
should be connect in series with primary, but circuit will be useless.
d) The above statement is
wrong
Ans: C
28. Which of the following
3-phase connection of a transformer causes interference with the neighboring communication
lines:
a) Star-delta b)
Delta-star
c) Star-star d) Delta-star
Ans: C
29. An Auto-transformer
(which has only one winding) may be used as a ______?
a) Step-Up Transformer b) Step-Down Transformer
c) Both Step-Up and
Step-Down transformer d)
None of these
Ans: C
30. The friction losses in
Real Transformers are _________?
a) 5% b) 25% c) 50% d) 0%
Ans: D
Two single phase transformers with equal turns have impedance of (0.5+j3)
Ω & (0.6 + j 10) Ω with respect to the secondary. If they operate in
parallel , how will they share a load of
100 kw at 0.8 p.f. lagging
A. 50 kw, 50kw
B. 62kw,38kw
C. 78.2kw, 21.8Kw
D. 85.5kw, 14.5kw
ANSWER: C
Two single phase transformers A & B are connected in parallel. They
have same KVA ratings but they have
different resistances are respectively 0.005 & 0.01 per unit & their
leakage reactances 0.05 & 0.04 per unit. If A is operated on full –load at
p.f.. of 0.8 lagging what will be the over load & power factor of
transformer B.
A. Transformer B is overloaded by 44 % its power factor is 0.878 (lead)
B. Transformer B is overloaded by 22% its power factor is 0.878 (lag)
C. Transformer B is overloaded by 22% its power factor is 0.878 (lead)
D. Transformer B is overloaded by 44% its power factor is 0.878
(lag)
ANSWER: B
Two single phase transformers A & B rated at 250 kVA each are
operated in parallel on both sides. Percentage impedance for both A & B are
(1+j6) and (1.2+j4.8) respectively. Compute the load shared by each when the
total load is 500kVA at 0.8 pf lagging
A. 200KW, 300KW
B. 225KW, 275KW
C. 275KW , 225KW
D. 250KW, 250KW
ANSWER: B
A 500 kVA transformer with 1% resistance & 5 % reactance is connectd
in pareallel with a 250 kVA transformer with 1.5% resistance & 4%
reactance. The secondary voltage of each transformer is 400 volt on no load.
Find how they share a load of 750 kVA at a p.f. of 0.8 lagging
A. 300KW, 450KW
B. 375KW, 375KW
C. 280KW , 470KW
D. 470KW, 280KW
ANSWER: D
Two single phase transformers A & B of equal voltage ratio are running in paralleland supply a load of
1000A at 0.8 p.f lag. The equivalent impedance for both A & B are (2+j3)
and (2.5+j5) ohms respectively. Compute the current supplied by transformers A
& B.
A. 609.7 A, 392.6 A
B. 392.6 A, 609.7 A
C. 500A, 500A
D. Nona of these
ANSWER: A
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%
ANSWER: B
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
ANSWER: D
In which of the transformer, the tertiary winding is used:
A. Delta-delta
B. Star-star
C. Delta-star
D. Star-delta
ANSWER: B
The magnetizing current in a transformer is rich in
A. 3rd harmonic
B. 5th harmonic
C. 7th harmonic
D. 11th harmonic
ANSWER: A
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
ANSWER: C
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
ANSWER: B
In conversion of 3. phase to 2-phase supply with T connection, the
transformation ratio of the teaser will be__ times to that of main transformer:
A. 1.732
B. 1.15
C. 0.866
D. Unity
ANSWER: C
Two transformers of identical voltages but different capacities are
operated in parallel, for satisfactory load sharing:
A. Impedances should be equal
B. Per unit impedance must be equal
C. Per unit impedance and X/R ratio must be equal
D. Impedance and X/R ratio must be equal
ANSWER: C
Which of the following 3-phase connection of a transformer causes
interference with the neighboring communication lines:
A. Delta-star
B. Star-delta
C. Star-star
D. Delta-star
ANSWER: C
Which of the following transformer connection will give highest secondary
voltage
A. Delta primary, delta secondary
B. Delta primary, star secondary
C. Star primary, delta secondary
D. Star primary, star secondary
ANSWER: B
Two transformers are connected in parallel. These transformers do not
have equal percentage impedance which results
A. Short-circuiting of the secondaries
B. Power factor of one of the transformers is leading while that of the
other lagging
C. Transformers having higher copper losses will have negligible core
losses
D. Loading of the transformers not in proportion to their kVA ratings
ANSWER: D
Two transformers connected in parallel with wrong polarities results
A. Dead Short-circuiting of the secondaries
B. Power factor of one of the transformers is leading while that of the
other lagging
C. Transformers having higher copper losses will have negligible core
losses
D. Loading of the transformers not in proportion to their kVA
ratings
ANSWER: A
Which type of winding is used in 3 phase shell type transformer?
A. Circular type
B. Sandwich type
C. Cylindrical type
D. Rectangular type
ANSWER: B
As compared to Δ − Δ bank, the capacity of the V − V bank of transformers
is ......... percent
A. 57.7
B. 66.7
C. 50
D. 86.6
ANSWER: A
If three transformers in a Δ − Δ are delivering their rated load and one
transformer is removed, then overload on each of the remaining transformers is
......... percent.
A. 66.7
B. 173.2
C. 73.2
D. 58
ANSWER: C
In a three-phase Y-Y transformer connection, neutral is fundamental to
the
A. suppression of harmonics
B. passage of unbalanced currents due to unbalanced loads
C. provision of dual electric service
D. balancing of phase voltages with respect to line voltages.
ANSWER: A
Which of the following connections is best suited for 3-phase, 4-wire
service?
A. Δ – Δ
B. Y− Y
C. Δ –Y
D. Y− Δ
ANSWER: C
In a three phase star - delta transformer, what is the angle difference
between primary and secondary phase voltages
A. delta side lags by − 300
B. star side lags by − 300
C. star side leads by 300
D. delta side leads by 300.
ANSWER: D
Transformers operating in parallel will share the load depending upon
their
A. Leakage reactance
B. Rating
C. Efficiency
D. Percentage impedance
ANSWER: D
When a closed − Δ bank is converted into an open − Δ bank, each of the
two remaining transformers supplies ......... percent of the original load.
A. 66.7
B. 57.7
C. 50
D. 73.2
ANSWER: B
Two transformers, with equal rating & negligible excitation current,
connected in parallel share the load in the ratio of their kVA ratings only, if
their pu impedance (based on their own kVA )are
A. Equal
B. In the inverse ratio of their ratings
C. In the direct ratio of their ratings
D. Pure reactive
ANSWER: A
Two transformer of different kVA rating are being operated in parallel
they will share load in proportion to their kVA rating if
A. Per unit impedance on respective kVA are rating equal
B. Per unit impedance on common kVA are rating equal
C. Ohmic values of impedances are equal
D. Ohmic values of impedances are proportional to their rating
ANSWER: A
Out of the following given choices for poly phase transformer connections
which one will you select for three-to-two phase conversion?
