Electrical Machine Objective Questions and Answers PDF

GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS NO OF UNIT NAME QNS 1A DC GENERATORS 124...

GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS NO OF UNIT NAME QNS 1A DC GENERATORS 124 1B DC MOTORS 123 2 TRANSFORMERS 135 THREE PHASE INDUCTION 3A MOTORS 101 SINGLE PHASE INDUCTION 3B MOTORS 110 4 SYNCHRONOUS MOTORS 124 TRANSMISSION AND 5A DISTRIBUTION 102 5B CABLES 56 TOTAL 875 1. A. DC GENERATORS 1. Laminations of core are generally made of (a) case iron (b) carbon (c) silicon steel (d) stainless steel Ans: c 2. Which of the following could be lamina-proximately the thickness of laminations of a D.C. machine ? (a) 0.005 mm (b) 0.05 mm (c) 0.5 m (d) 5 m Ans: c 3. The armature of D.C. generator is laminated to (a) reduce the bulk (b) provide the bulk (c) insulate the core (d) reduce eddy current loss Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS Ans: d 4. The resistance of armature winding depends on (a) length of conductor (b) cross-sectional area of the conductor (c) number of conductors (d) all of the above Ans: d 5. The field coils of D.C. generator are usually made of (a) mica (b) copper (c) cast iron (d) carbon Ans: b 6. The commutator segments are connected to the armature conductors by means of (a) copper lugs (b) resistance wires (c) insulation pads (d) brazing Ans: a 7. In a commutator (a) copper is harder than mica (b) mica and copper are equally hard (c) mica is harder than copper (d) none of the above Ans: c 8. In D.C. generators the pole shoes are fastened to the pole core by (a) rivets (b) counter sunk screws (c) brazing (d) welding Ans: b Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS 9. According to Fleming's right-hand rule for finding the direction of induced e.m.f., when middle finger points in the direction of induced e.m.f., forefinger will point in the direction of (a) motion of conductor (b) lines of force (c) either of the above (d) none of the above Ans: b 10. Fleming's right-hand rule regarding direction of induced e.m.f., correlates (a) magnetic flux, direction of current flow and resultant force (b) magnetic flux, direction of motion and the direction of e.m.f. induced (c) magnetic field strength, induced voltage and current (d) magnetic flux, direction of force and direction of motion of conductor Ans: b 11. While applying Fleming's right-hand rule to And the direction of induced e.m.f., the thumb points towards (a) direction of induced e.m.f. (b) direction of flux (c) direction of motion of the conductor if forefinger points in the direction of generated e.m.f. (d) direction of motion of conductor, if forefinger points along the lines of flux Ans: d 12. The bearings used to support the rotor shafts are generally (a) ball bearings (b) bush bearings (c) magnetic bearmgs (d) needle bearings Ans: a 13. In D.C. generators, the cause of rapid brush wear may be (a) severe sparking (b) rough commutator surface (c) imperfect contact (d) any of the above Ans: d Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS 14. In lap winding, the number of brushes is always (a) double the number of poles (b) same as the number of poles (c) half the number of poles (d) two Ans: b 15. For a D.C. generator when the number of poles and the number of armature conductors is fixed, then which winding will give the higher e.m.f. ? (a) Lap winding (b) Wave winding (c) Either of (a) and (b) above (d) Depends on other features of design Ans: b 16. In a four-pole D.C. machine (a) all the four poles are north poles (b) alternate poles are north and south (c) all the four poles are south poles (d) two north poles follow two south poles Ans: b 17. Copper brushes in D.C. machine are used (a) where low voltage and high currents are involved (b) where high voltage and small cur-rents are involved (c) in both of the above cases (d) in none of the above cases Ans: a 18. A separately excited generator as compared to a self-excited generator (a) is amenable to better voltage con-trol (b) is more stable (c) has exciting current independent of load current (d) has all above features Ans: d 19. In case of D.C. machines, mechanical losses are primary function of (a) current Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (b) voltage (c) speed (d) none of above Ans: c 20. Iron losses in a D.C. machine are independent of variations in (a) speed (b) load (c) voltage (d) speed and voltage Ans: b 21. In D.C. generators, current to the external circuit from armature is given through (a) commutator (b) solid connection (c) slip rings (d) none of above Ans: a 23. Brushes of D.C. machines are made of (a) carbon (b) soft copper (c) hard copper (d) all of above Ans: a 24. If B is the flux density, I the length of conductor and v the velocity of conductor, then induced e.m.f. is given by (a)Blv (b)Blv2 (c)Bl2v (d)Bl2v2 Ans: a 25. In case of a 4-pole D.C. generator provided with a two layer lap winding with sixteen coils, the pole pitch will be (a) 4 (b) 8 (c) 16 (d) 32 Ans: b Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS 26. The material for commutator brushes is generally (a) mica (b) copper (c) cast iron (d) carbon Ans: d 27. The insulating material used between the commutator segments is normally (a) graphite (b) paper (c) mica (d) insulating varnish Ans: c 28. In D.C. generators, the brushes on commutator remain in contact with conductors which (a) lie under south pole (b) lie under north pole (c) lie under interpolar region (d) are farthest from the poles Ans: c 29. If brushes of a D.C. generator are moved in order to bring these brushes in magnetic neutral axis, there will be (a) demagnetisation only (b) cross magnetisation as well as magnetisation (c) crossmagnetisation as well as demagnetising (d) cross magnetisation only Ans: c 30. Armature reaction of an unsaturated D.C. machine is (a) crossmagnetising (b) demagnetising (c) magnetising (d) none of above Ans: a 31. D.C. generators are connected to the busbars or disconnected from them only under the floating condition (a) to avoid sudden loading of the primemover (b) to avoid mechanicaljerk to the shaft (c) to avoid burning of switch contacts Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (d) all above Ans: d 32. Eddy currents are induced in the pole shoes of a D.C. machine due to (a) oscillating magnetic field (b) pulsating magnetic flux (c) relative rotation between field and armature (d) all above Ans: c 33. In a D.C. machine, short-circuited field coil will result in (a) odour of barning insulation (b) unbalanced magnetic pull producing vibrations (c) reduction of generated voltage for which excitation has to be increased to maintain the voltage (d) all above Ans: 34. Equilizer rings are required in case armature is (a) wave wound (b) lap wound (c) delta wound (d) duplex wound Ans: b 35. Welding generator will have (a) lap winding (b) wave winding (c) delta winding (d) duplex wave winding Ans: a 36. In case of D.C. machine winding, number of commutator segments is equal to (a) number of armature coils (b) number of armature coil sides (c) number of armature conductors (d) number of armature turns Ans: a 37. For a D.C. machines laboratory following type of D.C. supply will be suitable (a) rotary converter (b) mercury are rectifier (c) induction motor D.C. generator set Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (d) synchronous motor D.C. generator set Ans: c 38. The function of pole shoes in the case of D.C. machine is (a) to reduce the reluctance of the magnetic path (b) to spread out the flux to achieve uniform flux density (c) to support the field coil (d) to discharge all the above functions Ans: d 39. In the case of lap winding resultant pitch is (a) multiplication of front and back pitches (b) division of front pitch by back pitch (c) sum of front and back pitches (d) difference of front and back pitches Ans: d 40. A D.C. welding generator has (a) lap winding (b) wave moving (c) duplex winding (d) any of the above Ans: a 41. Which of the following statement about D.C. generators is false ? (a) Compensating winding in a D.C. machine helps in commutation (b) In a D. C. generator interpoles winding is connected in series with the armature winding (c) Back pitch and front pitch are both odd and approximately equal to the pole pitch (d) Equilizing bus bars are used with parallel running of D.C. shunt generators Ans: d 42. The demagnetising component of armature reaction in a D.C. generator (a) reduces generator e.m.f. (b) increases armature speed (c) reduces interpoles flux density (d) results in sparking trouble Ans: a 43. Magnetic field in a D.C. generator is produced by (a) electromagnets (b) permanent magnets (c) both (a) and (b) Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (d) none of the above Ans: a 44. The number of brushes in a commutator depends on (a) speed of armature (b) type of winding (c) voltage (d) amount of current to be collected Ans: d 45. Compensating windings are used in D.C. generators (a) mainly to reduce the eddy currents by providing local short-circuits (b) to provide path for the circulation of cooling air (c) to neutralise the cross-magnetising effect of the armature reaction (d) none of the above Ans: c 46. Which of the following components of a D.C, generator plays vital role for providing direct current of a D.C. generator ? (a) Dummy coils (b) Commutator (c) Eye bolt (d) Equilizer rings Ans: b 47. In a D.C. generator the ripples in the direct e.m.f. generated are reduced by (a) using conductor of annealed copper (b) using commutator with large number of segments (c) using carbon brushes of superior quality (d) using equiliser rings Ans: c 48. In D.C. generators, lap winding is used for (a) high voltage, high current (b) low voltage, high current (c) high voltage, low current (d) low voltage, low current Ans: b 49. Two generators A and B have 6-poles each. Generator A has wave wound armature while generator B has lap wound armature. The ratio of the induced e.m.f. is generator A and B will be (a) 2 : 3 Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (b) 3 : 1 (c) 3 : 2 (d) 1 : 3 Ans: b 50. The voltage drop for which of the following types of brush can be expected to be least ? (a) Graphite brushes (b) Carbon brushes (c) Metal graphite brushes (d) None of the above Ans: c 51. The e.m.f. generated by a shunt wound D.C. generator isE. Now while pole flux remains constant, if the speed of the generator is doubled, the e.m.f. generated will be (a) E/2 (b) 2E (c) slightly less than E (d) E Ans: b 52. In a D.C. generator the actual flux distribution depends upon (a) size of air gap (b) shape of the pole shoe (c) clearance between tips of the ad¬jacent pole shoes (d) all of the above Ans: 53. The armature core of a D.C. generator is usually made of (a) silicon steel (b) copper (c) non-ferrous material (d) cast-iron Ans: a 9.63. Satisfactory commutation of D.C. machines requires (a) brushes should be of proper grade and size (b) brushes should smoothly run in the holders (c) smooth, concentric commutator