Transformers · Electrical Machines · GATE EE
Marks 1
1
Which one of the following options represents possible voltage polarities in a single phase two winding transformer? Here, $V_p$ is the applied primary voltage, $E_p$ is the induced primary voltage, $V_s$ is the open circuit secondary voltage, and $E_s$ is the induced secondary voltage.
GATE EE 2024
2
The type of single-phase induction motor, expected to have the maximum power factor during steady state running condition, is
GATE EE 2022
3
A single-phase 100 kVA, 1000 V / 100 V, 50 Hz transformer has a voltage drop of 5%
across its series impedance at full load. Of this, 3% is due to resistance. The percentage
regulation of the transformer at full load with 0.8 lagging power factor is
GATE EE 2018
4
The following figure shows the connection of an ideal transformer with primary to secondary turns ratio of 1 : 100. The applied primary voltage is 100 V (rms), 50 Hz, AC. The rms value of the current I, in ampere, is __________.
GATE EE 2016 Set 2
5
If an ideal transformer has an inductive load element at port 2 as shown in the figure below, the
equivalent inductance at port 1 is
GATE EE 2016 Set 1
6
The self inductance of the primary winding of a single phase, 50 Hz, transformer is 800
mH, and that of the secondary winding is 600 mH. The mutual inductance between these
two windings is 480 mH. The secondary winding of this transformer is short circuited and
the primary winding is connected to a 50 Hz, single phase, sinusoidal voltage source. The
current flowing in both the winding is less than their respective rated currents. The
resistance of both windings can be neglected. In this connection, what is the effective
inductance (in mH) seen by the source?
GATE EE 2015 Set 1
7
Assuming an ideal transformer, The Thevenin's equivalent voltage and impedance as seen
from the terminals x and y for the circuit in figure are
GATE EE 2014 Set 2
8
A single phase, 50 kVA, 1000 V/100 V two winding transformer is connected as an
autotransformer as shown in the figure.
The kVA rating of the autotransformer is _________.
The kVA rating of the autotransformer is _________.GATE EE 2014 Set 2
9
For a specified input voltage and frequency, if the equivalent radius of the core of a
transformer is reduced by half, the factor by which the number of turns in the primary should
change to maintain the same no load current is
GATE EE 2014 Set 1
10
A single-phase transformer has no-load loss of 64 W, as obtained from an open circuit
test. When a short-circuit test is performed on it with 90% of the rated
currents flowing in its both LV and HV windings, he measured loss is 81 W. The
transformer has maximum efficiency when operated at
GATE EE 2013
11
A single phase air core transformer, fed from a rated sinusoidal supply, is
operating at no load. The steady state magnetizing current drawn by the
transformer from the supply will have the waveform
GATE EE 2011
12
A single-phase transformer has a turns ratio of 1:2, and is connected to a purely
resistive load as shown in the figure. The magnetizing current drawn is 1 A, and
the secondary current is 1 A. If core losses and leakage reactances are neglected,
the primary current is
GATE EE 2010
13
The single phase, $$50$$ $$Hz$$ iron core transformer in the circuit has both the vertical arms of cross sectional area $$20\,\,c{m^2}$$ and both the horizontal arms of cross sectional area $$10\,\,c{m^2}$$. If the two windings shown were wound instead on opposite horizontal arms, the mutual inductances will
GATE EE 2009
14
It is desired to measure parameters of $$230$$ $$V/115$$ $$V,$$ $$2$$ $$kVA$$, single-phase transformers. The following watt-meters are available in a laboratory:
$${W_1}:250\,\,V,\,\,\,10\,\,A,\,\,\,\,\,\,$$ Low Power Factor
$${W_2}:250\,\,V,\,\,\,5\,\,A,\,\,\,\,\,\,$$ Low Power Factor
$${W_3}:150\,\,V,\,\,\,10\,\,A,\,\,\,\,\,\,$$ High Power Factor
$${W_4}:150\,\,V,\,\,\,5\,\,A,\,\,\,\,\,\,$$ High Power Factor
$${W_1}:250\,\,V,\,\,\,10\,\,A,\,\,\,\,\,\,$$ Low Power Factor
$${W_2}:250\,\,V,\,\,\,5\,\,A,\,\,\,\,\,\,$$ Low Power Factor
$${W_3}:150\,\,V,\,\,\,10\,\,A,\,\,\,\,\,\,$$ High Power Factor
$${W_4}:150\,\,V,\,\,\,5\,\,A,\,\,\,\,\,\,$$ High Power Factor
The watt-meters used in open circuit test and short circuit test of the transformer will respectively be
GATE EE 2008
15
In a transformer, zero voltage regulation at full load is
GATE EE 2007
16
In transformers, which of the following statements is valid?