A. Scott
B. Star/Star
C. Double scott
D. Star/Double delta
ANSWER: A
Of the following statements concerning parallel operation of
transformers, the one which is not correct is
A. transformers must have equal voltage ratings
B. transformers must have same ratio of transformation
C. transformers must be operated at the same frequency
D. transformers must have equal kVA ratings.
ANSWER: D
In Scot –connections the teaser transformer operates on 0.866 of its rated
A. Impedance
B. Current
C. Voltage
D. power
ANSWER: C
Keeping in view he requirement of parallel operation which of the 3-phase
connections given follows are possible
A. Delta-delta to Delta –star
B. Delta-delta to Star –
delta
B. Star – star to Delta-delta
D. Delta –star to Star – delta
ANSWER: C
Which of the following connections of transformer will give the highest
secondary voltage?
A. Delta primary, delta secondary
B. Delta primary, star
secondary
C. Star primary, star
secondary
D. Star primary, Delta secondary
ANSWER: B
A Delta/star transformer has a phase -phase voltage transformation ratio
of K, [K=(star phase voltage)/(delta phase voltage)]. The line-line voltage
ratio of star/delta connection is given by
A. k√3
B. k
C. k/√3
D. √3 / k
ANSWER: A
A Star/Delta transformer has a phase - phase voltage transformation ratio
of K , [K=(delta phase voltage)/(star phase voltage)]. The line-line voltage
ratio of star/delta connection is given by
A. k√3
B. k
C. k/√3
D. √3 / k
ANSWER: D
If per unit impedance of two transformers connected in parallel are not
equal which one of the following statement is correct?
A. The power factor of the two transformer will be different from that of
the connected load
B. Transformers will get overloaded
C. Dead short circuit occurs
D. The transformer with higher per unit impedance will share more load
ANSWER: A
A 3-phase transformer ,over a bank of 3 – single phase transformers of
equal rating has the advantages of
A. Low cost
B. Less weight
C. Occupation of less space
D. All of the above
ANSWER: D
Three -phase transformer connections most commonly used are:
A. Δ – Δ
B. Y− Y
C. Δ –Y and Y− Δ
D. Δ – Δ and Δ –Y
ANSWER: C
The 3 ph transformers were constructed by contributing …….. single phase
transformer
A. 3
B. 6
C. 9
D. 2
ANSWER: A
The core of ….. transformer consist of 3 limbs
A. Core type
B. Shell type
C. Bery type
D. Sandwich type
ANSWER: A
In the star star connection of 3 ph transformer , the phase shift between
the line voltage & phase voltage is …… degrees on both primary &
secondary sides
A. 0
B. 30
C. 60
D. 90
ANSWER: B
In Y-Y connection, the angular displacement between primary &
secondary is …………. Degrees
A. 0
B. 90
C. 180
D. 120
ANSWER: A
Y-Y connection is used only
A. As distribution transformer
B. At the receiving end
C. For power measurement
D. For small high voltage transformers
ANSWER: D
The Y-Y connection works
satisfactorily only if the load is
A. Y type
B. Δ type
C. Unbalanced
D. Balanced
ANSWER: D
For Y-Y connection we have to phase a problem called … unbalanced load
A. Neutral shift
B. Earth shift
C. Earth leakage
D. None of these
ANSWER: A
In Δ-Δ connection the primary & secondary voltages are …… degrees
phase shifted with respect to each other
A. 30
B. 60
C. 120
D. 90
ANSWER: C
For Y-Y connection we have to phase a problem called … unbalanced load
A. Neutral shift
B. Earth shift
C. Earth leakage
D. None of these
ANSWER: A
In Δ-Δ connection the primary & secondary voltages are …… degrees
phase shifted with respect to each other
A. 30
B. 60
C. 120
D. 90
ANSWER: C
In Δ-Δ connection the primary & secondary line voltages are
A. Equal to Vph
B. √3 Vph
C. Vph/√3
D. √3/ Vph
ANSWER: A
………… connection is economical for large, low voltage transformers
A. Y- Y
B. Δ-Δ
C. Δ-Y
D. Y-Δ
ANSWER: B
…... connection can be used for both balanced & unbalanced load
A. Y- Y
B. Δ-Δ
C. Δ-Y
D. Y-Δ
ANSWER: B
In Δ-Y connection the angular
displacement in degrees between primary & secondary is…
A. 0
B. 60
C. 30
D. 120
ANSWER: C
The 3 ph transformers were constructed by contributing …….. single phase
transformer
A. 3
B. 6
C. 9
D. 2
ANSWER: A
It is possible to remove even commen leg in ………. Transformer
A. Core type
B. Shell type
C. Bery type
D. Sandwich type
ANSWER: A
For Δ-Δ connection with transformation ratio K=Vph2/Vph1 , line current IL2 =
A. Iph2/√3
B. Iph2√3
C. Iph2
D. Iph2/√2
ANSWER: B
The ……. Configuration of 3 ph transformer can be used for serving the
three phase power equipment as well as the single phase lighting loads
A. Y-Y
B. Δ-Δ
C. Δ-Y
D. Y-Δ
ANSWER: C
For Δ-Y connection with transformation ratio
K=Vph2/Vph1 the line voltage VL2 is
equal to
A. VL1/K
B. K VL1
C. VL1/√3K
D. √3K VL1
ANSWER: D
Delta star transformers are basically used
A - As distribution transformer
B-At the receiving end
C-For power measurement
D-For small high voltage transformers
ANSWER: A
The main application of …. Transformer is the substation end of the
transmission line, where the voltage has to be stepped down
A-Y-Y
B-Δ-Δ
C-Δ-Y
D-Y-Δ
ANSWER: D
In star – delta transformer with transformation ratio K=Vph2/Vph1 IL2= ………
A. √3K IL1
B. IL1/√3K
C. IL1/K
D. √3 IL1 /K
ANSWER: D
The star- delta transformers are used
A. As distribution transformer
B. At the receiving end
C. For power measurement
D. For small high voltage transformers
ANSWER: B
…….. is used when 3 ph load is too small to use a full 3 phase
transformer bank
A. Y-Y
B. Δ-Δ
C. Δ-Y
D. open delta
ANSWER: D
The actual power factor at which the open delta configuration operates,
is ……… %of the balanced load power factor
A. 50
B. 46.6
C. 86.906
D. 90
ANSWER: C
V-V connection can be obtained by removing one transformer from
A. Y-Y
B. Δ-Δ
C. open delta
D. Y-Δ
ANSWER: B
A 2 ph supply can be obtained by means of transformer. One of the
transformer is called…….. transformer.
A. Current
B. Auto
C. Voltage
D. teaser
ANSWER: D
The voltage relation between the windings of teaser transformer is VRM
=….. in scott connection
A. VYB/√3
B. (√3)/2 VYB
C. √3 VYB
D. VYB/2
ANSWER: B
The two secondary voltages of teaser transformer are……..0 phase shifted
with each other in scott connection
A. 30
B. 60
C. 90
D. 120
ANSWER: C
The transformers (single phase or three phase) are connected in … in
oreder to supply load that is higher than the rating of one transformer
A. Series
B. Cascade
C. Cascade
D. Parallel
ANSWER: D
The essential condition for successful parallel operation of two three
phase transformers ….
