Figure 12-4.750-kW turbine generator set.
The type of ships service generator commonly
used aboard ships in the Navy is shown in
figure 12-4. Although generator sets (turbo-
generators) are built differently, all have the same
arrangement of major parts.
Turbines used for driving the ships service
generators differ from other auxiliary turbines;
they usually operate on superheated steam. The
service generator turbine exhausts to a separate
auxiliary condenser that has its own circulating
pumps, condensate pumps, and air ejectors.
Cooling water for the condenser is provided by
the auxiliary circulating pump through separate
injection and overboard valves.
Superheated steam is supplied to the ships
service generator turbine from either the main
steam line or a special turbogenerator line
that leads directly from the boiler. Aboard some
ships, the turbinein the event of condenser
casualtymay be discharged directly to the
atmosphere or to the main condenser when the
main plant is in operation.
The ships service generator must supply
electricity at a constant voltage and frequency
(hertz), which requires the turbine to run at a
constant speed even when loads vary. Constant
speed is maintained by a speed-regulating
governor. The turbine also has overspeed and
back-pressure trips, which automatically close the
throttle if the turbine exceeds acceptable operating
conditions. A manual trip is used to close the
throttle quickly if there is damage to the turbine
or to the generator. The shaft glands of the ships
service generator turbine are supplied with gland-
sealing steam. The system is similar to that used
for main propulsion turbines. Other auxiliary
turbines in naval use are seldom, if ever, provided
with gland-sealing systems.