The transformer connection given in the figure is part of a balanced 3-phase circuit where the phase sequence is "". The primary to secondary turns ratio is . If , then the relationship between  and  will be

Which one of the following options represents possible voltage polarities in a single phase two winding transformer? Here,  is the applied primary voltage,  is the induced primary voltage,  is the open circuit secondary voltage, and  is the induced secondary voltage.

When the winding  of the single-phase, , two winding transformer is supplied from an AC current source of frequency , the rated voltage of  (rms),  is obtained at the open-circuited terminals . The cross sectional area of the core is  and the average core length traversed by the mutual flux is . The maximum allowable flux density in the core is  and the relative permeability of the core material is 5000. The leakage impedance of the winding  and winding  at  are and , 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).

In a single-phase transformer, the total iron loss is 2500 W at nominal voltage of 440V and frequency 50 Hz. The total iron loss is 850 W at 220 V and 25 Hz. Then, at nominal voltage and frequency, the hysteresis loss and eddy current loss respectively are

An air-core radio-frequency transformer as shown has a primary winding and a secondary winding. The mutual inductance M between the windings of the transformer is __________ μH. (Round off to 2 decimal places.)

A single-phase, 4 kVA, 200 V/100 V, 50 ~Hz transformer with laminated CRGO steel core has rated no-load loss of 450 W. When the high-voltage winding is excited with 160 V, 40 Hz sinusoidal AC supply, the no-load losses are found to be 320 W. When the high-voltage winding of the same transformer is supplied from a 100 V, 25 Hz sinusoidal AC source, the no-load losses will be …………… W (rounded off to 2 decimal places).

Windings 'A', 'B' and 'C' have 20 turns each and are wound on the same iron core as shown, along with winding 'X which has 2 turns. The figure shows the sense (clockwise/anti-clockwise) of each of the windings only and does not reflect the exact number of turns, If windings 'A', 'B' and 'C' are supplied with balanced 3 -phase voltages at 50 Hz and there is no core saturation, the no-load RMS voltage (in V, rounded off to 2 decimal places) across winding ' X is ____________

A 5 kVA, 50 V/100 V, single-phase transformer has a secondary terminal voltage of 95 V when loaded. The regulation of the transformer is.

A single-phase transformer of rating 25 kVA, supplies a 12 kW load at power factor of 0.6 lagging. The additional load at unity power factor in kW (round off to two decimal places) that may be added before this transformer exceeds its rated kVA is __________.

The magnetic circuit shown below has uniform cross-sectional area and air gap of 0.2 cm. The mean path length of the core is 40 cm. Assume that leakage and fringing fluxes are negligible. When the core relative permeability is assumed to be infinite, the magnetic flux density computed in the air gap is 1 tesla. With same Ampere-turns, if the core relative permeability is assumed to be 1000 (linear), the flux density in tesla (round off to three decimal places) calculated in the air gap is ____________.

A single-phase 100kVA, 1000V/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

A 3-phase 900kVA, , 50Hz transformer has primary (high voltage side) resistance per phase of and secondary (low voltage side) resistance per phase of . Iron loss of the transformer is 10kW. The full load % efficiency of the transformer operated at unity power factor is ______ (up to 2 decimal places).

A three-phase, three winding  (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 ____________.

(Given the answer up to one decimal place).

If the primary line voltage rating is 3.3 kV (Y side) of a 25 kVA,  transformer (the per phase turns ratio is 5:1), then the line current rating of the secondary side (in Ampere) is ____________ .

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

If the star side of the star-delta transformer shown in the figure is excited by a negative sequence voltage then,

A single-phase 400V, 50Hz transformer has an iron loss of 5000W at the rated condition. When operated at 200V, 25Hz, the iron loss is 2000W. When operated at 416V, 52Hz, the value of the hysteresis loss divided by the eddy current loss is _______.

A single-phase, 22KVA, 2200V/220V, 50Hz, distribution transformer is to be connected as an auto-transformer to get an output voltage of 2420V. Its maximum KVA rating as an auto-transformer is

The following figure shows the connections of an ideal transformer with primary to secondary turns ratio of 1:100. The applied primary voltage is 100V (rms), 50Hz, AC. The rms value of the current I, in ampere, is ____________.

A single-phase, 2kVA, 100/200 V transformer is reconnected as an auto-transformer such that its kVA rating is maximum. The new rating, in kVA, is ___________.

Three-phase transformers are connected to form a delta-star three-phase transformer of . The transformer supplies at 11kV a load of 8 MW at 0.8 p.f. lagging to a nearby plant. Neglect the transformer losses. The ratio of phase current in delta to star side is

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 windings is less than their respective rated currents. The resistance of both windings can be neglected. In this condition, what is the effective inductance (in mH) seen by the source?