A. Polarities of the transformer are same
B. Phase sequences of the transformers are same
C. Phase displacement between primary and secondary line voltages of the
transformer are the same
D. All the above
ANSWER: D
Three Single phase transformer, each of 100 KVA rating, are connected in
a closed delta arrangement. If one of them
is taken out, it would be possible to load the bank in such a manner
that each one is loaded to the extent of
A. 86.6 KVA
B. 66.7 KVA
C. 57.7 KVA
D. 33.33 KVA
ANSWER: A
Two single phase 100 kVA transformers, each having different leakage impedances
are connected in parallel. When a load of 150 kVA at 0.8 pf lagging is applied
A. Both the transformers will operate at power factor more than 0.8
lagging
B. Both the transformers will operate at power factor less than 0.8
lagging.
C. One of the transformer will operate at pf more than 0.8 lagging and other will operate
at pf less than 0.8 lagging.
D. Both the transformers will operate at identical power factors
ANSWER: C
In the statement , “In star /delta transformer, there exists a phase difference
of “X” between the corresponding phases
of primary and secondary “Y”. “X” and “Y” stand resp. for
A. 60 and voltages.
B. 60 and currents.
C. 30 and voltages
D. 30 and currents.
ANSWER: C
Three single phase 11,000/220 V transformer are connected to form 3-phase
transformer bank. High voltage side is
connected in star, and low voltage side is connected in delta. What are the
voltage ratings and the turn ratio of 3-phase transformer?
A. 19,052/220 V ,50
B. 19,052/381 V, 5
C. 11,000/381 V, 50
D. 11000/220 V, 50
ANSWER: A
The magnetizing current in transformer is rich in
A. 3rd harmonic
B. 5th harmonic
C. 7th harmonic
D. 13th harmonic
ANSWER: A
Which of the following connection is suitable for V-V connection
A. YY
B. YD
C. DY
D. DD
ANSWER: D
The capacity of V-V connection as compared to DD is
A. 57.7%
B. 73.3%
C. 66.67%
D. None of these
ANSWER: A
Average power factor at which V-V bank separate is_________when load is
at unity Power factor
A. 86.6%
B. 73.3%
C. 66.67%
D. None of these
ANSWER: A
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%
ANSWER: B
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
ANSWER: C
For successful parallel operation of two single phase transformers, the
most essential condition is that there:
A. Percentage impedances are equal
B. Polarities are properly connected
C. Turn-ratios are exactly equal
D. KVA ratings are equal
ANSWER: B
In conversion of 3-phase to 2-phase supply with T connection, the
transformation ratio of the teaser will be__ times to that of main transformer:
A. 1.732
B. 1.15
C. 0.866
D. Unity
ANSWER: C
Two transformers of identical voltages but different capacities are
operated in parallel, for satisfactory load sharing:
A. Impedances should be equal
B. Per unit impedance must be equal
C. per unit impedance and X/R ratio must be equal
D. Impedance and X/R ratio must be equal
ANSWER: C
Which of the following 3-phase connection of a transformer causes
interference with the neighboring communication lines:
A. Delta-star
B. Star-delta
C. Star-star
D. Delta-star
ANSWER: C
Which of the following transformer connection will give highest secondary
voltage
A. Delta primary, delta secondary
B. Delta primary, star secondary
C. Star primary, delta secondary
D. none
ANSWER: B
Two transformers are connected in parallel. These transformers do not
have equal percentage impedance which results
A. Short-circuiting of the secondary’s
B. Power factor of one of the transformers is leading while that of the
other lagging
C. Transformers having higher copper losses will have negligible core
losses
D. Loading of the transformers not in proportion to their KVA ratings
ANSWER: D
Two transformers connected in parallel with wrong polarities results
A. Dead Short-circuiting of the secondary’s
B. Power factor of one of the transformers is leading while that of the
other lagging
C. Transformers having higher copper losses will have negligible core
losses
D. Loading of the transformers not in proportion to their KVA ratings
ANSWER: A
Which type of winding is used in 3 phase shell type transformer?
A. Circular type
B. Sandwich type
C. Cylindrical type
D. Rectangular type
ANSWER: B
As compared to Δ − Δ bank, the capacity of the V − V bank of transformers
is ......... percent
A. 57.7
B. 66.7
C. 50
D. 86.6
ANSWER: A
Which of the following connections is best suited for 3-phase, 4-wire
service?
A. Δ – Δ
B. Y− Y
C. Δ –Y
D. Y− Δ
ANSWER: C
Transformers operating in parallel will share the load depending upon
their
A. Leakage reactance
B. Rating
C. Efficiency
D. Percentage impedance.
ANSWER: D
Two transformers, with equal rating & negligible excitation current,
connected in parallel share the load in the ratio of their KVA ratings only, if
their pu impedance (based on their own KVA )are
A. Equal
B. In the inverse ratio of their ratings
C. In the direct ratio of their ratings
D. Pure reactive
ANSWER: A
Two transformer of different KVA rating are being operated in parallel
they will share load in proportion to their KVA rating if
A. Per unit impedance on respective KVA are rating equal
B. Per unit impedance on common KVA are rating equal
C. Ohmic values of impedances are equal
D. Ohmic values of impedances are proportional to their rating
ANSWER: A
Out of the following given choices for poly phase transformer connections
which one will you select for three-to-two phase conversion?
A. Scott
B. Star/Star
C. Double Scott
D. Star/Double delta
ANSWER: A
Of the following statements concerning parallel operation of
transformers, the one which is not correct is
A. transformers must have equal voltage ratings
B. transformers must have same ratio of transformation
C. transformers must be operated at the same frequency
D. Transformers must have equal KVA ratings.
ANSWER: D
In Scot –connections the teaser transformer operates on 0.866 of its
rated
A. Impedance
B. Current
C. Voltage
D. power
ANSWER: C
Keeping in view the requirement of parallel operation which of the
3-phase connections given are possible
A. Delta-delta to Delta –star
B. Delta-delta to Star – delta
C. Star – star to Delta-delta
D. Delta –star to Star – delta
ANSWER: C
If per unit impedance of two transformers connected in parallel are not
equal which one of the following statement is correct?