GATE EE 2006
17
Which three-phase connection can be used in a transformer to introduce a phase
difference of 30° between its output and corresponding input line voltages
GATE EE 2005
18
A single phase transformer has a maximum efficiency of 90% at full load and
unity power factor. Efficiency at half load at the same power factor is
GATE EE 2003
19
A 1 kVA, 230V/100V, single phase, 50 Hz transformer having negligible winding
resistance and leakage inductance is operating under saturation, while 250 V, 50
Hz sinusoidal supply is connected to the high voltage winding. A resistive load is
connected to the low voltage winding which draws rated current. Which one of
the following quantities will not be sinusoidal?
GATE EE 2002
20
A single-phase transformer is to be switched to the supply to have minimum
inrush current. The switch should be closed at
GATE EE 2001
21
The core flux of a practical transformer with a resistive load
GATE EE 2001
22
In a constant voltage transformer (CVT), the output voltage remains constant
due to
GATE EE 2000
23
If an ac voltage wave is corrupted with an arbitrary number of harmonics, then
the overall voltage waveform differs from its fundamental frequency component
in terms of
GATE EE 2000
24
The magnetizing current in a transformer is rich in
GATE EE 1998
25
The laws of electromagnetic induction (Faraday's and Lenz's law) are summarized
in the following equation:
GATE EE 1998
26
The efficiency of a 100 kVA transform is 0.98 at full as well as at half load. For
this transformer at full load the copper loss.
GATE EE 1998
27
The low voltage winding of a $$400/230V,$$ $$1$$-phase, $$50$$ $$Hz$$ transformer is to be connected to a $$25$$ $$Hz,$$ the supply voltage should be
GATE EE 1997
28
Keeping in view the requirement of parallel operation, which of the $$3$$-phase connections given below are possible?
GATE EE 1996
29
Auto-transformer is used in transmission and distribution
GATE EE 1996
30
The function of oil in a transformer is
GATE EE 1996
31
Supply to one terminal of a $$\triangle$$ - Y connected three-phase core type
transformer which is on no-load, fails. Assuming magnetic circuit symmetry,
voltages on the secondary side will be:
GATE EE 1995
32
The percentage impedance of a 100 kVA, 11 kV/400V, delta/wye, 50 Hz
transformer is 4.5%. For the circulation of half the full load current during short
circuit test, with low voltage terminals shorted, the applied voltage on the high
voltage side will be __________.
GATE EE 1995
33
When a transformers winding suffers a short-circuit, the adjoining turns of the same winding experience
GATE EE 1994
34
Two transformers of identical voltage but of different capacities are operating in parallel. For satisfactory load sharing
GATE EE 1994
35
Two transformers of the same type, using the same grade of iron and conductor materials, are designed to work at the same flux and current densities; but the linear dimensions of one are two times those of the other in all respects. The ratio of $$kVA$$ of the two transformers closely equals
GATE EE 1992
36
Two transformers of different $$kVA$$ ratings workings in parallel share the load in proportion to their ratings when their
GATE EE 1992
Marks 2
1
When the winding c-d of the single-phase, 50 Hz, two winding transformer is supplied from an AC current source of frequency 50 Hz, the rated voltage of 200 V (rms), 50 Hz is obtained at the open-circuited terminals a-b. The cross sectional area of the core is 5000 mm$$^2$$ and the average core length traversed by the mutual flux is 500 mm. The maximum allowable flux density in the core is $$B_{max} = 1$$ Wb/m$$^2$$ and the relative permeability of the core material is 5000. The leakage impedance of the winding a-b and winding c-d at 50 Hz are (5 + j100$$\pi$$ $$\times$$ 0.16) $$\Omega$$ and (11.25 + j100$$\pi$$ $$\times$$ 0.36) $$\Omega$$, respectively. Considering the magnetizing characteristics to be linear and neglecting core loss, the self-inductance of the winding a-b in millihenry is ___________ (Round off to 1 decimal place).
