•
•
Type
50-DH-50
Air Circuit Breaker
Contact Assembly
The breaker contact assembly, Figure 5, is lo
cated above the operating mechanism and operated
by an operating rod, shaft and pull rods. This
contact assembly must be capable of carrying
normal load currents and drawing the arc during
the interrupting periods in a manner that after
circuit interruptions the contacts will be in such
condition that the load current can be carried
without undue temperature rise. The moving con
tacts are of the blade type with silvered hinged
joints forming the lower contact. The upper mov
ing main contacts consist of silvered serrations on
the upper part of the blades. These serrations en
gage the silvered tongues of the upper studs when
the breaker is in the closed position. The stationary
arcing contacts are fastened to the top of and
project over the stationary main tongues so that
they engage the arcing contact surface on the
blades as the breaker is opening or closing, how
ever, these arcing contact surfaces do not engage
each other when the breaker is in the fully closed
position. The entire contact arrangement is so de
signed that the arcing contacts, which have arc
resisting surfaces, part last on opening and engage
first in closing to protect the main contact sur-
600AMPERE
1200AMPERE
SECTION A-A
SECTION B-B
Fig. 4-Type 50-DH-50, "De-ion" Air Circuit Breaker,
Primary Disconnecting Contacts
faces from any arcing that might be caused by
either of these operations. Contact pressure is
maintained on the earlier models by bronze spring
cup washers; conical springs are used on the later
designs.
MOVING
TIP
STATIONARY
ARCING TIP
STATIONARY
I.AAINS
MOVING CONTACT
fRONT VIEW SHOWING CONTACT
ARRANGEMENT THROUGH SERRATIONS
Fig. 5-Breaker ContactAssembly
5
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