26 PROBLEMS IN ALTERNATING CURRENT MACHINERY 



If the coil pitch is 1.0 what is the generated armature voltage 

 per turn? What is the form factor of this e.m.f.? 



15. With normal excitation the resultant air-gap flux in a 60- 

 cycle alternator is 10 6 lines per pole. The equation of the curve 

 which represents the flux density in the air-gap is: 



B = Bi sin X+B& sin 5x 



x is the electrical angle measured from the point midway between 

 the poles. Take B b = 0.2#!. 



If the coil pitch is 1.0, what is the generated armature voltage 

 per turn? What is the form factor of this e.m.f.? 



16. In problem 15 if the coil pitch is 0.8, what is the generated 

 armature voltage per turn? What is the form factor of this 

 e.m.f.? 



17. In problem 15 if the coil pitch is 0.67 what is the generated 

 armature voltage per turn? What is the form factor of this 

 e.m.f.? 



18. With normal excitation the resultant air-gap flux in a 

 60-cycle alternator is 10 6 lines per pole. The equation of the 

 curve which represents the flux density in the air-gap is: 



B = Bi sin xB$ sin 5x 



x is the electrical angle measured from the point midway between 

 the poles. 



If the coil pitch is 1.0, what is the generated armature voltage 

 per turn? What is the form factor of this e.m.f.? 



19. With normal excitation the resultant air-gap flux in a 60- 

 cycle alternator is 10 6 lines per pole. The flux density is con- 

 stant under the pole face and is zero between the poles. The 

 armature has 8 equally spaced slots per pole. The ratio of pole 

 arc to pole pitch is 0.67 and the coil pitch is 1.0. 



(a) If the armature winding consists of 2 inductors in series 

 per pole placed in adjacent slots, what is the generated armature 

 voltage per pole? What is the form factor of this e.m.f. ? Sketch 

 the graphs of the flux density and the e.m.f. 



(b) Compare this e.m.f. and form factor with what they 

 would have been had the winding been concentrated i.e., with 

 2 inductors in series per pole, placed in the same slot. 



20. In problem 19 if the armature winding consists of 4 induc- 

 tors in series per pole placed in adjacent slots, what is the gene- 



