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1 SUBJECT: COURSE: Engineering Academy is providing Best Junior Engineer (Civil, Mechanical, Electrical and Electronics) and Assistant Engineering (Civil, Mechanical, Electrical and Electronics) coaching in the north region. It took lots of hard work and dedication to become best Engineer coaching centre in Dehradun and its credit goes to our highly qualified and experienced faculties.. "Always dream and shoot higher than you know you can do. Don't bother just to be better than your contesmporaries or predecessors. Try to be better than yourself."

2 1. The basic function of a transformer is to change (A) The level of the voltage (B) The power level (C) The power factor (D) The frequency 2. In an ordinary transformer which of the following does not change (A) Voltage (B) Current (C) Frequency (D) All of the above 3. The efficiency of a power transformer is around (A) 50% (B) 60% (C) 80% (D) 95% 4. In a transformer, electrical power is transferred from primary to secondary (A) Through air (B) By magnetic flux (C) Through insulating medium (D) None of these 5. The two winding of a transformer are (A) Conductively linked (B) Inductively linked (C) Not linked at all (D) Electrically linked 6. Transformer action requires a (A) Constant magnetic flux (B) Increasing magnetic flux (C) Alternating magnetic flux (D) Alternating electrical flux 7. The flux created by the current flowing through the primary winding induced EMF is (A) Primary winding only (B) Secondary winding only (C) Transformer core only (D) Both primary and secondary winding 8. The primary and secondary winding of a power transformer always have (A) A common magnetic circuit (B) Separate magnetic circuit (C) Wire of same size (D) Same number of turns 9. The iron core in a transformer provides a path to the main flux (A) Low reluctance (B) High reluctance (C) Low resistance (D) High conductivity 10. If rated DC voltage is applied instead of AC to the primary of a transformer (A) Secondary of transformer will burn (B) Primary of transformer will burn (C) Secondary voltage will be excessively high (D) There will be no secondary voltage 11. A transformer transforms (A) Voltage (B) Current (C) Voltage and current (D) Frequency 12. For an ideal transformer the winding should have (A) Maximum resistance on primary side and least resistance on secondary side (B) Least resistance on primary side and maximum resistance on secondary side (C) Equal resistance on primary and secondary side (D) No ohmic resistance on either side 13. The core flux in transformer depends mainly on (A) Supply voltage (B) Supply voltage and frequency (C) Supply voltage, frequency and load (D) Supply voltage and load but independent on frequency 14. When voltage is transformed from primary to secondary then it is (A) Multiplied by K 2 (B) Multiplied by K (C) Divide by K 2

3 (D) Divide by K 15. A transformer step up the voltage by a factor 100. The ratio of current in the primary to that in the secondary is (A) 1 (B) 100 (C) 0.01 (D) If the applied voltage to a transformer primary is increased by keeping the V/f ratio fixed, then the magnetizing current and the core loss will, respectively (A) Decrease and remain the same (B) Increase and decrease (C) Both remain the same (D) Remain the same and increase 17. The applied voltage of a certain transformer is increased by 75%.while the frequency of the applied voltage is reduced by 25%. The maximum core flux density will (A) Increase by seven time (B) Increase by three time (C) Reduced to one quarter (D) Remain the same 18. The low voltage winding of a 400/230 V single phase 50 HZ transformer is to be connected to a 25 HZ supply. In order to keep the magnetization current at the same level in both the cases the voltage at 25 HZ should be (A) 230 V (B) 460 V (C) 115 V (D) 65 V 19. A single phase transformer rated for 220/240 V, 50 HZ operates at no load at 220 V, 40 HZ. This frequency operation at rated voltage results in which one of the following? (A) Increase of both eddy-current and hysteresis losses. (B) Reduction of both eddy-current and hysteresis losses. (C) Reduction of hysteresis loss and increase in eddy-current losses. (D) Increase of hysteresis loss and no change in the eddy-current losses. 20. A single phase transformer when supplied from 220 V, 50 HZ has eddy current loss of 50 W. if the transformer is connected to a voltage of 330 V, 50 HZ, the eddy current loss will be (A) W (B) W (C) 75 W (D) 50 W KVA, 230 V, 50 HZ, single phase transformer has an eddy current loss of 30 watts. The eddy current loss when the transformer is excited by a DC source of same voltage will be (A) 30 W (B) More than 30 W (C) Less than 30 W (D) Zero Watt 22. At 50 HZ operation, a single phase transformer has hysteresis loss of 200 W and eddy current loss of 100 W. its core loss at 60 HZ operation will be (A) 432 W (B) 408 W (C) 384 W (D) 360 W 23. Can a 50 HZ transformer be used for 25 HZ, if the input voltage is maintained constant at the rated value corresponding to 50 HZ? (A) Yes, since the voltage is constant current level will not change (B) No, flux will be doubled which will drive the core to excessive saturation (C) No, owing to decrease resistance of transformer, input current will be doubled at the load. (D) Yes, at constant voltage, insulation will not be overstressed 24. On no load phasor diagram of transformer, the core loss component of the current remain in phase with

