i) 
“DIRECT-CURRENT DYNAMOS AND MOTORS. 
hence the approximate friction loss is obtained as 9 X 3 
x 10 = 270 watts. Formula (67), therefore, bas 
3000 __ 3000 
Com. Eff. = ~ 8000+ 200-125-254 10 + 270 3630 
.826, or 82.62. 
(3) The hysteresis a of the 50 K. W. compound-wound 
generator given in Example (3), Par. 83, ts 350 
watts, its eddy current loss 65 watts; cohtt ts its 
commercial efficiency ? 
Solution.—Table 29 gives w; = 2500 watts; by means 
of formula (68) we therefore obtain: 
50,000 
Com. EG. = 59 000 + 1660 4-925 + 3504 65 4 2500 
50,000 | 
= 55,500 90, or 90%. 
(4) What is the commercial heiekey of the 220-volt 
series motor of EKxample (4), Par. 83, its power loss 
by hysteresis being 200 watts, and od eddy current 
loss 50 watts? 
Solution.—The current taken by this motor is given as 
100 amperes, hence its capacity is 220 x 100 = 22,000 
watts, or 22 K. W., for which Table 29 gives'a friction 
loss of approximately 6%. Therefore, we = 6 X 22 X 10 
= 1320 watts, and by (69): 
22,000 — (1250 + 200 + 50 + 1320) 
Cot EE oe 22,000 
19,180 
=a i eee 872, or 87.2%. 
(5) Determine the commercial efficiency of the shunt- 
wound motor given in Examples (2) and (5) of Par. 
83, if tts tron losses are the same as given above for 
the 3 K. W. generator. 
Solution.— By: (70): 
_ 3250 — (325 + 35 + 270) _ 2620 
Com. Eff. cee 3250 7 = 3950 
= .806, or 80.6%. | 
