JNTUK ONLINE EXAMINATIONS [Mid 1 - em3]

1. The frequency of voltage generated by an alternator having 4-poles and rotating at 1800 r.p.m is ---------hertz [01M01]

a. 60 b. 7200 c. 120 d. 450

2. The frequency generated in a 8-pole alternator that rotates at 750 r.p.m is [01M02]

a. 30 Hz b. 40 Hz c. 50 Hz d. 60Hz

3. If P is the number of poles , f=frequency in Hz , N=speed in r.p.m, the relationship between the three for a synchronous alternator is given by [01M03]

a. f = (P / 120 N) b. f = (P / 60 N) c. P = (120 f / N) d. P = (60 f / N)

4. Turbo-alternators are generally used to run to [01M04]

a. 1500 r.p.m b. 3000 r.p.m c. 5000 r.p.m d. 150000 r.p.m

5. Alternator operates on the principle of [01S01]

a. Electro-magnetic induction b. Self induction c. Mutual induction d. Self or mutual induction

6. Synchronous machine can operate [01S02]

a. only as a generator b. only as a motor c. both as a generator and as a motor d. neither generator not motor

7. In a synchronous machine, if the field flux axis is ahead of the armature field axis in the direction of rotation, the machine operating is [01S03]

a. Synchronous motor b. Synchronous generator c. Asynchronous motor d. Asynchronous generator

8. An alternator generates [01S04]

a. dc b. ac c. pulsating dc d. dc as well as ac

9. In modern alternators, the rotating part is [01S05]

a. Field system b. Armature c. Armature as well as field system d. Neither armature nor field

10. The frequency of emf generated by an alternator depends upon the alternator speed (N in rpm) and number of poles ( P )on the alternator field and is given as [01S06]

a. PN/60

b. (60N) / P c. PN/120 d. (120N) / P

11. Squirrel cage bars placed in the rotor pole faces of an alternator help reducing hunting [02D01]

a. Above synchronous speed only b. Below synchronous speed only c. Above and below synchronous speeds both d. Equal to synchronous speed

12. Salient pole field structure, the pole shoes cover about ---of pole pitch [02D02]

a. one-third b. one half c. two-third d. whole

13. The high-speed turbo-alternator has rotor of ----diameter and ---- axial length in comparison to those of rotor for a low speed hydro-generator. [02M01]

a. smaller, smaller b. larger, larger c. smaller, larger d. larger, smaller

14. Salient pole field structure has the advantages of [02M02]

a. Adaptability to low and moderate speed operations b. Reduced noise c. Reduced friction and windage losses d. Reduced bearing loads

15. Larger diameter salient pole rotors have shorter axial length because [02M03]

a. It occupies much less space b. It saves lot of copper in stator winding c. It reduces weight of the rotor d. Number of conductors held in large circumference of rotor is very large and so they

need not be long 16. The stator core of a synchronous machine is built up of------laminations [02S01]

a. stainless steel b. silicon steel c. cast iron d. cast steel

17. The stator core of a synchronous machine is laminated so as to reduce [02S02]

a. Eddy current loss b. Hysteresis loss c. Both eddy current and hysteresis loss d. The size and weight of the machine

18. Slots provided on the stator core of a synchronous machine are of -----type [02S03]

a. open b. semi-closed c. totally closed d. either open or semi closed

19. The rotor of an alternator may be of [02S04]

a. salient pole type

b. non-salient or cylindrical type c. squirrel cage type d. salient pole or smooth cylindrical type

20. The Salient pole type rotor has [02S05]

a. Smaller diameter and smaller axial length b. Larger diameter and larger axial length

c. Larger diameter and smaller axial length d. Smaller diameter and larger axial length

21. If the field winding of a synchronous machine is placed in the stator and armature Winding on the rotor, under steady running conditions, the air gap field [03D01]

a. Rotates at synchronous speed with direction of rotation of the rotor b. Rotates of synchronous speed with speed with respect to stator c. Remains stationary with respect to rotor d. Remains stationary with respect to stator

22. Advantage of a direct connected exciter [03D02]

a. Economy of space b. Larger space c. Gives low speeds d. Gives high speeds

23. A 50-Hz alternator will run at the greatest possible speed if it is wound for------poles [03D03]

a. 8 b. 6 c. 4 d. 2

24. The stator of an alternator is wound for---on the rotor [03M01]

a. More number of poles than b. Less number of poles than c. The same number of poles as d. More or less number of poles than

25. Salient pole rotors are used where [03M02]

a. Floor space is available in plenty b. High speed prime movers are available c. High frequency current is required d. Low and medium-speed prime movers are available

26. Cylindrical pole type rotors, as compared to Salient pole type, are [03S01]

a. Large in diameter as well as axial length

b. Larger in diameter and smaller in axial length c. Small in diameter as well as axial length d. Smaller in diameter and larger in axial length