4 (A) No load current (B) Primary supply voltage (C) Core flux (D) Primary induced voltage 25. If a sinusoidal voltage source is connected to a power transformer, its no load current will be (A) Sinusoidal and lagging the voltage by 90 (B) Sinusoidal and lagging the voltage by less than 90 (C) Rich in third harmonic and its fundamental would lag the voltage by 90 (D) Rich in third harmonic and its fundamental would lag the voltage by less than The transformer exciting current has two components, magnetizing component and core loss component. Neglecting impedance drop (A) Both of them are in phase with the supply voltage (B) The former lags the supply voltage by 90 while the latter is in phase with supply voltage (C) Both of them lag the supply voltage by 90 (D) The former is in phase with the supply voltage while the latter lag the supply voltage by A single phase transformer has a turn s ratio of 1:2 and is connected to a purely resistive load as shown in the figure. The magnetizing current drown is 1 A, and the secondary currents is 1 A. if core losses and leakage reactance are neglected, the primary current is (A) 1.41 A (B) 2 A (C) 2.24 A (D) 3 A 28. At which condition of the transformer the equivalent circuit will be as shown in the figure (A) Under short circuit (B) under rated load (C) under open circuit (D) under load and no load 29. At which condition of the transformer the equivalent circuit will be as shown in the figure

5 (A) Under short circuit (B) under rated load (C) under open circuit (D) under load and no load 30. In a transformer, the exciting current will be in phase quadrature with the impressed voltage provided (A) Only the leakage impendence drop (B) Only the core loss is ignored (C) Both the leakage impendence drop and the core loss are ignored (D)Only the no load copper loss is ignored 31. The power factor of a power transformer on no load will be about (A) Unity (B) 0.75 (C) 0.5 (D) The power factor of a transformer on no load is poor due to (A) Magnetizing reactance of the transformer (B) Open circuited secondary (C) Low primary winding resistance (D) Low no load current 33. If in a transformer core, a material having high reluctance path but having same hysteresis loop is employed (A) I e will increase (B) I m will increase (C) I m will decrease (D) both I m and I e will increase 34. Primary winding of a transformer comprise of two identical winding in parallel. If one winding is removed, magnetizing current will be (A) Halved (B) the same (C) doubled (D) increased four time 35. The core flux of a practical transformer with a resistance load (A) Is strictly constant with load change (B) Increase linearly with load (C) Increase as the square root of the load (D) Decrease with increase of load 36. The inductive reactance of a transformer depends on (A) Electromotive force (B) magneto motive force (C) magnetic flux (D) leakage flux 37. The flux in transformer core (A) Increase with load (B) decrease with load (C) remains constant irrespective of load (D) none of the above 38. The mutual flux in a loaded transformer can be varied by varying

