TRANSMISSION OF POWER FOR SUBSTATIONS. I41 
output without overheating is by building the transformer 
core of bunches of iron laminze separated by air spaces of 
1/ in. to 14 in., subdividing the coils in a similar manner, 
and then forcing through the whole structure a stream of 
cool air from a small blower. This construction both keeps 
the transformer cool and by subdividing the primary and 
secondary coils renders it easy to insulate for high voltages. 
  
  
  
\ STRyTourmAL | 
  
  
FIG, 81, 
Fig. 81 shows a large substation transformer made in 
the fashion just described, stripped of its connections and 
external casing so as to be more easily seen. The coilsare 
wound rather deep and thin and the primary and second- 
ary sections alternate with heavy insulation between each 
section. ‘The cooling blast is introduced from the bottom. 
Channels for the air are arranged under each transformer 
and a small motor blower furnishes the blast, a single