106 DIRECT-CURRENT DYNAMOS AND MOTORS. 
The approximate winding depth for a bipolar 10-inch coreis 
found in Table 2'7 to be 14 inches; the length of the coil 
space on each core is 124 inches; hence, the total cooling 
surface of the two coils: 
Sy = (10 + 2 x 14) X w~xX 124 K 24+ 37.3 x 14x 4 
= 1,360 square inches. 
For a rise of 30° C., which we will assume to be pre- 
scribed in this case, we find by (51): 
C., — 30 x 1,360 
oh ae SB OO 
Dividing this into the number of cg Sgehaiia the re- 
quired number of turns is obtained: 
T= 17,630 
1.09 
The number of wires that can be placed in one layer is 
124 + .041 = 300; hence, the number of layers needed is 
8,100 + 300 = 27. The actual height occupied by these 
27 layers will be 
27 xX .041 = 1.1 inches, 
making a winding depth of about 1} inches, which is 
considerably less than the height assumed above by the 
aid of Table 2%. Since for this height the cooling sur- 
face would be appreciably smaller than obtained above, 
the shunt current would have to be correspondingly 
smaller, which in turn would increase the number of 
turns, making the winding depth larger. Taking, there- 
fore, a value between the two, or, say, 14 inches, the 
cooling surface becomes: 
Sy = (10 +2 x 14) mw xX 128 x24+11¢x7xl1ex4 
= 1,287 square inches, 
and we have: 
= 1,09 amperes. 
= 16,200 turns, total, or 8,100 turns per core, 
_ 30 X 1,237 _ 
Shunt current: Can = Bsc B00 = .99 ampere; 
Number of turns: 77 = hale S 17,800; 
.99 
