PROCEDURE IN DESIGN OF D.C. GENERATOR 209 



Item (39): Flux Density in Teeth. Refer Art. 31, page 102, 

 and Art. 32, page 104. Before calculating the flux density in 

 the teeth, it is necessary to correct the figure for flux per pole 

 (item (19)), because the number of face conductors (Z) has been 

 changed. Thus, 



350 

 $ = 6,290,000 X = 6,430,000 maxwells. 



The apparent flux density at the center of the tooth, under 

 open-circuit conditions, is therefore, 



6,430,000 

 48.6 X 6.45 = 20,500 gausses. 







Referring to the table on page 104, it will be seen that a maximum 

 tooth density of 22,000 is permissible when the frequency is 20. 

 We do not yet know what will be the actual flux density at the 

 root of the teeth under full-load conditions; but it is not likely 

 to be excessive, and we may proceed with the design. 



At this stage it might be well to alter the gross length of the 

 armature core from 11.1 to exactly 11 in., reducing the net 

 length accordingly. This will account for the corrected values 

 of items (37) to (39) in the last column of figures of the design 

 sheets. 



Item (40): Length per Turn of Armature Coil. Referring to 

 Art. 30, page 97, we have, 



1.15s 1.15X0.5 



whence 

 and 



a = 32 20' 

 cos a = 0.845 



By formula (52), page 98, 



L-i^m^ 



3 = 43.3 in. 



0.845 



Therefore the total length per turn = l e + 2l a = 43.3 + 22 = 

 65.3 in. 



Item (41) : Ratio of Copper in Slots to Total Armature Copper. 

 Refer Art. 34, page 109. 



2Z a 22 



65.3 



~ 



Items (42) to (45) : Armature Resistance. Refer Art. 30, page 

 97. The total length of one turn of the armature winding is 



14 