27. A coil consists of [03S02]

a. two conductors

b. two coil-sides c. two turns d. one turn

28. In a cylindrical rotor how much portion of the rotor is wound? [03S03]

a. half b. full

c. one third d. two third

29. The field winding of an alternator is ----excited [03S04]

a. d.c b. a.c c. both d.c or a.c

d. neither a.c nor d.c 30. The a.c armature winding of an alternator is ---- [03S05]

a. Always star-connected b. Generally delta connected c. Star delta connected d. Delta-delta connected

31. Distributed winding is preferred over concentrated winding as it [04D01]

a. reduces noise b. reduces the machine size c. reduces the amount of copper required d. improves the generated emf wave-form and adds rigidity and mechanical strength

to the winding. 32. In a synchronous alternator, which of the following coils will have EMF closer to sine

wave form? [04D02]

a. Concentrated winding in full pitch coils b. Concentrated winding in short pitch coils c. Distributed winding in full pitch coils d. Distributed winding in short pitch coils

33. In a concentrated winding, the induced emf will be maximum when the two sides of a coil are--------- pole pitch apart [04M01]

a. one-half b. one c. one and half d. two

34. For a two layer winding the number of stator slots is equal to the number of [04M02]

a. poles b. conductors c. coil sides d. coils

35. For a concentrated winding the polar group of each phase is -----electrical degrees apart [04M03]

a. 360 b. 180 c. 120 d. 60

36. Armature winding in A.C machines [04S01]

a. Is always closed one

b. Is always open one c. May be either closed one giving delta connections or open one giving star

connections d. Always semi closed

37. A pole pitch electrical machines is equal to [04S02]

a. 180 electrical degrees b. 90 electrical degrees c. 120 electrical degree d. 360 electrical degrees

38. The stator of modern alternators are wound for--- phase groups [04S03]

a. 1800

b. 1200 c. 600 d. 2400

39. In concentrated winding, the number of slots is equal to the number of [04S04]

a. coil sides b. poles

c. conductors d. coils

40. Concentrated winding has [04S05]

a. One coil per phase b. Two coil per phase c. One coil per pair of poles per phase

d. One coil side per pole pair per phase 41. Usually concentrated windings are not used in alternators because [05D01]

a. Concentrated windings require deep slots for accommodation which leads to increased armature leakage and reactance

b. Concentrated windings decrease the capacity of the machine c. Concentrated windings decrease induced emf/ phase d. Harmonics increase in concentrated windings

42. For a full pitch winding, the induced EMF in both coil sides are [05M01]

a. additive b. subtractive c. in quadrature d. either additive, subtractive, in quadrature

43. In a 3-Phase cylindrical-rotor alternator, [05M02]

a. field mmf leads the air-gap flux and air-gap flux leads the armature mmf b. the armature mmf leads the air-gap flux and the air-gap flux leads the field flux c. the armature mmf leads the air-gap flux and the air-gap lags the field- fux d. field mmf leads the air-gap flux and air-gap flux lags the armature mmf

44. Chording and distribution of armature windings for ac machines results in [05S01]

a. Reduction in air-gap mmf harmonics

b. Increase fundamental components or induced emf c. Increase in fundamental component of induced emf d. Reduction in noise and machine size

45. In an alternator short pitch coils are used [05S02]

a. To reduce the size of the machine b. To reduce the stray losses

c. To reduce the harmonics in generated emf d. To provide accurate phase difference of 1200 between each phase

46. Short pitched coils in the alternator are used to [05S03]

a. Reduce the size of the alternator b. Reduce the harmonics from the generated emf of the alternator c. Reduce the copper loss in the alternator

d. Reduce the size of the alternator, and copper loss in the alternator 47. Which material is used for construction of stator core [05S04]

a. Copper b. Copper alloy c. Silicon Steel

d. Mild steel 48. Which material is used for construction of stator windings [05S05]

a. Copper b. Silver c. Silicon Steel d. Mild steel

49. Which material is used for construction of slip rings? [05S06]

a. Silver b. Copper alloy c. Silicon Steel d. Mild steel

50. Which material is used for construction of rotor core [05S07]

a. Copper b. Copper alloy c. Silicon Steel d. Mild steel

51. In 36 slot, 4-pole, 3Φ alternator the winding pitch is 7. The electrical angle by which the winding is chorded is equal to [06M01]

a. 400 b. 300 c. 600 d. 150

52. The Winding of a 4-pole alternator having 36 slots and a coil span of 1 to 8 is short pitched by ------------- degrees electrical [06M02]

a. 140 b. 80 c. 20 d. 40

53. In the armature winding of an alternator the coil span falls short of full-pitch by 600 (electrical). The pitch factor is --------- [06M03]

a. 0.866 b. 0.5 c. 0.25 d. 0.75

54. 3-phase alternator has 3-slots per pole. The distribution factor of the winding is [06M04]

a. 0.866 b. 0.5 c. 1 d. 0.75

55. The pitch factor is defined as the ration of emf induced in a [06S01]

a. Chorded coil to that in a full pitch coil b. Full pitch winding to that in a concentrated winding c. Full pitch coil to that in a chorded coil d. Distributed winding to that in a full pitch winding

