Transformers Objective Questions

1) What is the unit of resistance?

A. ohms
B. watts
C. Ampere
D. mho

2) The primary and secondary winding of transformer are linked each other by

A. Conduction.
B. Mutual induction.
C. Not linked at all.
D. Self induction.

3) Which parameter does not change during transformation action in transformer?

A. Voltage
B. Frequency
C. Current
D. None of these

4) Secondary current of a step down transformer is

A. Lower than primary current
B. Higher than primary current
C. Equal to primary current
D. Double than primary current

5) The core of transformer must have

A. Low reluctance
B. High resistance
C. High reluctance
D. Low resistance

6) The working principle of transformer depends upon

A. Ohms law
B. Lenz’s Law
C. Fleming’s left hand rule
D. Faraday’s Law of Electromagnetic Induction.

7) An ideal transformer is one which has

A. No winding resistance
B. No leakage reactance
C. No losses
D. All of above

8) In an ideal transformer the magnetizing current lags behind applied primary voltage by an angle of

A. 90^o
B. 75^o
C. - 90^o
D. 45^o

9) In an ideal transformers

A. Both primary and secondary induced emfs are self induced emfs
B. Both primary and secondary induced emfs are mutually induced emfs
C. Primary induced emf is self induced and secondary induced emf is mutually induced
D. Primary induced emf is mutually induced and secondary induced emf is self induced

10) The input power under no load condition of transformer consists of

A. Core losses in transformer
B. core losses and very small amount of copper loss in primary.
C. copper loss in transformers
D. significant amount of copper loss along with negligible amount of core losses.

11) In a transformer the coils of primary and secondary are placed concentrically to achieve

A. reduced leakage flux between primary and secondary winding
B. reduced copper losses in the winding
C. reduced insulation cost of the windings
D. reduced voltage per turn in the winding

12) Iron loss in transformer can be determined by

A. Short Circuit Test
B. Open Circuit Test
C. Both Short Circuit and Open Circuit Tests
D. None of the above

13) No Load Losses in transformer can be minimized by using steel of

A. high silicon content and very thin lamination
B. only high silicon content
C. only very thin lamination
D. low silicon content and very thin lamination

14) Which of the following losses remain constant during normal operation of transformer?

A. Copper loss
B. Core loss
C. Stray loss
D. All losses in transformer vary with load

15) Which of the following losses varies with load in transformer?

