Operation; Startup; On-Speed Operation; Field Excitation - Generac Power Systems GP Series Diagnostic And Repair Manual

Section 1 Description and Components

Operation

Startup

When the engine is started, residual plus field boost
magnetism from the rotor induces a voltage into the
stator AC power windings, the stator excitation or DPE
windings, and the stator battery charge windings. In an
"on-speed" (engine cranking) condition, residual plus
field boost magnetism
approximately one-half the rated unit voltage.

On-Speed Operation

As the engine accelerates, the voltage induced into the
stator windings increases rapidly, with the increasing
rotor speed.

Field Excitation

An AC voltage is induced into the stator excitation (DPE)
windings. The DPE winding circuit is completed to the
voltage regulator, via wire 2, excitation circuit breaker,
wire 162, and wire 6. Unregulated alternating current can
flow from the winding to the regulator.
The voltage regulator senses AC power winding output
voltage and frequency via stator wires 11S and 44S, or
11S and 22S.
The regulator changes the AC from the excitation
winding to DC. In addition, based on the 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 windings, 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 windings,
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.
4
are capable of creating
The AC power winding voltage initially sensed by the
regulator is low. The regulator reacts by increasing the
flow of field excitation current to the rotor until voltage
increases to a desired level. The regulator then monitors
and maintains the desired voltage. For example, if
voltage exceeds the desired level, the regulator will
decrease the flow of field excitation current. However, if
voltage drops below the desired level, the regulator
responds by increasing the flow of field 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.

Battery Charge Winding Output

A voltage is induced into the battery charge winding.
Output from these windings is delivered to a battery
charge rectifier (BCR2), via wires 55A, 66A and 77A. The
resulting direct current from the BCR is delivered to the
unit battery, via wire 15, a 10 amp fuse, and wire 13. This
output is used to maintain battery state of charge during
operation.

10 Amp Battery Charge Winding Output

A voltage is induced into the battery charge winding.
Output from these windings is delivered to a battery
charge rectifier (BCR1), via wires 55, 66 and 77. The
resulting direct current from the BCR is delivered to the
12 VDC receptacle, via wire 13A, CB1, and wire 15A.
This receptacle allows the capability to recharge a 12
VDC storage battery with provided battery charge cables.
Diagnostic Repair Manual