56. The ratio of phasor sum of induced emfs per coil to the arithmetic sum of induced emfs per coil is known as [06S02]

a. distributed factor b. winding factor c. coil span or pitch factor d. breadth factor

57. The ratio of phasor sum of the emfs induced in all the coils distributed in a number of slots under one pole to the arithmetic sum of the emfs induced is known as [06S03]

a. breadth or distribution factor b. coil span factor c. pitch factor d. winding factor

58. For a 3-phase stator winding having 5 slots per pole per phase and coil span of 12 slot pitch as, the value of pitch factor wil be [06S04]

a. 1.05 b. 0.98 c. 0.951 d. 0.851

59. If a coil be having a span of 2/3 pole pitch, the coil span-factor of winding of alternator will be [06S05]

a. unity b. 0.5 c. 0.707 d. 0.866

60. For eliminating 7th harmonic from the emf wave of an alternator the fractional pitch must be [06S06]

a. 2 / 3 b. 5 / 6

c. 7 / 8 d. 6 / 7

61. An alternator has rated field current of 2A . It develops 220 V at rated speed for 1A exciting current. What will be the terminal voltage at rated speed and rated field current at no load [07D01]

a. 220 V b. 420 V c. 440 V d. 480 V

62. The maximum possible speeds in rpm at which an alternator can be driven to generate voltages at 60 Hz and 50 Hz are respectively: [07M01]

a. 2000, 2400 b. 3000, 3600 c. 2400, 2000 d. 3600, 3000

63. The synchronous generators used in thermal power stations have [07M02]

a. Cylindrical rotors b. Slip rings and brushes c. Laminated rotor d. 3-Phase star connected stator windings

64. The most appropriate speeds in rpm of generators used in thermal, nuclear and hydro-power plants would respectively be [07M03]

a. 3000 , 300 and 150 b. 3000 , 3000 and 300 c. 1500, 1500 and 3000 d. 1000, 900 and 750

65. If the number of poles of an alternator is increased, the generated emf [07S01]

a. Increases b. decreases c. remains the same d. Decreases and remains same

66. The emf generated in an alternator depends upon [07S02]

a. frequency b. flux per pole c. number of turns in the coils d. frequency, flux per pole, number of turns in the coils

67. The emfs generated in three phases of an alternator are ---- electrical degreees apart [07S03]

a. 60 b. 90 c. 120 d. 180

68. In ac rotating machines, the generated emf [07S04]

a. Is in phase with the working flux Φ b. Lags behind Φ by 900 c. Leads Φ by 900 d. Lags Φ by 1800

69. The angle between induced emf and terminal voltage on no-load for a single phase alternator is [07S05]

a. 1800 b. 900 c. 00 d. 600

70. When speed of an alternator is changed from 3600 rpm to 1800 rpm the generated emf/phase will become [07S06]

a. one half b. twice c. four times d. one fourth

71. To eliminate rth harmonic from the induced emf in a phase of synchronous machine the pitch of the coil must be [08D01]

a. fraction of full pitch

b. fraction of full pitch

c. fraction of full pitch

d. fraction of full pitch 72. The pitch factor for 3rd harmonic in an alternator having 18 slots/pole and coil span

5/6 of pole pitch is [08M01]

a. 0.707 b. 0.259 c. 0.966 d. 1

73. A salient pole synchronous generator connected to an infinite bus will deliver maximum power at a power angle of [08M02]

a. δ=00 b. δ=900 c. δ=450 d. δ=1800

74. The power factor of an alternator under short circuit conditions is almost near [08M03]

a. Zero leading b. Zero lagging c. Unity d. Zero leading or Zero lagging depending upon the type of alternator

75. The harmonic component in generated emf will be more in case of ----- pitch coils [08S01]

a. short b. full c. long d. wide

76. In an alternator, the use of short pitch coils having pitch of 160? will elimate---harmonic component for the emf generated [08S02]

a. 3rd b. fifth c. 7th d. ninth

77. To eliminate the 5th harmonic from the emf generated in an alternator, the pitch fraction will be [08S03]

a. 4/5 b. 5/4 c. 5/6 d. 6/5

78. A coil of 1500 pitch has third harmonic pitch factor as [08S04]

a. sin 450 b. cos 450 c. sin 2250 d. cos 2250

79. The stator winding of an alternator is normally connected in star to eliminate the ---harmonic component of the voltage waveform [08S05]

a. third

b. fifth c. seventh d. 13th

80. In a synchronous generator operating at zero power factor, lagging the effect of [08S06]

a. magnetizing b. demagnetizing c. cross- magnetizing d. both magnetizing and cross- magnetizing

