built-in test equipment (BITE) box assembly and, if
APU Lubrication System
required, the engine is shut down.
The APU lubricating oil system provides
lubrication to the high-speed input pinion, the reduction
Generators
integral lubrication system consists of an oil pump, a
The generators driven by the APUs produce a
falter, a falter bypass relief valve, a pressure relief valve,
120/208-V ac, 400-Hz, 60-kW, 3-phase current. The
an oil pressure switch, an oil distribution ring assembly,
g e n e r a t o r is a salient-pole, brushless, permanent-
and an oil sump. All components of the APU lubrication
magnet type that incorporates a fan and generator air
system are contained within the reduction gear and
inlet adapter for cooling. The ac voltage generated by
accessory drive assembly.
the permanent magnet rotor and stator is connected to
an external voltage regulator where it is rectified and
A high oil temperature switch is installed in the
regulated. When both generators are operating, the load
r e d u c t i o n gear drive. The switch is electrically
is divided, but either generator can supply total craft
connected to the electronic sequence unit (ESU) to
power requirements under normal operating conditions.
enable the ESU to monitor the oil temperature and shut
down the APU when the oil temperature reaches 275
The control components consist of two governor
5F.
control units (GCUs), ESUs, current transformers,
BITE boxes, an APU start panel, and generator start
APU Fuel System
boxes. The controls are used to monitor operating
conditions for both the engine and generator. The
The APU fuel system automatically provides proper
control components for each gas turbine generator set
engine acceleration and maintains a nearly constant
are mounted in a control enclosure.
operating speed under all operating conditions. Fuel is
supplied to the GTE at 5 to 40 psig with a minimum flow
Generator Control Unit
capacity of 200 pounds per hour. The main components
of this system are an inlet fuel filter, a fuel pump, an
e n g i n e acceleration control assembly, start-fuel,
A GCU is installed for each ac generator. The GCU
m a i n - f u e l , an d maxi m u m - f u e l s o l e n o i d va l v e s ,
circuits are functionally divided into the power supply,
regulator, generator relay controls, contactor relay
start-fuel nozzle, purge valve, and a manifold assembly.
controls, feeder fault, overvoltage sensing,
During the APU start, the start-fuel solenoid valve
undervoltage sensing, underfrequency, and
opens. The resulting fuel pressure forces the piston in
overfrequency sensing sections. Each GCU monitors
the purge valve to one side in the valve chamber to allow
and controls generator output parameters. The GCU
f u e l to flow through the start fuel nozzle. At
provides voltage regulation, controls the generator
approximately 65 percent engine speed, the start-fuel
o u t p u t voltage, and protects the generator from
solenoid valve closes to cut off the fuel pressure. A
frequency and current malfunctions. Generator input
return spring transfers the piston in the purge valve to
power application and output power regulation is
the purge position. In the purge position, compressor
accomplished by controlling the excitation applied to
discharge air flows through the start-fuel nozzle to clear
the generator by the GCU. The GCU also controls the
the nozzle of residual fuel. The residual fuel is then
excitation to the line contactor that distributes generator
directed to the combustor to be burned.
feeder lines to the load. The GCU also contains features
that are used to establish a test mode of operation for the
Electronic Sequence Unit
generator.
The ESU is a control device that monitors APU
ELECTRICAL DISTRIBUTION
speed, turbine exhaust temperature, low oil pressure,
sequence failure, APU temperature, and APU
u n d e r s p e e d . The ESU shuts down the APU if
The electrical distribution system aboard the LCAC
m a l f u n c t i o n s occur in these circuits. Each 40
is composed of a 400-Hz/208-V ac system, and a 28-V
milliseconds, the ESU checks all functions and confirms
dc system. The generators each supply separate 400-Hz
that input data is greater or lesser than programmed
switchboards which serve as central control points for
v a l u e s . In the event input data is outside the
power distribution. We will take a brief look at these two
programmed values, an indication is provided in the
power systems in the following paragraphs.
7-17
