Lincoln Electric SAE-300 HE, Service Manual, Page: 13 / 84

LINCOLN ELECTRIC SAE-300® HE Service Manual
8
WELDER GENERATOR AND EXCITOR
FIGURE F.5 – WELDING GENERATOR AND EXCITER
Overview:
The welding generator is coupled directly to the engine
and produces the DC current required for welding and
arc gouging. The welding power is induced in the windings
of the armature when it spins in a magnetic field. The
power produced in the armature is converted to direct
current (DC) by a commutator and a set of carbon brushes,
which are then connected to the interpole coils, the series
coils and the reactor assembly. The weld current is
controlled by varying the field (Fine Current and O.C.V.
Control) and the reactor (Coarse Current Control) setting,
using the front panel control knobs.
EXCITATION AND FIELD CONTROL:
Before any welding current can be produced, there must be
a strong magnetic field in which the armature can spin.
Creating this magnetic field is often described as exciting
the generator and is accomplished by passing controlled DC
current through two shunt coils in the generator stator.
The power used to excite the main welding generator is the
same rectified DC current used to power the rotating field
of the exciter alternator. (See the section
EXCITER/AUXILIARY ALTERNATOR OPERATION ). This DC
current passes through the remote / local switch and then
through either the panel mounted rheostat (Fine Current
and O.C.V. control), or a remote fine current control
rheostat. The controlled DC current then passes through
the two series connected shunt field coils in the welding
generator stator.
When the remote/local switch is moved from one position
to another, there is a brief period of time when the coils
are disconnected. When this happens, the magnetic field
around the shunt field coils collapses causing a very high
induced voltage spike in the shunt coil circuit. A flyback
spike without damaging insulation or the remote/local
switch.