81. A 3-phaes synchronous machine has an unsaturated synchronous reactance equal to 3 ohms per phase. The saturated synchronous reactance [09D01]

a. Will be more than 3 ohm b. Will be less than 3 ohm c. Will be more or less than 3 ohm d. Will be 3 ohm or more than 3 ohm

82. In modern large size synchronous machines,the synchronous impedance is about [09D02]

a. 0.2 pu b. 0.5 pu c. 1.0 pu d. 0.05 pu

83. The emf set up by the leakage flux due to self induction is called the ------ emf [09M01]

a. leakage b. reactance c. self-induced d. mutual-induced

84. In an alternator short-circuit current is limited by the [09M02]

a. Saturated synchronous impedance b. Unsaturated synchronous impedance c. Both Saturated & Unsaturated synchronous impedance d. Neither Saturated nor Unsaturated synchronous impedance

85. Unsaturated synchronous impedance limits [09M03]

a. Short circuit current b. Open circuit voltage c. Resistance d. Reactance

86. Synchronous reactance of alternator represents [09S01]

a. Armature reactance and leakage reactance b. A reactance operating at synchronous speed c. Field winding reactance d. A reactance connected in series with a synchronous generator

87. Armature reactance and leakage reactance represents [09S02]

a. Synchronous reactance b. Synchronous resistance c. Synchronous conductance d. Synchronous admittance

88. The synchronous reactance of an alternator is due to [09S03]

a. Leakage flux only b. Reactance because of armature reaction only c. Synchronous machine reactance d. Both leakage flux as well as armature reaction

89. The saturated synchronous reactance of an alternator is ------------ its unsaturated reactance [09S04]

a. more than b. less than c. equal to d. two times

90. The magnitude of leakage flux depends upon [09S05]

a. The magnitude of armature current b. Phase angle between armature current and terminal voltage c. Air gap thickness d. Both the magnitude of armature current, Phase angle between armature current

and terminal voltage 91. In an alternator when Ia is in phase with generated voltage E under balanced load

conditions, the phase difference between resultant armature flux and main-field flux is [10D01]

a. 900 lagging b. zero c. 1800 d. 900 leading

92. At leading power factor operation, an alternator [10M01]

a. is over-excited b. is under-excited c. has no residual magnetism d. has negative torque angle

93. In an alternator the terminal voltage drops due to [10M02]

a. Armature resistance b. Armature leakage reactance c. Armature reaction d. Armature resistance,reaction,leakage reactance

94. In a synchronous machine, armature reaction is considered equivalent to [10S01]

a. Fictitious reactance b. fictitious resistance c. Fictitious impedance d. fictitious conductance

95. In an alternator, the armature reaction influences the magnitude of [10S02]

a. no load loss b. speed of the machine c. terminal voltage per phase d. wave form of voltage generated

96. The fictitious part of synchronous reactance takes care of [10S03]

a. voltage regulation b. inductive reactance c. armature reaction d. efficiency

97. With capacitive load, armature reaction flux of alternator will be [10S04]

a. Helping the main magnetic field b. Opposing the main magnetic field c. Either helps or opposes the main magnetic field d. Fluctuating

98. With a load power factor of unity the effect of armature reaction on main field flux of an alternator is [10S05]

a. Distortional b. Magnetizing c. Demagnetizing d. Nominal

99. At lagging loads armature reaction in an alternator is [10S06]

a. Cross magnetizing b. Demagnetizing c. Non-effective d. Magnetizing

100. At leading power factor the armature flux in an alternator -------- the rotor flux [10S07]

a. opposes b. aids c. distorts d. does not effect

101. In an alternator, the flux created by the armature mmf -------directly from the main Flux for the following condition of the load power factor is zero lagging [11M01]

a. Subtracts b. Additive c. Multiplicative d. Remains same

102. As load power factor of an alternator becomes more leading the value of generated voltage required to give rated terminal voltage [11M02]

a. increases b. remains unchanged c. decreases d. varies with rotor speed

103. In an alternator running with a balanced zero power factor lagging load,phase difference between the resultant armature (or stator) flux and main field flux is always [11M03]

a. 1800 b. zero c. 900 leading d. 900 lagging

104. For which condition of the load power factor, in an alternator, the flux crated by the armature m.m.f subtract directly from the main flux for the following conditions of the load [11M04]

a. load power factor is zero lagging b. load power factor is zero leading c. load power factor is unity d. load power factor is 0.6 lagging

105. The load sharing between two steam driven alternators operating in parallel may be adjusted by varying the [11M05]

a. Field strengths of the alternators b. Power Factors of the alternators c. Steam supply to their prime movers d. Speed of the alternators

106. When the load (inductive) is thrown off, the terminal voltage will [11S01]

a. increase b. decrease c. remains unchanged d. may increase or decrease

107. In an alternator terminal voltage will rise [11S02]

a. When unity power factor load is thrown off b. When leading load is thrown off c. When lagging load is thrown off d. When unity and leading load is thrown off

