a loss of excitation voltage. If a short circuit
individual generator takes on an increased
occurs, a relay internal to the regulator will
share of reactive current, its voltage will
transfer excitation from the regulator to the PMA.
droop more. This, in turn, will tend to
This is done if the voltage drops below 225 volts.
transfer some of that reactive current to the
This will allow the generator to supply enough
other machine. If both machines have
current to activate overcurrent devices. It will also
equal voltage droop, they will tend to share
trip the generator breaker to clear the fault.
reactive currents at various loads. The
voltage droop is not self-regulating.
In manual operation, the generator excitation
is controlled by the motor-operated variac
mounted in the SWBD. Power is received from
the PMA. It is scaled by the variac, then rectified
LOCAL OPERATING CONTROL
and conducted to the exciter field. You can make
PANEL
adjustments at the SWBD by turning the manual
mode volt adjuster knob (with the VOLT REG
The LOCOP is the major operator interface
MODE switch in the MAN position). When in the
with the GTGS. It has the controls and indicators
manual mode, you may make voltage adjustments
necessary to start, stop, motor, and monitor the
from the EPCC. Operation of the voltage
GTGS operation. The LOCOP is also the
interface with the ECSS which provides control
LOWER/RAISE control on the EPCC activates
the motor-operated variac. In the manual mode,
of each GTGS at the EPCC. Many of the
generator voltage will decrease with load unless
indicators available at the GTGS LOCOP are not
field excitation is increased. Thus when operating
available at the EPCC. This feature requires
in the manual mode, observe generator operation
personnel to monitor the LOCOP during GTGS
operation. Usually this monitor is a junior GS.
carefully.
For this reason, you should know and become
In automatic operation (fig. 3-32), the voltage
very familiar with the material in this section.
regulator output supplies control current to the
Two LOCOPs are used to control the two
exciter fields. The GCU internal motor-driven
different GTGS models. Their construction is very
rheostat sets the required voltage. Control of this
different. They are made by two different
motor is from the SWBD voltage raise/lower
control for local operation and the EPCC for
manufacturers. Even though they are very
different, they provide the engine and the operator
remote operation. When in automatic, the
MASTER VOLTAGE ADJ located on the EPCC
almost identical signals and data. Their main
will also operate the motor-operated rheostat in
difference lies in the method in which their data
and signals are provided.
the GCU. It changes the reference for the voltage
regulator. This command will be parallel to the
MODEL 104 LOCOP
GCUs. It will raise or lower the reference to all
regulators.
A line current signal is brought in from the
The model 104 LOCOP (fig. 3-33, view A) is
contained in a cabinet mounted on the generator
paralleling CT. It provides two functions in
end of the module. On the outside of the cabinet
automatic mode.
doors are the controls and indicators for local
GTGS operation. Inside the cabinet are the
1. When two generators are operating in
electronic components of the system (view B).
parallel, t h e i r voltages are equal.
Among these components are the logic cards (or
T h e r e f o r e , any adjustments in the
PCBs), the 28-volt dc power line filter, power
excitation of individual machines can only
change the power factor of both machines.
supplies, relays, fuses, and the temperature and
This creates circulating reactive currents
speed control unit. Both 115 volts ac and 28 volts
between machines. In this case, the current
dc are required for the operation of the equip-
ment. The 115-volt ac circuits are protected by
signal brought in from the paralleling CT
the F1 and F2 fuses. The control elements of the
will help regulate the division of reactive
system are powered by 28 volts dc from the
line current. This reduces circulating
SWBD. The 28-volt dc electronic circuits are
current between machines.
supplied through a power line filter, the F3 fuse,
2. When two generators are operating in
and the dc power switch. The ignition exciter is
parallel and in droop mode, the reactive
supplied through the F4 fuse and the contacts of
current signal will produce a fixed droop
a relay operated from the logic circuits.
in the voltage output of a generator. If an
3-46
