194 POWER DISTRIBUTION FOR ELECTRIC RAILROADS. 
sume the grades to be moderate so that the power required 
would be fairly uniform throughout the line. TLe cars 
stop at fixed points only, with good opportunity for clcar 
running over a large part of the system. With ordinary 
conditions of load the use of two twenty-five horse power 
or thirty horse power motors per car would be suflicient 
and the normal current demanded should not exceed filty 
amperes per car or one hundred amperes per car, at 5co 
volts as a maximum for the system. The total output to 
be delivered tc the cars may then be taken at 3oo k. w. 
average and 6oo k. w. maximum. 
For such a line as this four methods of supply would 
be worth investigation: I, direct supply from two sym- 
metrically placed stations; II, supply from a single station 
with boosters; III, supply from one station with a rotary 
transtformer substation; IV, supply from a single station by 
alternating currents and static transformers. For sim- 
plicity, we will assume the cost of track and overhead 
structure to be the same for all four. So, in fact, it would 
be for the first three methods, and the extra working volt- 
age readily obtained with the alternating system at least 
compensates for lagging current in the trolley wire or the 
extra expense of stringing and maintaining two trolley 
wires, if the polyphase system is used. We will compare 
the systems on the basis of the same loss of energy 
reckoned from generator to motor, since the efficiency 
of generators and motor is substantially the same through- 
out, and for simplicity will not figure out close details of 
distribution, but reckon the copper required in the simplest 
possible manner. ‘The permissible loss of energy from gen- 
erator to working conductor, we will take as fifteen per 
cent at maximum load, allowing five per cent loss in the 
trolley wire. We have already seen that if maximum load 
is taken care of, the average load will look out for itself. 
In supplying current from two separate power houses 
these would naturally be placed 15 miles apart and 74 
miles from each end of the line. FEach power house 
would then feed half the line, 734 miles on each side cf its