ELECTRIC TRUNK-LINE OPERAT1ION—SPRAGUE. 137 
Generally speaking, it will be noted that, starting at 500 revolu- 
tions for a 39-minute run, the capacity of the direct-current motor 
averages approximately nearly double that of the alternating cur- 
rent throughout the thermal range; the speed of the alternating- 
| 
u ! 
COMPARISON ON THERMAL BASIS 
OF TWO DIRECT-CURRENT AND 
SINGLE-PHASE ALTERNATING CURRENT MOTORS 
OF EQUAL WEIGHTS 
8 
HORSE-POWER OUTPUT 
~ 
= 
Oo 
— 
tye) 
vn 
WEIGHT-COEFFICIENTS 
HOURS TO RISE 75° CENT. 
2 3 
ies 1 
current motor rises at a much more rapid rate, until on a 5-hour run 
it is double that of the direct-current motor, despite the fact that 
it is only developing one-half the power; the direct-current motor 
has a 5-hour capacity in excess of the 1-hour capacity of the alter- 
nating-current motor; and the ratio of the weight coefficients, begin- 
