Siemens vacuum circuit breaker 38-3AH3 38 kV - Manual (Page 39)

Vacuum interrupter/
operator
The spring-dump cam raises the
spring-dump interlock upon
insertion of the circuit breaker into
the compartment, or upon
withdrawal from the compartment.
The interlock is raised at about the
time the front wheels pass over the
cubicle sill.
It allows the spring-dump interlock
to be in the reset (lowest) position at
all other times.
The operation of the spring-dump
interlock may be seen in Figure 34:
Interlock mechanisms on the type
38-3AH3 vacuum circuit breaker on
page 37. As the interlock rises (5.0),
it causes the 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 spring-
dump condition as the tube rises.
The rising tube raises a lever
attached to the base of the
operating-mechanism enclosure.
This lever raises the trip-free
pushrod, that elevates the closing-
spring release cam. The closing-
spring release cam moves the
closing-spring latch, that causes the
closing springs to discharge.
However, the trip-free interlock is
raised, so that the operating
mechanism is held trip-free (refer to
"Trip-free interlock" on page 33).
Thus, the energy in the closing
springs is released (spring-dump),
without movement of the jack shaft
or the vacuum-interrupter contacts.
D. Trip-free interlock position -
mechanical interlock
In order to prevent the motor-
charging circuit from "making and
breaking" as the circuit breaker and
cubicle secondary disconnects make
or break physical contact, an
electrical switch is provided. This
switch is mounted in the line of
action taken by the trip-free
interlock plunger that follows the
racking-mechanism cam and is
elevated at all times while the circuit
breaker is in the drawout
compartment except when in the
TEST or CONNECT positions.
A striker plate, integral with the trip-
free interlock plunger, engages and
operates (opens) the switch when
the plunger is in an elevated position
blocking spring-charging motor
operation. The switch is closed when
the circuit breaker occupies the TEST
or CONNECT position, allowing the
charging motor to operate
automatically.
39