30 DIRECT-CURRENT DYNAMOS AND MOTORS. 
required? Determine the flux densities in the air gaps. 
and in the tooth-section for the dimensions shown in 
answer to Question 26% ; to find the former, add 50 
per cent. to the gap density at the pole faces to allow 
for concentration of the lines due to the teeth; and to 
obtain the latter, divide the armature flux by the tooth- 
section at the root of the teeth. 
298. A 16-pole ring-type generator for 540 volts and 3,700 am- 
peres has the following dimensions: External diameter 
of armature core, 144 inches; internal diameter, 124 
inches; length, 31 inches; actual length occupied by 
the discs, 264 inches; number of slots, 336; width of 
slots, 14 inch; depth of slots, 3 inches; winding, 6 
turns of armature conductor per slot; magnet frame, 
cast steel; cores, rectangular, 25 xX 13 inches in cross- 
section, 16 inches long; yoke, 191 inches in’ diameter, 
32 inches wide, 5 inches thick; pole plates, 32 inches 
long, 20 inches wide, 14 inches thick in center, embrac- 
ing anyles of 16° each; bore of polepieces, 144 inches. 
The armature flux required to produce the rated output 
is 190,000,000 lines; leakage factor, 1.15. Calculate 
the ampere-turus necessary for the excitation of this 
machine, if the average flux density in the air gap is 
50 per cent. in excess of the density at the pole faces, 
and if the mean length of the path in the air gap is 50 
per cent. greater than the distance between pole face 
and armature. 
299. Determine the magnetizing force required for a 10 pole 
dynamo from the following data: Type: radial inner- 
pole or star type, having cores supported radially from 
a central yoke in the form of a star. Materzal: cores 
and polepieces, wrought iron; yoke, cast iron. Arma- 
ture: external core diameter, 120 inches; internal core 
diameter, 1093 inches; length, 20 inches; winding, 
1,700 turns of rectangular copper bar. Magnet frame: 
diameter of polepiece circle, 107 inches; thickness at 
center of pole shoes, 3} inches; polar embrace, 80 per 
