The Diseases Of Electrical Machinery 1904
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ELECTRIC AL MACHINERY.
5
ture the two sides of a winding are not at an angle
of i8o° to one another (fig. i), but are wound with a
shortened pitch, so that the angle which the two sides
Fig. i.
Fig. 2.
of a coil build one with another is only a little larger
than the angle subtended by the pole piece (fig. 2).
With this type of armature the brushes must not be
placed in the middle between two poles, but must be
moved a considerable distance doser to one pole tip.
It is therefore necessary, since the type of winding can
but rarely be seen from the finished armature, to place
the brushes according to the mark which is placed by
the maker on the brush gear of almost every machine
Most modern machines are provided with one mark
only. This is because the same position is correct for
both no load and full load. It is usually necessary,
at any rate for motors, to specify that this should be
the case. Machines of earlier date, however, were pro-
vided with two marks—one for no load and the other
for full load. It should be noticed that for dynamos
the brush-holder must be shifted in the direction of
rotation with increased load to give them a forward
lead, while for motors the brushes must be moved in
the opposite direction, giving them a backward lead.