Instruction manual

Vehicle function and operational
interlocks
A type 38-3AH3 vacuum circuit breaker is
comprised mainly of the vacuum
interrupter/operator module fitted to a
vehicle. This vacuum interrupter/operator
module is an integral arrangement of
operating mechanism, dielectric system,
vacuum interrupters and means of
connecting the primary circuit. The vehicle
supports the vaccum interrupter/operator
module, providing mobility and fully
coordinated application in Siemens type
GM38 switchgear.
Successful coordinated application of the
fully assembled type 38-3AH3 vacuum
circuit breaker is achieved through precise
alignment in fixtures during manufacture,
and important functional interlocking.
Alignment
All aspects of the circuit breaker structure
impacting alignment and
interchangeability are checked using
master fixtures at the factory. Field
adjustment will not normally be required.
Interlocks
Circuit breaker racking-interlocks
The vacuum interrupter/operator module,
the vehicle portion of the circuit breaker
and the racking mechanism in the
switchgear all cooperate to provide
important operational interlocking
functions.
1. Rating interlock
The rating interlock consisting of a
coded-interference plate is mounted on
the vehicle (refer to Figure 32: Circuit-
breaker interlocks and ground
disconnect on page 33). A mating-
interference blocking plate is mounted
in the drawout compartment (refer to
Figure 33: Circuit-breaker compartment
(MOC/TOC switch cover removed for
photo on page 34).
When circuit breakers are located above
floor level, handling of the circuit breakers
requires the use of a lifting device or a
crane with a lift sling.
Racking mechanism
Figure 33: Circuit-breaker compartment
(MOC/TOC switch cover removed for
photo) on page 34 shows the racking
mechanism in the switchgear used to
move the circuit breaker among the
DISCONNECT, TEST and CONNECT
positions. This mechanism contains a
circuit-breaker racking-block that mates
with the bottom of the circuit-breaker
housing, and locks the circuit breaker to
the racking mechanism during in and out
movement.
A racking crank (refer to Figure 2: Type 38-
3AH3 vacuum circuit breaker racking on
page 11) mates to the threaded square-
shaft of the racking mechanism. Clockwise
rotation of the crank moves the circuit
breaker into the switchgear, and
counterclockwise rotation removes it.
The racking and trip-free interlocks provide
several essential functions.
1. They prevent racking a CLOSED circuit
breaker into or out of the switchgear
assembly.
2. They discharge the closing springs
whenever the circuit breaker is inserted
into or withdrawn from the switchgear.
3. They prevent closing of the circuit
breaker unless it is in either the TEST or
CONNECT positions, and the racking
crank is not engaged.
The rating interlock prevents insertion of a
lower-rated circuit breaker into a cubicle
intended for a circuit breaker of higher
ratings.
Vacuum interrupter/
operator
36