46 ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 
and an effective system of lubrication. The friction 
losses of the slip rings are usually comparatively small. 
By adopting a magnet wheel of sound mechanical construec- 
tion, the designer can considerably reduce the air friction 
losses, and also by remembering that the energy consumed 
by air friction can be effectively utilized for ventilating 
and cooling, in a properly arranged magnet wheel. 
100 
9000 — 
a 
£000 -” 
» 7000 
, 
NS 6000 J 
N VY 
N 5000 ie 
S 4000 
R 
S 
‘ pas ea 
feat 7 
7000 V 
9 100 R00 3800 400 300 690 Yoo S800 900 000 
OUTPUT IN KV¥A. 
Fig. 25.—AVERAGE FRICTION AND VENTILATION LOSSES FOR 
DIFFERENT SIZES OF ALTERNATORS. 
86. Bearing Friction Losses.—For the calculation of bear- 
ing friction losses, the formula 
Watts =0.9xXdx1xX Vv? ....:... (9) 
can be advantageously applied, where d = shaft diameter 
in inches; | = effective bearing length in inches; and vy = 
peripheral speed in feet per second of the shaft inside the 
bearing. It is assumed that the specific pressure inside - 