properly undercut (d) all of the above Ans: d 54. Open circuited armature coil of a D.C. machine is (a) identified by the scarring of the commutator segment to which open circuited coil is Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS connected (b) indicated by a spark completely around the commutator (c) both (a) and (b) (d) none of the above Ans: c 55. In a D.C. machine, fractional pitch winding is used (a) to increase the generated voltage (b) to reduce sparking (c) to save the copper because of shorter end connections (d) due to (b) and (c) above Ans: 56. For the parallel operation of two or more D.C. compound generators, we should ensure that (a) voltage of the incoming generator should be same as that of bus bar (b) polarity of incoming generator should be same as that of bus bar (c) all the series fields should be run in parallel by means of equilizer connection (d) series fields of all generators should be either on positive side or negative side of the armature (e) all conditions mentioned above should be satisfied Ans: d 57. D.C. series generator is used (a) to supply traction load (b) to supply industrial load at constant voltage (c) voltage at the toad end of the feeder (d) for none of the above purpose Ans: c 58. Following D.C. generator will be in a position to build up without any residual magnetism in the poles (a) series generator (b) shunt generator (c) compound generator (d) self-excited generator Ans: d 59. Interpole flux should be sufficient to (a) neutralise the commutating self induced e.m.f. (b) neutralise the armature reaction flux (c) neutralise both the armature reaction flux as well as commutating e.m.f. induced in the coil Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (d) perform none of the above functions Ans: c 60. D.C. generator generally preferred for charging automobile batteries is (a) series generator (b) shunt generator (c) long shunt compound generator (d) any of'the above Ans: c 61. In a D.C. generator the number of mechanical degrees and electrical degrees will be the same when (a) r.p.m. is more than 300 (b) r.p.m. is less than 300 (c) number of poles is 4 (d) number of poles is 2 Ans: d 62. Permeance is the reciprocal of (a) flux density (b) reluctance (c) ampere-turns (d) resistance Ans: b 63. In D.C. generators the polarity of the interpoles (a) is the same as that of the main pole ahead (b) is the same as that of the immediately preceding pole (c) is opposite to that of the main pole ahead (d) is neutral as these poles do not play part in generating e.m.f. Ans: a 64. The e.m.f. generated in a D.C. generator is directly proportional to (a) flux/pole (b) speed of armature (c) number of poles (d) all of the above Ans: b 65. In a D.C. generator the magnetic neutral axis coincides with the geometrical neutral axis, when (a) there is no load on|he generator (b) the generator runs on full load Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (c) the generator runs on overload (d) the generator runs on designed speed Ans: a 66. In a D.C. generator in order to reduce sparking at brushes, the self-induced e.m.f. in the coil is neutralised by all of the following except (a) interpoles (b) dummy coils (c) compensating winding (d) shifting of axis of brushes Ans: b 67. In D.C. generators on no-load, the air gap flux distribution in space is (a) sinusoidal (b) triangular (c) pulsating (d) flat topped Ans: d 68. A shunt generator running at 1000 r.p.m. has generated e.m.f. as 200 V. If the speed increases to 1200 r.p.m., the generated e.m.f. will be nearly (a) 150 V (b) 175 V (c) 240 V (d) 290 V Ans: c 69. The purpose of providing dummy coils in a generator is (a) to reduce eddy current losses (b) to enhance flux density (c) to amplify voltage (d) to provide mechanical balance for the rotor Ans: d 70. In a shunt generator the voltage build up is generally restricted by (a) speed limitation (b) armature heating (c) insulation restrictions (d) saturation of iron Ans: 71. If a D.C. generator fails to build up the probable cause could not be (a) imperfect brush contact Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (b) field resistance less than the critical resistance (c) no residual magnetism in the generator (d) faulty shunt connections tending to reduce the residual magnetism Ans: b 72. Flashing the field of D.C. generator means (a) neutralising residual magnetism (b) creating residual magnetism by a D.C. source (c) making the magnetic losses of forces parallel (d) increasing flux density by adding extra turns of windings on poles Ans: b 73. The e.m.f. induced in the armature of a shunt generator is 600 V. The armature resistance is 0.1 ohm. If the armature current is 200 A, the terminal voltage will be (a) 640 V (b) 620 V (c) 600 V (d) 580 V Ans: d 74. In a D.C. generator the critical resistance refers to the resistance of (a) brushes (b) field (c) armature (d) load Ans: b 75. To achieve sparkless commutation brushes of a D.C. generator are rockedm ahead so as to bring them (a) just ahead of magnetic neutral axis (b) in magnetic neutral axis (c) just behind the magnetic neutral axis Ans: a 76. Armature coil is short circuited by brushes when it lies (a) along neutral axis (b) along field axis (c) in any of the above positions (d) in none of the above positions Ans: a 77. A cumulatively compounded long shunt generator when operating as a motor would be (a) cumulatively compounded long shunt Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (b) differentially compounded long shunt (c) cumulatively compounded short shunt (d) differentially compounded short shunt Ans: b 78. To avoid formation of grooves in the commutator of a D.C. machine (a) the brushes of opposite polarity should track each other (b) the brushes of same polarity should track each other (c) brush position has no effect on the commutator grooving Ans: a 79. The following constitute short-circuit in the armature winding. (a) Insulation failure between two com-mutator bars (6) Insulation failure between two turns of a coil (c) Two of more turns of the same coil getting grounded (d) All of the above Ans: d 80. The rapid wear of brushes takes place due to (a) abrasion from dust (b) excessive spring pressure (c) rough commutator bars (d) high mica insulation between com-mutation bars (e) all of the above factors Ans: e 81. Number of tappings for each equilizer ring is equal to (a) number of pole pairs (b) number of poles (c) number of parallel paths (d) number of commutator segments Ans: a 82. A D.C. generator can be considered as (a) rectifier (b) primemover (c) rotating amplifier (d) power pump Ans: c 83. In any rotating machine that part which houses the conductors and in which e.m.f. induced is to be utilised is called (a) rotor Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (b) stator (c) field (d) armature Ans: d 84. In a D.C. machine stray loss is the sum of (a) total copper loss and mechanical loss (b) armature copper loss and iron loss (c) shunt field copper loss and mechanical loss (d) iron loss and mechanical loss Ans: d 85. Lap winding is composed of (a) any even number of conductors (b) any odd number of conductors (c) that even number which is exact multiple of poles + 2 (d) that even number which is exact multiple of poles Ans: a 86. In a D.C. generator in case the resistance of the field winding is increased, then output voltage will (a) increase (b) decrease (c) remain unaffected (d) fluctuate heavily Ans: b 87. An exciter for a turbo generator is a (a) separately excited generator (b) shunt generator (c) series generator (d) compound generator Ans: b 88. In case of a flat compounded generator (a) voltage generated is less than the rated voltage (b) generated voltage is proportional to the load on the generator (c) voltage remains constant irrespec¬tive of the load (d) speed varies in proportion to the load on the generator Ans: c 89. Which of the following generator will have negligible terminal voltage while running on no-load ? Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (a) Series generator (b) Shunt generator (c) Compound generator (d) Separately excited generator Ans: a 90. Which of the following D.C. generators will be in a position to build up without any residual magnetism in the poles ? (a) Series generator (b) Shunt generator (c) Compound generator (d) None of the above Ans: d 91. In over compounded generator, full load terminal voltage is (a) almost zero (b) less than noload terminal voltage (c) more than noload terminal voltage (d) equal to no-load terminal voltage Ans: c 92. In a level compounded D.C. generator, full load terminal voltage is (a) negligibly low (b) equal to no-load terminal voltage (c) more than no-load terminal voltage (d) less than no-load terminal voltage Ans: b 93. The terminal voltage of a D.C. shunt generator drops on load because of all of the following reasons except (a) armature reaction (b) armature resistance drop (c) field weakening due to armature reaction and armature (d) commutation Ans: d 94. In a D.C. generator (a) external resistance = internal char-acteristic - armature reaction (b) internal characteristic = magnetisation characteristic - ohmic drop (c) external characteristic = magnetisation characteristic - ohmic drop - armature reaction (d) magnetisation characteristic = external characteristic Ans: c Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS 95. A sinusoidal voltage of 5 Hz is applied to the field of a shunt generator. The armature voltage wave (a) will be zero (b) will be of 5 Hz (c) willbeof5xiVHz (d) will be of v Hz 5 Ans: b 96. A 220 V D.C. generator is run at full speed without any excitation. The open circuit voltage will be (a) zero (b) about 2 V (c) about 50 V (d) 220 V Ans: b 97. In a separately excited generator supplying rated load the armature reaction , (a) is always present (b) is always absent (c) may be sometimes present (d) none of the above Ans: a 98. If residual magnetism is present in a D.C. generator, the induced e.m.f. at zero speed will be (a) zero (b) small (c) the same as rated voltage (d) high Ans: a 99. Armature reaction in a generator results in (a) demagnetisation of leading pole tip and magnetisation of trailing pole tip (b) demagnetisation of trailing pole tip and magnetisation of leading pole tip (c) damagnetising the centre of all poles (d) magnetising the centre of all poles Ans: a 100. Following energized winding of a D.C. machine should not be opened as it would produce high inductive voltage which may be dangerous to personnel and may cause its own insulation failure. (a) Series field (b) Compensating field Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (c) Inter pole field (d) Shunt field Ans: d 101. Wave winding is composed of (a) any even number of conductors (b) any odd number of conductors (c) that even number which is exact multiple of poles + 2 (d) that even number which is exact multiple of poles Ans: c 102. The critical resistance of the D.C. generator is the resistance of (a) field (b) brushes (c) armature (d) load Ans: a 103. When