TRANSMISSION OF POWER FOR SUBSTATIONS. 135 
the ordinary manner for pressutes of 5000 volts or so, the 
thorough insulation of the moving armature becomesa very 
difficult matter. ; 
Under these circumstances it is far better to design the 
generator in such wise that the high voltage armature 
wires shall be stationary, and the field magnet then be- 
comes the moving part of the machine. 
  
  
  
ST By ToURNAL . 
  
  
¥IG. 7S. 
The commonest way of arranging such a generator is 
to place the armature coils in slots cut in the inner face of a 
laminated iron ring and to revolve within this ring a star 
shaped multipolar magnet, occupying the position of the 
armature in Fig. 75. Such a generator is shown in Fig. 
26. 'T'he proper insulation of the armature coils is here com- 
paratively easy and the chance of their breaking down is very 
much reduced. It should be remembered that 5000 volts 
will actually spark across an air space of about 74 in., 
s