Transformer Multiple Choice Questions


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Transformer Multiple Choice Questions

1.In a transformer

(a) All turns are equally insulated (b) The end turns are more strongly insulated
© The end turns are closely wound (d) The end turns are widely separated

2.Laminated insulations coated with varnish are norm ally used in the transformer

(a) To reduce reluctance of magnetic path
(b) To reduce the effect of eddy current
© To increase the reluctance of magnetic path
(d) To reduce the hysteresis effect

3.The required thickness of lamination in a transformer decreases when

(a) The applied frequency increases (b) The applied frequency decreases
© The applied voltage increases (d) The applied voltage decreases

4.Oil in transformer is used to

(a) Transfer electrical energy (b) Insulate the windings
© Cool the windings (d) None of the above

5.The following arrangement will reduce the reluctance of magnetic path of the transformer.

boxes

6.The windings of a transformer are divided into several coils because

(a) It is difficult to wind as one coil (b) It reduces voltage per coil
© It requires less insulation (d) none of the above

7.The size and construction of bushings in a transformer depend upon the

(a) Size of winding (b) Size of tank
© Current flowing (d) Voltage supplied

8.Transformer humming sound is reduced by the

(a) Proper bracing of transformers assemblies
(b) Proper insulation
© Proper design
(d) Proper design of winding

9.Sludge in transformer oil is due to

(a) Decomposition of oil (b) Decomposition of insulation
© Moisture content in oil (d) None of the above

10.A transformer used only for electrical isolation between two circuits has turns ratio which is

(a) More than unity (b) Less than unity © Equal to unity (d) More than 0.5

11.If 90 per cent of norm al voltage and 90 percent of norm al frequency are applied to a transformer, the percent charge in hysteresis losses will be

(a) 20% (b) 4.7% © 19% (d) 21%

12.If 110 per cent of norm al voltage and 110 per cent of normal frequency is applied to a transformer, the percentage change of eddy current losses will be

(a) 10% (b) 20% © 25% (d) 21%

13.A transformer has two 2,400 V primary coils and two 240 V coils. By proper connection of the windings, the transformation ratio that can be obtained is

(a) 10 (b) 5 © 20 (d) 9

14.A single-phase, 2,200/200 V transformer takes 1 A at the HT side or no load at a power factor of 0.385 lagging. The iron losses are

(a)167 W (b) 847 W © 88 W (d) 98 W

15.Neglecting resistance, at constant flux density, the power required per kilogram to magnetize the iron core of a transformer is 0.8 W at 25 Hz and 2.04 W at 60 Hz. The power required per kilogram for 100 Hz is

(a)3.8 W (b) 3.63 W © 3.4 W (d) 5.2 W

16.Select the correct statement:

(a)Emf per turn of both the windings are equal
(b)Emf per turn in HV winding is more than the emf per turn in LV winding
©Emf per turn in HV winding is less than the emf per turn in LV winding

17.The flux involved in the emf equation of a transformer has

(a) rms value (b) Average value © Total value (d) Maximum value

18.The no-load current in a transformer lags the applied voltage by

(a)90° – 95° (b) About 80° – 85° © 0° – 15° (d) About 110°

19.High leakage impedance transformers are used for applications such as

(a)Power distribution (b) Electrical toys
© Arc welding (d) Fluorescent lamps

20.A transformer 2,000 kVA, 250 Hz is operated at 50 Hz. Its kVA rating should be revised to

(a) 400 kVA (b) 10,000 kVA
© 2,000 kVA (d) cannot be revised

21.The transformer which will have the largest size is

(a) 100 kVA, 25 Hz (b) 100 kVA, 100 Hz
© 100 kVA, 50 Hz (d) 100 kVA, 60 Hz

22.The magnetic flux of a transformer follows

(a) High reluctance path (b) Low reluctance path
© Low conductivity path (d) High conductivity path

23.The efficiency of a transformer is usually in the range of

(a) 50–60% (b) 65–75%
© 70–90% (d) 90–98%

24.Transformer is laminated to reduce

(a) Hysteresis loss (b) Eddy current loss
© Partly (a) and partly (b) (d) Increases exciting current

25.Transformer changes the value of

(a) Power (b) Frequency
© Voltage (d) Current

26.Transfer of electrical power from primary to secondary in a transformer takes place