A. The power factor of the two transformer will be different from that of the connected
load
B. Transformers will get overloaded
C. Dead short circuit occurs
D. The transformer with higher per unit impedance will share more load
ANSWER: A
A 3-phase transformer ,over a bank of 3 – single phase transformers of
equal rating has the advantages of
A. Low cost
B. Less weight
C. Occupation of less space
D. All of the above
ANSWER: D
The 3 ph transformers were constructed by contributing …….. single phase
transformer
A. 3
B. 6
C. 9
D. 2
ANSWER: A
In Yy 0 connection, the angular displacement between primary &
secondary line voltage is …………. Degrees
A. 0
B. 90
C. 180
D. 120
ANSWER: A
Y-Y connection is used only
A. As distribution transformer
B. At the receiving end
C. For power measurement
D. For small high voltage transformers
ANSWER: D
The Y-Y connection works
satisfactorily only if the load is
A. Y type
B. Δ type
C. Unbalanced
D. Balanced
ANSWER: D
For Y-Y connection we have to phase a problem called … unbalanced load
A. Neutral shift
B. Earth shift
C. Earth leakage
D. None of these
ANSWER: A
In Δ-Δ connection the primary & secondary line voltages are
A. Equal to Vph
B. √3 Vph
C. Vph/√3
D. √3/ Vph
ANSWER: A
………… connection is economical for large, low voltage transformers
A. Y-Y
B. Δ-Δ
C. Δ-Y
D. Y-Δ
ANSWER: B
……..connection can be used for both balanced & unbalanced load
A. Y-Y
B. Δ-Δ
C. Δ-Y
D. Y-Δ
ANSWER: B
InΔy 11 connection the angular displacement in degrees between primary
& secondary line voltage is… degree
A. 0
B. 30 lagging
C. 30 leading
D. 120
ANSWER: C
The 3 ph transformers were constructed by contributing …….. single phase
transformer
A. 3
B. 6
C. 9
D. 2
ANSWER: A
It is possible to remove even common leg in ………. Transformer
A. Core type
B. Shell type
C. Berry type
D. Sandwich type
ANSWER: A
For Δ-Δ connection with transformation ratio K=Vph2/Vph1 , line current IL2 =
A. Iph2/√3
B. Iph2.√3
C. Iph2
D. Iph2/ √2
ANSWER: B
The ……. Configuration of 3 ph transformer can be used for serving the
three phase power equipment as well as the single phase lighting loads
A. Y-Y
B. Δ-Δ
C. Δ-Y
D. Y-Δ
ANSWER: C
For Δ-Y connection with transformation ratio
K=Vph2/Vph1 the line voltage VL2 is
equal to
A. VL1/K
B. K VL1
C. VL1/√3K
D. √3K VL1
ANSWER: D
Delta star transformers are basically used
A. As distribution transformer
B. At the receiving end
C. For power measurement
D. For small high voltage transformers
ANSWER: A
The main application of …. Transformer is the substation end of the
transmission line, where the voltage has to be stepped down
A. Y-Y
B. Δ-Δ
C. Δ-Y
D. Y-Δ
ANSWER: D
…….. is used when 3 ph load is too small to use a full 3 phase
transformer bank
A. Y-Y
B. Δ-Δ
C. Δ-Y
D. open delta
ANSWER: D
The actual power factor at which the open delta configuration operates,
is ……… %of the balanced load power factor
A. 50
B. 46.6
C. 86.906
D. 90
ANSWER: C
V-V connection can be obtained by removing one transformer from
A. Y-Y
B. Δ-Δ
C. open delta
D. Y-Δ
ANSWER: B
A 2 ph supply can be obtained by means of transformer. One of the
transformers called…….. transformer
A. Current
B. Auto
C. Voltage
D. teaser
ANSWER: D
The two secondary voltages of teaser transformer are……0 phase shifted
with each other in Scott connection
A. 30
B. 60
C. 90
D. 120
ANSWER: C
The transformers (single phase or three phase) are connected in … in
order to supply load that is higher than the rating of one transformer
A. Series
B. Cascade
C. Cascade
D. Parallel
ANSWER: D
Three Single phase transformer, each of 100 KVA rating, are connected in
a closed delta arrangement. If one of them
is taken out , it would be possible to load the bank in such a manner
that each one is loaded to the extent of
A. 86.6 KVA
B. 66.7 KVA
C. 57.7 KVA
D. 33.33 KVA
ANSWER: A
Which three-phase connection can be used in a transformer to introduce a
phase difference of 〖30〗^0between its output and corresponding input line
voltages?
A. Star-star
B. Star-Delta
C. Delta-Delta
D. Delta-Zigzag
ANSWER: B
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.
ANSWER: C
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 rating equal
ANSWER: B
Possible three-to-three phase transformer connection for parallel
operation is
A. ∆-Y to ∆-Y.
B. ∆-∆to ∆-Y.
C. Y-Yto ∆-Y.
D. ∆-Yto Y-∆.
ANSWER: A
If the transformers operated in parallel are not connected with regard to
polarity
A. The transformers will not share the load in proportion to their k V A
ratings.
B. Dead short-circuit will take place.
C. The transformer of lower rating will be out of operation.
D. None of the above .
ANSWER: B
Two transformers, when operating in parallel will share the load
depending upon which of the following?
A. Magnetizing current
B. Leakage reactance
C. Per unit impedance
D. Efficiency.
ANSWER: C
When two transformers of different KVA ratings are connected in parallel,
they will divide the total in proportion to their respective kVA ratings when
their
A. Efficiencies are equal.
B. Equivalent impedances are equal.
C. Equivalent impedances are inversely proportional to their respective
ratings.
D. None of the above.
ANSWER: C
Two transformers of identical voltages but of different capacities are
operating in parallel .for satisfactory load sharing
A. Impedances must be equal.
B. Per unit Impedances must be equal.
C. Per unit Impedances and X/R ratio must be equal.
D. Impedances and X/R ratio must be equal.
ANSWER: C
Star/delta connection for three phase distribution transformers is very
common for
A. Large rating, low voltage transformers
B. Small rating, high voltage transformers
C. Power supply transformers
D. Distribution transformers
ANSWER: C
Most suitable connection of three phase distribution transformers is.
A. delta/ delta
B. delta/ star
C. Star/ delta
D. Star/ Star
ANSWER: B
Witch of the following three phase transformers cannot be operated in
parallel?
A. Transformer l, Star/ Star; Transformers 2, delta/ delta
B. Transformers l, Star/ delta; Transformers 2, delta /Star
C. Transformers l, Star/ delta; Transformers 2, delta/ delta
D. None of the above
ANSWER: C
In Scott-connected transformers, 50% tapping should be provided on the
A. Primary of teaser transformers
B. Primary of main transformers
C. Secondary of main transformers
D. Secondary of teaser transformers
ANSWER: B
For converting a three phase balanced system into a two phase system ,the
number of transformers needed are,
A. One three phase transformer
B. Three single phase transformers
C. Two single phase transformers
D. One single phase transformer
ANSWER: C
In scott-connection, tapping essential on the primary of teaser transformer is,
A. 50%
B. 28.8%
C. 100%
D. 86.6%
ANSWER: D
The neutral point divides the teaser primary winding in Scott-connected
transformers in the ratio of,
A. 1:2
B. 1:1.5
C. 1:3
D. 1:4
ANSWER: A
If the number of turns on the primary and secondary of the teaser
transformer of scott-connection are the same, then the ratio of primary to
secondary currents in the teaser transformer is,
A. 1.0
B. 1.15
C. 1.28
D. 0.866
ANSWER: B
Which of the following two, three phase transformers can be operated in
parallel
A. ∆/∆ and ∆⥾
B. Y/Y and Y/∆
C. Y/Y and ∆/∆
D. None of these combinations
ANSWER: C
In Scott connected transformer,50% tapping should be provided on the
A. Primary of teaser transformer
B. Primary of main transformer
C. Secondary of main transformer
D. Secondary of teaser transformer
ANSWER: B
In Scott connected transformer, neutral point is available on the
A. Main transformer primary
B. Teaser transformer primary
C. Primary of main transformer
D. secondary of main transformer
ANSWER: B
In Scott connection, tapping essential on the primary of teaser
transformer is
A. 50%
B. 28.8%
C. 100%
D. 86.6%
ANSWER: D
If the number of turns on the primary & secondary of the teaser
transformer of Scott-connection are the same ,then the primary to secondary
currents in the ratio of primary to secondary currents in teaser transformer
A. 1.0
B. 1.15
C. 1.28
D. 0.866
ANSWER: B
Three single phase transformer, each with a 10 kVA rating are connected
in a closed delta arrangement. If one transformer is taken out, the output
capacity of the system will be
A. 20 kVA
B. 8.66 kVA
C. 17.32 kVA
D. 10 kVA
ANSWER: C
Three number of 10:1 transformers are connected in star-delta to supply a
load at 230 V.The supply voltage of this transformer must be
A. 2300 V
B. 4000 V
C. 23 V
D. 40 V
ANSWER: C
Three units of 1:5 transformers are connected in delta-star to supply a 3
phase load from a 400 V, 3 phase source. The line voltage on the load side is
A. 1000 V
B. 80 V
C. 3464 V
D. 803 V
ANSWER: C
Two transformer A & B having equal outputs and voltage ratios but
unequal percentage impedance of 4 & 2 are operating in parallel transformer
A will ne running over load by how much %?
