CHAPIER V. 
SUBSTATIONS. 
From what has already been said it is evident that 
even with the assistance of boosters, the total amount of 
copper required for the distribution of power over consid- 
erable distances rapidly becomes burdensome. It there- 
fore becomes necessary either to lessen the distance of 
transmission by multiplying generating stations or to adopt 
more economical means of transmission than is to be found 
in the direct supply of continuous current as ordinarily 
employed. In either case it is necessary to consider the 
conditions of economy to which the distribution of power 
from several working centers is subject. 
In practice substation working takes one of the three 
following forms: 1. Auxiliary stations maintained at 
various points of an extensive network, and designed to 
reinforce a main station in the supply of distant districts. 
2. Distributed stations essentially separate and serving to 
supply consecutive sections of a line or network. 3. Pure 
substations effecting local supply of power in connection 
with transmission from a central station. 
Into one or another of these classes fall with more or 
less exactness all cases of multiple centers of distribution. 
The first named is found generally in large urban railway 
systems, which have gradually grown beyond the effective 
reach of the main generating station. It is the natural 
and legitimate outcome of extensive growth. ‘The finest 
example of such practice is to be found in the West En.l 
system of Boston, Mass. This case is shown in Fig. 61. 
Here A is the central Albany Street power house of 10,500 
k.w. aggregate output. Itis reinforced by four auxil- 
iary stations—B the Alston station of 300 k. w., C the