Technical data

Non-sliding current transfer
The vacuum interrupter movable stem is
connected to the lower disconnect stab
of the circuit breaker by a reliable flexible
connector, a method pioneered by
Siemens in the 1970s. This provides a
low-resistance current transfer path, not
subject to the wear and contamination
problems associated with sliding or
rolling joints used in some designs.
Primary disconnects
The primary connection between the
circuit breaker and the cubicle is made of
multiple sets of silver-plated copper
finger contacts that engage with silver-
plated copper stationary contacts. The
cubicle primary disconnect studs have a
tapered leading edge, that contributes to
smooth racking of the circuit breaker.
The contacts, mounted on the ends of
the circuit breaker disconnect stabs, have
multiple fingers and are compression
spring loaded (one spring per double pair
of fingers). This arrangement offers a
large number of contact points to ensure
proper alignment. The circuit breaker
finger assemblies are withdrawn with the
circuit breaker, and are available for
inspection without de-energizing the
switchgear main bus.
“Universal” spare circuit breaker
The physical configuration and interlock
logic allow the use of a single circuit
breaker to serve as a “universal” spare
circuit breaker at an installation site. The
rating interlock logic checks the principal
rating characteristics (continuous
current, maximum voltage and
interrupting current), and allows a circuit
breaker to be inserted in a circuit breaker
cell provided that the ratings of the
circuit breaker equal or exceed the
ratings required by the circuit breaker
cell.
Secondary disconnects
Circuit breaker-to-cubicle secondary
disconnects are of the silver-plated
sliding finger design. The secondary
disconnects are automatically engaged as
the circuit breaker is racked into the test
position. They remain engaged as the
circuit breaker is racked to the connected
position. Since the secondary disconnects
automatically engage in both the test and
connected positions, there is no need to
operate a separate linkage for testing.
The secondary disconnects are located on
the top of the circuit breaker element,
where they are shielded from accidental
damage. They are of an extremely rugged
design, in contrast to other designs,
which employ light-duty electronics-style
disconnects located in hidden or
inaccessible locations. Alignment of the
disconnects can be visibly observed, if
desired, allowing positive verification of
secondary integrity, a feature not
possible with designs employing a
disconnect underneath or behind the
circuit breaker.
Vacuum circuit breakers
18
Figure 21: Primary disconnects
Figure 22: Secondary disconnect (cell portion)
Figure 23: Secondary disconnect (circuit breaker
portion)