GATE EE 2023
2
A transformer with toroidal core of permeability $$\mu $$ is shown in the figure. Assuming
uniform flux density across the circular core cross-section of radius r $$ \ll $$ R, and neglecting
any leakage flux, the best estimate for the mean radius R is
GATE EE 2018
3
A 3-phase 900 kVA, 3 kV / $$\sqrt 3 $$ kV (Δ/Y), 50 Hz transformer has primary (high voltage
side) resistance per phase of 0.3 Ω and secondary (low voltage side) resistance per phase of
0.02 Ω. Iron loss of the transformer is 10 kW. The full load % efficiency of the transformer
operated at unity power factor is _______ (up to 2 decimal places).
GATE EE 2018
4
If the primary line voltage rating is 3.3 kV (Y side) of a 25 kVA. $$Y-\triangle$$ transformer (the per phase turns ratio is 5:1), then the line current rating of the secondary side (in Ampere) is_______.
GATE EE 2017 Set 2
5
A three-phase, three winding $$\triangle$$ / $$\triangle$$ / Y (1.1 kV/6.6 kV/400 V) transformer is energized from AC
mains at the 1.1 kV side. It supplies 900 kVA load at 0.8 power factor lag from the 6.6 kV
winding and 300 kVA load at 0.6 power factor lag from the 400 V winding. The RMS line
current in ampere drawn by the 1.1 kV winding from the mains is _______.
GATE EE 2017 Set 1
6
A single-phase, 2 kVA, 100/200 V transformer is reconnected as an auto-transformer such that its kVA rating is maximum. The new rating, in kVA, is ______.
GATE EE 2016 Set 2
7
Three single-phase transformers are connected to form a delta-star three-phase transformer of
110 kV/ 11 kV. The transformer supplies at 11 kV a load of 8 MW at 0.8 p.f. lagging to a nearby
plant. Neglect the transformer losses. The ratio of phase currents in delta side to star side is
GATE EE 2016 Set 2
8
If the star side of the star-delta transformer shown in the figure is excited by a negative sequence voltage, then
GATE EE 2016 Set 1
9
A single-phase 400 V, 50 Hz transformer has an iron loss of 5000 W at the condition. When
operated at 200 V, 25 Hz, the iron loss is 2000 W. When operated at 416 V, 52 Hz, the value of the
hysteresis loss divided by the eddy current loss is ________.
GATE EE 2016 Set 1
10
A single-phase, 22 kVA, 2200 V/220 V, 50 Hz, distribution transformer is to be connected as an autotransformer
to get an output voltage of 2420 V. Its maximum kVA rating as an auto-transformer is
GATE EE 2016 Set 1
11
Two single-phase transformers T1 and T2 each rated at 500 kVA are operated in parallel. Percentage impedances of T1 and T2 are (1 + j6) and (0.8 + j4.8), respectively. To share a load of 1000 kVA at 0.8 lagging power factor, the contribution of T2 (in kVA) is ________.
GATE EE 2015 Set 1
12
A 200/400 V, 50 Hz, two-winding transformer is rated at 20 kVA. Its windings are connected as an auto-transformer of rating 200/600 V. A resistive load of 12 Ω is connected to the high voltage (600 V) side of the auto-transformer. The value of equivalent load resistance (in Ohm) as seen from low voltage side is _____.
GATE EE 2015 Set 1
13
A balanced (positive sequence) three-phase AC voltage source is connected to a balanced, star connected load through a star-delta transformer as shown in the figure. The line-to-line voltage rating is 230 V on the star side, and 115 V on the delta side. If the magnetizing current is neglected and $${\overline{\mathrm I}}_\mathrm s=100\angle0^\circ$$, then what is the value of $${\overline{\mathrm I}}_\mathrm p$$ in Ampere?
GATE EE 2015 Set 2
14
Two three-phase transformers are realized using single-phase transformers as shown in the figure.
