PROCEDURE IN DESIGN OF D.C. GENERATOR 207 



Item (25) : Cross-section of Armature Conductors. By formula 

 (51), page 97. 



500,000 3,070 



" 2 ' 075 



475 



QQ A 



' 



whence area of cross-section = ' 7C . = 0.0402 sq. in. 



Z,Ui O 



Items (26) to (31): Conductor and Slot Dimensions. It is neces- 

 sary to find by trial the best arrangement of slots and conductors 

 to provide approximately 350 inductors (item (16)). The number 

 of slots per pole should not be less than 10 (Art. 23, page 85 

 and Art. 26, page 93), and there must be an even number of 

 conductors in each slot. A winding consisting of 44 or 45 slots, 

 each with eight conductors, would be a possible arrangement; 

 but the slot pitch would be large with so few slots. It would 

 seem advisable to have a winding with six conductors per slot. 

 The number of slots would then be approximately, 35 % = 58.3. 

 Either 14 or 15 slots per pole would be suitable for a parallel 

 winding; but since it is usual to provide the armature punchings 

 of four-pole machines with an uneven number of slots, so that 

 the armature core can be used for a two-circuit winding, we 

 shall adopt a winding of 57 slots with six conductors per slot, 

 making the corrected value of Z = 57 X 6 = 342. 



The slot pitch (refer Art. 25, page 92 for definition), is, 



TT X 19.5 

 X = - w - = 1.076 



The number of teeth between pole tips is, 

 15.34 - 11 



1.076 



= 4.03 



Had this figure been less than 3.5 (see Art. 26, page 93), it 

 might have been advisable to increase the number of teeth, or 

 widen the space between pole tips. 



In order to determine the actual dimensions of the armature 

 conductors, it will be found convenient to assume a width of slot. 

 This should be about one-half the slot pitch, or, say, 0.5 in. 

 (see Art. 25, page 92). If we adopt the arrangement of con- 

 ductors in the slot shown in Fig. 77, the width of each conductor 

 will be one-third of the total width available for copper. The 

 cotton covering on each conductor would add, say, 16 mils total 

 to its thickness; and the slot insulation will be about 0.035 in. 