A. Copper loss
B. Hysteresis loss
C. Eddy Current loss
D. All losses in transformer vary with load.

16) The maximum efficiency of a transformer occurs when

A. Iron loss > Copper loss
B. Iron loss < Copper loss
C. Iron loss = Copper loss
D. Iron loss = zero

17) Which one of the following is not a condition of parallel operation of transformer? A. MVA Rating of transformers must be same B. Voltage ration of transformers must be same C. Percentage Impedance of transformers should be same D. Polarity of transformers must be identical 18) If the supply frequency of a transformer increases the output voltage of the transformer will A. decrease. B. increase proportionately C. remain same D. increases very rapidly 19) In a core type transformer A. HV winding is placed nearer to the core limb. B. LV winding is placed nearer to the core limb. C. Any of the LV or HV can be placed nearer to the core limb. D. HV and LV windings are placed in different core limbs. 20) The primary and secondary winding of a transformer are A. conductively linked. B. inductively linked. C. electrically linked. D. mechanically linked 21) At what power factor, the voltage regulation of a transformer can be zero ? A. Leading power factor B. Lagging power factor C. Unity power factor D. Zero power factor Now, if Voltage regulation is zero, R2/X2 = − sinθ2/cosθ2 = − tanθ2 = tan( − θ2 ). − θ2 means leading power factor. 22) In a three phase star - delta transformer, what is the angle difference between primary and secondary phase voltages. A. delta side lags by − 30o. B. star side lags by − 30o. C. star side leads by 30o. D. delta side leads by 30o. 23) What will be the the eddy current loss if the supply frequency of a transformer becomes double ? A. Eight times B. Remain same C. Doubled D. Four times 24) The efficiency of a transformer is mainly dependent on A. core losses. B. copper losses. C. stray losses. D. dielectric losses. 25) If supply frequency of a transformer decreases, A. Both eddy current and hysteresis losses will increase. B. eddy current loss will increase but hysteresis loss will decrease. C. Both eddy current and hysteresis losses will decrease. D. eddy current loss will decrease but hysteresis loss will increase. 26) Transformers operating in parallel will share the load depending upon their A. Leakage reactance. B. Rating. C. Efficiency. D. Percentage impedance. 27) No load primary current in a transformer A. lags behind applied voltage somewhat less than 90o B. lags behind applied voltage by exactly 90o C. leads the applied voltage by exactly 90o D. leads the applied voltage somewhat less than 90o 28) Which of the following is minimized by laminating the core of a transformer? A. Hysteresis loss B. Eddy current loss C. Copper loss D. Stray loss 29) Breather is provided in a transformer to A. absorb moisture from air entering in transformer as well as provide breathing to the transformer. B. provide cold air in transformer C. absorb moisture from air entering in transformer D. filter the transformer oil 30) Iron loss in transformer mainly occurs in A. Iron made tank of transformer B. Steel core in transformer C. Winding of transformer D. Transformer insulating oil 31) Which of the following losses in the transformer varies with load? A. Copper loss B. Eddy current loss C. Hysteresis loss D. Stray loss 32) In a transformer the magnetic coupling between the primary and secondary winding can be increased by A. increasing the number of turns B. using soft material for winding C. using the magnetic core of low reluctance D. using transformer oil of better quality
33) The short circuit test on a transformer is conducted to obtain A. copper losses. B. core loses only. C. eddy current loss D. hysteresis loss 34) In a transformer short circuit test and open circuit test are conducted A. in LV side of transformer B. in HV side and LV side of transformer respectively C. in LV side and HV side of transformer respectively D. in HV side of transformer 35) In one 132/33KV transformer the LV resistance is 0.02 per unit. The resistance referred to HV side is A. 0.08 pu B. 0.02 pu C. 0.16 pu D. 0.01 pu 36) Lamination of transformer core is made of A. cast iron. B. silicon steel. C. wrought iron. D. cast steel. 37) Oil is provided in an Oil filled transformer A. both cooling and insulation B. insulating C. lubrication D. cooling 38) Air core transformer as compared to iron core transformer, has A. more copper loss B. less magnetic core loss C. more magnetic core loss D. no magnetic core loss. 39) CRGO Steel is used in the core of transformer to reduce A. Eddy Current loss B. Ohmic loss C. both Eddy Current and Hysteresis loss D. Hysteresis loss 40) If input of a transformer is square wave the output will be A. puled wave. B. square wave. C. triangular wave. D. sine wave. 41) Two transformers with identical rating, are designed with flux densities of 1.2 and 1.4 Wb/m2 respectively. The weight of first transformer per KVA is A. less than that of second transformer B. equal to that of second transformer C. more than that of second transformer D. None of these 42) The flux involved in the emf equation of a transformer has A. r.m.s value B. maximum value. C. average value D. total value 43) The no load current in a transformer lags the applied voltage by A. About 75o B. 0o C. 90o D. About 115o. 44) The leakage flux in a transformer depends upon A. the applied voltage B. the load current C. the frequency D. the mutual flux. 45) For satisfactory parallel operation of two transformers which of the following conditions is most essential, A. Polarities of all transformer operated in parallel must be connected properly. B. Percentage impedance of all transformers operated in parallel must be same. C. Voltage ratio of all transformer operated in parallel must be same. D. MVA rating of all transformer operated in parallel must be same. 46) If a transformer has turns ration K, the primary and secondary current are I1 and I2 respectively and magnetizing current and core loss component of no load current Iμ and Iw respectively, then A. I1 = K.I2 + Iw B. I1 = K.I2 + Iw + Iμ C. I1 = K.I2 + Iμ D. I1 = K.I2 47) Which of the following transformer insulating oil generally used in India A. paraffin based insulating oil B. naphtha based insulating oil C. aromatics based insulating oil D. olefin based insulating oil 48) Winding conductors of an electrical power transformer are mainly insulated by A. Cotton Insulation. B. Rubber Insulation. C. Paper Insulation. D. Wooden Insulation

