Explore topic-wise MCQs in Transformers.

This section includes 293 Mcqs, each offering curated multiple-choice questions to sharpen your Transformers knowledge and support exam preparation. Choose a topic below to get started.

51.

A 10 kVA, 400 / 200 V single phase transformer with resistance 4 percent and reactance 6 percent supplies a current of 50 A a resistive load. Voltage across the load is:

A. 190 V
B. 188 V
C. 192 V
D. 194 V
Answer» D. 194 V
Discussion
52.

A 600 kVA, 11 kV/400 V single-phase transformer having 0.15 pu leakage impedance is connected in parallel with a 300 kVA, 11 kV/400 V single transformer having 0.05 pu leakage impedance. The maximum permissible kVA loading of the two in parallel without overloading any one is

A. 300 kVA
B. 400 kVA
C. 800 kVA
D. 1200 kVA
Answer» C. 800 kVA
Discussion
53.

In an auto-transformer, power is transferred, through

A. Conduction process only
B. Induction process only
C. Both conduction and induction processes
D. Mutual coupling
Answer» D. Mutual coupling
Discussion
54.

A single-phase transformer has maximum efficiency of 98 %. The core losses are 80 W and the equivalent winding resistance as seen from the primary side is 0.5 Ω. The rated current on the primary side is 25 A. The percentage of the rated input current at which the maximum efficiency occurs is

A. 35.7%
B. 50.6%
C. 80.5%
D. 100%
Answer» C. 80.5%
Discussion
55.

If the output power of a transformer is 600 W whereas the losses are 200 W, the efficiency of the transformer will be:

A. 50%
B. 41.4%
C. 75%
D. 66.6%
Answer» D. 66.6%
Discussion
56.

A transformer may have negative voltage regulation if the load power factor (p.f.) is

A. Leading for some values of p.f.
B. Unity p.f.
C. Lagging but not zero p.f.
D. Only zero p.f. lag
Answer» B. Unity p.f.
Discussion
57.

Hysteresis and eddy current losses of single-phase transformer working on 200 V, 50 Hz is Ph and Pc respectively. The percentage decrease in Ph and Pc, when the transformer operates on 160 V, 40 Hz supply, will respectively be

A. 32, 36
B. 25, 50
C. 20, 36
D. 40, 80
Answer» D. 40, 80
Discussion
58.

Ferrite cores are used in high frequency transformer because it has:

A. Low resistance
B. High resistance
C. Low hysteresis
D. Low permeability
Answer» C. Low hysteresis
Discussion
59.

Copper loss is negligible at _____.

A. Half load
B. No load
C. 1/4 load
D. Full load
Answer» C. 1/4 load
Discussion
60.

A 2000/1000/500 V, single-phase, three winding autotransformer is to be used as an autotransformer with a supply voltage of 3000 V. Two loads, one of 1050 kVA at 3500 V, and the other of 180 kVA at 1000 V, are to be energized from this autotransformer output. The currents in the three parts of the winding are:

A. 100 A, 210 A, 80 A
B. 80 A, 320 A, 410 A
C. 180 A, 120 A, 410 A
D. 110 A, 70 A, 300 A
Answer» E.
Discussion
61.

A transformer on no-load is switched on to a source of voltage. It will draw a current _______

A. which is the same as the steady-state magnetizing current
B. which is several times the steady-state magnetizing current, depending upon the initial state of the residual flux in the transformer core
C. which is several times the steady-state magnetizing current, independent of the initial state of the residual flux in the transformer core
D. which is twice the steady-state magnetizing current provided the core has no residual flux
Answer» C. which is several times the steady-state magnetizing current, independent of the initial state of the residual flux in the transformer core
Discussion
62.

In transformer, ________ is found by the short circuit test.

A. Copper loss
B. Hysteresis loss
C. Eddy current loss
D. Iron loss
Answer» B. Hysteresis loss
Discussion
63.

For an ideal transformer, if I2 / I1 = 2 and E2 = 100 V, E1 will be:

A. 200 V
B. 100 V
C. 25 V
D. 50 V
Answer» B. 100 V
Discussion
64.

A short-circuit test on a transformer is usually performed with

A. high voltage side short-circuited
B. low voltage side short-circuited
C. low voltage side open-circuited
D. low and high voltage side open-circuited
Answer» C. low voltage side open-circuited
Discussion
65.

Open circuit test is conducted on a transformer to get:

A. Core loss
B. Copper loss
C. Insulation resistance
D. Total loss
Answer» B. Copper loss
Discussion
66.

In a transformer, maximum voltage regulation occurs at ______.

A. leading power factor of the load
B. lagging power factor of the load
C. unity power factor of the load
D. None of the above
Answer» C. unity power factor of the load
Discussion
67.

In scott connections, the teaser transformer operates on 0.866 of its rated ________.

