Electrical Machines Questions and Answers – MMF Produced by Distributed Windings

This set of Electrical Machines Multiple Choice Questions & Answers (MCQs) focuses on “MMF Produced by Distributed Windings”.

1. The winding MMF in rotating machines depends on ___________
a) winding arrangement
b) winding current
c) air gap length,slot openings etc
d) both winding arrangement and winding current
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2. A knowledge of the air gap flux distribution in a machine helps in determining the ___________
a) generated EMF waveform and its magnitude
b) electrical torque
c) winding MMF
d) both generated EMF waveform and electrical torque
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3. If the current in the coil is DC, then MMF doesn’t vary with ____________
a) space
b) time
c) both space and time
d) none of the mentioned
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4. If the current in a coil is AC, the amplitude of MMF ___________
a) varies with time but not with space
b) varies with space but not with time
c) varies with both space and time
d) doesn’t vary with both space and time
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5. Peak value of fundamental component of MMF produced by one N-turn coil carrying a current ‘i’ is ____________
a) 4/Π(Ni)
b) 2/Π(Ni)
c) 1/Π(Ni)
d) 1/2Π(Ni)
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6. The armature MMF wave in a DC machine is ____________
a) sinusoidal and depends on the speed
b) square and independent of speed
c) triangular and depends on speed
d) triangular and independent of speed
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7. Which of the following statements are correct regarding the current sheet?
a) it is a thin strip of conducting material carrying the current in the dot
b) it is wrapped around stator or rotor
c) it develops MMF identical to that produced by the winding it replaces
d) any of the mentioned
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8. A current sheet with sinusoidal current produces?
a) sinusoidal MMF wave lagging it by 90°
b) sinusoidal MMF wave leading it by 90°
c) trapezoidal MMF wave leading it by 90°
d) trapezoidal MMF wave lagging it by 90°
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9. A uniformly distributed winding on the stator has three full pitched coils, each coil having N turns and each turn carrying a current i. The MMF produced by the winding is?
a) sinusoidal in waveform with an amplitude 3Ni
b) sinusoidal in waveform with an amplitude 3Ni/2
c) trapezoidal in waveform with an amplitude of 3Ni
d) trapezoidal in waveform with an amplitude of 3Ni/2
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10. MMF produced by one N-turn coil carrying a current i is ____________
a) rectangular of amplitude Ni/2
b) trapezoidal of amplitude Ni/2
c) rectangular of amplitude Ni
d) trapezoidal of amplitude Ni
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11. A winding of 20 full pitched series turns, distributed over a band of 60° under each pole, carries a current of 3A. The winding produces a uniform current sheet of density (in AT’s per electrical radiangs) of ___________
a) 180/Π
b) 120/Π
c) 90/Π
d) 60/Π
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12. A sinusoidal current sheet in a rotating electrical machine has peak value along q-axis. The peak value of sinusoidal MMF would be ___________
a) in phase with current peak
b) 90° lagging the current peak
c) 90° leading the current peak
d) may lag or lead depending upon the type of machine
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13. In a DC machine, z, p, I_a and a are respectively the number of conductors, number of poles, armature current and number of parallel paths. The peak value of fundamental component of armature MMF wave is ____________
a) 8/Π[(z/2p)(I_a/a)]
b) 8/Π²[(z/p)(I_a/a)]
c) 4/Π[(z/2p)(I_a/a)]
d) 8/Π²[(z/p)(I_a/a)]
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14. Which of the following statements are true regarding the armature MMF wave in a DC machine when it is triangular?

(i) rotates with respect to stator
(ii) is stationary with respect to stator
(iii) rotates with respect to armature
(iv) is stationary with respect to armature 

a) (ii) only
b) (iii) only
c) (i) and (iv)
d) (ii) and (iii)
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