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GATE 2014 EE (EE2) – Question 48

Electrical Machines · Synchronous machines: cylindrical and salient pole machines, performance and characteristics, regulation and parallel operation of generators, starting of synchronous motors · 2 marks · Multiple choice

A 20-pole alternator has 180 identical stator slots with six conductors each; coils of each phase are in series. Generated single-phase voltage is V₁. Reconnect for three-phase star winding with phase voltage V₂. Assume full-pitch, single-layer winding. Find V₁/V₂.

  1. $1/\sqrt3$
  2. $1/2$
  3. $\sqrt3$
  4. $2$

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Correct answer: (D) $2$

Explanation

There are9slots per pole,with electrical slot angle20°. Single-phase q=9gives kd1=sin90°/[9sin10°]. Three-phase q=3gives kd3=sin30°/[3sin10°]. Each three-phase phase has one-third as many series turns. Thus V1/V2=3kd1/kd3=3×(2/3)=**2,D**;full-pitch factors cancel.