IX AMPLE OF ALTERNATOR DESIGN 



343 



filled with material equal in weight to the copper and insulation 

 in the wound slots, in order to improve the balance and equalize 

 the stresses at high speeds; and the proportion of magnetic to 

 non-magnetic metal can be so adjusted as to obtain any desired 

 tooth reluctance. If we provide wedges having a thickness of 

 J in. at the bottom of the slot, we can get the equivalent of a 

 center tooth 2.2 in. wide with parallel sides. This calls for an 

 additional curve in Fig. 139, which can be calculated in the same 

 manner as the curve previously drawn, except that the correction 

 for taper of teeth (SIMPSON'S rule) has hot to be applied. 



If we decide upon a rotor winding with 9,000 ampere-con- 



FIG. 







Electrical Degrees 



141. Air-gap flux-distribution curves 8000 k.v.a. turbo-generator. 



ductors per slot as indicated by the stepped curve in the lower 

 part of Fig. 140, we shall obtain an open-circuit flux curve (A) 

 as plotted in Fig. 141. This curve would be exactly similar in 

 shape to the flux curve of Fig. 140 if it were not for the fact that 

 the widening of the tooth at the center of the rotor pole face 

 has lowered the reluctance at this point rather more than would 

 have been necessary in order to obtain the perfect sine curve 

 of flux distribution. The slightly higher ordinate at the center 

 of the new flux curve adds so little to the area of this curve that 

 we shall not trouble to measure this. It is evident that the 

 proposed excitation with 9,000 ampere-conductors per slot will 

 generate the required open-circuit voltage. 