two D.C. series generators are running in parallel, an equilizer bar is used (a) to increase the speed and hence generated e.m.f. (b) to increase the series flux (c) so that two similar machines will pass approximately equal currents to the load (d) to reduce the combined effect of ar-mature reaction of both machines Ans: c 104. Which of the following generating machine will offer constant voltage on all loads ? (a) Self-excited generator (b) Separately excited generator (c) Level compounded generator. (d) All of the above Ans: c 105. Which of the following generators will be preferred if they are required to be run in parallel ? (a) Shunt generators (b) Series generators (c) Compound generators (d) None of the above Ans: a 106. Two generators are running in parallel. One of the generators may run as motor for which of the following reasons ? (a) The direction of that generator is reversed Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (b) The speed of that generator is increased (c) The field of that generator is weakened (d) That generator takes large share of loads Ans: d 107. A D.C. generator works on the principle of (a) Lenz's law (b) Ohm's law (c) Faraday's law of electromagnetic induction (d) none of the above Ans: c 108. A series generator can self-excite (a) only if the load current is zero (b) only if the load current is not zero (c) irrespective of the value of load current (d) none of the above Ans: b 109. A shunt generator can self-excite (a) only if the resistance of the field circuit is less than critical value (b) only if the resistance of the field circuit is greater than critical value (c) irrespective of the value of the resis-tance in the field circuit Ans: a 110. The terminal voltage of a series generator is 150 V when the load current is 5 A. If the load current is increased to 10 A, the terminal voltage will be (a) 150 V (b) less than 150 V (c) greater than 150 V (d) none of the above Ans: c 111. The open circuit voltage of a compound generator is 250 V. At full load the terminal voltage (a) will be less than 250 V (b) will always be 250 V (c) may be greater or less than 250 V (d) none of the above Ans: c 112. Two D.C. shunt generators, each with armature resistance of 0.02 ohm and field resistance of 50 ohm run in parallel and supply a total current of 1000 amperes to the load Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS circuit. If their e.m.fs. are 270 V and 265 V, their bus bar voltage will be (a) 270 V (b) 267.5 V (c) 265 V (d) 257.4 V Ans: b 113. The essential condition for parallel operation of two D.C. generators is that they have ' (a) same kW rating (b) the same operation r.p.m. (c) the same drooping voltage charac-teristics (d) same percentage regulation Ans: c 114. When two D.C. generators are running in parallel an equilizer bar is used (a) to increase the series flux (b) to increase the generated e.m.f. (c) to reduce the combined effect of ar-mature reaction of both the machines (d) so that the two identical machines will pass approximately equal currents to the load Ans: d 115. With a D.C. generator which of the following regulation is preferred ? (a) 100% regulation (b) infinite regulation (c) 50% regulation (d) 1% regulation Ans: d 116. Which generator would you prefer for feeding long D.C. transmission lines ? (a) Series generator (b) Shunt generator (c) Over compound generator (d) Flat compound generator Ans: c 117. In a D.C. generator the critical resistance can be increased by (a) increasing its field resistance (b) decreasing its field resistance (c) increasing its speed (d) decreasing its speed Ans: c Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS 118. The number of armature parallel paths in a two-pole D.C. generator having duplex lap winding is (a) 2 (b) 4 (c) 6 (d) 8 Ans: b 119. For both lap and wave windings, there are as many commutator bars as the number of (a) slots (b) armature conductors (c) winding elements (d) poles Ans: c 120. The series field of a short-shunt D.C. generator is excited by (a) external current (b) armature current (c) shunt current (d) load current Ans: d 121. As a result of armature reaction, the reduction in the total mutual air gap flux in a D.C. generator is approximately (a) 40 percent (b) 25 percent (c) 10 percent (d) 5 percent Ans: d 122. Shunt generators are most suited for stable parallel operation because of their (a) rising voltage characteristics (b) identical voltage characteristics (c) drooping voltage characteristics (d) linear voltage characteristics Ans: c 123. The main factor which leads to unstable parallel operation of flat and over compounded generators is (a) their rising voltage characteristics (b) unequal number of turns in their series field windings (c) unequal speed regulation of their primemovers (d) unequal series field resistances Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS Ans: a 124. If a self excited D.C. generator after being installed, fails to build up on its first trial run, the first thing to do is to (a) reverse the field connections (b) increase the field resistance (c) increase the speed of primemover (d) check armature insulation resis¬tance Ans: a 1. B. DC MOTOR 1. No-load speed of which of the following motor will be highest ? (a) Shunt motor (b) Series motor (c) Cumulative compound motor (d) Differentiate compound motor Ans: b 2. The direction of rotation of a D.C. series motor can be changed by (a) interchanging supply terminals (b) interchanging field terminals (c) either of (a) and (b) above (d) None of the above Ans: b 3. Which of the following application requires high starting torque ? (a) Lathe machine (b) Centrifugal pump (c) Locomotive (d) Air blower Ans: c 4. If a D.C. motor is to be selected for conveyors, which rriotor would be preferred ? (a) Series motor (b) Shunt motor (c) Differentially compound motor (d) Cumulative compound motor Ans: a 5. Which D.C. motor will be preferred for machine tools ? (a) Series motor (b) Shunt motor Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (c) Cumulative compound motor (d) Differential compound motor Ans: b 6. Differentially compound D.C. motors can find applications requiring (a) high starting torque (b) low starting torque (c) variable speed (d) frequent on-off cycles Ans: b 7. Which D.C. motor is preferred for elevators ? (a) Shunt motor (b) Series motor (c) Differential compound motor (d) Cumulative compound motor Ans: d 8. According to Fleming's left-hand rule, when the forefinger points in the direction of the field or flux, the middle finger will point in the direction of (a) current in the conductor aovtaat of conductor (c) resultant force on conductor (d) none of the above Ans: a 9. If the field of a D.C. shunt motor gets opened while motor is running (a) the speed of motor will be reduced % (b) the armature current will reduce (c) the motor will attain dangerously high speed 1 (d) the motor will continue to nuvat constant speed Ans: c 10. Starters are used with D.C. motors because (a) these motors have high starting torque (b) these motors are not self-starting (c) back e.m.f. of these motors is zero initially (d) to restrict armature current as there is no back e.m.f. while starting Ans: d 11. In D.C. shunt motors as load is reduced (a) the speed will increase abruptly (b) the speed will increase in proportion to reduction in load (c) the speed will remain almost/constant Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (d) the speed will reduce Ans: c 12. A D.C. series motor is that which (a) has its field winding consisting of thick wire and less turns (b) has a poor torque (c) can be started easily without load (d) has almost constant speed Ans: a 13. For starting a D.C. motor a starter is required because (a) it limits the speed of the motor (b) it limits the starting current to a safe value (c) it starts the motor (d) none of the above Ans: b 14. The type of D.C. motor used for shears and punches is (a) shunt motor (b) series motor (c) differential compoutid D.C. motor (d) cumulative compound D.C. motor Ans: d 15. If a D.C. motor is connected across the A.C. supply it will (a) run at normal speed (b) not run (c) run at lower speed (d) burn due to heat produced in the field winding by.eddy currents Ans: d 16. To get the speed of D.C, motor below the normal without wastage of electrical energy is used. (a) Ward Leonard control (b) rheostatic control (c) any of the above method (d) none of the above method Ans: a 17. When two D.C. series motors are connected in parallel, the resultant speed is (a) more than the normal speed (b) loss than the normal speed (c) normal speed Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (d) zero Ans: c 18. The speed of a D.C. shunt motor more than its full-load speed can be obtained by (a) decreasing the field current (b) increasing the field current (c) decreasing the armature current (d) increasing the armature current Ans: a 19. In a D.C. shunt motor, speed is (a) independent of armature current (b) directly proportional to the armature current (c) proportional to the square of the current (d) inversely proportional to the armature current Ans: a 20. A direct on line starter is used: for starting motors (a) iip to 5 H.P. (b) up to 10 H.P. (c) up to 15 H.P. (d) up to 20 H.P. Ans: a 21. What will happen if the back e.m.f. of a D.C. motor vanishes suddenly? (a) The motor will stop (b) The motor will continue to run (c) The armature may burn (d) The motor will run noisy Ans: c 22. In case of D.C. shunt motors the speed is dependent on back e.m.f. only because (a) back e.m.f. is equal to armature drop (b) armature drop is negligible (c) flux is proportional to armature current (d) flux is practically constant in D:C. shunt motors Ans: d 23. In a D.C. shunt motor, under the conditions of maximum power, the current in the armature will be (a) almost negligible (b) rated full-load current (c) less than full-load current Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (d) more than full-load current Ans: d 24. These days D.C. motors are widely used in (a) pumping sets (b) air compressors (c) electric traction (d) machine shops Ans: c 25. By looking at which part of the motor, it can be easily confirmed that a particular motor is D.C. motor? (a) Frame (b) Shaft (c) Commutator (d) Stator Ans: c 26. In which of the following applications D.C. series motor is invariably tried? (a) Starter for a car (b) Drive for a water pump (c) Fan motor (d) Motor operation in A.C. or D.C. Ans: a 27. In D.C. machines fractional pitch winding is used (a) to improve cooling (b) to reduce copper losses (c) to increase the generated e.m.f. (d) to reduce the sparking Ans: d 28. A three point starter is considered suitable for (a) shunt motors (b) shunt as well as compound motors (c) shunt, compound and series motors (d) all D.C. motors Ans: b 29. In case-the conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be (a) 100% (b) around 90% Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (c) anywhere between 75% and 90% (d) less than 50% Ans: d 30. The