Westinghouse DBN-1016 Technical Manual page 24

CIRCUIT BREAKER
the armature rises pin (363) will lift crank
(350) to trip breaker instantly. Clip (333) is
cemented to screw (334) to protect factory
setting.
The short delay pickup is factory set by
turning screw (342) which moves pointer (340)
and lower end of spring (339). Spring (339) will
hold down lever (335), link (337) and armature
(338) until magnetic attraction of yoke (336) lifts
armature. When the armature rises, lever (335)
will lift valve (334) and allow a controlled amount
of air to flow thru port to vacuum chamber.
This controlled air flow will allow long delay
tripping parts to react for short delay tripping.
Turning screw (346) moves bracket (345) which
limits motion of lever (335). This adjustment
controls air flow around valve (344) and pre-
determined short delay time required to trip
hreaker. Two clips (341) are cemented to screws
(342) and (346) to protect factory setting.
These overcurrent trip units have a quick
reset valve. If a unit has partially or com-
pletely reacted to an overcurrent condition and
then the current subsides to zero or normal, a
quick reset is desirable. As stem assembly
(313) comes down, air is expelled thru port to
bottom of long delay valve (324). Pressure
moves disc (347) down providing a large open-
ing for the expelled air. Spring (348) returns
the disc to the sealed position after reset is
completed.
When selective coordination requires that
instantaneous tripping
be
omitted, a discrimi-
nator trip is supplied. The discriminator will
NOT trip a breaker that is closed; but will in-
stantaneously trip a breaker that is closing if
the inrush current is above 40,000 amperes.
The discriminator trip operates similar to an
instantaneous trip except additional parts are
required and slot (E) is added to crank (358).
If
breaker is closed, spring (361) forces
projection (c) on lever (359) to rotate latch (356)
away from projection
(D)
on crank (358). Al-
though high fault currents will rotate armature
(330) NEITHER pin (363) nor latch (356) can en-
gage crank (358) and breaker will not trip un-
less fault current doration allows short delay
tripping.
If
breaker is open, contact arm movement
of roller (355) will rotate lever (359) away from
latch (356). Spring (357) places latch (356) into
position to engage crank projection (D). Piston
(360) and cylinder (362) create a small time de-
lay so that latch (356) will not rotate on clos-
ing stroke of breaker until breaker is com-
pletely closed. If On the closing stroke, a fault
1-18
current of 40,000 amperes or more appear then
armature (330) will carry latch (356) with it
and rotate crank (358) and cause breaker to
trip.
1_2_1_12 Auxiliary Switch-(Soe Figure 1-2-11)
The auxiliary switch is mounted on top of
the circuit breaker shelf to the left of the op-
erating mechanism.
The eight pole auxiliary switch (400) con-
sists of two four pole switches; one mounted
above the other. A third switch case, which
contains a terminal block (422), is mounted
above the switches.
Each auxiliary switch is a shaft operated
four pole rotary type containing either normally
open or normally closed contacts or a combina-
tion of normally open and normally closed con-
tacts. The normally open or "a" contacts are
open when the circuit breaker is in the open
position and the normally closed contacts or
''b'' contacts are closed when the circuit breaker
is open.
The rotor assembly consists of a square
shaft (404), rotor ends (415) and (417), three
rotor sections (416), moving contacts (401), arm
(412), bushing (418) and SCrew (419) which
clamps together the rotor assembly.
Each contact finger (405) backed by spring
(406), is secured by a rivet and is attached to
stem (407), which is secured to the case by
collar (408)_ Screws (411) and a crimp washer
provide the terminal connections.
Link (420) is attached to the breaker lever
of the operating mechanism. As the link is
rotated by the action of the operating mecha-
nism, arm (412) rotates the shaft (404) to re-
position the moving contacts.
The mOving contacts
ar~
set 90 degrees
apart for a 90 degree rotation of the shaft.
The contacts can
be
converted in the field to
either normally open or normally closed by
rotating the appropriate rotor section 90 de-
gree s on the shaft.
1-2-1-13 Main Disconnects-(S .. Figure 1-2 ... 12)
The main disconnects are mounted on the
studs of the moving component of the circuit
breaker, one on each of the six breaker studs.
Each main disconnect consists of a finger
retainer (428), the finger cluster (426) and two
finger springs (427). The assembly is held on
r
(