SUBSTATIONS. 119 
good point. If properly handled it should produce power 
at a price not more than one mill per kilowatt hour greater 
than the best that can be done in the principal station. 
This difference is so small as to be more than offset by the 
mere loss in energy that would be incurred in transmitting 
the power concerned from the main station without involv- 
ing an overwhelming expenditure for copper. A loss of 
ten per cent in transmission would wipe out the difference 
and involve the expenditure of many thousand dollars in 
copper to boot. A general idea of the economy of this 
and other auxiliary stations can be had as follows: 
Given 1000 k. w. to be delivered an average distance 
of 10,000 ft. from the principal station for twenty hours 
per day, and a difference in cost of generation of one mill 
per kilowatt hour between principaland auxiliary stations. 
Is it cheaper to run the auxiliary stations or transmit the 
power ? 
The amount of power under consideration will cost at 
the substation $20 per day more than at the principal 
station—g$7300 per year. * To offset this we have the in- 
terest on the copper necessary for transmission and the loss 
incurred in the transmission. Allowing five per cent loss 
in transmission we have a net loss of 1000k. w. h. per day, 
costing not less than $10 and in most stations more. 
T'he copper necessary for the feeder line at five per cent 
loss would be about 168 tons not including the insulation, 
costing in place not less than $50,000. At ten per cent for 
interest, depreciation, repairs and miscellaneous charges, 
the annual charge would be $5000 per year, leaving an 
annual balance of $1350 in favor of the auxiliary station 
method. 
T'his advantage would exist pro rafa for smaller power 
transmitted so long as the difference of one mill per kilowatt 
hour might hold. With a difference proportionately so small 
one may say that auxiliary stations will begin to pay ata 
radius.of from a mile and a half to two miles from the 
principal station and at greater distances become rapidly 
more and more profitable.