A. 50
B. 66
C. 33
D. 25
ANSWER: C
An auto transformer having a transformation ratio of 0.8 supplies a load
of 3 Kw. The power transferred conductively from primary to secondary is how
much kilo watt?
A. 0.6
B. 2.4
C. 1.5
D. 0.27
ANSWER: B
For two transformers connected in parallel the circulating current is
given by
% Ic = ---------- x 100
A. % e / (%Z1 + % Z2)
B. % e / I (%Z1 + % Z2)
C. % e / (%I1 + % I2)
D. (%IZ1 + %I Z2) / % e
ANSWER: B
Three single-phase, 50 kVA, 2300/ 230 V, 60 Hz transformers are connected
to form
a 3-phase, 4000V / 230-V transformer bank. The equivalent impedance of
each transformer referred to low-voltage is 0.012 + j 0.016 Ω . The 3-phase
transformer supplies a 3-phase, 120 kVA, 230 V, 0.85 power-factor (lagging)
load. Determine the winding currents of the transformer.
A. 30.1
B. 40.2
C. 25.1
D. 45.1
ANSWER: A
Three single-phase, 50 kVA, 2300/ 230 V, 60 Hz transformers are connected
to form a 3-phase, 4000V / 230-V transformer bank. The equivalent impedance of
each transformer referred to low-voltage is 0.012 + j 0.016 Ω. The 3-phase
transformer supplies a 3-phase, 120 kVA, 230 V, 0.85 power-factor (lagging)
load. Determine the primary voltage (line to line) required.
A. 2000 V
B. 3000 V
C. 4000 V
D. 5000 V
ANSWER: C
A two windings transformer is converted into an auto transformer. If we
apply additive polarity and subtractive polarity for the connections, then the
secondary voltage is 2640V and 2160V respectively.
What is the ratio of primary voltage of original transformer?
A. 66:54
B. 54:66
C. 10:1
D. 1:10
ANSWER: C
Three Single phase transformer, each of 100 KVA rating, are connected in
a closed delta arrangement. If one of them is taken out , it would be possible
to load the bank in such a manner that each one is loaded to the extent of
A. 86.6 KVA
B. 66.7 KVA
C. 57.7 KVA
D. 33.33 KVA
ANSWER: A
Two single phase 100 kVA transformers,
each having different leakage impedances are connected in parallel. When
a load of 150 kVA at 0.8 pf lagging is applied.
A. Both the transformers will operate at power factor more than 0.8
lagging
B. Both the transformers will operate at power factor less than 0.8
lagging.
C. One of the transformer will operate at pf more than 0.8 lagging and
other will operate at pf less than 0.8 lagging.
D. Both the transformers will operate at identical power factors
ANSWER: C
Two 3 phase transformers are to be connected for parallel operation.
Which one of the arrangements impossible?
A. Transformer A: primary Y: secondary Y
Transformer B: primary ∆:
secondary∆
B. Transformer A: primary ∆: secondary Y
Transformer B: primary ∆:
secondary∆
C. Transformer A: primary Y: secondary ∆
Transformer B: primary ∆:
secondary Y
D. Transformer A: primary ∆: secondary ∆
Transformer B: primary ∆:
secondary∆
ANSWER: B
When two transformers of different kVA ratings are connected in parallel,
they will divide the total load in proportion to their respective to their
respective kVA rating when their
A. Efficiencies are equal.
B. Equivalent impedances are equal.
C. Equivalent impedances are inversely proportional to their respective
ratings.
D. None of the above
ANSWER: C
If two transformers are connected in parallel and sharing a load of I
amperes then their individual currents are -------
A. I1 = I / Z1, I2 = I / Z2
B. I1 = I / Z2 I2 = I / Z1
C. I1 = I Z1/ (Z1 + Z 2 ), I2 = I Z2 / ( Z1 + Z2)
D. I1 = I Z2 (Z1 + Z 2 ), I2 = I Z1 / ( Z1 + Z2)
ANSWER: D
Three single phase 11,000/220 V transformer are connected to form 3-phase
transformer bank. High voltage side is
connected in star, and low voltage side is connected in delta. What are the
voltage ratings and the turn ratio of 3-phase transformer ?
