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Siemens 38-3AH3 38 kV Instruction Manual page 38

Vacuum circuit breaker
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Enclosure rear
Trip-pushrod cam
Interlock levers
Figure 35: CLOSED circuit-breaker interlock mechanism in stored-energy mechanism
Vacuum interrupter/
Close-latch lever
Closing-spring release cam
Normal operating position
Trip-pushrod cam
Trip-latch lever
Trip-free pushrod
Retaining rings
Spring-dump tube
The racking-cam profile on the
racking mechanism allows the trip-
free racking-interlock to be in the
lowest position (reset) only when
the circuit breaker is in the TEST or
the CONNECT position. Thus, during
racking, the trip-free interlock is held
in an elevated condition except
when the circuit breaker reaches the
TEST or the CONNECT position. The
circuit breaker can be closed only
when the interlock plunger is down,
and will trip if the plunger is moved
The operation of the trip-free
racking-interlock may be seen in
Figure 34: Interlock mechanisms on
the type 38-3AH3 vacuum circuit
breaker on page 37. As the interlock
(6.0) rises, it moves a series of
linkages, that cause a guided tube
(4.0) to rise, and enter the
operating-mechanism enclosure.
Figure 35: CLOSED circuit breaker
interlock mechanism in stored-
energy mechanism shows the
operating mechanism detail
components that establish a trip-
free condition as the tube (4.0)
rises. The rising tube raises a lever
attached to the base of the
operating-mechanism enclosure.
This lever raises the trip-free
The rising trip-free pushrod elevates
the trip-free pushrod cam, that
pushes the trip-free coupling lever
(62.8.3) (refer to Figure 15: Stored-
energy operating mechanism on
page 20) toward the rear of the
The movement of the trip-free
coupling lever toward the rear of the
enclosure is transmitted through the
trip-free coupling link (62.8.2) to the
spring-return latch (62.8.1). With the
latch displaced from a normal reset
position, the trip-free coupling rod
(62.8) cannot apply closing effort to
the jack shaft (63.0). Thus, upon
release, the closing-spring energy
will not be transmitted to the jack
C. Automatic closing-spring energy
The automatic closing-spring
energy-release (spring-dump) (refer
to Figure 32: Circuit-breaker
interlocks and ground disconnect on
page 33) is a plunger with a roller on
the lower end. The spring dump has
a return spring that returns the
spring dump to the reset or lowered
The plunger roller tracks the shape
of the spring discharge cam on the
racking mechanism in the
switchgear (refer to Figure 33:
Circuit-breaker compartment (MOC/
TOC switch cover removed for
photo) on page 34).



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