ratio of starting torque to full-load torque is least in case of (a) series motors (b) shunt motors (c) compound motors (d) none of the above Ans: b 32. In D.C. motor which of the following can sustain the maximum temperature rise? (a) Slip rings (b) Commutator (c) Field winding (d) Armature winding Ans: c 33. Which of the following law/rule can he used to determine the direction of rotation of D.C. motor ? (a) Lenz's law (b) Faraday's law (c) Coloumb's law (d) Fleming's left-hand rule Ans: d 34. Which of the following load normally needs starting torque more than the rated torque? (a) Blowers (b) Conveyors (c) Air compressors (d) Centrifugal pumps Ans: b 35. The starting resistance of a D.C. motor is generally (a) low (b) around 500 Q (c) 1000 Q (d) infinitely large Ans: a 36. The speed of a D.C. series motor is (a) proportional to the armature current Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (b) proportional to the square of the armature current (c) proportional to field current (d) inversely proportional to the armature current Ans: d 37. In a D.C. series motor, if the armature current is reduced by 50%, the torque of the motor will be equal to (a) 100% of the previous value (b) 50% of the previous value (c) 25% of the previous value (d) 10% of the previous value (e) none of the above Ans: c 38. The current drawn by the armature of D.C. motor is directly proportional to (a) the torque required (b) the speed of the motor (c) the voltage across the terminals (d) none of the above Ans: a 39. The power mentioned on the name plate of an electric motor indicates (a) the power drawn in kW (b) the power drawn in kVA (c) the gross power (d) the output power available at the shaft Ans: d 40. Which D.C. motor has got maximum self loading property? (a) Series motor (b) Shunt motor (c) Cumulatively compounded 'motor (d) Differentially compounded motor Ans: d 41. Which D.C. motor will be suitable alongwith flywheel for intermittent light and heavy loads? (a) Series motor (b) Shunt motor (c) Cumulatively compounded motor (d) Differentially compounded motor Ans: c Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS 42. If a D.C. shunt motor is working at no load and if shunt field circuit suddenly opens (a) nothing will happen to th£ motor (b) this will make armature to take heavy current, possibly burning it (c) this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses (d) motor will run at very slow speed Ans: c 43. D.C. series motors are used (a) where load is constant (b) where load changes frequently (c) where constant operating speed is needed (d) in none of the above situations. Ans: d 44. For the same H.P. rating and full load speed, following motor has poor starting torque (a) shunt (b) series (c) differentially compounded (d) cumulativelyc'ompounded Ans: c 45. In case of conductively compensated D.C. series motors, the compensating winding is provided (a) as separately wound unit (6) in parallel with armature winding (c) in series with armature winding (d) in parallel with field winding Ans: c 46. Sparking at the commutator of a D.C. motor may result in (a) damage to commutator segments (b) damage to commutator insulation (c) increased power consumption (d) all of the above Ans: d 47. Which of the following motor is preferred for operation in highly explosive atmosphere ? (a) Series motor (b) Shunt motor (c) Air motor (d) Battery operated motor Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS Ans: c 48. If the supply voltage for a D.C. motor is increased, which of the following will decrease ? (a) Starting torque (b) Operating speed (c) Full-load current (d) All of the above Ans: c 49. Which one of the following is not the function of pole shoes in a D.C. machine ? (a) To reduce eddy current loss (b) To support the field coils (c) To spread out flux for better unifor-mity (d) To reduce the reluctance of the mag-netic path Ans: a 50. The mechanical power developed by a shunt motor will be maximum when the ratio of back e.m.f. to applied voltage is (a) 4.0 (b) 2.0 (c) 1.0 (d) 0.5 Ans: d 51. The condition for maximum power in case of D.C. motor is (a) back e.m.f. = 2 x supply voltage (b) back e.m.f. = | x supply voltage (c) supply voltage = | x back e.m.f. (d) supply voltage = back e.m.f. Ans: b 52. For which of the following applications a D.C. motor is preferred over an A.C. motor ? (a) Low speed operation (b) High speed operation (c) Variable speed operation (d) Fixed speed operation Ans: c 53. In D.C. machines the residual magnetism is of the order of (a) 2 to 3 per cent (6) 10 to 15 per cent (c) 20 to 25 per cent Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (d) 50 to 75 per cent Ans: a 54. Which D.C. motor is generally preferred for cranes and hoists ? (a) Series motor (b) Shunt motor (c) Cumulatively compounded motor (d) Differentially compounded motor Ans: a 55. Three point starter can be used for (a) series motor only (b) shunt motor only (c) compound motor only (d) both shunt and compound motor Ans: d 56. Sparking, is discouraged in a D.C. motor because (a) it increases the input power con-sumption (b) commutator gets damaged (c) both (a) and (b) (d) none of the above Ans: b 57. Speed control by Ward Leonard method gives uniform speed variation (a) in one direction (b) in both directions (c) below normal speed only (d) above normal speed only. Ans: b 58. Flywheel is used with D.C. compound motor to reduce the peak demand by the motor, compound motor will have to be (a) level compounded (b) under compounded (c) cumulatively compounded (d) differentially compounded Ans: c 59. Following motor is used where high starting torque and wide speed range control is required. (a) Single phase capacitor start (b) Induction motor Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (c) Synchronous motor (d) D.C. motor (e) None of the above Ans: d 60. In a differentially compounded D.C. motor, if shunt field suddenly opens (a) the motor will first stop and then run in opposite direction as series motor (b) the motor will work as series motor and run at slow speed in the same direction (c) the motor will work as series motor and run at high speed in the same direction (d) the motor will not work and come to stop Ans: a 61. Which of the following motor has the poorest speed regulation ? (a) Shunt motor (b) Series motor (c) Differential compound motor (d) Cumulative compound motor Ans: b 62. Buses, trains, trolleys, hoists, cranes require high starting torque and therefore make use of (a) D.C. series motor (b) D.C. shunt motor (c) induction motor (d) all of above motors Ans: a 63. As -the load is increased the speed of D.C. shunt motor will (a) reduce slightly (b) increase slightly (c) increase proportionately (d) remains unchanged Ans: a 64. The armature torque of the D.C. shunt motor is proportional to (a) field flux only (b) armature current only (c) both (a) and (b) (d) none of the above Ans: b 65. Which of the following method of speed control of D.C. machine will offer minimum efficiency ? Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (a) Voltage control method (b) Field control method (c) Armature control method (d) All above methods Ans: c 66. Usually wide and sensitive speed control is desired in case of (a) centrifugal pumps (b) elevators (c) steel rolling mills (d) colliery winders Ans: d 67. The speed of a motor falls from 1100 r.p.m. at no-load to 1050 r.p.m. at rated load. The speed regulation of the motor is (a) 2.36% (6) 4.76% (c) 6.77% (d) 8.84% Ans: b 68. The armature voltage control of D.C. motor provides (a) constant torque drive (b) constant voltage drive (c) constant current drive (d) none of the above Ans: a 69. As there is no back e.m.f. at the instant of starting a D.C. motor, in order to prevent a heavy current from flowing though the armature circuit (a) a resistance is connected in series with armature (b) a resistance is connected parallel to the armature (c) armature is temporarily open circuited (d) a high value resistor is connected across the field winding Ans: a 70. The speed of a D.C. shunt motor can be increased by (a) increasing the resistance in armature circuit (b) increasing the resistance in field circuit (c) reducing the resistance in the field circuit (d) reducing the resistance in the armature circuit Ans: b Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS 71. If I2 be the armature current, then speed of a D.C. shunt motor is (a) independent of Ia (b) proportional to la (c) varies as (Ia) (d) varies as la Ans: a 72. In case the back e.m.f. and the speed of a D.C. motor are doubled, the torque developed by the motor will (a) remain unchanged (6) reduce to one-fourth value (c) increase four folds (d) be doubled Ans: a 73. At the instant of starting when a D.C. motor is put on supply, it behaves like (a) a highly resistive circuit (6) a low resistance circuit (c) a capacitive circuit (d) none of the above Ans: b 74. The speed of a D.C. motor can be varied by varying (a) field current (b) applied voltage (c) resistance in series with armature (d) any of the above Ans: d 75. Which one of the following is not necessarily the advantage of D.C. motors over A.C. motors ? (a) Low cost (b) Wide speed range (c) Stability (d) High starting torque. Ans: a 76. For a D.C. shunt motor if the excitation is changed (a) torque will remain constant (b) torque will change but power will remain constant (c) torque and power both will change (d) torque, power and speed, all will change Ans: b Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS 77. Which motor has the poorest speed control? (a) Differentially compounded motor (b) Cumulatively compounded motor (c) Shunt motor (d) Series motor Ans: d 78. The plugging gives the (a) zero torque braking (b) smallest torque braking (c) highest torque braking (d) none of the above Ans: c 79. The armature voltage control of D.C. motor provides (a) constant voltage drive (b) constant current drive (c) constant torque drive (d) none of the above Ans: c 80. If a D.C. motor designed for 40°C ambient temperature is to be used for 50°C ambient temperature, then the motor (a) of lower H.P. should be selected (6) of higher H.P. should be selected (c) can be used for 50°C ambient temperature also (d) is to be derated by a factor recom-mended by manufacturer and select the next higher H.P. motor Ans: d 81. If the terminals of armature of D.C. motor are interchanged, this action will offer following kind of braking (o) regenerative (b) plugging (c) dynamic braking (d) none of the above (e) any of the above Ans: b 82. Which of the following motors one will choose to drive the rotary compressor ? (a) D.C. shunt motor (b) D.C. series motor Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (c) Universal motor (d) Synchronous motor Ans: d 83. If the speed of a D.C. shunt motor is increased, the back e.m.f. of the motor will (a) increase (b) decrease (c) remain same (d) become zero Ans: a 84. Why are the D.C. motors preferred for traction applications ? (a) Torque and speed are inversely proportional to