The phase difference (in degree) between voltages V1 and V2 is _______.
The phase difference (in degree) between voltages V1 and V2 is _______.GATE EE 2015 Set 2
15
A three-winding transformer is connected to an AC voltage source as shown in the figure. The number of turns are as follows: N1=100, N2=50, N3=50. If the magnetizing current is neglected, and the currents in two windings are $${\overline I}_2=2\angle30^\circ$$ A and $${\overline I}_3=2\angle30^\circ$$ A, then what is the value of the current $${\overline I}_1$$ in Ampere?
GATE EE 2015 Set 2
16
The load shown in the figure absorbs 4 kW at a power factor of 0.89 lagging.
Assuming the transformer to be ideal, the value of the reactance X to improve the input
power factor to unity is ___________.
Assuming the transformer to be ideal, the value of the reactance X to improve the input
power factor to unity is ___________.GATE EE 2014 Set 3
17
An open circuit test is performed on 50 Hz transformer, using variable frequency source and
keeping V/f ratio constant, to separate its eddy current and hysteresis losses. The variation of
core loss/frequency as function of frequency is shown in the figure
The hysteresis and eddy current losses of the transformer at 25 Hz respectively are
The hysteresis and eddy current losses of the transformer at 25 Hz respectively areGATE EE 2014 Set 3
18
The mean thickness and variance of silicon steel laminations are 0.2 mm and 0.02
respectively. The varnish insulation is applied on both the sides of the laminations. The mean
thickness of one side insulation and its variance are 0.1 mm and 0.01 respectively. If the
transformer core is made using 100 such varnish coated laminations, the mean thickness and
variance of the core respectively are
GATE EE 2014 Set 3
19
The parameters measured for a 220V/110V, 50 Hz, single-phase transformer are:
Self inductance of primary winding = 45 mH
Self inductance of secondary winding = 30 mH
Mutual inductance between primary and secondary windings = 20 mH
GATE EE 2014 Set 3
20
For a single phase, two winding transformer, the supply frequency and voltage are both
increased by 10%. The percentage changes in the hysteresis loss and eddy current loss,
respectively are
GATE EE 2014 Set 2
21
The core loss of a single phase, 230/115 V, 50 Hz power transformer is measured from 230 V
side by feeding the primary (230 V side) from a variable voltage variable frequency source
while keeping the secondary open circuited. The core loss is measured to be 1050 W for
230 V, 50 Hz input. The core loss is again measured to be 500W for 138 V, 30 Hz input. The
hysteresis and eddy current losses of the transformer for 230 V, 50 Hz input are respectively.
GATE EE 2014 Set 1
22
The following arrangement consists of an ideal transformer and an attenuator
which attenuates by a factor of 0.8. An ac voltage VWX1 = 100V is applied across
WX to get an open circuit voltage VYZ1 across YZ. Next, an ac voltage VYZ2 =100V is
applied across YZ to get an open circuit voltage VWX2 across WX. Then,
$$\frac{V_{YZ1}}{V_{WX1}}$$, $$\frac{V_{WX2}}{V_{YZ2}}$$
are respectively,
GATE EE 2013
23
A single phase 10 kVA, 50 Hz transformer with 1 kV primary winding draws 0.5 A and 55 W, at
rated voltage and frequency, on no load. A second transformer has a core with all its linear
dimensions $$\sqrt2$$ times the corresponding dimensions of the first transformer. The core material and
lamination thickness are the same in both transformers. The primary windings of both the
transformers have the same number of turns. If a rated voltage of 2 kV at 50 Hz is applied to the
primary of the second transformer, then the no load current and power, respectively, are
GATE EE 2012
24
A balanced star-connected and purely resistive load is connected at the secondary
of a star-delta transformer as shown in the figure. The line-to-line voltage rating of
the transformer is 110 V/220 V. Neglecting the non-idealities of the transformer, the
impedance 'Z' of the equivalent star-connected load, referred to the primary side of
the transformer, is
GATE EE 2010
25
The figure above shows coil $$1$$ and $$2,$$ with dot markings as shown, having $$4000$$ and $$6000$$ turns respectively. Both the coils have a rated current of $$25$$ $$A.$$ Coil $$1$$ is excited with single phase, $$400$$ $$V,$$ $$50$$ $$Hz$$ supply.
