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BRUSH HOLDER AND BRUSHES
(12-20 KW)
The brush holder is retained to the rear bearing car-
rier by means of two #10-32 x 9/16 Taptite screws. A
positive (+) and a negative (-) brush are retained in
the brush holder, with the positive (+) brush riding on
the slip ring nearest the rotor bearing.
Wire 4 connects to the positive (+) brush and Wire 0
to the negative (-) brush. Wire 0 connects to frame
ground. Rectified and regulated excitation current, as
well as current from a field boost circuit, are delivered
to the rotor windings via Wire 4, and the positive (+)
brush and slip ring. The excitation and field boost cur-
rent passes through the windings and to frame ground
via the negative (-) slip ring and brush, and Wire 0.
This current flow creates a magnetic field around the
rotor having a flux concentration that is proportional to
the amount of current flow.
0
4
-
+
Figure 4. Brush Holder and Brushes (12-20 kW)
OTHER AC GENERATOR COMPONENTS
Some AC generator components are housed in the
generator control panel enclosure, and are not shown
in Figure 1. These are (a) a voltage regulator, and (b)
a main line circuit breaker.
VOLTAGE REGULATOR (12-20 KW):
A typical voltage regulator is shown in Figure 5.
Unregulated AC output from the stator excitation
winding is delivered to the regulator’s DPE terminals,
via Wire 2 and Wire 6. The voltage regulator rectifies
that current and, based on stator AC power winding
sensing, regulates it. The rectified and regulated
excitation current is then delivered to the rotor wind-
ings from the positive (+) and negative (-) regulator
terminals, via Wire 4 and Wire 0. Stator AC power
winding “sensing” is delivered to the regulator “SEN”
terminals via Wires 11 and 22.
The regulator provides “over-voltage” protection, but
does not protect against “under-voltage”. On occur-
rence of an “over-voltage” condition, the regulator will
“shut down” and complete loss Of excitation current
to the rotor will occur. Without excitation current, the
generator AC output voltage will drop to approximately
one-half (or lower) of the unit’s rated voltage.
Figure 5. Typical Voltage Regulator
A single red lamp (LED) glows during normal opera-
tion. The lamp will become dim if excitation winding
AC output diminishes. It will go out on occurrence of
an open condition in the sensing AC output circuit.
An adjustment potentiometer permits the stator AC
power winding voltage to be adjusted. Perform this
adjustment with the generator running at no-load, and
with a frequency of 60 Hz
At the stated no-load frequency, adjust to obtain a
line-to-line AC voltage of 247-249 volts.
MAIN LINE CIRCUIT BREAKER:
The main line circuit breaker protects the generator
against electrical overload. See “Specifications” in
front of manual for amp ratings.
PART 2
Page 34
AC GENERATORS
SECTION 2.1
DESCRIPTION & COMPONENTS