ELECTRIC TRUNK-LINE OPERATION—SPRAGUE. 135 
upon the series-wound, commutating, single-phase motor with com- 
pensated fields, operated at 25 cycles. 
Lowering the number of cycles to increase the capacity of the 
single-phase motor, as has been suggested, although not yet devel- 
oped in commercial practice, of course merits serious consideration, 
and I shall add some comments upon this proposed change. * * * 
Types of motor.—Among the many types of motors proposed for 
railway service, four are now being exploited: Polyphase alternat- 
ing-current motor; single-phase alternating-current motor, repulsion 
type; single-phase alternating-current motor, series type; direct-cur- 
rent motor. 
Of these, two, the direct-current and the three-phase motors, each 
have a continuous rate of energy-input, while the single-phase motor 
has an intermittent and variable rate. Moreover, there is combined in 
the single-phase motor two distinct functions, those of a motor and a 
transformer, and the latter can not be entirely eliminated. The result 
is a reduction in both continuous and overload capacities. * * * 
When considering locomotives, the net result is that the total 
weight of a single-phase alternating-current locomotive, with a serv- 
ice capacity equal to that of a direct-current locomotive of like arma- 
ture speeds and permissible temperature-rise (this temperature-rise 
being the ultimate limitation of a motor for continuous service), 
will easily be from 30 to 50 tons more. 
An increase in the total weight of a train amounting to from 3 to 
10 per cent is perhaps not of itself of so much importance, because 
such a difference in net power demand can easily appear for various 
reasons; but a ratio of 2 to 1 in capacity for the limit of equipment 
possible to install within given allowable dimensions and number 
of units is a matter of vital importance. 
Comparative weights of direct-current and 25-cycle single-phase 
alternating-current motors.—While the testimony is practically uni- 
versal that not only is any single-phase motor, whatever the number 
of alternations, more or less inefficient than a direct-current motor of 
hike weight or capacity, the differences of efficiency, excluding the 
losses in the gearing, are variously estimated. * * * 
An increase of 10 per cent in the amount of current used on a 
direct-current system, because of improper gear-ratio, change of 
schedule, or careless handling of equipments by motormen, does not 
mean that this excess energy is dissipated in internal losses in the 
motors, for these may be increased only about 1 per cent. The situa- 
tion in regard to the single-phase motor is, however, entirely different 
for it is subject not only to increased power consumption with its 
proportionate losses because of careless operation, but it also has its 
individual increased internal loss, which is variously estimated to be 
41780—08——138 