The coils are to be connected to obtain a single-phase, $${{400} \over {1000}}\,\,V,$$ auto-transformer to drive a load of $$10$$ $$kVA.$$ Which of the options given should be exercised to realize the required auto-transformer?
GATE EE 2009
26
The figure above shows coil $$1$$ and $$2,$$ with dot markings as shown, having $$4000$$ and $$6000$$ turns respectively. Both the coils have a rated current of $$25$$ $$A.$$ Coil $$1$$ is excited with single phase, $$400$$ $$V,$$ $$50$$ $$Hz$$ supply.
In the auto-transformer obtained in Question $$30,$$ the current in each coil is
GATE EE 2009
27
The star-delta transformer shown above is excited on the star side with balanced, $$4$$-wire, $$3$$-phase, sinusoidal voltage supply of rated magnitude. The transformer is under no load condition.
With both $$S1$$ and $$S2$$ open, the core flux waveform will be
GATE EE 2009
28
The star-delta transformer shown above is excited on the star side with balanced, $$4$$-wire, $$3$$-phase, sinusoidal voltage supply of rated magnitude. The transformer is under no load condition.
With $$S2$$ closed and $$S1$$ open, the current waveform in the delta winding will be
GATE EE 2009
29
The circuit diagram shows a two-winding, lossless transformer with no leakage flux, excited from a current source, $$i(t)$$, whose waveform is also shown. The transformer has a magnetizing inductance of $$400/\pi \,\,mH.$$
The peak voltage across $$A$$ and $$B$$, with $$S$$ open is
GATE EE 2009
30
The circuit diagram shows a two-winding, lossless transformer with no leakage flux, excited from a current source, $$i(t)$$, whose waveform is also shown. The transformer has a magnetizing inductance of $$400/\pi \,\,mH.$$
If the waveform of $$i\left( t \right) = 10\sin \left( {100\pi t} \right)A,$$ the peak voltage across $$A$$ and $$B$$ with $$S$$ closed is
GATE EE 2009
31
Three single-phase transformers are connected to form a $$3$$-phase transformer bank. The transformers are connected in the following manner.
The transformer connection will be represented by
GATE EE 2008
32
The core of two-winding transformer is subjected to a magnetic flux variation as indicated in the figure.
The induced $$emf$$ $$\left( {{e_{rs}}} \right)$$ in the secondary winding as a function of time will be of the form
GATE EE 2008
33
A single-phase $$50$$ $$kVA,$$ $$250$$ $$V/500V$$ two winding transformer has an efficiency of $$95\% $$ at full load, unity power factor. If it is reconfigured as a $$500V/750V$$ auto-transformer, its efficiency at its new rated load at unity power factor will be
GATE EE 2007
34
A $$300$$ $$kVA$$ transformer has $$95\% $$ efficiency at full load $$0.8$$ $$pf$$ lagging and $$96\% $$ efficiency at half load, unity $$pf.$$
What is the maximum efficiency (in %) at unity $$pf$$ load?
GATE EE 2006
35
Two transformers are to be operated in parallel such that they share load in proportion to their $$kVA$$ ratings. The rating of the first transformer is $$500$$ $$kVA$$ and its $$pu$$ leakage impedance is $$0.05$$ $$pu.$$ If the rating of second transformer is $$250$$ $$kVA,$$ its $$pu$$ leakage impedance is
GATE EE 2006
36
A $$300$$ $$kVA$$ transformer has $$95\% $$ efficiency at full load $$0.8$$ $$pf$$ lagging and $$96\% $$ efficiency at half load, unity $$pf.$$
The iron loss $$\left( {{P_i}} \right)$$ in $$kW,$$ under full load operation are
GATE EE 2006
37
The resistance and reactance of a 100 kVA 11000|400 V, $$\triangle$$ - Y distribution
transformer are 0.02 and 0.07 pu respectively. The phase impedance of the
transformer referred to the primary is
GATE EE 2004
38
A 500 kVA, 3-phase transformer has iron loses of 300 W and full load copper
losses of 600 W. The percentage load at which the transformer is expected to
have maximum efficiency is
GATE EE 2004
39
A 50 kVA, 3300/230 V single-phase transformers is connected as an
autotransformer shown in figure. The nominal rating of the autotransformer will
be
GATE EE 2004
40
Figure shows an ideal single-phase transformer. The primary and secondary
coils are wound on the core as shown. Turns ratio $$\left(\frac{N_1}{N_2}\right)$$=2.