The primary mmf is least affected by the secondary terminal conditions in a

A 200/400V, 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 (600V) side of the auto-transformer. The value of equivalent load resistance (in Ohm) as seen from low voltage side is _____________.

Two single-phase transformers  and  each rated at 500 kVA are operated in parallel. Percentage impedances of   and  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  (in kVA) is ______________

Find the transformer ratios a and b such that the impedance ( ) is resistive and equals  when the network is excited with a sine wave voltage of angular frequency of 5000 rad/s.

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  A, then what is the value of  in Ampere?

A three-winding transformer is connected to an AC voltage source as shown in the figure. The number of turns are as follows: . If the magnetizing current is neglected, and the currents in two windings are  = and =  A, then what is the value of the current  in Ampere?

Two three-phase transformers are realized using single-phase transformers as shown in the figure.

The phase difference (in degree) between voltages  and  is ___________.

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

The core loss of a single phase, 230/115 V, 50Hz power transformer is measured from 230V side by feeding the primary (230V side) from a variable voltage frequency source while keeping the secondary open circuited. The core loss is measured to be 1050 W for 230V, 50Hz input. The core loss is again measured to be 500W for 138V, 30Hz input. The hysteresis and eddy current losses of the transformer for 230V, 50Hz input are respectively,

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

A single phase, 50kVA, 1000V/100V two winding transformer is connected as an autotransformer as shown in the figure.

The kVA rating of the autotransformer is ________________.

For a single phase, two windings transformer, the supply frequency and voltage are both increased by 10%. The percentage changes in the hysteresis loss and eddy current loss, respectively, are        

An open circuit test is performed on 50Hz 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 25Hz respectively are

The load shown in the figure absorbs 4kW 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 ________________.

The parameters measured for a 220V/110V, 50Hz, single-phase transformer are:

Self inductance of primary winding = 45mH

Self inductance of secondary winding = 30mH

Mutual inductance between primary and secondary windings = 20mH

using the above parameters, the leakage  and magnetizing  inductance as referred to primary side in the equivalent circuit respectively, are

A single-phase transformer has no-load loss of 64W, 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, the measured loss is 81W. The transformer has maximum efficiency when operated at  

The following arrangement consists of an ideal transformer and an attenuator which attenuates by a factor of 0.8. An ac voltage is applied across WX to get an open circuit voltage across YZ. Next, an ac voltage is applied across YZ to get an open circuit voltage across WX. Then,  are respectively,

A single phase 10kVA, 50Hz transformer with 1kV primary winding draws 0.5A and 55W, at rated voltage and frequency, on no load. A second transformer has a core with all its linear dimensions  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 2kV at 50Hz is applied to the primary of the second transformer, then the no load current and power, respectively, are

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

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 reactance are neglected, the primary current is

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 110V/220V. 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:

The single phase, 50Hz, iron core transformer in the circuit has both the vertical arms of cross sectional area  and both the horizontal arms of cross sectional area . If the two windings shown were wound instead on opposite horizontal arms, the mutual inductances will

With both S1 and S2 open, the core flux waveform will be

With S2 closed and S1 open, the current waveform in the delta winding will be

The circuit diagram shows a two-winding, loss less 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/π mH.

The peak voltage across A and B, with S open is

The circuit diagram shows a two-winding, loss less 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/π mH.

If the waveform of i(t) is changed to , the peak voltage across A and B with S closed is

The figure below shows coils 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, 400/1000 V, auto-transformer to drive a load of 10kVA. Which of the options given should be exercised to realize the required auto-transformer?

The figure below shows coils 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 autotransformer obtained in Question 57, the current in each coil is

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         

The core of a two-winding transformer is subjected to a magnetic flux variation as indicated in the figure.  

The induced emf in the secondary winding as a function of time will be of the form

It is desired to measure parameters of 230V / 115V, 2kVA, single-phase transformer. The following watt-meters are available in a laboratory:

: 250V, 10A. Low Power Factor

: 250V, 5A. Low Power Factor

: 150V, 10A. High Power Factor

: 150V, 5A. High Power Factor

The watt-meters used in open circuit test and short circuit test of the transformer will respectively be

In a transformer zero voltage regulation at full load is

A single-phase 50kVA, 250V/500V two winding transformer has an efficiency of 95% at full load, unity power factor. If it is reconfigured as a 500V/750V autotransformer, its efficiency at its new rated load at unity power factor will be

In the figure, transformer , has two secondary, all three windings having the same number of tums and with polarities as indicated. One secondary is shorted by a 10 Ω resistor R, and the other by a 15 µF capacitor.  The switch SW is opened (t = 0) when the capacitor is charged to 5V with the left plate as positive. At t=0+ the voltage and current are

In transformers, which of the following statements is valid?

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, then its pu leakage impedance is

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  and copper loss  in kW, under full load operation are

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?

