Question

An 3 phase synchronous motor is 90 electrical degree an 6 slots what is the distrubution factor

Answer 1



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Electrical Machines Questions and Answers – EMF Polygon – 2

This set of Electrical Machines Multiple Choice Questions & Answers (MCQs) focuses on “EMF Polygon – 2”.
1. The winding’s for a 3-phase alternator are:
(i) 36 slots, 4 poles, span 1 to 8
(ii) 72 slots, 6 poles, span 1 to 10
(iii) 96 slots, 4 poles, span 1 to 21
The winding’s having pitch factor of more than 0.97 are
a) (i) and (ii) only
b) (ii) and (iii) only
c) (i) and (iii) only
d) (i),(ii) and (iii)
View Answer

Answer: c
Explanation: Kp=cosε/2
(i) Slots per pole= 36/4=9, for a coil span of 8 slots, the coil is short pitched by 1 slot and the chording angle is ε=γ= 20° ⇒ Kp=cos10°=0.985
(ii) Slots per pole= 72/6=12, for a coil span of 10 slots, the coil is short pitched by 2 slots and the chording angle is ε=2γ and γ=180/12 ⇒ ε= 30° ⇒ Kp=cos15°=0.9659
(iii) Slots per pole= 96/4=24, for a coil span of 21 slots, the coil is short pitched by 3 slots and the chording angle is ε=3γ and γ=180/24 ⇒ ε= 24.5° ⇒ Kp=cos12.25°=0.97723.