field dc power level in the MANUAL mode. When
EXCOP. Each AVR provides generator field excitation
the switchboard AUTO/OFF/MANUAL switch is in
through the other major components. The AVR selection
MANUAL, the MVA will move the motor-operated
is made at the switchboard, with only one AVR active at
variable ratio transformer on demand from either
a time. Unless it is disabled, the inactive AVR becomes
the EPCC or the switchboard LOWER/RAISE
an automatic backup.
control.
A PMA output is required for field excitation. A dc
bridge rectifier contains silicon controlled rectifiers
MOTOR-OPERATED POTENTIOMETER.
(SCRs) that convert the PMA ac voltage output to dc
With the VOLTAGE RAISE/LOWER switch in the
voltage. The SCR circuits are influenced by system
AUTO mode, the MOP will adjust the AVR operating
adjustments and controls.
level by establishing a reference voltage for automatic
voltage regulation operation.
NOTE
DIODE FAULT DETECTOR. The DFD protects
On the switchboard operating panels, each
the exciter armature from high current damage resulting
AVR switch is labeled voltage regulator (VR).
from open, shorted, or leaking (unwanted current)
rotating diodes. The three LED-type DIODE STATUS
indicators on the module labeled DETECTOR
POWER CONTROL MODULE. The PCM
STATUS/OPEN/SHORTED can be seen through
routes PMA power to the DFD, OVL, and primary AVR
chassis openings.
modules. The PCM also converts the PMA power into
28 volts dc for use by the EXCOP electronic circuits.
FAILURE DETECTOR MODULE.- The FDM
has two principal functional areas: (1) AVR switching
OVERVOLTAGE LIMITER. The OVL limits
and (2) signaling the LOCOP of failures.
the field excitation if the output voltage should
e x c e e d the 552-volt trip point value or the
CURRENT LIMITER. The CL monitors the
instantaneous trip setting of 590 volts. An OVL trip
current phase transformers. Transformer signal
is set to hold the voltage at 518 volts (a setting that
values representing more than 3.2 times the rated
can be adjusted), to start the cooling fan, and to
current (12.9 kA) will override the other AVR
illuminate the LIMITING IN CONTROL indicator
signal inputs, reducing the field excitation and, in
on the LOCOP. The OVL can be reset by either of
turn, reducing the generator voltage and current.
the following two methods:
The CL has three adjusting rheostats, one for each
phase, that are used to set the maximum current
1. Placing the switchboard VOLT REG SELECT
output. The rheostats are mounted on the EXCOP
switch in the OFF position. This will shut down the
cover.
exciter and turn the fan off. (This switch is labeled
EXCITATION SELECTOR SWITCH (ESS) in the
There are three junction boxes in the K34's CL.
SSGTG technical manual.)
They are installed in the area where you would normally
find the LOCOP on the CG-, DD-, or DDG-993 class
2. Securing the SSGTG by normal means. This will
ships.
cause a reset to occur as the voltage drops to half the
450-volt ac rated value.
Local Operating Panel (LOCOP)
INTERFACE MODULE. The IFM connects the
EXCOP to the ship's cables and the SSGTG auxiliaries.
The LOCOP controls and monitors the SSGTG
The IFM also routes the control signals within the
operation. Control and monitoring functions include
EXCOP and controls the signals to the LOCOP and
starting control, events sequencing, indicating
exciter armature.
parameters, and stopping the SSGTG.
MANUAL VOLTAGE ADJUST. The MVA
On the Allison 501-K34, the LOCOP is located on
controls the generator output voltage by using a
the base assembly front edge. (See fig. 7-1.) The
variable ratio transformer to change the exciter
LOCOP has two front doors with attached control and