49) The overall power factor of a on load transformers

A. depends on the power factor of the load.
B. is always lagging.
C. is always unity.
D. is always leading.

50) If in a sub – station there is one 132/33KV transformer whose secondary is connected with primary of one 33/11KV transformer, the total transformation ratio of the sub – station will be,

A. 7
B. 12
C. 4
D. 3

51) A short circuit test on a transformer gives

A. Copper loss at full load
B. Copper loss at any load
C. Copper loss at half load
D. Copper loss at over load

52) A step up transformer increases

A. Power
B. Voltage
C. Current
D. Frequency

53) In a step down transformers which one statement of following is true?

A. All of above
B. secondary power is less than primary power
C. secondary current is more than primary current.
D. number of secondary turns is less than that of primary

54) When a transformer is loaded, the secondary terminal voltage drops. That means power factor is

A. zero
B. leading
C. unity
D. lagging

55) When a transformer is loaded, the secondary terminal voltage gains. That means power factor is

A. lagging
B. zero
C. unity
D. leading

56) If K_h is hysteresis constant, f is supply frequency, B_m maximum flux density in core of transformer, the expression of hysteresis loss in transformer, is given by

A. K_h.f.B_m^1.6
B. K_h.f.B_m²
C. K_h.f².B_m^1.6
D. K_h.f.B_m.

57) If K_e is eddy current constant, K_f is form factor, f is supply frequency, B_m maximum flux density in core of transformer, the expression of eddy current loss in transformer, is given by

A. K_e.f². K_fB_m²
B. K_e.f. K_f².B_m²
C. K_e.f².K_f².B_m²
D. K_e.f². K_f².B_m

58) Stray losses in transformer occurs in

A. Steel core
B. Winding conductors and steel structures of transformer
C. Transformer insulating oil
D. Paper insulation in transformers

59) If iron loss and full load copper loss of any transformer are denoted by P_i and P_c, then the load corresponding to maximum efficiency is given by

A. (P_i / P_c)^0.5 X Full Load
B. (P_i / P_c)² X Full Load
C. (P_i / P_c) X Full Load
D. (P_i / P_c)^1.6 X Full Load

60) Secondary winding of an auto transformer is also called

A. compensating winding
B. common winding
C. tertiary winding
D. damping winding

61) Saving of copper in auto transformer is increased as compared to two winding transformer, when transformation ratio K approaches to

A. unity
B. infinity
C. two
D. zero

62) Tertiary winding in a transformer mostly

A. star connected
B. delta connected
C. zig-zag star connected
D. zig-zag delta connected

63) The main purpose of providing tertiary winding in a three phase transformer

A. to suppress harmonic voltages and to limit voltage unbalance when the main load is asymmetrical
B. to inter connect three supply systems operated at different voltages
C. to carry adding extra load to the transformer which for some reason must be kept isolated
D. none of the above

64) When operating two or more transformers in parallel, % impedance of these transformers should be

A. inversely proportional to MAV rating of transformers.
B. proportionate to MAV rating of transformers.
C. same.
D. such that actual impedance of all transformers would be same

