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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.
Circuit breaker handling wheels
The type GMSG vacuum circuit breaker is
designed for easy movement into and out of
the metal-clad switchgear assembly.
A section of indoor or Shelter-Clad switchgear
does not require a transfer truck or lifting
truck for handling of the circuit breaker when
all circuit breakers are located at floor level.
Once the circuit breaker is racked out of the
switchgear, the unit can be pulled using the
handles on the front of the circuit breaker.
The circuit breaker will roll on its bottom four
wheels.
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 29: Circuit breaker compartment (up to
50 kA shown) on page 30 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 GMSG
vacuum circuit breaker racking on page 12)
mates to the 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into or withdrawn from the switchgear.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, subject to the limitations detailed in
"Rating interlock".
Siemens integrated electric-racking
system (SIERS) (optional)
An electrical racking system integrated into
the racking mechanism of a circuit breaker (or
63 kA rollout tray in arc-resistant GM-SG-AR
switchgear) compartment is optionally
available. The SIERS system allows an
operator to control the racking of a circuit
breaker (or 63 kA rollout tray in arc-resistant
GM-SG-AR switchgear) from a remote location
(outside the arc-flash boundary) without the
need to install a portable racking accessory.
This reduces the need for personal protective
equipment required by NFPA-70E®.
The SIERS system is available in three
configurations:
1. Basic: Each circuit breaker cell is equipped
with an integrated electric-racking
system, which includes a fixed-mounted,
high-torque gear motor and logic-control
module. A control pendant is provided,
and a compartment mounted connector
for supplying control power from the
switchgear, or from an external supply
(either 120 Vac or 125 Vdc). Typically, one
control pendant is supplied per lineup.
2. Local HMI: Basic type as in configuration 1
plus local HMI panel personal computer
(PC) interface for use with the user's PC.
3. SCADA: Basic type as in configuration 1
plus custom interface with SCADA or
other control system.
For further information, refer to instruction
manual EMMS-T40013-00-4A00.
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