108. an alternator, when the load power factor is unity [11S03]

a. The armature flux will reduce to zero b. The armature flux will have square wave form

c. The armature flux will be demagnetizing d. The armature flux will be cross-magnetizing

109. When the terminal voltage of an alternator drops on throwing the load, it indicates that the load was predominantly [11S04]

a. Resistive b. Inductive c. Capacitive d. Resistive, inductive and capacitive

110. The power factor of an alternator is determined by its [11S05]

a. load b. speed c. excitation d. prime mover

111. If the excitation is kept constant in an alternator ,then the excitation voltage variation with speed would be [12D01]

a. First linear and the curved upwards b. First linear and then horizontal c. Linear d. First curved and then linear

112. In a slip test of an alternator armature flux, Voltage in field winding for Xq are respectively [12M01]

a. Minimum , Maximum b. Minimum, Minimum c. Maximum, Maximum d. Maximum , Minimum

113. In a slip test of an alternator Voltage in field winding, Armature current for Xq are respectively [12M02]

a. Maximum, Maximum b. Minimum, Maximum c. Maximum, Minimum d. Minimum, Minimum

114. In a slip test of an alternator Armature flux , Armature current for Xq are respectively [12M03]

a. Maximum, Minimum b. Minimum, Maximum c. Maximum, Maximum d. Minimum, Minimum

115. In a slip test of an alternator armature flux, Voltage in field winding, Armature current for Xq are respectively [12M04]

a. Maximum, Maximum , Minimum b. Minimum, Maximum, Minimum c. Maximum, Maximum, Maximum d. Minimum, Maximum, Maximum

116. In a synchronous generator [12S01]

a. The open circuit voltage leads the terminal voltage by an angle known as power angle

b. The open circuit voltage leads the terminal voltage by an angle known as overlap angle c. The open circuit voltage lags the terminal voltage by an angle known as power lag d. The open circuit voltage lags the terminal voltage by an angle known as overlap angle

117. Alternators are rated in terms of [12S02]

a. KW b. KWA c. KWh d. KVAR

118. For the same power rating, the higher voltage alternator is [12S03]

a. larger the size b. cheaper c. costlier d. smaller in size

119. An alternator is said to be under-excited if it operates at [12S04]

a. unity pf b. leading pf c. lagging pf d. exactly 0.2 pf

120. Under no load condition power drawn by the prime mover of an alternator goes to [12S05]

a. Produce induced emf in armature winding b. Meet no-load losses c. Produce power in the armature d. Meet Cu losses both in armature and rotor windings

121. Two mechanically coupled alternators deliver power at 50 Hz and 60Hz respectively. The highest speed of an alternators is [13D01]

a. 3600rpm b. 3000rpm c. 600 rpm d. 500 rpm

122. In a slip test of an alternator armature flux, Voltage in field winding for Xd are respectively [13M01]

a. Maximum, Zero b. Minimum, Zero c. Zero, Maximum d. Zero, Minimum

123. In a slip test of an alternator Voltage in field winding, Armature current for Xd are respectively [13M02]

a. Maximum, Zero b. Minimum, Zero c. Zero, Maximum d. Zero, Minimum

124. In a slip test of an alternator Armature flux , Armature current for Xd are respectively [13M03]

a. Maximum, Minimum b. Minimum, Maximum c. Maximum, Maximum d. Minimum, Minimum

125. In a slip test of an alternator armature flux, Voltage in field winding, Armature current for Xd are respectively [13M04]

a. Maximum, Zero , Minimum b. Minimum, Zero, Minimum c. Zero, Maximum, Minimum d. Zero, Minimum, Maximum

126. Slip test is peformed to determine [13S01]

a. Slip b. Direct axis and Quadrature axis reactance c. Positive and negative sequence reactance d. Sub transient reactance

127. While conducting SLIP TEST the rotor of the machine is run with a slip 's' and the stator supply frequency 'f' . The frequency of voltage induced across open field terminals is [13S02]

a. sf b. f

c. (1-s)f d. (2-s)f

128. While conducting SLIP TEST the rotor of the machine is run with a slip 's' and the stator supply frequency 'f' . The frequency of envelope of the armature terminal voltage [13S03]

a. sf b. f c. (1-s)f d. (2-s)f

129. While conducting SLIP TEST the rotor of the machine is run with a slip 's' and the stator supply frequency 'f' . The frequency of envelope of the armature current [13S04]

a. sf b. f c. (1-s)f d. (2-s)f

130. While conducting SLIP TEST the rotor of the machine is run with a slip 's' and the stator supply frequency 'f' . The frequency of armature current [13S05]

a. sf b. f c. (1-s)f d. (2-s)f

131. The voltage regulation of an alternator having 0.75 leading power factor load, no-load induced emf of 2400V and rated terminal voltage of 3000V is --------- [14D01]

a. 20 % b. -20 % c. 150 % d. -26.7 %

132. The zero-power- factor characteristic for the potier diagram can be obtained by loading the alternator using [14M01]

a. Lamp load b. Synchronous motor c. Water load d. Dc motor

133. Potier resistance of an alternator is almost the same as [14M02]

a. field winding reactance b. total armature reactance c. leakage reactance of field winding d. armature leakage reactance