The correct phasors
of voltages $$E_1,\;E_2$$ currents $$I_1,\;I_2$$ and core flux $$\phi$$ are as shown in
GATE EE 2003
41
Figure shows a $$\triangle$$ - Y connected 3-phase
distribution transformer used to step down
the voltage from 11000 V to 415 V line-to line.
It has two switches S1 and S2. Under
normal conditions S1 is closed and S2 is
open. Under certain special conditions S1 is
open and S2 is closed. In such a case the
magnitude of the voltage across the LV
terminals a and c is
GATE EE 2003
42
Figure shows an ideal three-winding transformer. The three windings 1,2,3 of
the transformer are wound on the same core as shown. The turn's ratio N1:N2:N3
is 4:2:1. A resistor of 10 Ω is connected across winding-2. A capacitor of
reactance 2.5 Ω is connected across winding-3. Winding-1 is connected across a
400 V, ac supply. If the supply voltage phasor $$\overline V=400\angle0^\circ$$, the supply current
phasor $${\overline I}_1$$ is given by
GATE EE 2003
43
A 400V/200V/200V, 50 Hz three winding transformer is connected as shown in Figure. The reading of the voltmeter 'V' will be
GATE EE 2002
44
The hysteresis loop of a magnetic material has an area of 5 cm2 with the scales
given as 1 cm = 2 AT and 1 cm = 50 mWb. At 50 Hz, the total hysteresis loss is
GATE EE 2001
45
A 3-phase transformer has rating of 20 MVA, 220 kV (star) / 33 kV (delta) with
leakage reactance of 12%. The transformer reactance (in ohms) referred to each
phase of the L.V. delta-connected side is
GATE EE 2001
46
A 3-phase delta/star transformer is supplied at 6000 V on the delta-connected
side. The terminal voltage on the secondary side when supplying full load as 0.8
lagging power-factor is 415 V. The equivalent resistance and reactance drops for
the transformer are 1% and 5% respectively. The turn's ratio of the transformer
is:
GATE EE 2000
47
The windings of a Q kVA, $$\frac{V_1}{V_2}$$
Volt, three-phase, Delta connected, core type
transformer are reconnected to work as a single phase transformer. The
maximum voltage and the power ratings of the new configuration are,
GATE EE 1999
48
A 10 kVA, 400 V/200 V single-phase transformers with 10% impedance draws a
steady short circuit line current of
GATE EE 1999
49
The percentage resistance and percentage reactance of a 10 kVA, 400 V/200 V,
3-phase transformer are 2% and 10% respectively. If the constant losses in the
machine are 1%, the maximum possible percentage efficiency of the transformer
is:
GATE EE 1999
50
A 400V/100V, 10 kVA two-winding transformer is reconnected as an autotransformer
across a suitable voltage source. The maximum rating of such an
arrangement could be
GATE EE 1999
51
A 10 kVA, 400 V/200 V, single phase transformer with a percentage resistance
of 3% and percentage reactance of 6% is supplying a current of 50 A to a
resistive load. The value of the load voltage is:
GATE EE 1999
52
A 50 Hz transformer having equal hysteresis and eddy current losses at rated
excitation is operated at 45 Hz at 90% of its rated voltage. Compared to rated
operating point, the core losses under this condition:
GATE EE 1998
53
A voltage $$V=400$$ sin $$314.16t$$ is applied to a $$1$$-phase transformer on no-load. If the no load current of the transformer is $$2\sin \left( {314.16t - {{85}^0}} \right),\,\,$$ then magnetization branch impedance will be approximately
GATE EE 1997
54
A $$3$$-phase transformer bank consists of three identical $$2300/230$$ $$V,$$ $$15$$ $$kVA$$ single-phase transformers connected in delta/delta. The bank supplies a $$20$$ $$kVA,$$ unity $$p.f.$$ $$3$$-phase load. If one of the single-phase transformer develops a fault, and is removed, the load carried by each of the two transformers now operating in open delta will be __________$$kVA.$$
