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Equipment Description
01.4IB.77020
PowlVac-ND
®
and PowlVac-NDA
™
Series 4
Vacuum Circuit Breakers
The camshaft would continue to rotate,
except that it is restrained by the close latch
arm
engaging against the close
latch shaft
. The main closing
cam, located between the mechanism
side sheets, is now in a position where the
fundamental linkage can move to the reset
position.
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
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
. At the end
of this spring is a spring yoke
,
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.
For each phase, bell cranks
are
located on the outside of the lower
primary disconnecting devices
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
, 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 auxiliary switch and MOC operating
linkage.