134. Which one of following methods would give a higher actual value of regulation of an alternator [14M03]

a. ZPF method b. MMF method c. EMF method d. ASA method

135. When an alternator feeds resistive or inductive load, regulation is [14S01]

a. Always positive b. Always negative c. Either positive or negative d. Zero

136. Voltage regulation obtained by synchronous impedance method is [14S02]

a. More than that given by actual tests b. Less than given by actual tests c. Equal to that given by actual tests d. Cannot be compared

137. Regulation of an alternator supplying leading load is [14S03]

a. Positive or negative depending upon load and power factor b. Always positive c. Always negative d. Always Zero

138. Zero power factor method of an alternator is generally used to determine [14S04]

a. Efficiency of alternator b. Synchronous impedance of alternator c. Voltage regulation of the alternator d. Power factor of alternator

139. Best method of finding the voltage regulation is [14S05]

a. MMF method

b. POTIER triangle method c. Synchronous impedance method d. MMF, EMF, POITER triangle method

140. The voltage regulation of an alternator for a p.f of 0.8 lagging is ---at unity [14S06]

a. greater than

b. smaller than c. same as d. cannot be compared

141. The phasor diagram by ASA method gives [15D01]

a. Reliable results for both regulation and power angle of a salient pole synchronous generator b. Reliable result for power angle but erroneous result for regulation

c. Reliable result for regulation but erroneous result for power angle d. Erroneous results for both regulation and power angle of salient-pole synchronous generator

142. The synchronous impedance method of determination of regulation of an alternator is also said to be the pessimistic method as it gives the value of synchronous impedance always [15M01]

a. More than its actual value under normal condition

b. Less than its actual value under normal condition c. Equal to synchronous reactance d. Zero

143. The regulation obtained by synchronous impedance method is always higher than actual value because [15M02]

a. Synchronous reactance is assumed variable while it is not b. Effective armature resistance is assumed constant c. Synchronous reactance is assumed constant while it is not d. Field current is increased to give short circuit current about twice of full-loadcurrent

144. Armature reaction mmf and leakage reactance of a synchronous machine are determined by [15M03]

a. Open-circuit and short-circuit tests b. Open-circuit and zero pf tests c. Open-circuit test only d. Zero pf test only

145. Match List I with List II and select the correct answer using the codes given below:

[15M04]

a. 1 2 4 3

b. 2 3 1 4 c. 4 3 1 2 d. 2 1 3 4

146. The regulation of an alternator is given as [15S01]

a. ((V-Eo)/v))*100 b. ((Eo-V)/V)*100 c. (V/Eo)*100 d. ((E0-V)/Eo)*100

147. Regulation of an alternator supplying resistive or inductive load is [15S02]

a. Always positive b. Always negative c. Always zero d. May be negative or equal to zero

148. The regulation of an alternator is likely to be negative in case of ---load [15S03]

a. Resistive b. Inductive c. Capacitive d. Resistive, inductive, capacitive

149. A leading pf load on an alternator implies that its voltage regulation shall be [15S04]

a. positive b. negative c. Zero d. Positive, negative or zero

150. The regulation of an alternator is defined as the [15S05]

a. Increase in terminal voltage when full-load is thrown off, assuming field current and speed remaining the same

b. Fall in terminal voltage when the full-load is thrown off, assuming field current and speed remaining unchanged

c. Increase in terminal voltage under the conditions of maximum and minimum excitations d. Decrease in terminal voltage under the conditions of maximum and minimum excitations

151. A synchronous generator connected to an infinite bus is over excited. Considering only the reactive power from point of view of the system the machine acts as [16D01]

a. a capacitor b. an inductor c. a resistor d. as RL circuit

152. During slip test the value of the direct axis synchronous reactance Xd is given by [16G01]

a. Xd = Vmax / Imin b. Xd = Vmax / Imin c. Xd = Vmax / Imin d. Xd = Vmin / Imax

153. In a synchronous machine [16M01]

a. Xd'' < Xd' <Xd b. Xd'' >Xd' >Xd c. Xd = Xd' d. Xd = Xd''

154. The phase of an alternator is RYB. If the direction of its field current is reversed the phase sequence will be [16M02]

a. RYB b. RBY c. YRB d. YBR

155. In a round rotor alternator, reactive power is maximum at a load angle of [16M03]

a. 900 b. 1800 c. 00 d. 450

156. During slip test the value of the quadrature axis synchronous reactance Xd is given by [16S01]

a. Xq = Vmin / Imax b. Xq = Vmin / Imin c. Xq = Vmax / Imax d. Xq = Vmax / Imin

157. The short circuit characteristics of synchronous machine [16S02]

a. Is always linear b. Is always non linear c. Is sometimes linear and some times non linear d. Depends upon the rating of the machine