(a) Electrically (b) Electromagnetically
© Magnetically (d) None of these

27.The thickness of a 50 Hz transformer lamination is

(a) 0.35 cm (b) 0.35 mm
© 0.33 m (d) 0.30 cm

28.A power transformer is a constant

(a) Current device (b) Voltage device
© Power device (d) Main flux device

29.The value of flux in the emf equation of a transformer is

(a) rms (b) Average
© Maximum (d) Integral wave cycle

30.The leakage flux in a transformer depends upon the value of

(a) Load current (b) Supply frequency
© Mutual flux (d) none of these

31.The voltage regulation of a transformer at full-load 0.8 power factor lag is 6 percent. Its voltage regulation at full- load 0.8 power factor lead will be

(a) Negative (b) 54% © Positive (d) Zero

32.The full-load efficiency of a transformer at 0.85 p.f. lag is 97 per cent. Its efficiency at full load 0.85 power factor lead will be
(a) 99% (b) 96% © 97% (d) 98%

33.If a load on secondary side of a transformer increases, the current on the primary side

(a) Remains constant (b) Increases © Decreases (d) None of these

  1. If a sinusoidal exciting current is applied to a transformer, the mutual flux produced is

(a) Negative (b) Sinusoidal © Zero (d) Flat top

  1. To get sinusoidal flux in a transformer the mutual flux produced is

(a) Non-sinusoidal (b) Sinusoidal © Direct current (d) Zero

  1. A 220V, 150V bulb is connected in series with the primary of a 220/1,100 V, 50 Hz transformer. If the load on the secondary side is disconnected, the brightness of the bulb will

(a) Decrease (b) Increase
© Be unaffected (d) Decrease to a very low value

  1. The open circuit test of a transformer gives information about

(a) Core losses of the transformer (b) Cu losses of the transformer
© Exciting current (d) None of these

  1. The short circuit test of a transformer gives the information of

(a) Cu losses of the transformer (b) Core losses of the transformer
© Winding circuit impedance (d) None of these

  1. During testing of a transformer

(a) Both SC and OC tests are performed at rated current
(b) Both SC and OC tests are performed at rated voltage
© OC test is performed at rated voltage
(d) SC test is performed at rated current

  1. All-day efficiency of a transformer is

(a) Equal to its power efficiency (b) Less than its power efficiency
© More than its power efficiency (d) None of these

  1. Routine efficiency of a transformer depends upon the value of

(a) Load current (b) Supply frequency
© Power factor of load (d) Both (a) and (b)

  1. A ferrite core has less eddy current loss than an iron core because ferrites have

(a) Lower permeability (b) High hysteresis
© Alnico as the main constituent (d) High resistance

  1. The maximum regulation of a transformer occurs at a power factor of

(a) Unity (b)X02/R02 lag © X02/R02 lead (d) R02/ X02 lead

  1. The zero of regulation of a transformer occurs at a power factor of

(a) Zero (b)R02/ X02 lead © R02/ X02 lag (d) X02/R02 lead

  1. Circular coil sections are used because they

(a) Reduce iron material (b) Reduce copper material
© Have the strongest mechanical shape (d) All of these

  1. A transformer is connected to a constant voltage source. If the supply frequency decreases, the magnetic flux in the core will

(a) Increase towards saturation (b) Decrease
© Remain unchanged (d) None of these

  1. The power in autotransformer is transferred through

(a) Inductive process (b) Convection process
© Conduction process (d) All of these

  1. The cross-sectional area of the common portion of an autotransformer is

(a) Kept constant (b) Proportionally decreased
© Proportionally increased (d) None of these

  1. The efficiency of an autotransformer for the same output compared to a two-winding transformer is

(a) Greater (b) Lesser © Poor (d) None of these

  1. The condition for successful parallel operation of transformer is

(a) Correct polarity
(b) Per unit impedance based on their rating should be equal
© Identical voltage and frequency rating
(d) Equal ratio of equivalent resistance to reactance
(e) All of these

  1. During parallel operation of transformers incorrect polarity will result in

(a) Open circuit
(b) Dead short circuit
© Regeneration of power
(d) Power factor of transformer will be different from that of the connected load

  1. In an autotransformer of voltage ratio V1/ V2 and V1 > V2, the fraction of power transferred inductively is

(a) V1 / (V1+V2) (b) V2 / V1 © (V1-V2 / (V1+V2) (d)(V1-V2) / V1V2

  1. A 10 kVA, 400/200 V sinlge-phase transformer with 10 per cent impedance draws a steady short circuit line
    current of

(a) 50 A (b) 150 A © 250 A (d) 350 A

  1. A 400/100 V, 10 kVA two-winding transformer is reconnected as an autotransformer across a suitable voltage
    source. The maximum kVA is