6 (A) Primary current (B) load impendence (C) secondary current (D) reluctance of the magnetic path 39. The primary ampere turns are counter balanced by (A) Secondary ampere turns (B) primary flux (C) increase in mutual flux (D) increase in secondary current 40. In a transformer decrease with the increase in leakage flux (A) Primary induced EMF (B)secondary induced EMF (C) secondary terminal voltage (D) none of the above 41. Power transformed from primary to secondary depends upon (A) Number of primary turns (B) number of secondary turns (C) current transformation ratio (D) magnetic coupling between primary and secondary windings 42. A transformer is supplying pure resistive (unity pf) load. The power factor on primary side will be (A) About 0.95 (lead) (B) About 0.95 (lag) (C) zero (D) unity 43. In a transformer supplying inductive load (A) The secondary current result in equivalent primary current in phase opposition (B) The secondary terminal voltage is less than the secondary induced EMF (C) The power factor on primary side will be lower than that of load (D) All of the above 44. The phasor diagram of a transformer on load can be drawn only if we know (A) Equivalent circuit parameters of the transformer (B) Load current (C) load p f (D) all of the above 45. When a transformer is operating on no load, the primary applied voltage is approximately balanced by (A) Primary induced EMF (B) Secondary induced EMF (C) Terminal voltage across the secondary (D) Voltage drop across the resistance and reactance 46. Consider the circuit shown in given figure. For maximum power transfer to the load, the primary to secondary turn ratio must be

7 (A) 9:1 (B) 3:1 (C) 1:3 (D) 1:9 47. In the transformer circuit mode, the core loss is represented as a (A) Series resistance (B) series inductance (C) shunt resistance (D) shunt inductance 48. Full load voltage regulation of a power transformer is zero when power factor of the load is near (A) Unity and leading (B) zero and leading (C) zero and lagging (D) unity and lagging 49. In a transformer, zero voltage regulation at full load is (A) Not possible (B) Possible at leading power factor load (C) Possible at lagging power factor load (D) Possible at unity power factor load 50. Positive voltage regulation is an indication of load (A) Inductive (B) capacitive (C) either inductive or capacitive (D) pure resistive 51. The looses in a transformer are (i) Copper losses (ii) Eddy current loss (iii) Hysteresis loss The constant power loss of a transformer is given by (A) (i) only (B) (i) and (ii) only (C) (ii) and (iii) only (D) (i), (ii) and (iii) 52. In a power transformer iron losses remain practically constant from no load to full load. This is because (A) Core flux remains constant (B) Leakage flux remains constant (C) Both (A) and (B) (D) neither (A) nor (B) 53. In a power transformer, if in place of sinusoidal wave, a peaked wave voltage is fed to the primary (A) Copper looses will be less (B) Noise level will be reduced (C) Iron looses will be more (D) Iron looses will be less 54. On which of the following factors does hysteresis loss dependent?

8 (i) Flux density (ii) frequency (iii) thickness or laminations (iv) time Select the correct answer using the code given below (A) (ii) and (iii) (B) (i) and (ii) (C) (iii) and (iv) (D) (i) and (iv) 55. The full load copper loss and iron loss of a transformer are 6,400 W and 5,000 W respectively. The copper loss and iron loss at half load will be, respectively (A) 3,200 W and 2,500 W (B) 3,200 W and 5,200 W (C) 1,600 W and 1,250 W (D) 1,600 W and 5,000 W 56. If the frequency of input voltage of a transformer is increased keeping the magnitude of voltage unchanged, then (A) Both hysteresis loss and eddy current loss in the core increase (B) hysteresis loss will increase but eddy current loss will decrease (C) hysteresis loss will decrease but eddy current loss will increase (D) hysteresis loss will decrease but eddy current loss will remain unchanged 57. The total iron loss in a transformer core at normal flux density was measured at 25 HZ and 50 HZ and was found to be 250 W and 800 W respectively. The hysteresis loss at 50 HZ would be (A) 100 W (B) 150 W (C) 200 W (D) 600 W 58. The main purpose of performing open circuit on a transformer is to measured is (A) Copper loss (B) core loss (C) total loss (D) insulation resistance 59. Open circuit test in a transformer is performed with (A) Rated transformer voltage (B) Rated transformer current (C) Direct current (D) High frequency supply 60. The open circuit test in a transformer is usually performed by exciting the low voltage winding. This is because (A) It draws sufficiently large no load current which can be conversely measured (B) The required power input is low (C) It is not advisable to work on high voltage side (D) The voltage required is low 61. The Open circuit test in a transformer gives (A) Equivalent resistance and leakage resistance (B) Magnetizing current and core loss at rated voltage (C) Copper looses (D) both (B) and (C) 62. In transformers, which of the following statements is valid?

