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This section describes the operation of each
major sub-assembly as an aid in the operation,
installation, maintenance and repair of the
type GMSG vacuum circuit breaker.
Type GMSG-GCB generator circuit breakers
The type GMSG-GCB generator circuit breaker
is a special variant of the type GMSG circuit
breaker family. The circuit breaker design,
construction, use and operation of the
generator circuit breaker is as described in
this instruction manual. Important variations
are noted in the text where appropriate.
Vacuum interrupters
The operating principle of the vacuum
interrupter is simple. Figure 9: Vacuum
interrupter cutaway view is a cutaway view of
a typical vacuum interrupter. The entire
assembly is sealed after a vacuum is
established. The vacuum-interrupter
stationary contact is connected to the upper-
disconnect stud of the circuit breaker. The
vacuum-interrupter movable contact is
connected to the lower-disconnect stud and
driving mechanism of the circuit breaker. The
metal bellows provides a secure seal around
the movable contact, preventing loss of
vacuum while permitting vertical motion of
the movable contact.
When the two contacts separate, an arc is
initiated that continues conduction up to the
following current zero. At current zero, the
arc extinguishes and any conductive metal
vapor that has been created by and supported
by the arc condenses on the contacts and on
the surrounding arc shield.
Contact materials and configuration are
optimized to achieve arc motion, resist
welding and to minimize switching
disturbances.
1
2
4
5
6
7
8
9
Primary disconnects
Figure 10: Upper and lower primary
disconnects is a side view of the circuit
breaker with the outer-insulating phase
barrier removed to show details of the
primary disconnects. Each circuit breaker has
three upper- and three lower-primary
disconnects. Upper-primary disconnects are
connected to the stationary contacts of the
vacuum interrupters, and the lower primary
disconnects are connected to the movable
contacts.
Each disconnect arm has a set of multiple
spring-loaded fingers that mate with bus bars
in the metal-clad switchgear. The number of
fingers in the disconnect assembly varies with
the continuous and/or interrupting rating of
the circuit breaker.
There are three insulating push rods. Each
push rod connects the movable contact of
one of the vacuum interrupters to the jack
shaft driven by the closing and tripping
mechanism. Flexible connectors provide
secure electrical connections between the
movable contacts of each vacuum interrupter
and its bottom-primary disconnect.
1
Fixed contact-current connection
2
Ceramic insulator
3
Arc shield
4
Fixed contact
5
Moving contact
6
Ceramic insulator
3
7
Metal bellows
8
Guide
9
Moving contact-current connection
Figure 9: Vacuum interrupter cutaway view
15
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