(a) 50 kVA (b) 15 kVA © 12.5 kVA (d) 8.75 kVA

  1. An autotransformer having a transformation ratio of 0.8 supplies a load of 10 kW. The power transferred
    inductively from the primary to the secondary is

(a) 10 kW (b) 8 kW © 2 kW (d) Zero

  1. A single-phase induction regulator is a constant input transformer to obtain smooth variation of the output
    voltage by varying the

(a) Ratio of turns between primary and secondary winding
(b) Frequency
© Flux-density in the core
(d) Angle between the magnetic forces of the primary and secondary windings

  1. In operating a 400 Hz transformer at 50 Hz

(a) Only voltage is reduced in the same proportion as the frequency
(b) Only kVA is reduced in the same proportion as the frequency
© Both voltage and kVA rating are reduced in the same proportion as the frequency
(d) None of the above

  1. In performing the short circuit test of a transformer

(a) High-voltage side is usually short-circuited
(b) Low-voltage side is usually short-circuited
© Any side is short-circuited with preference
(d) None of these

  1. In performing open circuit test of a transformer

(a) High voltage is usually kept open (b) Low voltage is usually kept open
© Any side can be kept open (d) None of the above

  1. Transformer core usually uses grain-oriented laminated sheets. The grain orientation reduces

(a) Copper loss (b) Eddy current loss
© Hysteresis loss (d) None of the above

  1. In the circuit model of a transformer, the core loss is represented as

(a) Series resistance (b) Series inductance
© Shunt resistance (d) Shunt inductance

  1. While performing short circuit test on a transformer, the impressed voltage magnitude is kept constant but the
    frequency is increased. The short circuit current will

(a) Increase (b) Decrease
© Remain the same (d) None of the above

  1. A transformer has a hysteresis loss of 30 W at 240 V, 60 Hz. The hysteresis loss at 200 V, 50 Hz will be

(a) 20.8 W (b) 25 W © 30 W (d) 36 W

  1. In a transformer, the exciting current will be in phase quadrature with the impressed voltage provided

(a) Only the leakage impedance drop is ignored
(b) Only the core loss is ignored
© Both the leakage and impedance drop and the core loss are ignored
(d) Only no-load copper loss is ignored

  1. Magnetizing impedance of a transformer is determined by

(a) Short circuit test
(b) Open circuit test
© Both open circuit and short circuit tests
(d) None of these

  1. A transformer is to be tested at full-load conditions consuming only losses from the mains. We do

(a) Load test (b) Open circuit and short circuit tests
© Back-to-back test (d) None of these

  1. In a transformer operating at constant voltage if the input frequency increases the core loss will

(a) Increase (b) Decrease
© Remain constant (d) Increase as the square of the frequency

  1. Grain-oriented laminated sheet steel in a transformer reduces

(a) Copper loss (b) Eddy current loss
© Hysteresis loss (d) None of above

  1. R1 is the resistance of the primary winding of a transformer. The turns ratio in terms of primary to secondary is a. The equivalent resistance of the primary referred to as secondary is

(a) R1/a (b) a2 R1 © R1/ a2 (d) None of these

  1. Choose the correct statement:

(a) emf per turn in high-voltage winding is more than the emf per turn in low-voltage
winding
(b) emf per turn in both the finding are equal
© emf per turn in both the windings are not equal
(d) None of these

  1. If E2 and V2 be the induced emf in secondary winding and V2 be the terminal voltage during load, the regulation
    of the transformer is given by

(a) (E2-V2)/V2

(b) (E2-V2)/E2

© (V2-E2)/E2

(d) (V2-E2)/V2

  1. One transformer has leakage impedance of 1 + j 4 Ω and 3 + j 4 Ω for its primary and secondary windings,
    respectively. The transformer has

(a) Low voltage primary (b) High voltage primary
© Medium voltage primary (d) Insufficient data

  1. A single-phase transformer has its maximum efficiency at 60 per cent of full load. At full load copper loss will be

(a) Equal to core loss (b) Less than core loss
© More than core loss (d) Zero

  1. The flux in a magnetic core is alternating sinusoidally at a frequency of 600 Hz. The maximum flux density is 2T and eddy current loss is 15 W. If the frequency is raised to 800 Hz and maximum flux density reduced to 1.5 T, the eddy current loss will be

(a) Same (b) Reduced to half
© Doubled (d) Increased by 50%

  1. The core flux in a transformer depends mainly on

(a) Supply voltage
(b) Supply voltage and frequency
© Supply voltage, frequency and load
(d) Supply voltage and load but independent of frequency

ANSWERS