9 (A) In an open circuit test, copper looses and obtained while in short circuit test, core looses are obtained (B) In an open circuit test, current is drawn at high power factor (C) In a short circuit, current is drawn at zero power factor (D) In an open circuit test, current is drawn at low power factor 63. A 10 KVA, 400 V/200 V single phase transformer with 10% impendence draws a steady short circuit line current of (A) 50 A (B) 150 A (C) 250 A (D) 350 A 64. While performing the open circuit and short circuit test on a transformer to determine parameters the status of the low voltage (LV) and high voltage (HV) winding will be such that (A) In OC,LV is open and in SC HV is shorted (B) In OC, HV is open and in SC LV is shorted (C) In OC,LV is open and in SC LV is shorted (D) In OC,LV is open and in SC HV is shorted 65. For a transformer to be tested at full load condition but consuming only looses from the mains, we do (A) Load test (B) Open circuit and short circuit tests (C) Back to back test (D) None of the above 66. The efficiency of two identical transformer under load condition can be determined by (A) Back to back test (B) open circuit test (C) short circuit test (D) any of the above 67. Two transformers, each having iron loss of P I watts and full load copper loss of P c, are put to back to back test and full load current is allowed to flow through the secondary s, the total input will be (A) 2P i (B) 2P c (C) P i + P c (D) 2(P i + P c ) 68. The efficiency of a power transformer can be determined indirectly by (A) Open circuit test alone (B) Short circuit test alone (C) Open circuit and short circuit test (D) Back to back test 69. The transformer efficiency at relatively light loads is quite low this is due to (A) Small copper looses (B) Small secondary output (C) High fixed loss in comparison to the output (D) Poor power factor 70. The transformer efficiency, under heavy loads, is comparatively low due to (A) Large increase in copper losses in comparison to the output

10 (B) Large increase in iron losses (C) Drop in power factor (D) None of the above 71. The full load copper loss and iron loss of a transformer are 6400 W and 500 W, respectively. The above copper loss and iron loss at half load will be (A) 3200 W and 250 W respectively (B) 3200 W and 500 W respectively (C) 1600 W and 125 W respectively (D) 1600 W and 500 W respectively 72. The efficiency of a 100 KVA transformer is 0.98 at full as well as half load. For this transformer at full load the copper loss (A) Is less then core loss (B) Is equal to core loss (C) Is more than core loss (D) None of the above 73. Transformer will operate at maximum efficiency when (A) Hysteresis loss = eddy current loss (B) Eddy current loss = copper loss (C) Copper loss = iron loss (D) Hysteresis loss = copper loss 74. Power transformer designed to have maximum efficiency around full load (A) Nearly (B) 70% of (C) 50% of (D) 25% of 75.The transformer efficiency will be maximum of a power factor of (A) 0.8 lead (B) unity (C) 0.8 lag (D) 0.5 lag or lead 76. If P c and P sc represent core and full load ohmic losses respectively. The maximum KVA delivered to load corresponding to maximum efficiency is equal to rated KVA multiplied by (A) P c / P sc (B) P c / P sc (C) (P c / P sc ) 2 (D)( P sc / P c ) If P 1 and P 2 be the iron and copper losses of a transformer at full load and the maximum efficiency is at 75% of the full load, than what is the ratio of P 1 and P 2 (A) 9/16 (B) 10/16 (C) ¾ (D) 3/ What is load at which maximum efficiency occurs in case of a 100 KVA transformer with iron loss of 1 KW and full load copper loss of 2 KW? (A) 100 KVA (B) 70.7 KVA (C) 50.5 KVA (D) 25.2 KVA 79. A 500 KVA transformer has constant loss of 500 W and cooper looses at full load are 2000 W. then at what load, is the efficiency maximum (A) 250 KVA (B) 500 KVA (C) 1000 KVA (D) 125 KVA 80. A 2 KVA transformer has iron loss of 150 W and full load copper loss of 250 W. the maximum efficiency of the transformer would occur when the total loss is (A) 500 W (B) 400 W (C) 300 W (D) 275 W