armature current (b) Torque is proportional to armature current (c) Torque is proportional to square root of armature current (d) The speed is inversely proportional to the torque and the torque is proportional to square of armature current Ans: d 85. Which of the following motors is usually used in house-hold refrigerators ? (a) D.C. shunt motor (b) D.C. series motor (c) Single phase induction motor (split phase start or induction run motor) (d) Reluctance motor (e) Synchronous motor Ans: c 86. Which of the following motors is most suitable for signalling devices and many kinds of timers ? (a) D.C. shunt motor (b) D.C. series motor (c) Induction motor (d) Reluctance motor Ans: d 87. Which motor should not be started on no-load ? (a) Series motor (b) Shunt motor (c) Cumulatively compounded motor (d) Differentially compounded motor. Ans: a 88. Ward-Leonard control is basically a Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (a) voltage control method (b) field divertor method (c) field control method (d) armature resistance control method Ans: a 89. For constant torque drive which speed control method is preferred ? (a) Field control (b) Armature voltage control (c) Shunt armature control (d) Mechanical loading system Ans: b 90. In Ward-Leonard control the lower limit of speed is imposed by (a) residual magnetism of the generator (b) core losses of motor (c) mechanical losses of motor and gen¬erator together (d) all of the above Ans: a 91. The main disadvantage of the Ward-Leonard control method is (a) high initial cost (b) high maintenance cost (c) low efficiency at Hght loads (d) all of the above Ans: d 92. Regenerative method of braking is based on that (a) back e.m.f. is less than the applied voltage (b) back e.m.f. is equal to the applied voltage (c) back e.m.f. of rotor is more than the applied voltage (d) none of the above Ans: b 93. The hysteresis loss in a D.C. machine least depends on (a) Frequency of magnetic reversals (b) Maximum value of flux density (c) Volume and grade of iron (d) Rate of flow of ventilating air Ans: d 94. In a D.C. generator all of the following could be the effects of iron losses except (a) Loss of efficiency Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (b) Excessive heating of core (c) Increase in terminal voltage (d) Rise in temperature of ventilating air Ans: c 95. The losses occurring in a D.C. generator are given below. Which loss is likely to have highest proportion at rated load of the generator ? (a) hysteresis loss (b) field copper loss (c) armature copper loss (d) eddy current loss Ans: c 96. Which of the following loss in a D.C. generator varies significantly with the load current ? (a) Field copper loss (b) Windage loss (c) Armature copper loss (d) None of the above Ans: c 97. Torque developed by a D.C. motor depends upon (a) magnetic field (b) active length of the conductor (c) current flow through the conductors (d) number of conductors (e) radius of armature (f) all above factors Ans: f 98. D.C. shunt motors are used for driving (a) trains (b) cranes (c) hoists (d) machine tools Ans: d 99. In a manual shunt motor starter (a) over load relay is connected in series and no volt relay in parallel with the load (6) over load relay is connected in paral¬lel and no volt relay in series with the load (c) over load relay and no volt relay are both connected in series with the load (d) over load relay and no volt relay are both connected in parallel with the load Ans: a Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS 100. Which of the following steps is likely to result in reduction of hysteresis loss in a D.C. generator ? (a) Providing laminations in armature core (b) Providing laminations in stator (c) Using non-magnetic material for frame (d) Using material of low hysteresis co-efficient for armature core material Ans: d 101. Which of the following loss in a D.C. generator is dissipated in the form of heat? (a) Mechanical loss (b) Core loss (c) Copper loss (d) All of the above Ans: d 102. Which of the following losses are significantly reduced by laminating the core of a D.C. generator ? (a) Hysteresis losses (b) Eddy current losses (c) Copper losses (d) Windage losses Ans: b 103. The total losses in a well designed D.C. generator of 10 kW will be nearly (a) 100 W (b) 500 W (c) 1000 W (d) 1500 W Ans: b 104. The condition for maximum efficiency for a D.C. generator is (a) eddy current losses = stray losses (b) hysteresis losses = eddy current losses (c) copper losses = 0 (d) variable losses = constant losses Ans: d 105. D.C. generators are normally designed for maximum efficiency around (a) full-load (b) rated r.p.m. (c) rated voltage (d) all of the above Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS Ans: a 106. In a D.C. generator, the iron losses mainly take place in (a) yoke (b) commutator (c) armature conductors (d) armature rotor Ans: d 107. D.C. generators are installed near the load centres to reduce (a) iron losses (b) line losses (c) sparking (d) corona losses Ans: b 108. The purpose of retardation test on D.C. shunt machines is to find out (a) stray losses (b) eddy current losses (c) field copper losses (d) windage losses Ans: a 109. Which of the following tests will be suitable for testing two similar D.C. series motors of large capacity ? (a) Swinburne's test (b) Hopkinson's test (c) Field test (d) Brake test Ans: c 110. Hopkinson's test on D.C. machines is conducted at (a) no-load (b) part load (c) full-load (d) overload Ans: c 111. During rheostat braking of D.C. series motors (a) motor is run as a generator (b) motor is reversed in direction (c) motor is run at reduced speed Ans: a Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS 112. For which types of D.C. motor, dynamic braking is generally used ? (a) Shunt motors (b) Series motors (c) Compound motors (d) All of the above Ans: d 113. Which method of braking is generally used in elevators ? (a) Plugging (b) Regenerative braking (c) Rheostatic braking (d) None of the above Ans: a 114. In variable speed motor (a) a stronger commutating field is needed at low speed than at high speed (b) a weaker commutating field is needed at low speed than at high speed (c) same commutating field is needed at low speed than at high speed (d) none of the above is correct Ans: b 115. When the armature of a D.C. motor rotates, e.m.f. induced is (a) self-induced e.m.f. (b) mutually induced e.m.f. (c) back e.m.f. (d) none of the above Ans: c 116. Where D.C. motor of H.P. 12 or more requires frequent starting, stopping, reversing and speed control (a) drum type controller is used (b) three point starter is used (c) four point starter is used (d) all above can be used Ans: a 117. If a D.C. shunt motor is working at full load and if shunt field circuit suddenly opens (a) this will make armature to take heavy current, possibly burning it (6) this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses (c) nothing will happen to motor (d) motor will come to stop Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS Ans: a 118. D.C. motor is to drive a load which has certain minimum value for most of the time and some peak value for short duration. We will select the (a) series motor (b) shunt motor (c) compound motor (d) any of the above Ans: a 119. D.C. motor is to a drive a load which is almost nil for certain part of the load cycle and peak value for short duration. We will select this (a) series motor (b) shunt motor (c) compound motor (d) any of the above Ans: c 120. Which D.C. motor has got maximum self relieving property ? (a) Series motor (6) Shunt motor (c) Cumulatively compounded motor (d) Differentially compounded motor Ans: a 121. In the D.C. motor the iron losses occur in (a) the field (b) the armature (c) the brushes (d) the commutator Ans: b 122. The speed of a D.C. shunt motor is required to be more than full load speed. This is possible by (a) reducing the field current (b) decreasing the armature current (c) increasing the armature current (d) increasing the excitation current (e) none of the above methods Ans: a 123. One D.C. motor drives another D.C. motor. The second D.C. motor when excited and Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS driven (a) runs as a generator (b) does not run as a generator (c) also runs as a motor comes to stop after sometime Ans: a 2. TRANSFORMERS 1. Which of the following does not change in a transformer ? (a) Current (b) Voltage (c) Frequency (d) All of the above Ans: c 2. In a transformer the energy is conveyed from primary to secondary (a) through cooling coil (b) through air (c) by the flux (d) none of the above Ans: c 3. A transformer core is laminated to (a) reduce hysteresis loss (b) reduce eddy current losses (c) reduce copper losses (d) reduce all above losses Ans: b 4. The degree of mechanical vibrations produced by the laminations of a transformer depends on (a) tightness of clamping (b) gauge of laminations (c) size of laminations (d) all of the above Ans: d Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS 5. The no-load current drawn by transformer is usually what per cent of the full-load current ? (a) 0.2 to 0.5 per cent (b) 2 to 5 per cent (c) 12 to 15 per cent (d) 20 to 30 per cent Ans: b 6. The path of a magnetic flux in a transformer should have (a) high resistance (b) high reluctance (c) low resistance (d) low reluctance Ans: d 7. No-load on a transformer is carried out to determine (a) copper loss (b) magnetising current (c) magnetising current and loss (d) efficiency of the transformer Ans: c 8. The dielectric strength of transformer oil is expected to be (a) lkV (b) 33 kV (c) 100 kV (d) 330 kV Ans: b 9. Sumpner's test is conducted on trans-formers to determine (a) temperature (b) stray losses (c) all-day efficiency (d) none of the above Ans: a 10. The permissible flux density in case of cold rolled grain oriented steel is around Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (a) 1.7 Wb/m2 (b) 2.7 Wb/m2 (c) 3.7 Wb/m2 (d) 4.7 Wb/m2 Ans: a The efficiency of a transformer will be maximum when (a) copper losses = hysteresis losses (b) hysteresis losses = eddy current losses (c) eddy current losses = copper losses (d) copper losses = iron losses Ans: d 12. No-load current in a transformer (a) lags behind the voltage by about 75° (b) leads the voltage by about 75° (c) lags behind the voltage by about 15° (d) leads the voltage by about 15° Ans: a 13. The purpose of providing an iron core in a transformer is to (a) provide support to windings (b) reduce hysteresis loss (c) decrease the reluctance of the magnetic path (d) reduce eddy current losses Ans: c 14. Which of the following is not a part of transformer installation ? (a) Conservator (b) Breather (c) Buchholz relay (d) Exciter Ans: d 15. While conducting short-circuit test on a transformer the following side is short circuited (a) High voltage side (b) Low voltage side Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (c) Primary side (d) Secondary side Ans: b 16. In the transformer following winding has got more cross-sectional area (a) Low voltage winding (b) High voltage winding (c) Primary winding (d) Secondary winding Ans: a 17. A transformer transforms (a) voltage (b) current (c) power (d) frequency Ans: c 18. A transformer cannot raise or lower the voltage of a D.C. supply because (a) there is no need to change the D.C. voltage (b) a D.C. circuit has more losses (c) Faraday's laws of electromagnetic induction are not valid since the rate of change of flux is zero (d) none of the above Ans: c 19. Primary winding of a transformer (a) is always a low voltage winding (b) is always a high voltage winding (c) could either be a low voltage or high voltage winding (d) none of the above Ans: c 20. Which winding in a transformer has more number of turns ? (a) Low voltage winding (b) High voltage winding (c) Primary winding (d) Secondary winding Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS Ans: b 21. Efficiency of a power transformer is of the order of (a) 100 per cent (b) 98 per cent (c) 50 per cent (d) 25 per cent Ans: b 22. In a given transformer for given applied voltage, losses which remain constant irrespective of load changes are (a) friction and windage losses (b) copper losses (c) hysteresis and eddy current losses (d) none of the above Ans: c 23. A common method of cooling a power transformer is (a) natural air cooling (b) air blast cooling (c) oil cooling (d) any of the above Ans: c 24. The no load current in a transformer lags behind the applied voltage by an angle of about (a) 180° (b) 120" (c) 90° (d) 75° Ans: d 25. In a transformer routine efficiency depends upon (a) supply frequency (b) load current (c) power factor of load (d) both (b) and (c) Ans: d Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS 26. In the transformer the function of a conservator is to (a) provide fresh air for cooling the transformer (b) supply cooling oil to transformer in time of need (c) protect the transformer from damage when oil expends due to heating (d) none of the above Ans: c 27. Natural oil cooling is used for transformers upto a rating of (a) 3000 kVA (b) 1000 kVA (c) 500 kVA (d) 250 kVA Ans: a 28. Power transformers are designed to have maximum efficiency at (a) nearly full load (b) 70% full load (c) 50% full load (d) no load Ans: a 29. The maximum efficiency of a distribution transformer is (a) at no load (b) at 50% full load (c) at 80% full load (d) at full load Ans: b 30. Transformer breaths in when (a) load on it increases (b) load on it decreases (c) load remains constant (d) none of the above Ans: b 31. No-load current of a transformer has (a) has high magnitude and low power factor Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (b) has high magnitude and high power factor (c) has small magnitude and high power factor (d) has small magnitude and low power factor Ans: d 32. Spacers are provided between adjacent coils (a) to provide free passage to the cool¬ing oil (b) to insulate the coils from each other (c) both (a) and (b) (d) none of the above Ans: a 33. Greater the secondary leakage flux (a) less will be the secondary induced e.m.f. (b) less will be the primary induced e.m.f. (c) less will be the primary terminal voltage (d) none of the above Ans: a 34. The purpose of providing iron core in a step-up transformer is (a) to provide coupling between primary and secondary (b) to increase the magnitude of mutual flux (c) to decrease the magnitude of mag-netizing current (d) to provide all above features Ans: c 35. The power transformer is a constant (a) voltage device (b) current device (c) power device (d) main flux device Ans: d 36. Two transformers operating in parallel will share the load depending upon their (a) leakage reactance (b) per unit impedance (c) efficiencies (d) ratings Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS Ans: b 37. If R2 is the resistance of secondary winding of the transformer and K is the transformation ratio then the equivalent secondary resistance referred to primary will be (a) R2/VK (b) R2IK2 (c) R22!K2 (d) R22/K Ans: b 38. What will happen if the transformers working in parallel are not connected with regard to polarity ? (a) The power factor of the two trans-formers will be different from the power factor of common load (b) Incorrect polarity will result in dead short circuit (c) The transformers will not share load in proportion to their kVA ratings (d) none of the above Ans: b 39. Ifthe percentage impedances of the two transformers working in parallel are different, then (a) transformers will be overheated (b) power factors of both the trans-formers will be same (c) parallel operation will be not possible (d) parallel operation will still be possible, but the power factors at which the two transformers operate will be different from the power factor of the common load Ans: d 40. In a transformer the tappings are generally provided on (a) primary side (b) secondary side (c) low voltage side (d) high voltage side Ans: c 41. The use of higher flux density in the transformer design (a) reduces weight per kVA (6) reduces iron losses Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (c) reduces copper losses (d) increases part load efficiency Ans: a 42. The chemical used in breather for transformer should have the quality of (a) ionizing air (b) absorbing moisture (c) cleansing the transformer oil (d) cooling the transformer oil. Ans: b 43. The chemical used in breather is (a) asbestos fibre (b) silica sand (c) sodium chloride (d) silica gel Ans: d 44. An ideal transformer has infinite values of primary and secondary inductances. The statement is (a) true (b) false Ans: b 45. The transformer ratings are usually expressed in terms of (a) volts (b) amperes (c) kW (d) kVA Ans: d 46. The noise resulting from vibrations of laminations set by magnetic forces, is termed as (a) magnetostrication (b) boo (c) hum (d) zoom Ans: c Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS 47. Hysteresis loss in a transformer varies as CBmax = maximum flux density) (a) Bmax (b) Bmax1-6 (C) Bmax1-83 (d) B max Ans: b 48. Material used for construction of transformer core is usually (a) wood (b) copper (c) aluminium (d) silicon steel Ans: d 49. The thickness of laminations used in a transformer is usually (a) 0.4 mm to 0.5 mm (b) 4 mm to 5 mm (c) 14 mm to 15 mm (d) 25 mm to 40 mm Ans: a 50. The function of conservator in a transformer is (a) to project against'internal fault (b) to reduce copper as well as core losses (c) to cool the transformer oil (d) to take care of the expansion and contraction of transformer oil due to variation of temperature of sur-roundings Ans: d 51. The highest voltage for transmitting electrical power in India is (a) 33 kV. (6) 66 kV (c) 132 kV (d) 400 kV Ans: d 52. In a transformer the resistance between its primary and secondary is (a) zero Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (b) 1 ohm (c) 1000 ohms (d) infinite Ans: d 53. A transformer oil must be free from (a) sludge (b) odour (c) gases (d) moisture Ans: d 54. A Buchholz relay can be installed on (a) auto-transformers (b) air-cooled transformers (c) welding transformers (d) oil cooled transformers Ans: d 55. Gas is usually not liberated due to dissociation of transformer oil unless the oil temperature exceeds (a) 50°C (b) 80°C (c) 100°C (d) 150°C Ans: d 56. The main reason for generation of harmonics in a transformer could be (a) fluctuating load (b) poor insulation (c) mechanical vibrations (d) saturation of core Ans: d 57. Distribution transformers are generally designed for maximum efficiency around (a) 90% load (b) zero load (c) 25% load Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (d) 50% load Ans: d 58. Which of the following property is not necessarily desirable in the material for transformer core ? (a) Mechanical strength (6) Low hysteresis loss (c) High thermal conductivity (d) High permeability Ans: c 59. Star/star transformers work satisfactorily when (a) load is unbalanced only (b) load is balanced only (c) on balanced as well as unbalanced loads (d) none of the above Ans: b 60. Delta/star transformer works satisfactorily when (a) load is balanced only (b) load is unbalanced only (c) on balanced as well as unbalanced loads (d) none of the above Ans: c 61. Buchholz's relay gives warning and protection against (a) electrical fault inside the transformer itself (b) electrical fault outside the transformer in outgoing feeder (c) for both outside and inside faults (d) none of the above Ans: a 62. The magnetising current of a transformer is usually small because it has (a) small air gap (b) large leakage flux (c) laminated silicon steel core (d) fewer rotating parts Ans: a Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS 63. Which of the following does not change in an ordinary transformer ? (a) Frequency (b) Voltage (c) Current (d) Any of the above Ans: a 64. Which of the following properties is not necessarily desirable for the material for transformer core ? (a) Low hysteresis loss (b) High permeability (c) High thermal conductivity (d) Adequate mechanical strength Ans: c 65. The leakage flux in a transformer depends upon (a) load current (b) load current and voltage (c) load current, voltage and frequency (d) load current, voltage, frequency and power factor Ans: a 66. The path of the magnetic flux in transformer should have (a) high reluctance (b) low reactance (c) high resistance (d) low resistance Ans: b 67. Noise level test in a transformer is a (a) special test (b) routine test (c) type test (d) none of the above Ans: c 68. Which of the foJIowing is not a routine test on transformers ? Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (a) Core insulation voltage test (b) Impedance test (c) Radio interference test (d) Polarity test Ans: c 69. A transformer can have zero voltage regulation at (a) leading power factor (b) lagging power factor (c) unity power factor (d) zero power factor Ans: a 70. Helical coils can be used on (a) low voltage side of high kVA trans¬formers (b) high frequency transformers (c) high voltage side of small capacity transformers (d) high voltage side of high kVA rating transformers Ans: a 71. Harmonics in transformer result in (a) increased core losses (b) increased I2R losses (c) magnetic interference with communication circuits (d) all of the above Ans: d 72. The core used in high frequency transformer is usually (a) copper core (b) cost iron core (c) air core (d) mild steel core Ans: c 73. The full-load copper loss of a trans¬former is 1600 W. At half-load, the copper loss will be (a) 6400 W (b) 1600 W Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (c) 800 W (d) 400 W Ans: d 1.74. The value of flux involved m the e.m.f. equation of a transformer is (a) average value (b) r.m.s. value (c) maximum value (d) instantaneous value Ans: c L.75. Silicon steel used in laminations mainly reduces (a) hysteresis loss (b) eddy current losses (c) copper losses (d) all of the above Ans: a 76. Which winding of the transformer has less cross-sectional area ? (a) Primary winding (b) Secondary winding (c) Low voltage winding (d) High voltage winding Ans: d 77. Power transformers are generally designed to have maximum efficiency around (a) no-load (b) half-load (c) near full-load (d) 10% overload Ans: c.78. Which of the following is the main advantage of an auto-transformer over a two winding transformer ? (a) Hysteresis losses are reduced (b) Saving in winding material (c) Copper losses are negligible (d) Eddy losses are totally eliminated Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS Ans: b 79. During short circuit test iron losses are negligible because (a) the current on secondary side is negligible (b) the voltage on secondary side does not vary (c) the voltage applied on primary side is low (d) full-load current is not supplied to the transformer Ans: c 80. Two transformers are connected in parallel. These transformers do not have equal percentage impedance. This is likely to result in (a) short-circuiting of the secondaries (b) power factor of one of the trans¬formers is leading while that of the other lagging (c) transformers having higher copper losses will have negligible core losses (d) loading of the transformers not in proportion to their kVA ratings Ans: d 81. The changes in volume of transformer cooling oil due to variation of atmospheric temperature during day and night is taken care of by which part of transformer (a) Conservator (b) Breather (c) Bushings (d) Buchholz relay Ans: a 82. An ideal transformer is one which has (a) no losses and magnetic leakage (b) interleaved primary and secondary windings (c) a common core for its primary and secondary windings (d) core of stainless steel and winding of pure copper metal (e) none of the above Ans: a 83. When a given transformer is run at its rated voltage but reduced frequency, its (a) flux density remains unaffected (b) iron losses are reduced (c) core flux density is reduced Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (d) core flux density is increased Ans: d 84. In an actual transformer the iron loss remains practically constant from noload to fullload because (a) value of transformation ratio remains constant (b) permeability of transformer core remains constant (c) core flux remains practically constant (d) primary voltage remains constant (c) secondary voltage remains constant Ans: c 85. An ideal transformer will have maximum efficiency at a load such that (a) copper loss = iron loss (b) copper loss < iron loss (c) copper loss > iron loss (d) none of the above Ans: a 86. If the supply frequency to the transformer is increased,"the iron loss will (a) not change (b) decrease (c) increase (d) any of the above Ans: c 87. Negative voltage regulation is indicative that the load is (a) capacitive only (b) inductive only (c) inductive or resistive (d) none of the above Ans: a 88. Iron loss of a transformer can be measured by (a) low power factor wattmeter (b) unity power factor wattmeter (c) frequency meter (d) any type of wattmeter Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS Ans: a 89. When secondary of a current transformer is open-circuited its iron core will be (a) hot because of heavy iron losses taking place in it due to high flux density (b) hot because primary will carry heavy current (c) cool as there is no secondary current (d) none of above will happen Ans: a 90. The transformer laminations are insulated from each other by (a) mica strip (6) thin coat of varnish (c) paper (d) any of the above Ans: b 91. Which type of winding is used in 3phase shell-type transformer ? (a) Circular type (b) Sandwich type (c) Cylindrical type (d) Rectangular type Ans: b 92. During open circuit test of a transformer (a) primary is supplied rated voltage (b) primary is supplied full-load current (c) primary is supplied current at reduced voltage (d) primary is supplied rated kVA Ans: a 93. Open circuit test on transformers is conducted to determine (a) hysteresis losses (b) copper losses (c) core losses (d) eddy current losses Ans: c 94. Short circuit test on transformers is conducted to determine Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (a) hysteresis losses (b) copper losses (c) core losses (d) eddy current losses Ans: b 95. For the parallel operation of single phase transformers it is necessary that they should have (a) same efficiency (b) same polarity (c) same kVA rating (d) same number of turns on the secondary side. Ans: b 96. The transformer oil should have _____ volatility and _____ viscosity. (a) low,low (b) high,high (c) low,high (d) high,low Ans: a 97. The function of breather in a transformer is (a) to provide oxygen inside the tank (b) to cool the coils during reduced load (c) to cool the transformer oil (d) to arrest flow of moisture when outside air enters the transformer Ans: d 98. The secondary winding of which of the following transformers is always kept closed ? (a) Step-up transformer (b) Step-down transformer (c) Potential transformer (d) Current transformer Ans: d 99. The size of a transformer core will depend on (a) frequency (b) area of the core Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (c) flux density of the core material (d) (a) and (b) both Ans: d 100. N atural air coo ling is generally restricted for transformers up to (a) 1.5 MVA (b) 5 MVA (c) 15 MVA (d) 50 MVA Ans: a 101. A shell-type transformer has (a) high eddy current losses (b) reduced magnetic leakage (c) negligibly hysteresis losses (d) none of the above Ans: b 102. A transformer can have regulation closer to zero (a) on full-load (b) on overload (c) on leading power factor (d) on zero power factor Ans: c 103. A transformer transforms (a) voltage (b) current (c) current and voltage (d) power Ans: d 104. Which of the following is not the standard voltage for power supply in India ? (a) llkV (b) 33kV (c) 66 kV (d) 122 kV Ans: d Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS 105. Reduction in core losses and increase in permeability are obtained with transformer employing (a) core built-up of laminations of cold rolled grain oriented steel (b) core built-up of laminations of hot rolled sheet (c) either of the above (d) none of the above Ans: a 106. In a power or distribution transformer about 10 per cent end turns are heavily insulated (a) to withstand the high voltage drop due to line surge produced by the shunting capacitance of the end turns (b) to absorb the line surge voltage and save the winding of transformer from damage (c) to reflect the line surge and save the winding of a transformer from damage (d) none of the above Ans: a 107. For given applied voltage, with the increase in frequency of the applied voltage (a) eddy current loss will decrease (b) eddy current loss will increase (c) eddy current loss will remain unchanged (d) none of the above Ans: c 108. Losses which occur in rotating electric machines and do not occur in trans formers are (a) friction and windage losses (b) magnetic losses (c) hysteresis and eddy current losses (d) copper losses Ans: a 109. In a given transformer for a given applied voltage, losses which remain constant irrespective of load changes are (a) hysteresis and eddy current losses (b) friction and windage losses (c) copper losses Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (d) none of the above Ans: a 110. Which of the following statements regarding an idel single-phase transformer having a turn ratio of 1 : 2 and drawing a current of 10 A from 200 V A.C. supply is incorrect ? (a) Its secondary current is 5 A (b) Its secondary voltage is 400 V (c) Its rating is 2 kVA (d) Its secondary current is 20 A (e) It is a step-up transformer Ans: d 111 The secondary of a current transformer is always short-circuited under operating conditions because it (a) avoids core saturation and high voltage induction (b) is safe to human beings (c) protects the primary circuit (d) none of the above Ans: a 112. In a transformer the resistance between its primary and secondary should be (a) zero (b) 10 Q (c) 1000 Q (d) infinity Ans: d 113. A good voltage regulation of a transformer means (a) output voltage fluctuation from no load to full load is least (b) output voltage fluctuation with power factor is least (c) difference between primary and secondary voltage is least (d) difference between primary and secondary voltage is maximum Ans: a 114. For a transformer, operating at constant load current, maximum efficiency will occur at (a) 0.8 leading power factor Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (b) 0.8 lagging power factor (c) zero power factor (d) unity power factor Ans: d 115. Which of the following protection is normally not provided on small distribution transformers ? (a) Overfluxing protection (b) Buchholz relay (c) Overcurrent protection (d) All of the above Ans: b 116. Which of the following acts as a protection against high voltage surges due to lightning and switching ? (a) Horn gaps (b) Thermal overload relays (c) Breather (d) Conservator Ans: a 117. The efficiency of two identical transformers under load conditions can be determined by (a) short-circuit test (b) back-to-back test (c) open circuit test (d) any of the above Ans: b 118. Which of the following insulating materials can withstand the highest temperature safely ? (a) Cellulose (b) Asbestos (c) Mica (d) Glass fibre Ans: c 119. Which of the following parts of a transformer is visible from outside ? Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (a) Bushings (b) Core (c) Primary winding (d) Secondary winding Ans: a 120. The noise produced by a transformer is termed as (a) zoom (b) hum (c) ringing (d) buzz Ans: b 121. Which of the following loss in a transformer is zero even at full load ? (a) Core loss (b) Friction loss (c) Eddy current loss (d) Hysteresis loss Ans: b 122. Which of the following is the most likely source of harmonics in a transformer ? (a) poor insulation (b) Overload (c) loose connections (d) Core saturation Ans: d 123. If a transformer is continuously operated the maximum temperature rise will occur in (a) core (b) windings (c) tank (d) any of the above Ans: b 124. The hum in a transformer is mainly attributed to (a) load changes (b) oil in the transformer Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (c) magnetostriction (d) mechanical vibrations Ans: c 125. The maximum load that a power transformer can carry is limited by its (a) temperature rise (b) dielectric strength of oil (c) voltage ratio (d) copper loss Ans: c 126. The efficiency of a transformer, under heavy loads, is comparatively low because (a) copper loss becomes high in proportion to the output (b) iron loss is increased considerably (c) voltage drop both in primary and secondary becomes large (d) secondary output is much less as compared to primary input Ans: a 127. An open-circuit test on a transformer is conducted primarily to measure (a) insulation resistance (b) copper loss (c) core loss (d) total loss (e) efficiency (f) none of the above Ans: c 128. A no-load test is performed on a transformer to determine (a) core loss (b) copper loss (c) efficiency (d) magnetising current (e) magnetising current and loss Ans: e 