158. In two reaction theory the armature current is decomposed into two components Id and Iq. If E and V are the generated emf and terminal voltage of the machine then [16S03]

a. Id is perpendicular to V and Iq is in phase with V b. Id is in phase with E and Iq is perpendicular to E c. Id is perpendicular to E and Iq is in phase with E d. Id is in phase with V and Iq is perpendicular to V

159. In two reaction theory the armature current is decomposed into two components Id and Iq. If E and V are the generated emf and terminal voltage of the machine then [16S04]

a. Id is perpendicular to V b. Id is in phase with E c. Id is perpendicular to E d. Id is in phase with V

160. In two reaction theory the armature current is decomposed into two components Id and Iq. If E and V are the generated emf and terminal voltage of the machine then [16S05]

a. Iq is in phase with V b. Iq is perpendicular to E c. Iq is in phase with E d. Iq is perpendicular to V

161. Two alternators are operating in parallel. For taking one of the alternators out form the system [17D01]

a. Load shared to the alternator is transferred to the other by adjusting the power fed to the prime mover before opening OCB

b. Power fed to the prime mover is stopped c. OCB is switched off d. Load connected to bus bar is reduced

162. Desirable feature for successful parallel operation of two alternators is that both should have [17G01]

a. Same resistance b. same reactance c. high reactance in comparison to resistance d.

163. Synchronising current means [17M01]

a. The total current supplied to the load by the alternators operating in parallel b. The current supplied by the synchronous generator

c. The current circulating in the local circuit of two alternators in synchronism once they are out of it

d. The total current supplied to the load by the alternators operating in series 164. If the voltage of one of the two machines operating in parallel suddenly falls

[17M02]

a. Both the machines will stop b. The machine whose voltage has suddenly decreased will stop. c. The synchronous torque will come into operation to restore synchronism d. Both machines will run

165. Synchronising torque will come into operation whenever [17M03]

a. There is a difference in the magnitude of Voltage b. There is no phase difference in the voltages c. There is no frequency difference between the two voltages d. Excitation of one of the alternators does not changes

166. Which of the following method used for synchronizing of 3-phase synchronous generators is considered best one? [17S01]

a. Three dark lamp method b. Two-bright and one dark lamp method c. Synchroscope d. three dark lamp and one dark lamp method

167. While synchronizing a 3-phase alternator to the bus-bar the paralleling switch should be closed [17S02]

a. Just before the pointer reaches the vertical position when moving in the fast direction

b. Just after the pointer passes the vertical position when moving in the fast direction c. When pointer indicates fast position d. When pointer indicates slow position

168. The two-bright and one dark lamp method is used for [17S03]

a. Determination of phase sequence b. Synchronizing of 3-phase alternators c. Synchronizing of single-phase alternators d. Transfer of load

169. An infinite bus-bar has [17S04]

a. constant voltage b. constant frequency c. infinite voltage d. constant voltage and constant frequency

170. A stationary alternator should not be connected to the live bus-bar because [17S05]

a. It is likely to operate as a synchronous motor b. It will get short-circuited c. It will reduce bus-bar voltage d. It reduce bus-bar frequency

171. After wiring up two 3-phase alternators you checked their frequency and voltage and found them to be equal. Before connecting them in parallel you would [18D01]

a. Check turbine speed b. Check phase rotation c. Lubricate every thing d. Check steam pressure

172. Some prefer 'lamps bright synchronization' to 'lamps dark synchronization' because: [18D02]

a. Brightness of lamps can be judged easily b. It gives sharper and more accurate synchronization c. Flicker is more pronounced d. It can be performed easily

173. The experimental data required for potier method of finding regulation of alternators are [18M01]

a. No-load curve, short circuit test values b. Zero power factor curves, short circuit test values c. No-load curve, zero power factor curves d. Only no-load curve

174. For proper parallel operation ,a.c polyphase alternators must have same [18M02]

a. Speed b. Voltage rating c. Kva rating d. Excitation

175. Of the following conditions the one which is does not met by an alternator working in parallel [18M03]

a. Terminal voltage of each machine must be same b. The machines must have the same phase rotation c. The machines must operate at the same frequency d. The machines must have equal rating

176. To have two alternators in parallel which of the following factors should be identical for both [18S01]

a. Voltage b. Phase sequence c. Frequency d. Voltage, phase sequence and frequency.

