Theory of operation, Dc generator machines – Lincoln Electric CLASSICII SVM125-A User Manual

Page 49

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DC GENERATOR MACHINES

The armature winding of a DC generator is located on
the rotating member. Current is conducted from it by
means of carbon brushes. The field winding is located
in the stator, which is stationary, and is excited by direct
current.

The armature coil sides are placed at opposite points
on the rotating shaft with the conductors parallel to the
shaft. The armature assembly is normally turned at a
constant speed by a source of mechanical power con-
nected to the shaft. Rotation of the armature through
the magnetic field produced by the stationary field
winding induces a coil voltage in the armature winding.
The voltage induced in an individual armature coil is an
alternating (AC) voltage, which must be rectified. In a
conventional machine, rectification is provided

mechanically by means of a commutator. A commuta-
tor is a cylinder formed of copper segments insulated
from each other and mounted on, but insulated from,
the rotating shaft. Each copper segment is connected
to a corresponding armature winding. Stationary car-
bon brushes held against the commutator surface con-
nect the armature windings to external terminals. The
commutator provides full-wave rectification, transform-
ing the voltage waveform between brushes and mak-
ing available a DC voltage to the external circuit.

THEORY OF OPERATION

E-5

CLASSIC II