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Equipment Description
IB-60201
The close latch, when released either by the
closing coil or the manual close operator,
allows the main closing spring to pull the
crank arms upward thus rotating the main
closing cam and driving the fundamental
linkage into the closed position. This
causes the main linkage to rotate the
jackshaft such that the operating pushrods
(Figure 3, y) are driven toward the current
carrying side of the circuit breaker.
Each operating pushrod assembly has a
recess at each end which encloses a contact
loading spring (Figure 3, x). At the end of
this spring is a spring yoke (Figure 3, v),
which connects with bell cranks. The spring
yoke is restrained by a lock nut on a stud
which passes through the contact loading
spring and is attached to the operating
pushrod assembly. The contact loading
spring has initial compression such that as
soon as the vacuum interrupter contacts
touch, the springs are preloaded to a value
sufficient to resist vacuum interrupter
contact separation under the highest
electromagnetic forces exerted by the rated
short circuit current. Further movement
of the operating pushrod assembly
compresses the contact loading spring
even more and produces a gap between
the face of the spring yoke and the lock
nut. This “nut gap” is used to evaluate the
erosion of the vacuum interrupter contacts.
For each phase, bellcranks (Figure 3, t) are
located on the outside of the lower
primary disconnecting devices
(Figure 3, g) and are supported by bearings.
Each bell crank is connected to an
operating pin, which passes through a slot
in the lower primary disconnecting devices
and engage an extension to the vacuum
interrupter assembly thus moving the
vacuum interrupter contact. The bell cranks
give an approximate 3 to 1 multiplication
of the contact loading spring force,
enabling a lower spring rate to be used.
It also multiplies the contact movement
by a factor of approximately 3, so that the
mechanism linkages have relatively large
movements and are less critical.
In the cam and fundamental linkage
positions (Figure 4, b & d), the contact
loading springs and the main opening
springs are both acting to compress the
three (3) main mechanism links. The
jackshaft extends from the left to the right
side of the circuit breaker frame and is
supported at the main circuit breaker frame
side sheets and by the mechanism side
sheets. The outer operating levers on the
jackshaft have connections to the circuit
breaker opening springs (Figure 2, b).
The fundamental linkage is restrained from
movement by the secondary trip prop
acting on the primary trip prop roller.
A component of force tends to make the
primary trip prop rotate upward, but it
is restrained by the secondary trip prop
face acting on the primary trip prop roller.
The clearance between the primary trip
prop roller and the secondary trip prop
is controlled by the primary trip prop
adjusting screw. When the trip shaft is
rotated by the action of the manual trip
operator or the primary shunt trip coil, the
secondary trip prop face moves downward
and permits the primary trip prop to rotate
upward, thus permitting the main linkage
to move upward and the jackshaft to
rotate, opening the circuit breaker. The left
jackshaft levers engage a shock absorber
(Figure 2, e), which controls the rebound
of the vacuum interrupter contacts on an
opening operation. An extension of the
jackshaft projects through the left circuit
breaker side sheet and operates the MOC
actuator (Figure 2, i).