A. 19,052/220 V ,50
B. 19,052/220 V, 50
C. 11,000/381 V, 50
D. 11000/220 V, 50
ANSWER: A
Three single phase transformer, each with a 10 kVA rating are connected
in a closed delta arrangement. If one transformer is taken out, the output
capacity of the system will be
A. 20 KVA
B. 8.66 KVA
C. 17.32 KVA
D. 10 KVA
ANSWER: C
The two transformers A and B having same KVA rating share a load of 120
KVA at 0.8 p.f. lagging. Their impedances are
ZA = 0.8 + j 10= 10.031<85.420
and ZB =1.66 + j 8.33 = 8.4937< 78.720 The load carried by transformer A is ------
A. 25 KVA
B. 80 KVA
C. 55 KVA
D. 65 KVA
ANSWER: C
The two transformers A and B having same KVA rating share a load of 120
KVA at 0.8 p.f. lagging. Their impedances are
ZA = 0.8 + j 10= 10.031<85.420
and ZB =1.66 + j 8.33 = 8.4937< 78.720 The load carried by transformer B is
A. 25 KVA
B. 80 KVA
C. 55 KVA
D. 65 KVA
ANSWER: D
The two transformers A and B having same KVA rating share a load of 120
KVA at 0.8 p.f. lagging. Their impedances are
ZA = 0.8 + j 10= 10.031<85.420
and ZB =1.66 + j 8.33 = 8.4937< 78.720 The power factor of transformer B is
A. 0.76 lag
B. 0.83 lag
C. 0.56 lag
D. 0.67 lead
ANSWER: B
The two transformers A and B having same KVA rating share a load of 120
KVA at 0.8 p.f. lagging. Their impedances are
ZA = 0.8 + j 10= 10.031<85.420
and ZB =1.66 + j 8.33 = 8.4937< 78.720 The power factor of transformer A is
A. 0.76 lag
B. 0.83 lag
C. 0.56 lag
D. 0.67 lead
ANSWER: A
The current in HV winding of a
25kVA, 6600/400 V,50Hz,3 phase D-Y transformer, at full load is
A. 1.26 A
B. 3.72 A
C. 2.18 A
D. 0.72 A
ANSWER: A
The current in HV winding of a
25kVA, 6600/400 V,50Hz,3 phase D. Y transformer, at full load is
A. 1.26 A
B. 3.72 A
C. 2.18 A
D. 0.72 A
ANSWER: A
The current in HV winding of a
25kVA, 6600/400 V,50Hz,3 phase Y-D transformer, at full load is
A. 1.26 A
B. 3.72 A
C. 2.18 A
D. 0.72 A
ANSWER: C
The current in LV winding of a 25kVA, 6600/400 V,50Hz,3 phase Y-D
transformer, at full load is
A. 36 A
B. 20.78 A
C. 65.32 A
D. 40.2 A
ANSWER: B
The current in HV winding of a
20kVA, 2200/220 V,50Hz,3 phase D-D transformer, at full load is
A. 3.03 A
B. 5.25 A
C. 10.5 A
D. None of these
ANSWER: A
The current in LV winding of a
20kVA, 2200/220 V,50Hz,3 phase D-D transformer, at full load is
A. 52.48 A
B. 30.30 A
C. 26.24 A
D. None of these
ANSWER: B
High frequency transformers sometimes make use of ferrite cores because
it has
A. High specific gravity
B. High resistance
C. High hysteresis
D. low permeability
ANSWER: B
Harmonics in transformer result in
A. Increased core losses
B. Increased I2R losses
C. Magnetic interference with communication circuits
D. All of the above
ANSWER: D
The full load copper loss of a transformer is 1600W. At half-load the
copper loss will be
A. 6400W
B. 1600W
C. 800W
D. 400W
ANSWER:D
Power transformers are generally designed to have maximum efficiency
around
A. No load
B. Half load
C.Near full load
D. 10% overload
ANSWER:C
Two transformers are connected in parallel. These transformers do not
have equal percentage impedance which results
A. Short-circuiting of the secondaries
B. Power factor of one of the transformers is leading while that of the
other lagging
C. Transformers having higher copper losses will have negligible core
losses
D. Loading of the transformers not in proportion to their kVA ratings.
ANSWER:D
The changes in volume of transformer cooling oil due to variation of
atmospheric temperature during day and night is taken care of by which part of
transformer?
A. Conservator
B. Breather
C. Bushings
D. Buchholz relay
ANSWER:A
The transformer laminations are insulated from each other by
A. Mica strip
B. Thin coat of varnish
C. Paper
D. Any of the above
ANSWER:B
Which type of winding is used in 3 phase shell type transformer?
A. Circular type
B. Sandwich type
C. Cylindrical type
D. Rectangular type
ANSWER: B
During open circuit test of a transformer
A. Primary is supplied rated voltage
B. Primary is supplied full load current
C. Primary is supplied current at reduced voltage
D. Primary is supplied rated kVA
ANSWER: A
Which of the following is not standard voltage for power supply in India
A. 11kV
B. 33kV
C. 66 kV
D. 122 kV
ANSWER: D
The low voltage winding of a 400/230 volt, 1-phase, 50Hz transformer is
to be connected to a 25Hz supply in order to keep the magnetization current at
the same level as that for normal 50Hz supply at 25Hz the voltage should be
[Gate 1997]
A. 230V
B. 460V
C. 115V
D. 65V
ANSWER: C
The primary current in the current transformer is dictated by [Gate 1997]
A. The secondary burden
B. The core of the transformer
C. The load current
D. None of the above
ANSWER:A
In Single Phase Transformer, The Primary Current and Primary Voltage is
4.55 and 11kV respectively. The Rating of the transformer would
be________? A. 86kVA
B. 100kVA
C. 150kVA
D. 50kVA
ANSWER:
A Transformer______________.
A. Steps up or down DC Voltages & Current
B. Changes DC to AC
C. Changes ac to DC
D. Steps up or down AC Voltages & Current
ANSWER: D
What would happen if a power transformer designed for operation on 50 Hz
(frequency) were connected to a 5 Hz (frequency) source of the same voltage?
A. Eddy Current and Hysteresis loss will be excessive
B. Current will be too much low
C. Transformer may start to smoke
D. No effect
ANSWER: C
In Three Phase Transformer, The load Current is 139.1A, and Secondary
Voltage is 415V. The Rating of the Transformer would be ___________.
A. 173 KVA
B. 50 KVA
C. 100KVA
D. 57.72 KVA
ANSWER: C
If the primary power of an ideal transformer having a 2:1 voltage ratio
is 100 W, the secondary power is
A. 50W
B. 100 W
C. 75 W
D. 200 W
ANSWER: B
Increasing the number of turns of wire on the secondary of a transformer
will
A. decrease the secondary current
B. have no effect on the secondary current
C. increase the primary current
D. increase the secondary current
ANSWER: A
Laminated insulations coated with varnish are normally used in the
transformer
A. To reducethe effect of eddy current
B. To reduce reluctance of magnetic path
C. To reduce the hysteresis effect
D. To increase the reluctance of magnetic path
ANSWER: A
The transformer turns ratio determines
A. the reflected impedance
B. the ratio of primary and secondary voltages
C. the ratio of primary and secondary currents
D. all
ANSWER: A
An Isolation Transformer Has Primary to Secondary turns ratio of
__________.
A. 1 : 2
B. 1 : 1
C. 2 : 1
D. Can be any ratio
ANSWER: B
The coefficient of coupling between two coils is 0.45. The first coil has
an inductance of 75 mH and the second coil has an inductance of 105 mH. What is
the mutual inductance between the coils?
A. 7.88 mH
B. 3.54 mH
C. 39.9 mH
D. 189.3 mH
ANSWER: C
In an Auto Transformer, The Primary and Secondary are__________Coupled.
A. Magnetically as well as Electrically
B. Only Magnetically
C. Only Electrically
D. None of the above
ANSWER: A
When does maximum power transfer happen from the source to the load?
A. When the source resistance is less than the load resistance
B. When there is negligible source resistance
C. When the source resistance is greater than the load resistance
D. When the source resistance equals the load resistance
ANSWER: D
A special transformer used to convert unbalanced signals to balanced
signals is the
A. autotransformer
B. step-across transformer
C. balun
D. center-tapped transformer
ANSWER: C
Under what condition is D.C supply applied safely to the primary of a
transformer?
A. We can't connect to DC Supply
B. We can connect directly to DC. No condition required
C. A High resistance should be connect in series with primary, but circuit
will be useless.
D. The above statement is wrong
ANSWER: C
Which of the following 3-phase connection of a transformer causes
interference with the neighbouring communication lines?
