Type ACB circuit breakers are used to
arc as soon as possible. The arc control section
contains an arc chute. The contacts are so
connect ship's service generators to the power
distribution system and bus ties.
arranged that when the circuit is closed, the
arcing contacts close first. Proper pressure is
When a CB is used to connect ship's service
generators to the SWBD, they must have a reverse
maintained by springs to be sure the arc contacts
power relay installed. The reverse-power relay is
close first. The main contacts then close.
mounted on a panel close to the CB. Other
When the circuit opens, the main contacts
automatic controls may be located at remote
open first. The current is then flowing through
points to give maximum protection to the circuit.
the arc contacts, which prevents burning of the
Circuit breakers designed for high currents
main contacts. When the arc contacts open, they
have a double-contact arrangement. The complete
pass under the front of the arc runner. This causes
contact assembly consists of the main bridging
a magnetic field to be set up, which blows the arc
contacts and the arcing contacts. Current-carrying
up into the arc chute and quickly extinguishes the
contacts are constructed of high-conductivity, arc-
arc.
resisting, silver-alloy material, which is bonded to
the contact surface for durability and longer wear.
AQB.--Type AQB circuit breakers, such as
Each contact assembly has a means of holding
the AQB-250 shown in figure 9-13, view A, are
the arcing to a minimum and of extinguishing the
mounted in supporting and enclosing housings of
Figure 9-13.--AQB-A250 circuit breaker. A. Front view. B. With cover removed. C. Shunt trip.
9-13