129. The voltage transformation ratio of a transformer is equal to the ratio of (a) primary turns to secondary turns (b) secondary current to primary current Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (c) secondary induced e.m.f. to primary induced e.m.f. (d) secondary terminal voltage to primary applied voltage Ans: c 130. Part of the transformer which is most subject to damage from overheating is (a) iron core (b) copper winding (c) winding insulation (d) frame or case (e) transformer tank Ans: c 131. If a transformer is switched on to a voltage more than the rated voltage (a) its power factor will deteriorate (b) its power factor will increase (c) its power factor will remain unaffected (d) its power factor will be zero Ans: a 132. Auto-transformer makes effective saving on copper and copper losses, when its transformation ratio is (a) approximately equal to one (b) less than one (c) great than one (d) none of the above Ans: a 133. Minimum voltage regulation occurs when the power factor of the load is (a) unity (b) lagging (c) leading (d) zero Ans: c 134. In a step-down transformer, there is a change of 15 A in the load current. This results in change of supply current of (a) less than 15 A (b) more than 15 A Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (c) 15 A (d) none of the above Ans: a 135. The efficiencies of transformers compared with that of electric motors of the same power are (a) about the same (6) much smaller (c) much higher (d) somewhat smaller (e) none of the above Ans: c 3. A. THREE PHASE INDUCTION MOTORS 1. Which of the following component is usually fabricated out of silicon steel ? (a) Bearings (b) Shaft (c) Statorcore (d) None of the above Ans: c 2. The frame of an induction motor is usually made of (a) silicon steel (b) cast iron (c) aluminium (d) bronze Ans: b 3. The shaft of an induction motor is made of (a) stiff (b) flexible (c) hollow (d) any of the above Ans: a 4. The shaft of an induction motor is made of (a) high speed steel (b) stainless steel (c) carbon steel (d) cast iron Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS Ans: c 5. In an induction motor, no-load the slip is generally (a) less than 1% (b) 1.5% (c) 2% (d) 4% Ans: a 6. In medium sized induction motors, the slip is generally around (a) 0.04% (b) 0.4% (c) 4% (d) 14% Ans: c 7. In squirrel cage induction motors, the rotor slots are usually given slight skew in order to (a) reduce windage losses (b) reduce eddy currents (c) reduce accumulation of dirt and dust (d) reduce magnetic hum Ans: d 8. In case the air gap in an induction motor is increased (a) the magnetising current of the rotor will decrease (b) the power factor will decrease (c) speed of motor will increase (d) the windage losses will increase Ans: b 9. Slip rings are usually made of (a) copper (b) carbon (c) phospor bronze (d) aluminium Ans: c 10. A 3-phase 440 V, 50 Hz induction motor has 4% slip. The frequency of rotor e.m.f. will be (a) 200 Hz (b) 50 Hz (c) 2 Hz Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (d) 0.2 Hz Ans: c 11. In Ns is the synchronous speed and s the slip, then actual running speed of an induction motor will be (a) Ns (b) s.N, (c) (l-s)Ns (d) (Ns-l)s Ans: c The efficiency of an induction motor can be expected to be nearly (a) 60 to 90% (b) 80 to 90% (c) 95 to 98% (d) 99% Ans: b 13. The number of slip rings on a squirrel cage induction motor is usually (a) two (b) three (c) four (d) none Ans: d 14. The starting torque of a squirrel-cage induction motor is (a) low (b) negligible (c) same as full-load torque (d) slightly more than full-load torque Ans: a 15. A double squirrel-cage induction motor has (a) two rotors moving in oppsite direction (b) two parallel windings in stator (c) two parallel windings in rotor (d) two series windings in stator Ans: c 16. Star-delta starting of motors is not possible in case of (a) single phase motors (b) variable speed motors (c) low horse power motors Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (d) high speed motors Ans: a 17. The term 'cogging' is associated with (a) three phase transformers (b) compound generators (c) D.C. series motors (d) induction motors Ans: d 18. In case of the induction motors the torque is (a) inversely proportional to (Vslip) (b) directly proportional to (slip)2 (c) inversely proportional to slip (d) directly proportional to slip Ans: d 19. An induction motor with 1000 r.p.m. speed will have (a) 8 poles (b) 6 poles (c) 4 poles (d) 2 poles Ans: b 20. The good power factor of an induction motor can be achieved if the average flux density in the air gap is (a) absent (b) small (c) large (d) infinity Ans: b 21. An induction motor is identical to (a) D.C. compound motor (b) D.C. series motor (c) synchronous motor (d) asynchronous motor Ans: d 22. The injected e.m.f. in the rotor of induction motor must have (a) zero frequency (b) the same frequency as the slip fre-quency Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (c) the same phase as the rotor e.m.f. (d) high value for the satisfactory speed control Ans: b 23. Which of the following methods is easily applicable to control the speed of the squirrel-cage induction motor ? (a) By changing the number of stator poles (b) Rotor rheostat control (c) By operating two motors in cascade (d) By injecting e.m.f. in the rotor circuit Ans: a 24. The crawling in the induction motor is caused by (a) low voltage supply (b) high loads (c) harmonics develped in the motor (d) improper design of the machine (e) none of the above Ans: c 25. The auto-starters (using three auto transformers) can be used to start cage induction motor of the following type (a) star connected only (b) delta connected only (c) (a) and (b) both (d) none of the above Ans: c 26. The torque developed in the cage induction motor with autostarter is (a) k/torque with direct switching (6) K x torque with direct switching (c) K2 x torque with direct switching (d) k2/torque with direct switching Ans: c 27. When the equivalent circuit diagram of doouble squirrel-cage induction motor is constructed the two cages can be considered (a) in series (b) in parallel (c) in series-parallel (d) in parallel with stator Ans: b Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS 28. It is advisable to avoid line-starting of induction motor and use starter because (a) motor takes five to seven times its full load current (b) it will pick-up very high speed and may go out of step (c) it will run in reverse direction (d) starting torque is very high Ans: a 29. Stepless speed control of induction motor is possible by which of the following methods ? (a) e.m.f. injection in rotor eueuit (b) Changing the number of poles (c) Cascade operation (d) None of the above Ans: b 30. Rotor rheostat control method of speed control is used for (a) squirrel-cage induction motors only (b) slip ring induction motors only (c) both (a) and (b) (d) none of the above Ans: b 31. In the circle diagram for induction motor, the diameter of the circle represents (a) slip (b) rotor current (c) running torque (d) line voltage Ans: b 32. For which motor the speed can be controlled from rotor side ? (a) Squirrel-cage induction motor (b) Slip-ring induction motor (c) Both (a) and (b) (d) None of the above Ans: b 33. If any two phases for an induction motor are interchanged (a) the motor will run in reverse direction (b) the motor will run at reduced speed (c) the motor will not run (d) the motor will burn Ans: a Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS 34. An induction motor is (a) self-starting with zero torque (b) self-starting with high torque (c) self-starting with low torque (d) non-self starting Ans: c 35. The maximum torque in an induction motor depends on (a) frequency (b) rotor inductive reactance (c) square of supply voltage (d) all of the above Ans: d 36. In three-phase squirrel-cage induction motors (a) rotor conductor ends are short-circuited through slip rings (b) rotor conductors are short-circuited through end rings (c) rotor conductors are kept open (d) rotor conductors are connected to insulation Ans: b 37. In a three-phase induction motor, the number of poles in the rotor winding is always (a) zero (b) more than the number of poles in stator (c) less than number of poles in stator (d) equal to number of poles in stator Ans: d 38. DOL starting of induction motors is usually restricted to (a) low horsepower motors (b) variable speed motors (c) high horsepower motors (d) high speed motors Ans: a 39. The speed of a squirrel-cage induction motor can be controlled by all of the following except (a) changing supply frequency (b) changing number of poles (c) changing winding resistance (d) reducing supply voltage Ans: c Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS 40. The 'crawling" in an induction motor is caused by (a) high loads (6) low voltage supply (c) improper design of machine (d) harmonics developed in the motor Ans: d 41. The power factor of an induction motor under no-load conditions will be closer to (a) 0.2 lagging (b) 0.2 leading (c) 0.5 leading (d) unity Ans: a 42. The 'cogging' of an induction motor can be avoided by (a) proper ventilation (b) using DOL starter (c) auto-transformer starter (d) having number of rotor slots more or less than the number of stator slots (not equal) Ans: d 43. If an induction motor with certain ratio of rotor to stator slots, runs at 1/7 of the normal speed, the phenomenon will be termed as (a) humming (b) hunting (c) crawling (d) cogging Ans: c 44. Slip of an induction motor is negative when (a) magnetic field and rotor rotate in opposite direction (b) rotor speed is less than the syn-chronous speed of the field and are in the same direction (c) rotor speed is more than the syn-chronous speed of the field and are in the same direction (d) none of the above Ans: c 45. Size of a high speed motor as compared to low speed motorfor the same H.P. will be (a) bigger (b) smaller (c) same Prepared by Mr. V. Arivumani, Asst Professor, Dept of EEE, GCE, Bargur  GOVERNMENT COLLEGE OF ENGINEERING, BARGUR ELECTRICAL ENGINEERING OBJECTIVE TYPE QUESTIONS (d) any of the above Ans: b 46. A 3-phase induction motor stator delta connected, is carrying full load and one of its fuses blows out. Then the motor (a) will continue running burning its one phase (b) will continue running burning its two phases (c) will stop and carry heavy current causing permanent damage to its winding (d) will continue running without any harm to the winding Ans: a 47. A 3-phase induction motor delta connected is carrying too heavy load and one of its fuses blows out. Then the motor (a) will continue running burning its one phase (b) will continue running burning its two phase (c) will stop and carry heavy current causing permanent damage to its winding (d) will continue running without any harm to the winding Ans: c 48. Low voltage at motor terminals is due to (a) inadequate motor wiring (b) poorely regulated power supply (c) any one of the above (d) none of the above Ans: c 49. In an induction motor the relationship between st