A. Star-delta
B. Delta-star
C. Star-star
D. Delta-star
ANSWER: C
An Auto-transformer (which has only one winding) may be used as a ______?
A. Step-Up Transformer
B. Step-Down Transformer
C. Both Step-Up and Step-Down transformer
D. None of these
ANSWER: C
The friction losses in Real Transformers are _________?
A. 5%
B. 25%
C. 50%
D. 0%
ANSWER: D
The expression for the induced emf in the primary winding of a
transformer is E1= ________.
A. 4.44 f N1Bm
B. 4.44 f N1Φm
C. 4.44 f N1V1
D. 4.44 f N1
ANSWER: B
If primary voltage is 230 V, 50 Hz, N1=500 &Bm=0.4144 T then the cross sectional area of the core is
a _________.
A. 50mm2
B. 50m2
C. 50 cm2
D. 50nm2
ANSWER: C
A 3300/200 V, 100 kVA transformer has N2 = 80 turns. The rated secondary
current I2= ________ Amp.
A. 30.3
B. 500
C. 50
D. 303
ANSWER: B
A 3300/200 V, 100 kVA transformer has N2= 80 turns. The rated primary
current I1= _______ Amp.
A. 30.3
B. 500
C. 50
D. 303
ANSWER: A
A 3300/200 V, 100 kVA transformer has N2 =80 then N1 = ________.
A. 1320
B. 4.84
C. 132
D. 484
ANSWER: A
The expression for the secondary induced emf is ________.
A. 4.44 fN2Bm
B. 4.44 fN2Øm
C. 4.44 fN2 V2
D. 4.44 f N2
ANSWER: B
A step down transformer operates on a 50 Hz ac supply. With a primary
voltage of 230 V. The maximum flux Øm= _________ if N1=500
A. 2.07Wb
B. 2.07mWb
C. 0.0408Wb
D. 0.0408mWb
ANSWER: B
The voltage ratio of a transformer is defined as the ratio of _______
& ________.
A. V1, V2
B. V2,V1
C. E1,E2
D. E2,E1
ANSWER: A
The ratio V2/V1 or N2/N1 of a
transformer is called as _________.
A. Voltage ratio
B. Reverse voltage ratio
C. Transformation ratio
D. Turns Ratio
ANSWER: C
The ratio N1/N2 of a transformer is called as _______ ratio.
A. Transformation
B. Turns
C. Reverse turn
D. Voltage
ANSWER: B
The transformer with _______ is called as step up transformer.
A. K<1
B. K=1
C. K>1
D. K=0
ANSWER: C
For the _______ transformer, the secondary voltage is greater than the
primary voltage.
A. Step up
B. Step down
C. Isolation
D. Auto
ANSWER: A
The transformer with K>1 is called as _______ transformer.
A. Step up
B. Step down
C. Isolation
D. Auto
ANSWER: A
The transformer with_______ is called as step down transformer.
A. K<1
B. K=1
C. K>1
D. K=0
ANSWER: A
The transformer with K<1 is called as _______ transformer.
A. Step up
B. Step down
C. Isolation
D. Auto
ANSWER: B
The transformer with K=1 is used
as ________ transformer.
A. Step up
B. Step down
C. Isolation
D. Auto
ANSWER: C
The ________ transformer is generally used as isolation transformer.
A. Step up
B. Step down
C. one to one
D. Auto
ANSWER: C
The transformation ratio K is defined as k=_____.
A. I2/I1
B. N1/N2
C. V1/ V2
D. I1/I2
ANSWER: D
The primary & secondary currents are _________ to the number of turns
of the corresponding windings.
A. Directly proportional
B. Inversely proportional
C. Independent
D. Equal
ANSWER: B
The transformer rating is in terms of _______
A. Watts
B. kW
C. VAR
D. kVA
ANSWER: C
The ratings of a transformer in terms of ______ power.
A. True
B. Apparent
C. Reactive
D. Active
ANSWER: B
The complete rating of transformer includes the ratio of primary
&secondary voltages, ________ & ________.
A. Flux, frequency
B. Number of turns, kVA
C. kVA, frequency
D. Number of turns, Flux
ANSWER: C
A 3300V/ 200V, 100 kVA transformer has N2=80. Then k=______ & N1
=_______.
A. 0.06, 1320
B. 16.67, 1320
C. 0.06, 4.84
D. 16.67, 4.84
ANSWER: A
A 3300V/200 V, transformer has rated primary& secondary currents of
30.303A & 500A respectively. Its rating would be _________.
A. 1650 kVA
B. 60.6 kVA
C. 100 kVA
D. 100 kW
ANSWER: C
A 10 kVA, 3300/240V, 50 Hz transformer has core area 300 cm2& flux
density 1.3 T. Then number of primary turns N1= ________.
A. 28
B. 382
C. 38.2
D. none of these
ANSWER: B
For a 6600/220 V, 50 Hz transformer, if N1=1500 &Bm=1.2 T. the
effective cross sectional area of the core is A=________.
A. 16.5cm2
B. 0.0165m2
C. 0.024m2
D. none of these
ANSWER: B
The total loss in a transformer is the sum of ______ loss & ______
loss.
A. Hysteresis, eddy current
B. copper, hysteresis
C. Iron, eddy current
D. copper,iron
ANSWER: D
If the copper loss at full load is 200 W then that atb the half load will
be _______ watt.
A. 100
B. 50
C. 800
D. 400
ANSWER: B
A 4000V/200V transformer has R2=0.009Ω. Find the value of transferred
resistance to primary side (R’2).
A. 4.5 x 10-4Ω
B. 0.18Ω
C. 3.6Ω
D. none of these
ANSWER: C
A 3300/110, 50 Hz, 60 kVA
transformer has R1=3.3Ω & R2=0.011Ω. What is the value of R1t ?
A. 3.3Ω
B. 13.4Ω
C. 33Ω
D. 1.34Ω
ANSWER: B
For a 4000/200 V transformer if R1= 3.45Ω & R2= 0.009Ω then calculate
the value oftotal resistance on the primary side i.e. R1t.
A. 7.05Ω
B. 0.018Ω
C. 3.45Ω
D. 3.63Ω
ANSWER: A
Alternating voltage can be raised or lowered with the help of ………..
A. Generator
B. Transformer
C. Induction motor
D. Universal motor
ANSWER: B
In a transformer electrical power is transformed from one circuit to
other without change in the…..
A. Voltage
B. Current
C. Frequency
D. None of these
ANSWER: C
A transformer is a .......... device
A. A.C.
B. D. C.
C. Both A. C. and D. C.
D. None of these
ANSWER: A
A transformer works on the principle of ……………
A. Faraday ‘s law
B. Mutual induction
C. Self induction
D. Superposition
ANSWER: A
The primary and secondary winding of a transformer are……coupled to each
other.
A. Electrically
B. Magnetically
C. Electrically and magnetically
D. None of these
ANSWER: B
The frequency of secondary voltage is …… that of the primary voltage
A. Greater than
B. Less than
C. Same as
D. None of these.
ANSWER: C
The ………on both sides of a transformer
remains same.
A. Voltage
B. Current
C. Power
D. Impedance
ANSWER: D
The d. c. supply is not used for the transformer as ………….