177. The dark and bright lamp method is used in alternator for [18S02]

a. Balancing of load b. Phase sequence c. Transfer of load d. Synchronizing

178. When two alternators run in parallel, their KVAR load shares and KW load share are changed by changing their [18S03]

a. Excitation and excitation b. Excitation, driving torque respectively c. Driving torque, excitation respectively d. Driving torque, driving torque respectively

179. In an alternator the frequency per revolution is equal to [18S04]

a. Number of poles b. Number of pairs of poles c. Number of armature conductors d. Forty

180. The synchronous impedance method to find voltage regulation of an alternator is not an accurate method because the value of synchronous impedance found is [18S05]

a. Always more than its value under normal conditions b. Always less than its value under normal conditions c. Only the synchronous reactance d. Only the armature resistance

181. When Two alternators are operating in parallel,if the power input to one of the alternators is cut-off the alternator will [19D01]

a. Continue to run as a synchronous motor rotating in the same direction b. Continue to run as a synchronous motor rotating in the opposite direction c. Stop running d. Get damaged due to burning of stator and rotor windings

182. If the excitation of an alternator connected to an infinite bus-bar is changed, keeping the power input to its prime-mover unchanged its ---------- will change [19M01]

a. Kw output b. Power-factor c. KVA & KVAR output d. Kw output, power factor, KVA & KVAR output

183. A 3-phase alternator with constant power input is supplying electrical power to an infinite bus at a lagging power factor. If its excitation is reduced [19M02]

a. Both power factor and power angle will increase b. Both power factor and power angle will decrease c. Power factor will increase but power angle will decrease d. Power factor will decrease but power angle will increase

184. A 3-phase alternator with constant excitation is supplying electrical power to an infinite bus at a lagging power factor. If the power input is reduced [19M03]

a. Both power factor and power angle will increase b. Both power factor and power angle will decrease c. Power factor will increase but power angle will decrease d. Power factor will decrease but power angle will increase

185. If the excitation of one of the alternators operating in parallel is increased while keeping input to its prime mover unchanged then the [19S01]

a. Reactive components of the output will change b. Active component of the output will change c. Power factors of the alternators will not change d. Kva supplied by the alternators will not change

186. Two alternators A and B are sharing an inductive load equally if the excitation of alternator A is increased [19S02]

a. Alternator B will deliver more current and alternator A will deliver less current b. Alternator B will deliver less current and alternator A will deliver more current c. Both will continue to share load equally d. Both will deliver more current

187. Two alternators are operating in parallel, If the power input to the prime movers of both the alternators is increased this will affect change in [19S03]

a. generated emf b. frequency c. terminal voltage d. generated emf and voltage

188. Two alternators are operating in parallel and sharing a common load. For increasing the load shared by one of them [19S04]

a. Power input is kept constant and excitation is increased b. Power input is kept constant and excitation is reduced c. Power input is increased keeping excitation constant d. Power input is reduced keeping excitation constant

189. The load shared between two alternators operating in parallel may be adjusted by varying [19S05]

a. their speed b. their excitation c. power input to their prime movers d. speed and excitation

190. The Kva/Kvar shared between two alternators operating in parallel sharing a common load are adjusted by varying [19S06]

a. their speed b. excitation c. power input to their prime movers d. speed and input to their prime movers

191. An alternator on open circuit generates 320 V at 50Hz when the field current 3.2A. Neglecting saturation, when the frequency is 25Hz and the field current is 2A, the open circuit emf is [20D01]

a. 50 V b. 100 V c. 200 V d. 150V

192. In a 3-Φ star connected alternator a field current of 40 A produces full-load current of 200A on short circuit and 1160 V on open circuit. If the resistance of the alternator is 0.5Ω the value of synchronous reactance is [20D02]

a. 5-7 Ω b. 8.73 Ω c. 3.31 Ω d. 9 Ω

193. A 3-Phase alternator has negligible stator resistance. A short circuit test is conducted o this alternator. At a particular speed, a field current of If1 is required to drive the rated armature current. If the speed of the alternator is reduced to half, the field current required to maintain rated armature current. [20M01]

a. would be equal to If1 b. would be equal to 2 If1 c. would be equal to 1f1/2 d. would be equal to 3 If1

194. A cylindrical rotor synchronous generator will deliver maximum output when [20M02]

a. load angle = synchronous impedance angle b. load angle = internal power- factor angle c. load angle = 900 d. input power factor is unity

195. A 3-phase synchronous generator is operating at constant load while the excitation is adjusted to give unity of pf current. If the excitation is increased, the pf will [20M03]

a. become leading b. become lagging c. remain at unity d. become zero

196. The Power factor of an alternator driven by constant prime mover input can be changed by changing [20S01]

a. field excitation b. phase sequence c. load d. speed

197. In case of two alternators running in parallel and perfectly synchronized, the synchronizing power is [20S02]

a. zero b. positive c. negative d. infinite

198. To run two alternators in parallel, the black lamp test is performed to ensure proper [20S03]

a. frequency matching b. phase difference matching c. voltage matching d. phase sequence matching

199. Drop in terminal voltage of an alternator due to armature reaction is countered by [20S04]

a. Damper winding b. effect of saliency c. increased prime mover input d. Automatic voltage regulation

200. The armature reaction of an alternator is safely determined by [20S05]

a. Amount of current drawn from the alternator b. Power factor of the load c. Speed of the prime mover driving the alternator d. Amount of voltage drawn from the alternator