Speed limit test. This test lowers the speed
pressure. If these parameters are not within limit
limit loop reference voltage by 25 percent. To test
during start-up, the sequencer will initiate an
this loop using the turbines, the PT would only
immediate automatic shutdown.
have to be run to 75 percent of real limit point.
(NOTE: Follow the PMS procedure to test speed
In the manual mode, an operator is required
limiting.)
to initiate the starter on, fuel on, and ignition on
commands. When the sequencer receives a manual
Overspeed test. Four push buttons are
start command, it provides the time sequence and
located in the FSEE, one each for channels A and
engine parameters for the operator's information.
B on each turbine. When you depress a push
The conditions that would cause shutdowns in the
button for testing the circuit, a frequency
automatic mode provide only an alarm in the
generator in each PWB introduces a signal
manual mode.
simulating a high-speed signal. This signal causes
the fuel valves to close and the overspeed light
In the auxiliary (or test) mode, an operator
to illuminate.
can test the engine start components without
activating the fuel and ignition at the same time.
START/STOP SEQUENCER
In this mode, the operator can check the fuel
system without causing a start of the engine. The
The start/stop sequencer is installed in the
operator does this by manually motoring an
FSEE on FFG-class ships. It provides signal
engine, and at 1,200 rpm, energizing the fuel
conditioning, monitoring, and logic circuits
valves. Then the operator checks the operation
required for safe GT starting and stopping. Nine
of the fuel system components. This is done by
circuit cards are used for this feature. Three cards
t h e operator monitoring the fuel supply
temperature, pressure, fuel flow, and fuel
(the X, Y, and Z cards) are signal conditioners.
Four of the cards are logic cards (the AB, AD,
manifold pressure. In this way, the operator
AE, and AC cards). The other two cards are a
checks the operation of the fuel pump, MFC, and
transmitter card (AA) and a thermocouple
fuel shutoff valves. The operator checks the fuel
amplifier card (V).
shutdown valves upon completion of the test by
The start/stop sequencer provides the follow-
de-energizing the valves. A fuel valve test mode
ing functions:
also allows you to test the valves to ensure
proper operation of the valves. Also, you can test
Signal conditioning of gas turbine
the ignition system using the auxiliary mode. The
parameters
ignition test will cause the igniters to be on as long
as you depress the igniter push button.
Monitoring of vital parameters
Sensing out-of-limits instrumentation
signals
SUMMARY
Signal conditioning output status signals
In this chapter and the previous one, we
discussed how the LM2500 GTE is constructed
Initiating automatic control signals
and the function of its various parts. We described
the operations of its many systems, including the
Receiving and processing operator com-
flow of air into the combustion section, the mix
of fuel and air, and how the fuel system and
mands
ignitor system cause combustion. We described
The start sequencer has three sequence modes
the operation of the lube oil system and looked
available. These modes are auto, manual, and
at a description of its function and how the engine
auxiliary (or test). In the auto mode, when
is controlled electronically by the FSEE. We
commanded by a signal from the PCC, an
briefly covered the control systems for the
automatic start-up of the GTE can be performed.
different class ships. We discussed the ECSS and
This auto start sequence using a programmed time
start/stop sequencer control.
sequence monitors and controls the engine
starting. Parameters monitored include N GG ,
We will describe the actual start, operation,
T5.4, fuel manifold pressure, and lube oil supply
and stopping of the LM2500 GTE in chapters 6,
2-57
