Technical data

Auxiliary switch (circuit breaker
mounted)
The auxiliary switch assembly is mounted
on the vacuum circuit breaker with
contacts for use in the circuit breaker
control circuit and as spare contacts for
other use. Normally, four auxiliary switch
contacts, two NO (52a) and two NC (52b)
can be wired out for purchaser use.
Mechanism operated cell (MOC) switch
When required, 6, 12, 18 or 24 stages of
MOC auxiliary switch can be mounted in
the circuit breaker cell. This switch is
operated by the circuit breaker
mechanism, so that the switch contacts
change state whenever the circuit
breaker is closed or tripped. Normally, the
MOC switch is operated only when the
circuit breaker is in the connected
position, but provisions for operation in
both the connected and the test positions
can be furnished. All spare MOC contacts
are wired to accessible terminal blocks, as
shown in Figure 24: MOCS (12 stages
shown) and TOCs (8 stages shown), for
user connections.
Truck operated cell (TOC) switch
When required, 4, 8, or 12 stages of TOC
switch can be mounted in the circuit
breaker cell. The TOC switch contacts
change state when the circuit breaker
moves into or out of the connected
position. All spare TOC contacts are wired
to accessible terminal blocks, as shown in
Figure 24: MOCS (12 stages shown) and
TOCs (8 stages shown), for user
connections.
Siemens vacuum heritage
The type 38-3AH3 vacuum circuit
breakers take full advantage of Siemens’
long history with vacuum interrupters for
power applications. While early work was
carried out in the 1920s, a successful
vacuum interrupter could not be
perfected until the high vacuum pump
became available in the 1960s. Focused
development effort began in 1969,
culminating in the introduction of the
type 3AF circuit breaker in 1976. The
knowledge gained over years of
application of this technology in the type
3AF and type 3AH circuit breakers is now
available in the type 38-3AH3 design. The
advantages inherent in vacuum
interruption are summarized as follows:
g
Ideal dielectric
In a vacuum, the dielectric strength
across a contact gap recovers very
rapidly, allowing a small contact
separation and an efficient interrupter
design. The vacuum does not interact
with the arc or its components as do
other dielectrics.
g
Quiet operation
Interruption of current by a vacuum
circuit breaker is very quiet as
compared to the loud report that
accompanies interruptions in some
other types of circuit breakers.
Vacuum circuit breakers
19
Figure 24: MOCs (12 stages shown) and TOCs (8
stages shown)