TRANSMISSION OF POWER FOR SUBSTATIONS. 137 
instead of brushes, just as in the generator shown in Fig. 
~»6, but in this latter machine there are not even brushes 
for the field current or any other purpose. These inductor 
dynamos may be safely wound for as high as 5000 volts 
even in machines of moderate size. 
With 5000 volts available at the terminals the trans- 
mission of power over moderate distances can be effected 
  
  
  
  
¥IG. 77 
more cheaply than by the use of higher voltages derived 
from raising transformers. The economics of the ques- 
tion involve no difficulties. The cost of raising trans- 
formers and their accessories in ordinarily large units may 
be taken as on the average about $1o per kilowatt of out- 
put. At 10,000 volts, the pressure generally used when 
raising transformers are employed, the cost of copper is but 
one-fourth that required for transmission at 5000 volts 
and the same loss. ‘The latter has the advantage of greater