main field connected in series with an armature.
When the rotor reaches about 75 percent of
The armature is similar in construction to any dc
synchronous speed, a centrifugally operated
motor. When electric power is applied, the
switch (fig. 9-4, view C) disconnects the starting
magnetic force created by the fields reacts with
winding from the line supply. The motor con-
the magnetic field in the armature to cause
tinues to run on the main winding alone. Then
rotation.
the rotating field is maintained by the interaction
of the rotor and stator electromagnetic forces.
CAPACITOR MOTOR.--The capacitor
60-HERTZ DISTRIBUTION
motor is single-phase and has a capacitor in series
SYSTEM COMPONENTS
with the starting winding. An external view is
shown in figure 9-5 with the capacitor located on
After the 450-volt , 60-Hz power is generated
top of the motor. The capacitor produces a greater
by an SSDG or an SSGTG, the power must be
phase displacement of currents in the starting and
distributed throughout the ship. Distribution is
running windings than is produced in the split-
accomplished by the use of SWBDs, CBs, power
phase motor. The starting winding in the capacitor
panels, automatic bus transfer (ABT) switches,
motor has many more turns of larger wire than
manual bus transfer (MBT) switches, transform-
the split-phase motor. The starting winding is con-
ers, and cables.
nected in series with the capacitor. The starting
Although each class ship has items peculiar
winding current is displaced about 90 degrees
only to that class, operation of switchboards is
from the running winding current. The axes of the
fairly common for all 60-Hz systems. You must
two windings are also displaced by an angle of
always use EOSS when operating the 60-Hz
90 degrees. Therefore, a higher starting torque is
switchboards. You will undergo extensive ship-
produced than that in the split-phase motor. The
board training using PQS to qualify as an
starting torque of the capacitor motor may be as
electrical watch stander.
much as 350 percent of the full-load torque.
SWITCHBOARDS AND PANELS
UNIVERSAL MOTOR.--A universal mot or
can be operated on either dc or single-phase ac.
A switchgear group is a single section or several
Aboard Navy ships, they are used extensively for
sections of switchboard mounted near each other.
portable tools. The motor is constructed with a
Switchgear groups are connected together with
cabling and disconnect links. They are enclosed
in a sheet-steel enclosure from which only handles,
knobs, and meters protrude. No live contacts are
externally exposed on any switchboard on a gas
turbine ship. The sections are identified with a
number and letter designation. When discussing
the entire switchgear group, the designation is its
number followed by the abbreviation SG. Each
section is identified by its number followed by S
or SA for the control section and SA or SB for
the distribution sections. On the FFG-7 class ship,
each SWBD has two sections. The SA is the con-
trol section; the SB is used for distribution
breakers. On the larger gas turbine ships, the SG
is composed of three sections. The control section
is the S section; the distribution breakers are on
the SA and SB sections.
Example:
FFG-7--No. 1 SSDG feeds the 1SG group
composed of 1SA and 1SB.
DDG, DD, CG--No. 2 SSGTG feeds the 2SG
group composed of 2S, 2SA, and 2SB.
Figure 9-5.--Capacitor motor.
9-6
