Magnum
1812.900A
23
Figure 3-11: Circuit Breaker Closing Springs Being Manually
Charged
3.4.2
Electrical operation
For electrically operated circuit breakers, the springs are
normally charged through the use of an electrical
operator (Figure 3-12). The springs can, however, be
charged manually as just described in the previous
paragraph (Figure 3-11).
Like the manually operated circuit breaker in the previous
paragraph, electrically operated circuit breakers can also
be manually closed and opened through the use of the
front mounted Manual “ON” and Manual “OFF”
buttons.
An electrically operated circuit breaker from the factory is
also equipped as standard with a spring release to close
the circuit breaker electrically. An optional shunt trip and
undervoltage release are also available to trip (open) an
electrically operated circuit breaker. Refer to paragraph
3.8 for more details on both standard and optional
devices.
3.4.3
Anti-pump feature
The Magnum circuit breaker has both mechanical and
electrical anti-pump features. If the circuit breaker is
closed on a fault condition (and trips open while the
CLOSE signal is maintained), using either the mechanical
pushbutton or the electrical close coil, it will not make
another attempt to close until the close command is
removed and reapplied. Note that if the close signal is
applied prematurely (before the breaker is completely
charged and latched), the close command will be ignored
until it is removed and reapplied.
Figure 3-12: Electrical Motor Operator to Charge Closing
Spring
1. Electrical Motor Operator
For electrical closing, a Latch Check Switch (LCS) option
is available (see paragraph 3.8.1) which will block the
application of the electrical close command until the
breaker is ready to close.
3.5 Arc
chambers
The Magnum circuit breaker utilizes arc chambers to
insulate and isolate individual poles from one another,
from the rest of the circuit breaker, and from operating
personnel. Arc chambers are molded and integral parts
of the circuit breaker frame. Enclosed within each arc
chamber is an arc chute which mounts over each set of
primary contacts.
After the main contacts part, any remaining current is
driven to the arcing contacts (Figure 3-13). Magnetic
action draws the arc to the arc chute. As the arcing
contacts separate, the moving arcing contacts discharge
into the arc chute plates while the integral arc runner
also helps to draw the arc into the arc chute
(Figure 3-14).
3.5.1 Arc
chute
The Magnum arc chute mounts down over the arcing
contact. Alternating V-shaped arc chute plates attract
the arc and interrupt it. The top arc plate, which is a part
of the arc chute itself, also helps to attract the arc away
from the moving arcing contact and up into the arc
chute’s V-shaped plates (Figure 3-14).
Arc chute components are assembled in an insulating
jacket which is removable from the top of the circuit
breaker, as previously described in paragraph 2.4. Each
arc chute has a baffled top cover.
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