Section 2.2 - Operational Analysis; Startup; On-Speed Operation; Field Excitation - Generac Power Systems CorePower Repair Manual

Section 2.2
Operational Analysis

STARTUP

When the engine is started, permanent magnets embedded in
the rotor induce a voltage into (a) the stator AC power windings,
(b) the stator excitation or DPE windings. In an "on-speed"
(engine cranking) condition, this magnetism is capable of
creating approximately one to three volts AC.

ON-SPEED OPERATION

As the engine accelerates, the voltage that is induced into the
stator windings increases rapidly, due to the increasing speed
at which the rotor operates.

FIELD EXCITATION

An AC voltage is induced into the stator excitation (DPE)
windings. The DPE winding circuit is delivered to the voltage
regulator through the two Blue Wires and C1-1 and C1-2.
Unregulated alternating current flows from the winding to the
regulator. The voltage regulator "senses" AC power winding
output voltage and frequency through the Green and White
Wires.
The regulator changes the AC from the excitation winding to DC
Field Excitation. In addition, based on the AC sensing wires,
it regulates the flow of direct current to the rotor. The rectified
ENGINE -
DIRECT
DRIVE
Page 26
TO LOAD
MLB
MLB = MAIN LINE CIRCUIT BREAKER
STATOR STATOR
POWER POWER
WINDING WINDING
MAGNETIC
FIELD
ROTOR
MAGNETIC
FIELD
Figure 18. Operating Diagram
PART 2
and regulated current flow from the regulator is delivered to the
rotor windings through the (+) Red Wire and the positive brush
and slip ring. This excitation voltage flows through the rotor
windings and through the negative (-) slip ring and brush on
the negative (-) Black Wire.
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.
Initially, the AC power winding voltage sensed by the regulator
is low. The regulator reacts by increasing the flow of field
excitation voltage to the rotor until voltage increases to a
desired level. The regulator then maintains the desired voltage.
For example, if voltage exceeds the desired level, the regulator
will decrease the flow of field excitation voltage. 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.
SENSING
STATOR
EXCITATION
WINDING
AC GENERATORS
VOLTAGE
REGULATOR