11 81. If P i be the iron loss and P c be the copper loss on full load, then which of the following condition had to be satisfied to obtained maximum efficiency at ¾ full load (A) P c = 3 P i /4 (B) P c = 4P i /3 (C) P c = 16 P i /9 (D) P c = 9P i / 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) 86.7% (B) 88.26% (C) 88.9% (D) 87.8% 83. The all day efficiency of a distribution transformer will be high with low (A) Copper losses (B) Iron losses (C) Operating temperature (D) Copper as well as iron losses 84. The all day efficiency of a transformer depends primarily on (A) Its copper loss (B) The amount of load (C) The duration of load (D) Both (B) and (C) 85. The desirable properties of transformer core material are (A) Low permeability and low hysteresis loss (B) High permeability and high hysteresis loss (C) High permeability and low hysteresis loss (D) Low permeability and high hysteresis loss 86. The use of higher flux density in the transformer design (A) Reduces the weight per KVA (B) Increase the weight per KVA (C) Has no relation with the weight of transformer (D) Increase the weight per KW 87. What does the use of higher flux density value in a transformer design lead to (A) Increase in weight per KVA (B) Decrease in weight per KVA (C) Reduced iron looses (D) Reduced copper looses 88. The size of the transformer core depends upon (A) Frequency (B) permissible flux density in the core material. (C) area of the core (D) both (A) and (B) 89. Ferrite cores are employed in high frequency transformer due to their (A) Low resistance (B) high resistance (C) low permeability (D) high hysteresis loss 90. Cores of large power transformers are made from which one of the following (A) Hot-rolled steel

12 (B) Cold-rolled non grain oriented steel (C) Cold-rolled grain oriented steel (D) Ferrite 91. Grain oriented laminated sheet steel in transformer reduces (A) Copper loss (B) eddy current loss (C) hysteresis loss (D) none of the above 92. Which of the following will improve the mutual coupling between primary and secondary circuits? (A) Transformer oil of high breakdown voltage (B) High reluctance magnetic core (C) Winding material of high resistivity (D) Low reluctance magnetic core 93. In order the reduce the hysteresis loss (A) Core may be laminated (B) Silicon steel may be used as the core material (C) Core may be constructed with any permanent magnet material such as Alnico (D) Core may be impregnated with varnish 94. Why is the core of the transformer built up of laminations? (A) To reduce eddy current loss (B) For convenience of fabrication (C) No specific advantage (D) For increase the permeability 95. When are eddy current losses in a transformer reduced? (A) If lamination are thick (B) If the number of turns in primary winding is reduced (C) If the number of turns in secondary winding is reduced (D) If lamination are thin 96. The yoke section of transformers are coated with an enamel layer in order to (A) Reduce hum (B) Attain adhesion between lamination (C) Insulate laminations from each other (D) Prevent corrosion of the laminations 97. The joint in the transformer core laminations are staggered so as to (A) Avoid continues gap causing increase in magnetizing current (B) Increase the mechanical strength of the assembled core (C) Avoid under humming noise (D) Facilitate assembly of core after putting performed coils on the core (E) All of the above 98. For CRGOS mitred overlap is preferred for the core yoke joints as it

13 (A) Reduces the magnetizing current and also the core losses. (B) Improves the mechanical strength (C) Reduce magnetostriction. (D) Makes better use of core space 99. The degree of mechanical vibrations caused by core laminations in a transformer depends on (A) Size of laminations (B) Gauge of laminations (C) Tightness of laminations (D) All of the above 100. The noise, in a transformer caused by vibration of laminations set by magnetic forces, is termed as (A) Zoom (B) hum (C) buzz (D) none of these 101. The primary and secondary winding are interlaced for (A) Easiness of coil making (B) reduced leaking reactance (C) reduced cost (D) uniform heating 102. The leakage flux of primary and secondary winding can be reduced to the maximum by (A) Winding primary and secondary coils on separate limbs (B) Winding primary and secondary coils one upon the other coaxially (C) Increasing the number of turns (D) Employing low permeability magnetic material core 103. The concentric winding are used in core type transformers with winding placed next to the core (A) Lv (B) primary (C) hv (D) secondary 104. Low voltage winding are placed next to the core in the case of concentric windings as in this case is/are reduced (A) Hysteresis loss (B) leakage fluxes (C) eddy current loss (D) copper loss (E) insulation requirement 105. In a power transformer (A) Primary winding is always wound with many turns of thin wire (B) Secondary winding is always wound with lesser number of turns of thin wire (C) Low voltage winding is always wound with lesser number of turns of thicker wire (D) High voltage winding is always wound with larger number of turns of thicker wire 106. In transformer, the primary and secondary are interlaced so that (A) There may be maximum flux linkage between the two windings (B) Copper is saved (C) both (A) and (B) (D) statement is false 107. In a large capacity transformer, 5% of the turns at the end of hv winding are provided with extra insulation so as to provide protection (A) Against corona