65) Tap changer is generally provided in A. Current transformer B. Power Transformer C. Voltage Transformer D. Earthing transformer 66) The heat generated in the transformer is dissipated mainly by A. conduction B. convection C. radiation D. all of the above. 67) Transformer cooling and insulating oil must be of A. low viscosity B. high viscosity C. low BDV D. low resistivity 68) Normally for the design of transformer the ambient temperature is taken as A. 27oC B. 45oC C. 35oC D. 32oC 69) Which of the following machine will have maximum efficiency? A. Electrical Power Transformer B. Electrical Power Generator C. DC Motor D. Induction Motor 70) The heat transfer by convection in a transformer least depends on A. temperature difference B. air velocity C. surface area D. color of the paint. 71) Which of the following is not a part of transformer? A. Commutator B. Radiator C. Tap changer D. Conservator tank 72) Maximum allowable acidity level of power transformer insulating oil is generally taken  as A. 1 mg of KOH/gm B. 0.5 mg of KOH/gm C. 0.3 mg of KOH/gm D. 2 mg of KOH/gm 73) Maximum allowable tan – delta (tanδ) of dielectric dispassion factor of power transformer insulating oil is generally taken as A. 0.5 at 90oC B. 2 at 90oC C. 3 at 90oC D. 1 at 90oC 74) Minimum allowable Resistivity of power transformer insulating oil is generally taken as A. 2X1012 ohm – cm at 27oC & 0.2X1012 ohm – cm at 90oC B. 1X1012 ohm – cm at 27oC & 0.1X1012 ohm – cm at 90oC C. 3X1012 ohm – cm at 27oC & 0.3X1012 ohm – cm at 90oC D. 4X1012 ohm – cm at 27oC & 0.4X1012 ohm – cm at 90oC 75) Minimum allowable dielectric strength or break down voltage ( BDV ) of power   transformer insulating oil is generally taken as A. 30 KV B. 40 KV C. 50 KV D. 20 KV 76) Maximum allowable moisture content of power transformer insulating oil is   generally taken as A. 45 ppm B. 35 ppm C. 25 ppm D. 20 ppm 77) Minimum allowable flash point of power transformer insulating oil is generally taken as A. 140o B. 240o C. 40o D. 100o 78) Dissolve gas analysis of transformer oil is carried out to determine A. condition of transformer oil B. condition of transformer C. condition of bushings D. condition of bushing stud 79) Fufuraldehyde analysis is to determine the A. condition of paper insulation in transformer B. condition of oil in transformer C. condition of lamination on CRGO Steel sheet D. condition of cork gaskets used in transformer 80) SFRA or Sweep Frequency Response Analysis is carried out on a transformer to   monitor the A. condition of transformer oil B. condition of bushings C. condition of transformer D. condition of bushing stud 81) Flash point transformer insulating oil should be more than A. 40oC B. 140oC C. - 40oC D. 100oC 82) A transformer has R2 secondary resistance, k is its transformation ratio, the this  resistance referred to primary will be A. k2/R2. B. k2.R2. C. k.R2. D. k.R22. 83) A transformer has R1 primary resistance, k is its transformation ratio, this  resistance referred to secondary will be A. R1/k2. B. k2.R1. C. k.R1. D. k.R12. 84) What is the thickness of laminated CRGO steel sheet used for core of transformer? A. Ranging from 0.018 mm to 0.035 mm B. Ranging from 0.18 mm to 0.35 mm C. Ranging from 1.8 mm to 3.5 mm D. Ranging from 2.3 mm to 3.0 mm 85) Insulated surface coating of laminated sheet in the core of transformer helps to reduce A. eddy current loss B. hysteresis loss C. both eddy current and hysteresis losses D. none of above 86) If supply frequency of a transformer is 50Hz, its magnetostriction frequency would be A. 25 Hz B. 200 Hz C. 50 Hz D. 100 Hz 87) Noise of transformer mainly due to A. magnetostriction in iron core B. noise generated by cooling fans C. mechanical vibration of different parts of transformer D. all of above 88) The ideal shape for the section of core is A. triangle B. rectangle C. circle D. pentagon 89) Percentage leakage reactance in core type construction, compared to shell   type construction of core, is A. double B. less C. more D. equal 90) The tap changer in