across the current transformers. This signal
represents the kilowatt load on the generator's
individual phase windings. At 1,000 kW, the
circuit is armed for high transient loads. With a
500-kW step increase, however, the sensor will
transmit a signal to close the turbine's 14-th
stage bleed air valve. This action of the sensor
will prevent engine stalls resulting from such
load variations.
The transient load sensor also monitors the
generator's main circuit breaker and its
shutdown relays. Consequently, other SSGTGs
on the bus will receive a bleed valve closure
signal if a shutdown should occur.
Hand Pump Assembly
Study figure 7-1 and focus your attention on
Figure 7-5.Garrett ship's service power unit
the space between the generator and the
(SSPU).
enclosure. On the Allison 501-K34, a new piece
of equipment, a hand pump-operated actuator
mounted on the module's exterior wall, has been
CONSTRUCTION AND DESIGN
added. The pump is used to close the fire damper
if ship's service air or power is not available.
The electric plant of the Garrett ME 031-800A
SSPU includes the following five systems:
Because of this new item, a change was
made to the K34's start air piping. The change
1. Electrical system
on the K34 provides a single manifold where the
high-pressure and low-pressure start air enter
2. Lubrication system
the starter inlet. In the older Allison model, the
3. Fuel system
high-pressure and low-pressure start air were
individually piped to the starter.
4. Water wash system
Now that we have discussed the important
5. Bleed air (de-icing) system
design differences in the Allison 501-K17 and
K34 models, let's take a look at the prime mover
Before we look at each of these systems and how they
used on the PHM-class ships, the Garrett ME
work, let's first describe the SSPU in terms of its two
831-800A.
major sections: (1) the power section and (2) the
gearbox assembly section. Figure 7-5 shows an
orthographic view of the SSPU. Refer to figure 7-5 as
GARRETT ME 831-800A
we describe the construction and design features of
both sections.
Manufactured by the Garrett Corporation,
the ME 831-800A ship's service power unit
The power section consists of the 2-stage
(SSPU) is the electrical and hydraulic power
centrifugal-flow compressor, the 3-stage axial-flow
source on the PHM-class ships. On these
turbine, the inlet plenum, and the combustion
hydrofoils, the SSPU provides the electrical
system. The power turbine is mounted on the rear of
power to (1) activate the compressed air system
the gearbox assembly.
that starts the foil borne engine, (2) drive the ac
generator, (3) support the speed and load control
The gearbox section consists of the reduction
circuitry and equipment, and (4) operate the two
gear train contained in a split-housing assembly.
hydraulic pumps.
Mounted on the reduction gear assembly are the ac
generator, two hydraulic pumps, and a load
compressor. A more detailed description of the
In chapter 6, we gave you an overview of
gearbox and its operations will be provided later in
this SSPU. Now, let's take a slightly closer look
this chapter.
at some of its systems and components.
