AQB
Type ACB circuit breakers are used to connect
ship's service and emergency generators to the power
distribution system, bus ties, shore connection circuits,
Type AQB circuit breakers (fig. 2-51) are mounted
and some feeder circuits from the ship's service
in supporting and enclosing housings of insulating
switchboard. They are also used on submarines to
material and have direct-acting automatic tripping
connect batteries, reactor coolant pump motors, and trim
devices. The y are used to protect single-load circuits
and drain pump motors.
and all feeder circuits coming from a load center
distribution panel.
The reverse-power relay is mounted on the panel
close to the circuit breaker when it is used with ship's
Where the requirements are low enough, the type
service and emergency generator breakers. Other
AQB may be used on generator switchboards. When it
automatic controls may be located at remote points to
becomes necessary to replace one of the older types of
give maximum protection to the circuit.
circuit breakers, replace it with the newer AQB-A101,
Circuit breaks designed for high currents have a
AQB-A250, AQB-A400, AQB-A600, or AQB-A800 as
double-contact arrangement. The complete contact
required.
assembly consists of the main bridging contacts and the
arcing contacts. All current-carrying contacts are
high-conductivity, arc-resisting silver or silver-alloy
inserts.
Each contact assembly has a means of holding the
arcing to a minimum and of extinguishing the arc as
soon as possible. The arc control section is called an arc
chute or arc runner. The contacts are so arranged that
when the circuit is closed, the arcing contacts close
first. Proper pressure is maintained by springs to ensure
the arc contacts close first. The main contacts then
close.
When the circuit opens, the main contacts open first.
The current is then flowing through the arc contacts,
which prevents burning of the main contacts. When the
arc contacts open, they pass under the front of the arc
runner. This causes a magnetic field to be set up, which
blows the arc up into the arc quencher and quickly
extinguishes the arc.
Type ACB circuit breakers are available in both
manually (hand-operated) and electrical] y operated
types. Electrically operated ACB breakers may be
operated from a remote location. The high interrupting
types are electrically operated because it is then
unnecessary for personnel to approach them to open or
close the circuit.
No circuit breaker, regardless of type, should be
worked on without opening the circuit. Remember,
certain terminals may have voltage applied to them even
Figure 2-51.--AQB-A250 circuit breaker complete, front view.
though the breaker is open. Aboard ship, power maybe
supplied to either end of the circuit breaker.
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