an electrical power transformer is provided on A. Both LV and HV Winding B. LV Winding C. Either LV or HV Winding D. HV Winding 91) Why HV winding is always placed above the LV winding in a core type transformer? A. to reduce copper cost B. to reduce insulation cost C. to provide better cooling D. to provide more mechanical strength 92) If silica gel breather of a transformer is blocked A. Cooling of transformer will be affected B. Oil deteriorates C. Buchholz relay will be operated D. Color of silica gel will be pink 93) Buchholz relay is provided on transformer to A. indicate minor faults inside the transformers B. indicate minor & major faults and isolate the transformer during major fault C. isolate the transformer during major fault D. indicate major fault inside the transformers 94) Full load copper loss in transformer is 1600 W. At half load the loss will be A. 400 W B. 1600 W C. 3200 W D. 6400 W 95) Iron loss for a transformer is 400 W. If the transformer is working at its maximum  efficiency then copper loss will be A. 1600 W B. 400 W C. 800 W D. 200 W 96) Which test on a transformer provides information about regulation, efficiency   and heating under load condition ? A. Back to back test B. Open circuit test C. Hopkinson test D. Short circuit test 97) If supply frequency of a transformer increases, the secondary output voltage of  the transformer A. decreases B. increases C. remains same D. decreases slightly 98) If the cross – sectional area of magnetic core of a transformer increases, the  secondary output voltage of the transformer A. decreases B. increases C. remains same D. decreases slightly 99) If the maximum flux density of core of a transformer increases, the secondary   output voltage of the transformer A. increases B. decreases C. remains same D. decreases slightly 100) If secondary numbers of turns in a transformer increases, the secondary output  voltage of the transformer A. decreases B. increases C. remains same D. decreases slightly 101) In an electrical power transformer A. emf per turn in primary = emf per turn in secondary. B. emf per turn in primary > emf per turn in secondary. C. emf per turn in primary < emf per turn in secondary. D. emf per turn in primary = (2/3) of emf per turn in secondary. 102) For a transformer if the full load copper loss are A and iron loss are B, then the  load at which these are B, then the load at which these two losses would be equal is  given by A. Full load X A/B. B. Full load X B/A. C. Full load X √(A/B). D. Full load X √(B/A). 103) If W is the weight of copper in 315MVA, 400/220KV two winding transformer   then what will be the weight of copper in an auto-transformer of same rating? A. 0.45 X W B. 0.55 X W C . 1.81 X W D. 0.81 X W 104) If a two winding step down transformer of voltage ration lv/hv = k is connected   as auto transformer, then what will be the MVA rating of this auto transformer ? A. same as MVA rating of two winding transformer. B. k. MVA rating of two winding transformer. C. (1 + k). MVA rating of two winding transformer. D. (1/k) X MVA rating of two winding transformer. 105) When a 400 Hz transformer is operated at 50 Hz, its kVA rating is A. reduced to 1/16 B. reduced to 1/4 C. reduced to 1/2 D. reduced to 1/8 106) For constant load current at which power factor the efficiency of transformer will be maximum? A. Zero power factor B. Unity power factor C. Leading power factor D. Lagging power factor 107) Distribution transformers are usually designed to have maximum efficiency A. at 50% of full load B. at 75% of full load C. near full load D. near no load. 108) Power transformers are usually designed to have maximum efficiency A. at 75% of full load. B. near full load. C. at 50% of full load. D. near no load. 109) The energy efficiency is the term related to A. Distribution transformer. B. Electrical Power Transformer. C. Current transformer. D. Voltage transformer. 110) The all day efficiency is the term related to A. Electrical Power Transformer. B. Distribution transformer. C. Current transformer. D. Voltage transformer. 