A. Inductance
B. Capacitance
C. Reactance
D. Voltage
Answer» E.
Discussion
68.

Can a 50 Hz transformer be used as 25 Hz, if the input voltage is maintained constant at the rated corresponding to 50 Hz?

A. Yes, since the voltage is constant, current levels will not change
B. No, flux will be doubled which will drive the core to excessive saturation
C. No, owing to decreased reactance of transformer, input current will be doubled at load
D. Yes, at constant voltage, insulation will not be overstressed
Answer» C. No, owing to decreased reactance of transformer, input current will be doubled at load
Discussion
69.

Buchholz relay is a

A. Voltage sensitive device
B. Current sensitive device
C. Frequency sensitive device
D. Gas actuated device
Answer» E.
Discussion
70.

A short-circuit test transformed on high-voltage side of 20 kVA, 2000/400 V, single-phase transformer gave the results as 60 V, 4 A, 100 W. If the lo-voltage side is delivering full-load current at 0.8 p.f. lag, at 400 V, the voltage applied to the high-voltage side is nearly

A. 2190 V
B. 2170 V
C. 2150 V
D. 2132 V
Answer» E.
Discussion
71.

A self-transformer with a voltage change ratio of 0.8 supplies a load of 10 kW. What will be the inductively transferred power at the load?

A. 10 kW
B. 8 kW
C. 12.5 kW
D. 2 kW
Answer» E.
Discussion
72.

An ordinary transformer works on:

A. A.C.
B. D.C.
C. Both A.C. and D.C.
D. Pulsating D.C.
Answer» B. D.C.
Discussion
73.

In a power transformer, at full load, the efficiency is

A. Minimum
B. Maximum
C. Half the normal efficiency
D. 20% of the maximum efficiency
Answer» C. Half the normal efficiency
Discussion
74.

Magnetizing inrush current in transformer is rich in

A. 3rd Harmonics
B. 7th Harmonics
C. 2nd Harmonics
D. 5th Harmonics
Answer» D. 5th Harmonics
Discussion
75.

A power supply should possess an ideal voltage regulation which is equal to _________ and practical voltage regulation measuring __________.

A. Small value, zero
B. Zero, small value
C. Zero, zero
D. Large value, zero
Answer» C. Zero, zero
Discussion
76.

Dispersion coefficient σ is the ratio of

A. Magnetizing current to supply voltage
B. Open circuit voltage to short circuit current for the same excitement
C. Magnetizing current to ideal short circuit current
D. Short circuit current to magnetizing current
Answer» D. Short circuit current to magnetizing current
Discussion
77.

In a power transformer, the breather is provided in order to _____.

A. filter transformer oil
B. prevent ingress of moisture with air
C. the cooling oil
D. provide fresh air for increasing cooling effect
Answer» C. the cooling oil
Discussion
78.

Find the current rating for the following system.An outdoor pole-mounted 11 kV / 415 V substation has to be installed for supply to an area having a load of 63 kVA.

A. 50 A
B. 88 A
C. 72 A
D. 65 A
Answer» C. 72 A
Discussion
79.

If a 220/440 V, 50 Hz, single phase transformer is operated on 220 V, 40 Hz supply then

A. the eddy current loss and hysteresis loss of the transformer will decrease
B. the eddy current loss and hysteresis loss of the transformer will increase
C. the hysteresis loss of the transformer increases while eddy current loss remains the same
D. the hysteresis loss remains the same, whereas eddy current loss decreases
Answer» D. the hysteresis loss remains the same, whereas eddy current loss decreases
Discussion
80.

In a transformer, the value of useful flux least depends on:

A. Voltage
B. Current
C. Load
D. Magneto motive force
Answer» D. Magneto motive force
Discussion
81.

A part of primary winding also serves as secondary winding in:

A. Potential transformers
B. Auto transformer
C. Current transformer
D. All types of transformers
Answer» C. Current transformer
Discussion
82.

1-ϕ transformer at no load has a core loss of 75 W and current of 5 A (RMS) and has an induced EMF of 230 V (RMS) Determine the magnetising current and core loss current respectively.

A. 10 A; 0.5 A
B. 5 A; 0.326 A
C. 0.326 A; 5 A
D. 0.5 A; 10 A
Answer» C. 0.326 A; 5 A
Discussion
83.

Generally the no-load losses of an electrical machine is represented in its equivalent circuit by a

A. Parallel resistance with a low value
B. Series resistance with a low value
C. Parallel resistance with a high value
D. Series resistance with a high value
Answer» D. Series resistance with a high value
Discussion
84.

