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Arcin� Chambers and Ma�netic Circuit
The arcing chambers are locat7d immediat�ly
above the arcing contacts and constst of assembhes
of laterally spaced ceramic plates, having V-shaped
slots and held together with a moisture and heat
resisting cement, e'!cased in a . protecti ':' e cove _r ing
J?.
of insulating matenal.
at each end of the ceramic plate assembhes and the
insulating sides of the covering extend downward
past the upp _ e r contacts. �he arcirw chambe � s are
held in positwn by magnetic pole pteces. On mter
ruption, the magnetic flux across the gap between
the pole £aces and through the arc chamber forces
the arc upward into the interrupting slot.
Interphase Barriers
Interphase insulating barriers, b _u ilt . as a single
unit are fastened to a support whtch 1s bolted to
the horizontal steel plate base.
Operation of Breaker in Extin�uishin� Arc
Figure 6 shows a typical arrangeme '! t o
fundamental parts of the Type DH Atr C1rcmt
Breaker. The operation of the circuit breaker will
more clearly understood by referring to that
oe
figure while reading the remainder of this para
graph. The arcing contacts are so arranged that
at the instant of parting they form a loop in
the current path through the breaker, 1.
magnetic effect of this loop extends the arc rapidly
upward as the contacts open, 2. pue to this looping
effect, the arc almost instantly impinges against the
fixed horn .in the arc chamber immediately above
the stationary arcing contact so that one arc termi
nal transfers to this horn; the other arc terminal re
maining on the moving arcing contact momentarily,
3. ·. The transfer of the arc to the horn alters the
current path through the breaker to include the
multi-turn coil as that coil is not carrying current
when the breaker is in the closed position. Current
flowing through that coil produces a magnetic flux
which moves the arc upward into the arc chamber
and t he second arc terminal from the moving arcing
contact to the arcing horn at the front end of the
arc chamber, 4. A shunt path connects this horn
&
Second ar y,
Arcing
Contact Platform
Fig. 6-Typical Arrangement of Component Parts
Type 50-DH-50 Air Circuit Breaker
n arcmg horn t . s provtded
!
�
t
The
Insulation Plates
Laminated
s
Iron Shoe
'-Outline Of
Arc Chamber
Arc Shield
Shunt Strap
Moving Contac t Arm
·
&
Arcing Contact
to the lower breaker terminal, thus relieving the
contacts of the current carrying duty until the arc
is extinguished in slot of the arc chamber, 5, 6.
SAFETY FOR PERSONNEL
The installation, operation, and maintenance of
circuit breaker equipment requires that certain pre
cautionary measures be taken to prevent accidents.
The following list presents a few suggestions of that
character.
(1)
Do not touch a live breaker:
Parts of the circuit breaker above the hor
izontal isolating barrier are at line potential
of the circuit to which the circuit breaker is
connected. The breaker should be isolated
from the circuit by disconnecting switches
and the contacts solidly grounded, in con
formance with conventional safety practice,
before attempting any work on the breaker.
e
(2)
Whenever possible the breaker should be
in the open position when any work is being
done on it. If that is impossible the trigger
should be secured in the latched position by
inserting a wooden block, approximately
2Ys"x %"x3" long, between the trigger and
the tripping lever in such a manner that it
is impossible to move the trigger to the trip
ping position. Such a blocking arrangement
is also useful when working with the under
voltage attachment.
(3)
Before placing the circuit breaker in serv
ice make certain that the frame is effectively
grounded and that minimum clearances for
the rated voltages are maintained between
live parts and ground. The same check as
to clearances should be made between
phases if barriers other than those supplied
with the breaker are to be used.
(4).
Never lay tools, such as wrenches and
screw drivers, on any portion of the circuit
breaker.
(5 )
\Vhen assembling the arcing chambers on
to the breaker, check to see that the contact
jaw on the stack has engaged the lead to the
blow-in coil and that the chambers are cen
trally located so that there is no interference
with the travel of the moving contacts.
( 6)
When lifting the breaker by cranes it is
advisable to remove the arcing chambers
and barriers before proceeding with such an
operation.
Do not replace any arc chamber after the
( 7)
ends of slots have become
through erosion.
under "Operation and Maintenance."
6
-fs
inches wide
(See "Arc Chambers"
•
•
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