Electrical Machines Questions and Answers – EMF Polygon – 1

This set of Electrical Machines Multiple Choice Questions & Answers (MCQs) focuses on “EMF Polygon – 1”.

1. The angular slot pitch, γ is given by __________
a) γ = πP/Total number of slots Elect radians
b) γ = 180P/Total number of slots Elect degrees
c) γ = 180/Slots per pole Elect degrees
d) Any of the mentioned
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2. Which of these statements are correct regarding the design of distributed armature winding in a 3-phase alternator?

(i) it reduces the phase-belt harmonics
(ii) it increases the utilization of the armature iron and copper
(iii) it increases rigidity and mechanical strength of the winding
(iv) it reduces copper in the overhang of the winding

a) (i), (iii), (iv)
b) (ii), (iii), (iv)
c) (i), (ii), (iii)
d) (i), (ii), (iii), (iv)
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3. What is the coil span for a 2 pole 18 slot machine?
a) 9
b) 4.5
c) 18
d) 6
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4. In a machine with coil span 9, if a coil has its one coil-side in slot 1, then its other coil-side must be in ____________
a) slot 9
b) slot 8
c) slot 10
d) slot 2
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5. The belt factor is defined as the ratio of __________
a) arithmetic sum of coil EMF to the phasor sum of coil EMFs
b) phasor sum of EMF per coil to the arithmetic sum of EMF per coil
c) phasor sum of coil EMFs to the arithmetic sum of coil EMFs
d) phasor sum of coil EMFs to per phase voltage
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6. The armature winding of a 2-pole, 3-phase alternator for each phase is distributed in a number of slots per phase. The RMS value of the voltage per phase is less than the RMS value of the voltage per coil multiplied by the number of coils in series because the _________
a) RMS value of the voltage in different coils of the phase is different
b) equal RMS voltages in different coils of the phase has mutual phase difference
c) maximum value of the induced voltage in different coils of the phase are different
d) different coils of the phase pass through different saturated regions of the magnetic circuit
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7. A 3-phase machine has integral slot winding with fundamental distribution factor k_d1, the distribution factor for n^th harmonic k_dn is ____________
a) less than k_d1
b) more than k_d1
c) equal to k_d1
d) depends upon the number of slots and poles
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8. If a stator has 48 slots, 6 poles and 3 phase with narrow spread winding, then the third harmonic belt factor is ____________
a) 0.9556
b) 0.6407
c) 0.1944
d) None of the mentioned
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9. A fraction pitch winding is used to reduce which of the following?

(i) amount of copper in the winding
(ii) size of the machine
(iii) harmonics in the generated EMF
(iv) cost of the machine

a) (i), (ii), (iii), (iv)
b) (i), (ii), (iii)
c) (ii), (iii), (iv)
d) (i), (iii), (iv)
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10. The pitch factor, in rotating electrical machinery, is defined as the ratio of resultant EMF of a _________
a) full-pitched coil to that of a chorded coil
b) full-pitched coil to the phase EMF
c) chorded coil to the phase EMF
d) chorded coil to that of a full-pitched coil
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Sanfoundry Global Education & Learning Series – Electrical Machines.

To practice all areas of Electrical Machines, here is complete set of 1000+ Multiple Choice Questions and Answers.

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