A. Eddy current losses are more
B. Hysteresis losses are more
C. D.C. winding resistance is very
high
D. Burning of windings due to high current is possible
ANSWER: D
The flux in the transformer core is …………
A. Rotating
B. Partly rotating
C. Partly alternating
D. Purely alternating
ANSWER: D
The core of the transformer is laminated to reduce…….
A. Eddy current loss
B. Hysteresis loss
C. Copper loss
D. Friction loss
ANSWER: A
The vertical portion on which coils are wound in a transformer is
called………
A. Core
B. Yoke
C. Joint
D. Limb
ANSWER: D
Generally …………….. is used for
laminations of a transformer core.
A. High grade silicon steel
B. Copper
C. Iron
D. Manganin
ANSWER: A
The core provides …….. Path to the
flux produced.
A. Low resistance
B. Low reluctance
C. Low voltage
D. None of these
ANSWER: B
The laminations in transformer core are overlapped so as …………..
A. To keep core resistance small
B. To increase the flux in the core
C. To avoid the air gap at the joints
D. To provide high reluctance path
ANSWER: B
In …………. of transformer, the coils can be easily removed from maintenance
point of view.
A. Berry type
B. Core type
C. Shell type
D. None of these
ANSWER: B
………. construction is used for high voltage transformer.
A. Berry type
B. Core type
C. Shell type
D. None of these
ANSWER: C
The value of flux used in e.m.f. equation of a transformer is ……………..
A. R.M.S.
B. Average
C. Maximum
D. Instantaneous
ANSWER: C
For a 50 Hz transformer the primary turns are 100 and maximum flux in the
core is 0.08 Wb then the primary induced e.m.f. is …………………..
A. 1856V
B. 1276 V
C. 176 V
D. 1776 V
ANSWER: D
Which is a type of transformer?
A. Step up Transformer
B. Step down Transformer
C. Isolation Transformer
D. 1:1 Transformer
ANSWER: B
Which is a type of transformer?
A. Step up Transformer
B. Step down Transformer
C. Isolation Transformer
D. None of above
ANSWER: C
Which is a type of transformer?
A. Step up Transformer
B. Step down Transformer
C. Isolation Transformer
D. 1:1 Transformer
ANSWER: A
The rating of transformer may be expressed in
A. kW
B. MVA
C. kVA
D. Both A. and C.
ANSWER: D
The friction losses in ideal Transformers are
A. 0%
B. 5%
C. 25%
D. 50%
ANSWER: A
A Transformer______________
A. Changes ac to DC
B. Changes dc to AC
C. Steps up or down DC Voltages & Current
D. Steps up or down AC Voltages & Current
ANSWER: D
In an Auto Transformer, The Primary and Secondary are__________CoupleD.
A. Only Magnetically
B. Only Electrically
C. Magnetically as well as electrically
D. None of the above
ANSWER: C
What will happen if the primary of a transformer is connected to D.C
supply?
A. Transformer will operate with low efficiency
B. Transformer will operate with high efficiency
C. No effect
D. Transformer may start to smoke and burn
ANSWER: D
In a Transformer, The primary flux is always _________ the secondary
(flux).
A. Greater then
B. Smaller then
C. Equal
D. Equal in both step up and Step down Transformer
ANSWER: D
Transformer is a device which don’t change in_________
A. Voltage
B. Current
C. Power
D. Frequency
ANSWER: D
Transformer core is laminated to
A. Reduce the hysterias losses
B. Reduce Eddy current losses
C. Reduce the copper losses
D. Reduce all of above losses
ANSWER: B
Direct loading on single phase transformer is use to determine
A. Efficiency & regulation
B. Efficiency only
C. Regulation only
D. Losses
ANSWER: A
Buchholz relay is operate when_________
A. During abnormal temperature
B. During Short circuit
C. During transformer set fire
D. All of above
ANSWER: D
A transformer transform_______
A. Power
B. Voltage
C. DC
D. All of above
ANSWER: A
The efficiency of an ideal transformer is
A. 90% to 91 %
B. 100%
C. Zero
D. Can’t say
ANSWER: B
Which of the following does not change in a transformer ?
A. Current
B. Voltage
C. Frequency
D. All of the above
ANSWER: C
In a transformer the energy is conveyed from primary to secondary
A. through cooling coil
B. through air
C. by the flux
D. none of the above
ANSWER: C
A transformer core is laminated to
A. reduce hysteresis loss
B. reduce eddy current losses
C. reduce copper losses
D. reduce all above losses
ANSWER: B
The degree of mechanical vibrations produced by the laminations of a
transformer depends on
A. tightness of clamping
B. gauge of laminations
C. size of laminations
D. all of the above
ANSWER: D
The no-load current drawn by transformer is usually what per cent of the
full-load current ?
A. 0.2 to 0.5 per cent
B. 2 to 5 per cent
C. 12 to 15 per cent
D. 20 to 30 per cent
ANSWER: B
The path of a magnetic flux in a transformer should have
A. high resistance
B. high reluctance
C. low resistance
D. low reluctance
ANSWER: D
No-load on a transformer is carried out to determine
A. copper loss
B. magnetising current
C. magnetising current and loss
D. efficiency of the transformer
ANSWER: C
The dielectric strength of transformer oil is expected to be
A. lkV
B. 33 kV
C. 100 kV
D. 330 kV
ANSWER: B
Sumpner's test is conducted on transformers to determine
A. temperature
B. stray losses
C. all-day efficiency
D. none of the above
ANSWER: A
The permissible flux density in case of cold rolled grain oriented steel
is around
A. 1.7 Wb/m2
B. 2.7 Wb/m2
C. 3.7 Wb/m2
D. 4.7 Wb/m2
ANSWER: A
The efficiency of a transformer will be maximum when
A. copper losses = hysteresis losses
B. hysteresis losses = eddy current losses
C. eddy current losses = copper losses
D. copper losses = iron losses
ANSWER: D
No-load current in a transformer
A. lags behind the voltage by about 75°
B. leads the voltage by about 75°
C. lags behind the voltage by about 15°
D. leads the voltage by about 15°
ANSWER: A
The purpose of providing an iron core in a transformer is to
A. provide support to windings
B. reduce hysteresis loss
C. decrease the reluctance of the magnetic path
D. reduce eddy current losses
ANSWER: C
Which of the following is not a part of transformer installation ?
A. Conservator
B. Breather
C. Buchholz relay
D. Exciter
ANSWER: D
While conducting short-circuit test on a transformer the following side
is short circuited
A. High voltage side
B. Low voltage side
C. Primary side
D. Secondary side
ANSWER: B
In the transformer following winding has got more cross-sectional area
A. Low voltage winding
B. High voltage winding
C. Primary winding
D. Secondary winding
ANSWER: A
Primary winding of a transformer
A. is always a low voltage winding
B. is always a high voltage winding
C. could either be a low voltage or high voltage winding
D. none of the above
ANSWER: C
Which winding in a transformer has more number of turns ?
A. Low voltage winding
B. High voltage winding
C. Primary winding
D. Secondary winding
ANSWER: B
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