136 POWER DISTRIBUTION FOR ELECTRIC RAILROADS.
and the power of such a pressure to break down insulation
is most formidable. If in addition to sc great an electric
strain the armature insulation has to stand prolonged
vibration and centr#fugal strain its life is likely to be some-
what uncertain. For these high voltages therefore a ma-
chine with a stationary armature is much to be preferred
to the ordinary types, especially since the latter have no
compensating advantages.
Another and a very ingenious form of generator with
two phase stationary armature is shown in Fig. 77. Here
the armature is composed of two laminated rings placed
side by side in a common frame a short distance apart.
Fach is slotted to receive heavily insulated rectangular
coils as shown in Fig. 78. The revolving part of this
machine, is simply a steel casting furnished with a set
of outwardly projecting laminated pole pieces at each
end. The field winding is a single fixed circular coil
around the field between the two armature rings. The
armature current is taken off from fixed binding posts
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