86 POWER DISTRIBUTION FOR ELECTRIC RAILROADS. 
sion. This extra lossamounts to seventy-five kilowatts. At 
two cents per kilowatt hour the cost of the lost energy is 
$1.50 per hour of continuous service. If the booster were 
a part of a system demanding the output rather steadily for 
the full day’s run, say eighteen hours, the cost of energy 
lost would be no less than $9855 per year. ‘This simply 
means that it seldom or never pays to lose so great a pro- 
portion of energy in transmission. It is evident, however, 
that it will pay to use the booster up to about three hours 
per day of service at full load. It is, therefore, well suited 
for helping to tide over the times of unusually heavy 
traffic. 
We have already seen that these extreme loads really 
determine the copper necessary for feeders, so that the 
booster system, if used judiciously, may save a large 
investment in copper at the cost of an amount of wasted 
energy that is well within the bounds of economy. The 
system is therefore much better suited to the operation of 
long feeders than to the more general use of a station. 
Such indeed was its original use in incandescent electric 
lighting at low voltage. It has proved for this purpose 
very useful indeed, rendering it possible to take up the 
loss in long feeders at times of heavy load, and to operate 
lines too long to form a proper part of the main system. 
It thus has a very useful field in connection with existing 
plants, but it is distinctly an adjunct, not a proper general 
method. ILine losses which necessitate the continuous 
waste of more energy than can be compensated by the ordi- 
nary compound wound generators are seldom or never jus- 
tifiable'even in a portion of an extended system. If thus 
partial they are simply less bad than if the whole plant 
violated the conditions of economy. In its proper sphere 
the booster accomplishes the same end as the employment 
of extra voltage in the generators in a case such as was 
suggested in the last chapter. 
As in every other case of heavy drop in the line the 
boosting system involves certain difficulties in preserving 
sufficiently uniform voltage along the whole line. When