14 (B) against lighting (C) due to surges occurring during switching operations (D) all of the above 108. When a transformer winding suffers a short circuit, the adjoining turn of the same winding experienced (A) An attractive force (B) a repulsive force (C) no force 109. Under short circuit condition, the winding of a transformer having 5% impendence will experience a redial force (A) 5 time of full load value (B) 20 time of full load value (C) 25 time of full load value (D) 400 time of full load value 110. Major insulation in a transformer is the insulation between the (A) 1 v winding and core (B) 1 v and hv windings (C) Turns of the winding turns (D) Both (A) and (B) 111. Minor insulation in a transformer is the insulation between the (A) 1 v winding and core (B) 1 v and hv windings (C) Turns of the winding (D) Layers of the winding (E) Both (C) and (D) 112. In a transformer, an insulating material may fail due to (A) Moisture (B) dust (C) voids in the winding (D) any one or more of the above 113. The function of oil in a transformer is (A) To provide insulation and cooling (B) To provide protection against lightning (C) To provide protection against short circuit (D) To provide lubrication 114. The color of fresh dielectric oil used in transformer is (A) Dark brown (B) pale yellow (C) pale pink (D) white grey 115. The transformer oil should have (A) Low volatility (B) high dielectric strength (C) good resistance to emulsion with water (D) low viscosity to provide good heat transformer (E) all of the above 116. Transformer oil must be free from

15 (A) Moisture (B) sludge (C) gases (D) sulphur 117. The core and winding of a transformer are put in a steel tank in order to (A) Make it suitable for outdoor operation (B) Provide protection against mechanical damages and provide additional cooling (C) Improve its appearance (D) All of the above 118. Conservator (for transformer ) is used (A) To take up the expansion of oil due to temperature rise (B) To act as an oil storage (C) For better cooling of transformer (D) None of the above 119. Sludge formation in transformer oil is due to which one of the following? (A) Ingress of dust particles and moisture in the oil (B) Appearance of small fragment of paper, varnish cotton and other organic materials in the oil. (C) Chemical reaction of transformer oil with the insulating materials (D) Oxidation of transformer oil In a power transformer, the breather is provided in order to (A) Filter transformer oil (B) Prevent ingress of moisture with air (C) Provide oxygen to the cooling oil (D) Provide fresh air increasing cooling effect The chemical used in breather of transformer should have the quality of (A) Absorbing moisture (B) Ionizing air (C) Cleansing the transformer oil (D) None of the above 122. Malfunctioning of the Buchholz relay may be caused due to (A) Heavy external short circuit (B) Improper breather action (C) Dropping of oil level below the relay level during operation (D) Excessive overheating 123. A Buchholz relay is used for (A) Protection of a transformer against all internal faults (B) Protection of a transformer against external faults (C) Protection of a transformer against both internal and external faults (D) Protection of induction motor 124. Which is the arrangement of winding in a core type single phase transformer?

16 (A) Half lv inside and half hv outside on each core limb (B) Lv on one core limb and hv on the other (C) Sandwiched lv and hv discs on each core limb (D) Half hv inside and hv outside on each core limb 125. For core type power transformer, both primary and secondary winding have circular coil sections, as it (A) Reduced core material requirement and so also reduces the core loss (B) Gives the strongest mechanical shape (C) Is easier to wind (D) Reduced the copper requirement With stepping in construction of transformer core (A) Copper losses are reduced (B) Copper is saved (C) High flux density can be achieved (D) Mechanical strength to the core is improved (E) Both (A) and (B) 127. A shall type transformer is commonly used at it has (A) Two magnetic path (B) Reduced magnetic flux leakage (C) Reduced copper losses (D) Both (A) and (B) 128. Spiral core transformer, in which core is made up of steel strip has the advantage(s) of (A) Minimum looses (B) lighter construction (C) lesser weight (D) all of these 129. Distribution transformer have core losses (A) > copper losses (B) < copper losses (C) = copper loss (D) = ½ (copper losses) 130. Distribution transformer are designed to have maximum efficiency nearly at of full load (A) 100% (B) 70% (C) 25% (D) 10% 131. A distribution transformer is selected on the basis of (A) Voltage regulation (B) efficiency (C) all day efficiency (D) none of these 132. The distribution transformers are designed with minimum possible iron losses. This is because (A) The primary of a distribution transformer is energized for all the 24 hours (B) Iron losses will cause undue heating (C) The iron losses may cause damage to the insulation

