located within the load sensor. It determines the
frequency proportional to the speed of the
percentage of the load that this generator handles
turbine.
7. The SPM synchronizer compares the phase
in a load sharing situation with other generators.
The droop potentiometer within the load
of the generator with that of the bus. If an
sensor determines the percentage of speed change.
error is sensed, a signal is applied to the
This is used when the turbine generator is
fuel control unit. Then the generator phase
operating in droop mode. The effect of operating
angle will be brought in phase with the bus.
in droop mode is a decrease in speed setting for
8. The master frequency trimmer is used when
an increase in load. A portion of the load gain
the turbine is in load sharing. It changes
voltage is applied to the speed channel as a droop
power system frequency without changing
the load division between engines.
signal.
When the turbine is in isochronous mode, the
load pulse amplifier provides a speed error
Governor Control Unit
correction signal in advance of the normal speed
error signal. This improves the short-term
The GCU supplies field excitation to its
transient response of the controller. The output
associated GTGS. Except for the remotely
of the load pulse amplifier is applied to the speed
mounted selector switches, the GCU components
control summing point in droop mode. It is
are mounted in the GCU cabinet. Each cabinet
applied to the load matching circuit in isochronous
contains the redundant voltage regulator systems
mode.
with associated relays, transformers, motor-
In the load sharing mode, a bridge within the
operated potentiometers, selector switch
load matching circuit is connected in parallel with
indicating lights, a reset button, and the governor
the bridges in other controls. When the load on
control assembly.
the generator varies, an error signal is generated
by the load matching circuit. This adjusts the load
Electronic Fuel Control Unit
carried by the generator. An LED indicator shows
the selection of isochronous or load sharing
The electronic fuel control unit is a modular'
modes.
solid-state electronic package. The nine major
modules are the load sensor, isolation, speed
ISOLATION MODULE.--The isolation
reference, speed channel, power supply, fuel
module provides buffering of the governor master
limiter, temperature channel, final driver, and
frequency trimmer and governor SPM syn-
motherboard modules. These modules are found
chronizer signals. Also, the discrete logic signals
in the governor box in the GCU. Figure 3-27 is
for the overspeed test, reset to 60 Hz, raise, lower,
a functional diagram of the governor control
isochronous, and load sharing control are
system. It shows the three major control functions
buffered through isolators on this module.
separated by broken lines. These functions are
speed control, temperature control, and fuel
SPEED REFERENCE MODULE.--The
metering.
speed reference module generates the dc reference
The following paragraphs describe the
signal used by the speed control module. The
operation of the electronic fuel control to the
reference values are selected by inputs from the
board level. The module titles are descriptive of
SWBD or the EPCC. When the command is made
their major function.
to change frequency, a digital counter within the
speed reference starts to count. It counts in an
LOAD SENSOR MODULE.--This module
increasing or decreasing direction toward the new
uses inputs from the generator voltage and CTs.
reference level. The counting process continues
Each phase is monitored for current and voltage
as long as the input command to change frequency
by potential transformers and CTs to determine
is present. It continues until the new reference
the actual load. Each CT develops a voltage across
level is reached. The output of the counter is
a burden resistor, proportional to generator
applied to a DAC. The converter changes the
current. The signal representing the load on the
digital output of the counter to the output analog
three phases is summed in the load sensor.
speed reference voltage. The speed reference
The current in all three phases is corrected for
module indicators show when it is at the reset,
power factor and summed in the load sensor
lower, or upper limits. They also show when they
module. This provides a signal proportional to the
are moving.
load on the bus. A load gain potentiometer is
3-36
