Generac Power Systems GP Series Diagnostic Repair Manual page 9

Other AC Generator Components
Some AC generator components are housed in the
generator control panel enclosure. These are the
excitation circuit breaker, the automatic voltage regulator
(AVR), and the main line circuit breaker.
Excitation Circuit Breaker
See Figure 1-5. The excitation circuit breaker (CB6) is
housed in the generator control panel enclosure and
electrically connected in series with the excitation (DPE)
winding output to the AVR. The breaker is self-resetting,
therefore its contacts will close again when excitation
current drops to a safe value.
If the circuit breaker has failed open, excitation current
flow to the AVR and rotor windings will be lost. Without
excitation current flow, AC voltage induced into the stator
AC power windings will drop to a value in proportion with
the rotor residual magnetism.
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Figure 1-5. Excitation Circuit Breaker
Automatic Voltage Regulator
The automatic voltage regulator (AVR) is shown in
Figure 1-6. Unregulated AC output from the stator
excitation winding is delivered to the regulator's DPE
terminals, via Wire 2, the excitation circuit breaker and
Wire 162, and Wire 6. The AVR rectifies and regulates
the current based on stator AC power winding sensing.
The rectified and regulated excitation current is then
delivered to the rotor windings 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, at the
AVR.
Figure 1-6. Automatic Voltage Regulator (AVR)
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Figure 1-7. Automatic Voltage Regulator (AVR)
The regulator provides over-voltage protection, but does
not protect against under-voltage. On occurrence 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.
Adjustment Procedure
A single red lamp (LED) illuminates during normal
operation. The lamp will become dim if excitation winding
AC output diminishes. It will extinguish 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 59.5–60.5 Hz AC frequency (60 Hz equals 3600
rpm). At the stated no-load frequency, adjust to obtain a
line-to-line AC voltage of approximately 245–247 volts.
Circuit Breakers
Each individual outlet on the generator is protected by a
circuit breaker to prevent overload.
Rotor Residual Magnetism
The generator revolving field (rotor) may be considered
to be a permanent magnet. Some residual magnetism is
always present in the rotor. This residual magnetism is
sufficient to induce a voltage into the stator AC power
windings of approximately 2-12 VAC.
Field Boost Circuit
The field boost relay (FBR) will be energized:
• briefly when the ignition key is turned to ON
position
• when the engine is cranked during start-up
• while the unit is running
The normally open contacts of the FBR will close and
Wire 14C will supply 12 VDC to Wire 14. Wire 14 is
connected to a resistor (R1) and a diode (D2). The
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