PROCEDURE IN DESIGN OF D.C. GENERATOR 217 



line in Fig. 81, which very closely expresses the true relation 

 between the tooth density and the average density over the slot 

 pitch, for the entire range of values from zero to the highest 

 attainable. 



Item (71): Saturation Curves for Air Gap, Teeth, and Slots. 

 Refer Art. 38, page 121, and Art. 42, page 132. We are now in 

 a position to plot curves similar to those of Fig. 49, page 133; 

 and, in order to obtain a proper value for the ampere-turns neces- 

 sary to overcome the reluctance of the teeth, the correction for 

 the taper of teeth should be applied. The results of the calcu- 

 lations for the teeth are shown in tabular form; the meaning of 

 the different columns of figures being as follows: 



First column: Assumed values of air-gap density B g , including 

 the highest value likely to be attained. 



Second column: The corresponding values of the density B t 

 at the bottom of the tooth (read off the full-line curve of Fig. 81). 



Third column: The magnetizing force H, calculated, when 

 necessary, by applying SIMPSON'S rule (Formula 64), as explained 

 in Art. 38. 



Fourth column: The ampere-turns required to overcome the 

 reluctance of the teeth, being 



Hd, X 2.54 



where d, is the "equivalent" length of tooth; its numerical value, 

 in this example, being (1 + 0.25) - 0.307 = 0.943 in. 



As an example of the method of calculation, consider the value 

 B = 10,000; the corresponding value of tooth density, as read 

 off Fig. 81, is B t = 22,100. This is the actual density at the 

 root of the tooth. Referring to items (32) and (34), it is seen 

 that, over a distance of 1 in., the width of tooth changes by the 

 amount 0.576 - 0.466 = 0.11 in. The width of tooth at the 

 distance d, from the bottom of tooth (see Fig. 38) is therefore 