111) The phase difference between primary and secondary voltages in an ideal   transformer is generally A. 180o B. 90o C. 0o D. 45o 112) A transformer has a full load of 900 W and copper loss of 1600 W. At what   percentage of the load the transformer will have maximum efficiency? A. 90% B. 100% C. 75% D. 50% 113) Two transformer A and B, with identical ratings, are to be designed with flux   densities of 1.2 and 1.4 Wb/m2 respectively. The weight of transformer A per kVA is A. less than that of transformer B B. more than that of transformer B C. equal to that of transformer B D. none of these 114) In a single phase transformer which of the following relation is true A. E1N1 = E2N2 and I1N1 = I2N2 B. E1N2 = E2N1 and I1N1 = I2N2 C. E1N2 = E2N1 and I1N2 = I2N1 D. E1N1 = E2N2 and I1N2 = I2N1 115) The flux involved in emf equation of a transformer is A. maximum flux B. rms flux C. average flux D. total flux 116) A transformer has N1 and N2 turns in primary and secondary winding respectively. Its  secondary winding reactance of x2 ohms, when referred to primary, is A. x2(N2/N1)2. B. x2(N1/N2)2. C. x2(N1/N2). D. x2(N2/N1). 117) In 132/66KV electrical power transformer has its LV resistance 0.02 pu. The  resistance when referred to HV side is A. 0.02 p.u. B. 0.04 p.u. C. 0.01 p.u. D. 0.08 p.u. 118) Leakage flux in a transformer depends on A. the applied voltage. B. the frequency. C. the mutual flux. D. the load current. 119) The efficiency of a transformer at full load 0.8 p.f. lag is 90%. Its efficiency at full load 0.8 lead will be A. 90 % B. less than 90 % C. more than 90 % D. none of the above The efficiency of transformer 120) Distribution transformer have core losses A. > copper losses B. = copper losses C. < copper losses D. = 0.5X(copper losses) 121) Eddy current loss in transformer depends on A. both voltage and frequency B. voltage alone C. frequency alone D. square of the frequency alone 122) Hysteresis loss in a transformer depends upon A. voltage alone B. both voltage and frequency C. frequency alone D. square of the voltage alone 123) In a transformer A. OC test is conducted on LV side and SC test on HV side. B. OC test is conducted on HV side and SC test on LV side. C. both OC and SC tests are conducted on LV side. D. both OC and SC tests are conducted on HV side. 124) One 200V, 100W bulb is connected in series with the primary of a 200V, 10 kVA   transformer. If its secondary is open circuited, then the bulb will have A. full brightness. B. poor brightness. C. little less than full brightness. D. more than full brightness. 125) The no load current in a power transformer in term of its rated current, is A. 2 to 6%. B. 10 to 20% C. 15 to 30% D. 30 to 50%. 126) Maximum efficiency of transformer for a constant load occurs at A. zero power factor. B. unity power factor. C. 0.8 power factor. D. 0.2 power factor. The efficiency of transformer η = V2.I2.cosθ2 X 100% V2.I2.cosθ2 + losses in transformer where cosθ2 is power factor. It can be proved that efficiency is maximum when cosθ2 = 1 127) For a 1.15 kVA 130/460V transformer connected to a standard 1 - phase 230V supply,  the no load current likely to be, A. 0.2 A B. 2.5 A C. 1 A D. 4 A 128) The primary of a 220/6 V, 50 Hz transformer is connected to a 110V, 60 Hz supply.  The secondary output voltage is A. 2.5 V B. 3.6 V C. 3.0 V D. 1.667 V Answers 1 A 26 B 51 B 76 B 101 A 126 B 2 B 27 A 52 B 77 A 102 D 127 A 3 B 28 B 53 A 78 B 103 A 128 C 4 B 29 A 54 D 79 A 104 C 5 A 30 B 55 D 80 C 105 D 6 D 31 A 56 A 81 B 106 B 7 D 32 C 57 C 82 B 107 A 8 A 33 A 58 B 83 A 108 B 9 C 34 B 59 A 84 B 109 A 10 B 35 B 60 B 85 A 110 B 11 A 36 B 61 A 86 D 111 A 12 B 37 A 62 B 87 A 112 C 13 A 38 D 63 A 88 C 113 B 14 B 39 D 64 C 89 C 114 B 15 A 40 A 65 B 90 D 115 A 16 C 41 C 66 B 91 B 116 B 17 A 42 B 67 A 92 A 117 A 18 B 43 A 68 B 93 B 118 D 19 B 44 B 69 A 94 A 119 A 20 B 45 A 70 D 95 B 120 C 21 A 46 B 71 A 96 A 121 C 22 D 47 A 72 C 97 B 122 B 23 D 48 C 73 D 98 B 123 A 24 A 49 A 74 B 99 A 124 B 25 C 50 B 75 A 100 B 125 A