GATE EE 1997
55
A $$220/440$$ $$V,$$ $$50$$ $$Hz$$ single phase transformer operates on $$220$$ $$V,$$ $$40$$ $$Hz$$ supply with secondary winding. Then
GATE EE 1993
Marks 5
1
A single phase $$6300$$ $$kVA,$$ $$50$$ $$Hz,$$ $$3300V/400V$$ distribution transformer is connected between two $$50$$ $$Hz$$ supply systems, $$A$$ and $$B$$ as shown in Fig. The transformer has $$12$$ and $$99$$ turns in the low and high voltage windings respectively. The magnetizing reactance of the transformer referred to the high voltage side is $$500\Omega .$$ The leakage reactance of the high and low voltage windings are $$1.0\Omega $$ and $$0.012\Omega $$ respectively. Neglect the winding resistance and core losses of the transformer. The Thevenin voltage of system $$A$$ is $$3300V$$ while that of system $$B$$ is $$400V.$$ the short circuit reactance of systems $$A$$ and $$B$$ are $$0.5\Omega $$ and $$0.010\Omega $$ respectively. If no power is transferred between $$A$$ and $$B,$$ so that the two system voltages are in phase, find the magnetizing ampere turns of the transformer.
GATE EE 2002
2
In a single phase $$3$$ winding transformer the turns ratio for primary: secondary: tertiary windings is $$20:4:1.$$ With the lagging currents of $$50A$$ at a power factor of $$0.6$$ in the tertiary winding find the primary current and power factor.
GATE EE 2002
3
An ideal transformer has a linear $$B-H$$ characteristic with a finite slope and a turns ratio of $$1:1.$$ The primary of the transformer is energized with an ideal current source, producing the signal i as shown in figure. Sketch the shape (neglecting the scale factor) of the following signals, labeling the time axis clearly
$$(a)$$ $$\,\,\,\,\,$$ the core flux $${\phi _{oc}}$$ with the secondary of the transformer open
$$(b)$$ $$\,\,\,\,\,$$ the open-circuited secondary terminal voltage $${V_2}\left( t \right).$$
$$(c)$$ $$\,\,\,\,\,$$ the short-circuited secondary current $${i_2}\left( t \right)$$
$$(d)$$ $$\,\,\,\,\,$$ the core flux $${\phi _{sc}},$$ with the secondary of the transformer short-circuited.
GATE EE 2001
4
Two single phase transformers $$A$$ and $$B$$ have the following parameters.
Transformer $$A$$: $$400V/200V,$$ $$10$$ $$kVA,$$ percentage resistance and percentage reactance are $$3\% $$ and $$4\% $$ respectively.
Transformer B: $$5$$ $$kVA,$$ $$400V/200V,$$ percentage resistance and percentage reactance are $$4\% $$ and $$3\% $$ respectively.
These two transformers are connected in parallel and they share a common load of $$12$$ $$kW$$ at a power factor of $$0.8$$ lag. Determine the active and reactive power delivered by transformer $$A.$$
Transformer $$A$$: $$400V/200V,$$ $$10$$ $$kVA,$$ percentage resistance and percentage reactance are $$3\% $$ and $$4\% $$ respectively.
Transformer B: $$5$$ $$kVA,$$ $$400V/200V,$$ percentage resistance and percentage reactance are $$4\% $$ and $$3\% $$ respectively.
These two transformers are connected in parallel and they share a common load of $$12$$ $$kW$$ at a power factor of $$0.8$$ lag. Determine the active and reactive power delivered by transformer $$A.$$
GATE EE 1999
5
In a $$50$$ $$KVA,$$ $$11$$ $$KV/400$$ $$V$$ transformers, the iron and copper losses are $$500$$ $$W$$ and $$600$$ $$W$$ respectively under rated conditions. Calculate the efficiency on unity power factor at full load. Find the load for maximum efficiency and the iron and copper losses corresponding to this load.
GATE EE 1998