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

The equivalent circuit of a transformer has leakage reactance and magnetizing reactance . Their magnitudes satisfy

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

A 50 kVA, 3300/230V single-phase transformer is connected as an autotransformer shown in figure. The nominal rating of the autotransformer will be

The resistance and reactance of a 100 kVA 11000/400V, Δ-Y distribution transformer are 0.02 and 0.07pu respectively. The phase impedance of the transformer referred to the primary is

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

Figure shows an ideal single-phase transformer. The primary and secondary coils are wound on the core as shown. Turns ratio .  The correct phasors of voltages  currents  and core flux φ are as shown in

Figure shows a Δ-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 and . Under normal conditions is closed and is open. Under certain special conditions is open and is closed. In such a case the magnitude of the voltage across the LV terminals a and c is

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 is 4:2:1. A resistor of 10Ω is connected across winding-2. A capacitor of reactance 2.5Ω is connected across winding-3. Widing-1 is connected across a 400 V, ac supply. If the supply voltage phasor = 400∠0°, the supply current phasor is given by

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?

A 400V/200V/200V, 50 Hz three winding transformer is connected as shown in Figure. The reading of the voltmeter, V, will be

A single phase 6300kVA, 50 Hz, 3300V/400V distribution transformer is connected between two 50 Hz supply systems, A and B as shown in Figure, 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 500Ω. The leakage reactance of the high and low voltage windings are 1.0Ω and 0.012Ω 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 400 V, the short circuit reactance of systems A and B are 0.5Ω and 0.010 Ω 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.

A single-phase transformer is to be switched to the supply to have minimum inrush current. The switch should be closed be

The core flux of a practical transformer with a resistive load

The hysteresis loop of a magnetic material has an area of 5 with the scales given as 1 cm = 2AT and 1 cm = 50mWb.  At 50 Hz, the total hysteresis loss is

A 3-phase transformer has rating of 20 MVA, 200 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

An ideal transformer has a linear B-H characteristic with a finite slope and a turns ratio 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 with the secondary of the transformer open
(b) The open-circuited secondary terminal voltage
(c)  The short-circuited secondary current
(d) The core flux  with the secondary of the transformer short-circuited.

In a constant voltage transformer (CVT), the output voltage remains constant due to

A 3-phase delta/star transformer is supplied at 6000V on the delta-connected side. The terminal voltage on the secondary side when supplying full load as 0.8 lagging power-factor is 415V. The equivalent resistance and reactance drops for the transformer are 1% and 5% respectively. The turns ratio of the transformer is:

In a single-phase, three –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 magnitude of primary current and power-factor.

The winding of a Q kVA,  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

A 10kVA, 400 V/200V single-phase transformers with 10% impedance draws a steady short circuit line current of

The percentage resistance and percentage reactance of a 10kVA, 400V/200V, 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:

A 400V/100V, 10 kVA two-winding transformer is reconnected as an auto-transformer across a suitable voltage source. The maximum rating of such an arrangement could be

A 10 kVA, 400V/200V, single transformer with a percentage resistance of 3% and percentage reactance of 6% is supplying a current of 50A to a resistive load. The value of the load voltage is:

Two single-phase transformers A and B have the following parameters:

Transformer A: 10V/200V, percentage resistance and percentage reactance 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 lagging. Determine the active and reactive power delivered by the transformer A.

The efficiency of a 100KVA transformer is 0.98 at full as well as at half load. For this transformer at full load the copper loss

The magnetizing current in a transformer is rich in

A 50Hz transformer having equal hysteresis and eddy current losses at rated excitation is operated at 45Hz at 90% of its rated voltage. Compared to rated operating point, the core losses under this condition:

In a 50 KVA, 11 KV/400V transformers, the iron and copper losses are 500W and 600W 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.

The low voltage winding of a 400/230V, 1-phase, 50Hz transformer is to be connected to a 25Hz supply, the supply voltage should be

A voltage v=400sin(314.16t) is applied to a 1-phase transformer on no-load. If the no load current of the transformer is 2sin(314.16t-85°), then magnetization branch impedance will be approximately equal to

A 3-phase transformer bank consists of three identical 2300/230V, 15 kVA single-phase transformers connect 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.

Given figure shows a magnetic circuit formed by an ideal core material. Determine the magnetic flux density in the air gap.

The function of oil in a transformer is

Auto-transformer is used in transmission and distribution

Keeping in view the requirement of parallel operation, which of the 3-phase connections given below are possible?

Supply to one terminal of a delta-wye connected three-phase core type transformer which is on no-load, fails. Assuming magnetic circuit symmetry, voltages on the secondary side will be:

When started by means of an auto-transformer with 50% tapping, supply current at start of an induction motor is reduced to ______________ of that when started by means of a star-delta starter.

The percentage impedance of a 100 kVA, 11 kV/400V, delta/wye, 50Hz 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 ________.