Generac Power Systems GP Series Diagnostic Repair Manual page 10

Section 1 Description and Components
resistor limits current flow, and the diode blocks AVR DC
output from feeding back into the field flash circuit. Once
through the resistor and diode Wire 4 supplies signal to
the positive brush.
The effect is to flash the field every time the engine is
cranked, or the key is just turned on. Field boost current
ensures sufficient pickup voltage is available on every
startup to turn the AVR on and build AC output voltage.
While the FBR remains energized, field boost current is
always available during cranking and running. Diode D2
prevents or blocks the higher AVR DC output from
reaching the Wire 14 run circuit.
Field boost voltage is reduced from battery voltage by
resistor R1. A digital multimeter (DMM) will indicate
approximately 4 to 5 VDC.
Operation
Startup
When the engine is running, magnetism from the rotor
induces a voltage into the stator AC power windings and
the stator excitation (DPE) windings. This magnetism
creates the initial excitation voltage to power the AVR,
which then increases output to regulated voltage.
Field Excitation
AC voltage is induced into the stator excitation (DPE)
windings. The DPE winding circuit is completed to the
AVR via Wire 2, excitation circuit breaker, Wire 162, and
Wire 6. Unregulated alternating current flows from the
winding to the regulator. The AVR senses AC power
winding output voltage and frequency via stator Wires 11
and 22 at the AVR. The regulator rectifies the AC from
the excitation winding to DC. In addition, based on the
ENGINE -
DIRECT DRIVE
4
TO LOAD
STATOR STATOR
POWER POWER
WINDING WINDING
MAGNETIC
FIELD
ROTOR
MAGNETIC
FIELD
STATOR
EXCITATION
(DPE) WINDING
Figure 1-8. Generator Operating Diagram
sensing signals, it regulates the flow of direct current to
the rotor. The rectified and regulated current flow from
the regulator is delivered to the rotor winding via Wire 4
and the positive brush and slip ring. This field excitation
current flows through the rotor windings and is directed to
ground through the negative (-) slip ring and brush, and
Wire 0.
The greater the current flow through the rotor winding,
the more concentrated the lines of flux around the rotor
become. The more concentrated the lines of flux around
the rotor that cut across the stationary stator windings,
the greater the voltage that is induced into the stator
windings.
Initially, the AC power winding voltage sensed by the
regulator is low. The regulator reacts by increasing the
flow of excitation current to the rotor until voltage
increases to the desired level. The regulator then
maintains the desired voltage. For example, if voltage
exceeds the desired level, the regulator will decrease the
flow of excitation current. Conversely, if voltage drops
below the desired level, the regulator responds by
increasing the flow of excitation current.
AC Power Winding Output
A regulated voltage is induced into the stator AC power
windings. When electrical loads are connected across
the AC power windings to complete the circuit, current
can flow in the circuit. The regulated AC power winding
output voltage will be in direct proportion to the AC
frequency. For example, on units rated 120/240 volts at
60 Hz, the regulator will try to maintain 240 Volts (line-to-
line) at 60 Hz. This type of regulation system provides
greatly improved motor starting capability over other
types of systems.
SENSING
FIELD BOOST
CIRCUIT
VOLTAGE
REGULATOR
CB6 = EXCITATION CIRCUIT BREAKER
CB6
014989
Diagnostic Repair Manual