Guardian 4721, Руководство по ремонту

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PREPACKAGED LIQUID
COOLED AC GENERATORS
SECTION 2.2
OPERATIONAL ANALYSIS
PART 2
Page 25
OPERATION
STARTUP:
When the engine is started, residual plus field boost
magnetism from the rotor induces a voltage into the
stator AC power windings and the stator excitation or
DPE windings. In an “on-speed” condition, residual
plus field boost magnetism are capable of creating
approximately one-half the unit’s rated voltage.
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 completed
to the voltage regulator, via Wire 2, excitation circuit
breaker, Wire 162, and Wire 6. Unregulated alternat-
ing current can flow from the winding to the regulator.
The voltage regulator “senses” AC power winding
output voltage and frequency via stator Wires S15
and S16.
The regulator changes the AC from the excitation
winding to DC. In addition, based on the Wires S15
and S16 sensing signals, it regulates the flow of direct
current to the rotor.
The rectified and regulated current flow from the reg-
ulator is delivered to the rotor windings, via Wire 4,
and the positive brush and slip ring. This excitation
current flows through the rotor windings and is direct-
ed to ground through the negative (-) slip ring and
brush, and Wire 1.
The greater the current flow through the rotor wind-
ings, 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 a desired level. The regulator then main-
tains 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 propor-
tion to the AC frequency. For example, on units rated
120/240 volts at 60 Hz, the regulator will try to main-
tain 240 volts (line-to-line) at 60 Hz. This type of regu-
lation system provides greatly improved motor start-
ing capability over other types of systems.