Siemens GMSG

Trip-free interlock
Figure 28: Circuit breaker interlocks and
ground disconnect on page 29 shows the
devices providing the trip-free interlock
function. The purpose of the trip-free
interlock is to hold the circuit breaker
operating-mechanism mechanically and
electrically trip-free. The circuit breaker is
held trip-free during racking and whenever
the circuit breaker is between the TEST and
CONNECT positions within the switchgear
enclosure.
This interlock functions so that the circuit
breaker primary contacts can only be
closed when in the CONNECT position, in
the TEST position or out of the switchgear
cell.
Rating interlock
Figure 28: Circuit breaker interlocks and
ground disconnect on page 29 shows the
rating-interlock interference plates
mounted on the circuit breaker frame.
The circuit breaker interference plates are
complemented by matching plates located
in the cubicle.
The interference plates (rating interlocks)
test the circuit breaker voltage, continuous
current and interrupting and momentary
ratings and will not allow circuit breaker
insertion unless the circuit breaker ratings
match or exceed the cell rating.
Vacuum interrupter/operator
Hazardous voltage and high-speed moving parts.
Will cause death, serious injury and property damage.
Do not by-pass interlocks or otherwise make interlocks
inoperative. Interlocks must be in operation at all times.
Read this instruction manual. Know and understand correct
interlock function. Check interlock function prior to inserting a
circuit breaker into a switchgear cubicle.
Type GMSG vacuum circuit breakers rated
up to 50 kA are designed such that a single
circuit breaker of the maximum ratings
(voltage, interrupting rating and
continuous current) can be installed in any
switchgear compartment. For example, a
type GMSG circuit breaker rated 15 kV,
50 kA interrupting and 3,000 A continuous
current can be installed in any type GM-SG
circuit breaker cell of equal or lower
ratings.
Type GMSG vacuum circuit breakers rated
63 kA are designed such that a circuit
breaker can be installed in any type GM-SG
circuit breaker cell rated 63 kA and of
equal or lower voltage and continuous
current ratings.
Circuit breaker frame
The frame of the type GMSG vacuum
circuit breaker contains several important
devices and features deserving of special
attention. These are the ground
disconnect, the four racking wheels and
the four handling wheels.
Ground disconnect
Figure 28: Circuit breaker interlocks and
ground disconnect on page 29 shows the
ground disconnect contact mounted at the
bottom of the circuit breaker. The spring-
loaded fingers of the disconnect contact
engage the ground bar (refer to Figure 29:
Circuit breaker compartment up to 50 kA
shown on page 30) at the bottom of the
switchgear assembly.
The ground bar is to the right of the
racking mechanism, shown at the bottom
center of the switchgear.
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