126 POWER DISTRIBUTION FOR ELECTRIC RAILROADS. 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
   
    
  
  
   
     
  
  
  
  
  
  
  
  
  
  
   
  
  
This Iowell-Nashua line is hardly long enough to 
give power transmission its full measure of economy. If 
this line were to be considered by itself it would be an 
open question whether the work could not have been done 
quite as economically by a carefully planned booster sys- 
tem, retaining the Nashua generating station. In case of 
considerable extension either beyond Nashua or in some 
other direction, the transmission plant will rise to its full 
importance. 
As. regards the economy of substations so constituted 
the case is somewhat as follows: without the transmis- 
sion the items to be considered would be the loss of energy 
and the cost of distributing the power generated in the 
ordinary way at one or more stations. On the other hand 
would be the cost of the transmission line and apparatus, the 
energy lost therein, and the cost of building, maintaining 
and operating the substations themselves. Substations with 
rotary converters or equivalent apparatus do not, it is true, 
require a Jarge amount of labor in their operation. But 
they do re%uire the constant attention of one or more dynamo 
tenders, and the same general care that would have to be 
given to the electrical part of a generating station of sim- 
ilar capacity. In this connection it is interesting to note 
that the rotary transformers at Nashua have recently been 
moved to Ayer’s Mills, and the line is now operated with 
a single substation. 
The whole matter can perhaps best be discussed by 
taking up a concrete case and treating it first by the ordi- 
nary methods of distribution, and second, by a transmission 
system. 
We will assume an interurban line twenty miles long, 
A B, Fig. 71. 'The suburban sections, A Cand B E, each re- 
quires an actual average output of 200 k.w. which may 
practically all be concentrated in A and B on occasion. 
The interurban portions, CD and D E, require together an 
average of 100 k.w. nearly uniformly distributed. What 
is the best arrangement for supplying power; stations at 
A and B, stations at C and E, a single station at D or