Figure 6-35.--Main deck switchboard.
outboard end. An external shroud collects the air and
meter to record the elapsed time the turbine has been
running. The start counter records the number of starts.
routes it out of the compartment.
AC GENERATORS
GENERATOR CONTROL UNIT
Each SSPU drives its own ac generator. The two ac
A GCU is installed in each switchboard to monitor
generators driven by the SSPUs are brushless, 250-kVA
the corresponding ac generator output. The GCU
units that produce 450-V ac, 400-Hz, 3-phase power.
monitors ac generator output to provide voltage
Each generator consists of three machines (generators)
regulation and control and to protect the generator and
in one housing. Two of these machines are 3-phase
its electrical load. The GCU provides these functions
salient-pole synchronous units (alternators). The third
through sensing, time delay, logic, and output control
machine is a permanent-magnet, high-frequency
circuits. These functions are mostly contained on eight
(4,800 Hz at 8,000 rpm), single-phase unit that provides
printed circuit boards (PCBs). The PCBs are mounted
a low power output used for initial excitation and control
within a natural convection ventilated enclosure. They
circuits.
are connected to the switchboard wiring by means of
The main generator is a rotating-field unit that
two multiple pin connectors.
develops the 400-HZ, 3-phase power supplied to the
The GCU regulates the generator output voltage by
output terminals. Excitation of the main field of the main
controlling the amount of power delivered to the
generator is received from the second 3-phase generator.
The second 3-phase generator is an acting exciter that
provides ac voltage. The ac voltage is rectified to dc
by monitoring the generator output for over/
voltage by rotor-mounted silicon diodes and capacitors.
undervoltage, overcurrent, underfrequency, over/
The generator is driven at a constant speed through a
underexcitation, and differential phase currents for both
splined shaft that connects the unit to the SSPU gearbox.
single and parallel operation. In its monitoring function,
the (ICU activates control circuits to isolate the faulty
The main generator provides its own internal
output from the ship's electrical distribution system.
coding. Compartment air is drawn in at the generator
