Question

How are the three different emfs generated in a three-phase AC generator? Show the graphical representation of these three emfs.

Answer 1

1. In three-phase AC generator, the armature has 6 slots cut on its inner rim. Each slot is 60° away from one another. Six armature conductors mounted in these slots.
2. The conductors 1 and 4 joined in series to form coil 1.
   The conductors 3 and 6 form coil 2.
   The conductors 5 and 2 form coil 3.
3. These coils are rectangular and 120° apart from one another.
4. The initial position of field magnets is horizontal and direction is perpendicular to plane of coil 1.
5. When rotates from clockwise direction alternating emf in coil 1 begins a cycle from 0.
6. The corresponding cycle for in coil 2 starts at A after field magnet rotated through 120°.
7. So phase difference between ε₁ and ε₂ is 120°.
8. Similarly, ε₃ in coil 3 would begin its cycle at B after 240° from the initial position.
9. Thus emfs produced in a three-phase AC generator have 120° phase difference between one another.
   
   Construction of three-phase AC generator
   
   

   Variation of emfs ε₁, ε_2, and ε₃ with time angle