17 (D) None of the above 133. Which part of transformer is subjected to maximum heating (A) Frame (B) core (C) winding (D) oil 134. Which of the following method is employed for cooling of power transformers of rating not exceeding 10 MVA? (A) Air blast cooling (B) natural oil cooling (C) forced oil cooling (D) natural air cooling 135. Transformer are rated in KVA instead of KW because (A) Load PF is often not known. (B) KVA is fixed where KW depends on load PF. (C) Total transformer load depends on volt-ampere (D) It has become customary 136. Two 3-limb phase delta-star connected transformers are supplied from the same source. One of the transformers is Dy1 and the other is Dy11 connection. The phase difference between the corresponding phase voltage of the secondary s would be (A) 0 (B) 30 (C) 60 (D) Which there phase connection can be used in a transformer to introduce a phase difference of 30 between its output and corresponding input line voltage? (A) Star-star (B) star-delta (C) delta-delta (D) delta-zigzag 138. Three single phase transformers are connected to form 3-phase transformer bank. The transformer are connected in the following manner The transformer connection will be represented by (A) Yd0 (B) Yd1 (C) Yd6 (D) Yd Which of the following connection of transformer will give the highest secondary voltage? (A) Delta primary, delta secondary (B) Delta primary, star secondary

18 (C) Star primary, star secondary (D) Star primary, delta secondary 140. Transformer core lamination are coated with an enamel layer in order to (A) Reduce hum (B) attain adhesion between laminations (C) insulate laminations from each other (D) prevent corrosion of the laminations ANSWER KEY:- 1. (A) 45. (A) 89. (B) 133. (C) 2. (C) 46. (B) 90. (C) 134. (B) 3. (D) 47. (C) 91. (C) 135. (C) 4. (B) 48. (A) 92. (D) 136. (C) 5. (B) 49. (B) 93. (B) 137. (B) 6. (C) 50. (C) 94. (A) 138. (B) 7. (D) 51. (C) 95. (D) 139. (B) 8. (A) 52. (A) 96. (B) 140. (C) 9. (A) 53. (D) 97. (E) 10. (B) 54. (B) 98. (A) 11. (C) 55. (D) 99. (D) 12. (D) 56. (D) 100. (B) 13. (B) 57. (C) 101. (B) 14. (B) 58. (B) 102. (B) 15. (B) 59. (A) 103. (A) 16. (D) 60. (A) 104. (E) 17. (B) 61. (B) 105. (C) 18. (C) 62. (D) 106. (A) 19. (D) 63. (C) 107. (C) 20. (B) 64. (B) 108. (A) 21. (D) 65. (C) 109. (D) 22. (C) 66. (A) 110. (D) 23. (B) 67. (D) 111. (E)

19 24. (B) 68. (C) 112. (D) 25. (D) 69. (C) 113. (A) 26. (B) 70. (A) 114. (B) 27. (C) 71. (D) 115. (E) 28. (C) 72. (C) 116. (A) 29. (A) 73. (C) 117. (B) 30. (C) 74. (A) 118. (A) 31. (D) 75. (B) 119. (D) 32. (A) 76. (B) 120. (B) 33. (B) 77. (A) 121. (A) 34. (C) 78. (B) 122. (C) 35. (A) 79. (A) 123. (A) 36. (D) 80. (C) 124. (A) 37. (C) 81. (C) 125. (B) 38. (D) 82. (D) 126. (E) 39. (A) 83. (D) 127. (D) 40. (C) 84. (D) 128. (D) 41. (D) 85. (C) 129. (B) 42. (B) 86. (A) 130. (B) 43. (D) 87. (B) 131. (C) 44. (D) 88. (D) 132. (A)

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