In a 440 V, 50 Hz transformer, the total iron loss is 3700 W. When the applied voltage is 220 V at 25 Hz, the total iron loss is 750 W. The eddy current loss at the normal voltage and frequency will be

A. 4600 W
B. 4400 W
C. 1200 W
D. 1000 W
Answer» C. 1200 W
Discussion
85.

If transformer has N1 : N2 = 1 : 1, then the transformer is a/an _____.

A. potential transformer
B. current transformer
C. isolation transformer
D. power transformer
Answer» D. power transformer
Discussion
86.

An Auto transformer is a/an:

A. Automobile transformer
B. Automatic transformer
C. Variable output voltage transformer
D. Variable input voltage transformer
Answer» D. Variable input voltage transformer
Discussion
87.

A transformer has maximum efficiency at ¾ full load. The ratio of its iron losses and full load copper loss is:

A. 16/9
B. 4/3
C. 3/4
D. 9/16
Answer» E.
Discussion
88.

A 50 kVA transformer has a core loss of 500 W and full-load loss of 900 W. The load at which the efficiency is maximum is:

A. 27.45 kVA
B. 37.75 kVA
C. 45.5 kVA
D. 47.5 kVA
Answer» C. 45.5 kVA
Discussion
89.

A transformer on no-load has a core-loss of 50 W, draws a current of 2 A and has an induced EMF of 230 V. Determine the no-load power factor and core-loss current.

A. Power factor = 0.208 lagging, core-loss current = 0.416 A
B. Power factor = 0.108 lagging, core-loss current = 0.216 A
C. Power factor = 0.108 lagging, core-loss current = 2 sin(cos-1 0.108) A
D. Power factor = 0.208 lagging, core-loss current = 2 sin(cos-1 0.208) A
Answer» C. Power factor = 0.108 lagging, core-loss current = 2 sin(cos-1 0.108) A
Discussion
90.

Air core and ferrite core inductors are used in

A. power supply filter circuits
B. audio frequency circuits
C. high frequency circuits
D. low pass filters
Answer» D. low pass filters
Discussion
91.

In electrical machines, laminated cores are used to reduce

A. Copper losses
B. Eddy current losses
C. Hysteresis losses
D. All of the above
Answer» C. Hysteresis losses
Discussion
92.

Copper loss of transformer at full load is 2800 W. At half load, the copper loss will be:

A. 700 W
B. 5600 W
C. 1400 W
D. 350 W
Answer» B. 5600 W
Discussion
93.

Oil is invariably used in large transformers to

A. Lubricate the core
B. Insulate the core
C. Lubricate the coils
D. Provide fuel for operation
Answer» C. Lubricate the coils
Discussion
94.

Distribution transformers have the rating of

A. up to 50 kVA
B. up to 100 kVA
C. up to 150 kVA
D. up to 200 kVA
Answer» E.
Discussion
95.

A three-phase transformer, connected in star-delta, is composed of three single-phase transformers, each rated 127 V / 13.2 kV. The line-to-line voltage ratio for the three-phase transformer is:

A. 220 / 13.2 kV
B. 127 / 13.2 kV
C. 127 / 220 kV
D. 220 / 220 kV
Answer» B. 127 / 13.2 kV
Discussion
96.

A 240 V/120 V, 12 kVA auto-transformer has 96.2% efficiency at full-load and unity power-factor. The full load efficiency at 0.85 pf lagging when connected to a load across 360 V would be

A. 89.5%
B. 92.8%
C. 98.5%
D. 88.9%
Answer» D. 88.9%
Discussion
97.

Iron loss of a transformer can be measured by:

A. Any type of watt meter
B. Unity power factor watt meter
C. Low power factor watt meter
D. None of these
Answer» D. None of these
Discussion
98.

A transformer with a 10:1 ratio and rated at 50 kVA, 2400/240 V, 50 Hz is used to step down the voltage of a distribution system. The low tension voltage is to be kept constant at 240 V. If the transformer is fully loaded at 0.8 power factor (lag), the load impedance connected to low tension side will be nearly

A. 3.15 Ω
B. 2.60 Ω
C. 1.15 Ω
D. 0.60 Ω
Answer» D. 0.60 Ω
Discussion
99.

In which of the following cases, will the same transformer have highest efficiency?

A. Supplying rated load at 0.8 pf lagging
B. Supplying rated load at 0.8 pf leading
C. Supplying rated load at unity pf
D. Supplying 10% overload (110% rated) at 0.8 pf lagging
Answer» D. Supplying 10% overload (110% rated) at 0.8 pf lagging
Discussion
100.

In order to minimize the inrush current in a single-phase transformer, the supply switch should be closed at the instant when:

A. supply voltage is \(\dfrac{1}{2}\) times the maximum voltage
B. supply voltage is \(\dfrac{1}{\sqrt2}\) times the maximum voltage
C. supply voltage is maximum
D. supply voltage is zero
Answer» D. supply voltage is zero
Discussion