GATE EE
Electrical Machines
Transformers
Previous Years Questions

## Marks 1

The type of single-phase induction motor, expected to have the maximum power factor during steady state running condition, is
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 res...
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...
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 ...
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 in...
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, 50 kVA, 1000 V/100 V two winding transformer is connected as an autotransformer as shown in the figure. The kVA rating of the autotra...
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 ...
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 t...
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 tr...
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...
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...
It is desired to measure parameters of $$230$$ $$V/115$$ $$V,$$ $$2$$ $$kVA$$, single-phase transformers. The following watt-meters are available in ...
In a transformer, zero voltage regulation at full load is
In transformers, which of the following statements is valid?
Which three-phase connection can be used in a transformer to introduce a phase difference of 30° between its output and corresponding input line volta...
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
A 1 kVA, 230V/100V, single phase, 50 Hz transformer having negligible winding resistance and leakage inductance is operating under saturation, while 2...
A single-phase transformer is to be switched to the supply to have minimum inrush current. The switch should be closed at
The core flux of a practical transformer with a resistive load
In a constant voltage transformer (CVT), the output voltage remains constant due to
If an ac voltage wave is corrupted with an arbitrary number of harmonics, then the overall voltage waveform differs from its fundamental frequency com...
The laws of electromagnetic induction (Faraday's and Lenz's law) are summarized in the following equation:
The magnetizing current in a transformer is rich in
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.
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
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?
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 shor...
Supply to one terminal of a $$\triangle$$ - Y connected three-phase core type transformer which is on no-load, fails. Assuming magnetic circuit symmet...
When a transformers winding suffers a short-circuit, the adjoining turns of the same winding experience
Two transformers of identical voltage but of different capacities are operating in parallel. For satisfactory load sharing
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; ...
Two transformers of different $$kVA$$ ratings workings in parallel share the load in proportion to their ratings when their

## Marks 2

A transformer with toroidal core of permeability $$\mu$$ is shown in the figure. Assuming uniform flux density across the circular core cross-section...
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 vo...
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 curre...
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 sup...
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 ___...
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 ...
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...
If the star side of the star-delta transformer shown in the figure is excited by a negative sequence voltage, then ...
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 oper...
Two three-phase transformers are realized using single-phase transformers as shown in the figure. The phase difference (in degree) between voltages V...
A balanced (positive sequence) three-phase AC voltage source is connected to a balanced, star connected load through a star-delta transformer as shown...
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 ...
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....
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 loa...
The parameters measured for a 220V/110V, 50 Hz, single-phase transformer are: Self inductance of primary winding = 45 mH Self inductance of secondary ...
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 ...
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 a...
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 im...
For a single phase, two winding transformer, the supply frequency and voltage are both increased by 10%. The percentage changes in the hysteresis loss...
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 vo...
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 applie...
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 transfor...
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...
The figure above shows coil $$1$$ and $$2,$$ with dot markings as shown, having $$4000$$ and $$6000$$ turns respectively. Both the coils have a rate...
The figure above shows coil $$1$$ and $$2,$$ with dot markings as shown, having $$4000$$ and $$6000$$ turns respectively. Both the coils have a rate...
The star-delta transformer shown above is excited on the star side with balanced, $$4$$-wire, $$3$$-phase, sinusoidal voltage supply of rated magnit...
The star-delta transformer shown above is excited on the star side with balanced, $$4$$-wire, $$3$$-phase, sinusoidal voltage supply of rated magnit...
The circuit diagram shows a two-winding, lossless transformer with no leakage flux, excited from a current source, $$i(t)$$, whose waveform is also sh...
The circuit diagram shows a two-winding, lossless transformer with no leakage flux, excited from a current source, $$i(t)$$, whose waveform is also sh...
Three single-phase transformers are connected to form a $$3$$-phase transformer bank. The transformers are connected in the following manner. The tr...
The core of two-winding transformer is subjected to a magnetic flux variation as indicated in the figure. The induced $$emf$$ $$\left( {{e_{rs}}} ... A single-phase$$50kVA,250V/500V$$two winding transformer has an efficiency of$$95\% $$at full load, unity power factor. If it is re... A$$300kVA$$transformer has$$95\% $$efficiency at full load$$0.8pf$$lagging and$$96\% $$efficiency at half load, unity$$pf.$$The ... Two transformers are to be operated in parallel such that they share load in proportion to their$$kVA$$ratings. The rating of the first transformer ... A$$300kVA$$transformer has$$95\% $$efficiency at full load$$0.8pf$$lagging and$$96\% $$efficiency at half load, unity$$pf.$$What... The resistance and reactance of a 100 kVA 11000|400 V,$$\triangle$$- Y distribution transformer are 0.02 and 0.07 pu respectively. The phase impedan... A 500 kVA, 3-phase transformer has iron loses of 300 W and full load copper losses of 600 W. The percentage load at which the transformer is expected ... A 50 kVA, 3300/230 V single-phase transformers is connected as an autotransformer shown in figure. The nominal rating of the autotransformer will be ... Figure shows an ideal single-phase transformer. The primary and secondary coils are wound on the core as shown. Turns ratio$$\left(\frac{N_1}{N_2}\ri...
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 t...
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:...
A 400V/200V/200V, 50 Hz three winding transformer is connected as shown in Figure. The reading of the voltmeter 'V' will be ...
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 ...
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...
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 loa...
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 ...
A 400V/100V, 10 kVA two-winding transformer is reconnected as an autotransformer across a suitable voltage source. The maximum rating of such an arran...
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 i...
A 10 kVA, 400 V/200 V single-phase transformers with 10% impedance draws a steady short circuit line current of
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 trans...
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 ...
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 $$2\sin \left( {3... A$$3$$-phase transformer bank consists of three identical$$2300/230V,15kVA$$single-phase transformers connected in delta/delta. The ... A$$220/440V,50Hz$$single phase transformer operates on$$220V,40Hz$$supply with secondary winding. Then ## Marks 5 In a single phase$$3$$winding transformer the turns ratio for primary: secondary: tertiary windings is$$20:4:1.$$With the lagging currents of$$50...
A single phase $$6300$$ $$kVA,$$ $$50$$ $$Hz,$$ $$3300V/400V$$ distribution transformer is connected between two $$50$$ $$Hz$$ supply systems, $$A$$ a...
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...
Two single phase transformers $$A$$ and $$B$$ have the following parameters. Transformer $$A$$: $$400V/200V,$$ $$10$$ $$kVA,$$ percentage resistance ...
In a $$50$$ $$KVA,$$ $$11$$ $$KV/400$$ $$V$$ transformers, the iron and copper losses are $$500$$ $$W$$ and $$600$$ $$W$$ respectively under rated con...
EXAM MAP
Joint Entrance Examination