Siemens SENTRON 3VL series, System Manual

Page: 19 / 360

Product description
3.3 Configuration
3VL molded-case circuit breakers
System Manual, 03/2009, 110 0110 - 02 DS 01
19
3.3 Configuration
3.3.1 Functional principle
Design - mechanical principle
All SENTRON VL circuit breakers have a trip-free mechanism that ensures the trip process
is not prevented even if the operating mechanism is blocked or manually held in the "ON"
position.
The contacts are opened and closed by a toggle handle positioned in the center. This is
attached to the front side on all circuit breakers.
All SENTRON VL circuit breakers are "joint trip units". This means all contacts open or close
simultaneously when the circuit breaker toggle handle is moved from "OFF" to "ON" or from
"ON" to "OFF", or when the tripping mechanism is activated by an overcurrent or with the
help of an auxiliary trip (shunt release or undervoltage release).
Current limiting
The SENTRON VL circuit breakers are designed on the principle of magnetic repulsion of
the contacts. The contacts open before the expected peak-value of the short-circuit current is
reached. Magnetic repulsion of the contacts very significantly reduces the thermal load I
2
t as
well as the mechanical load resulting from the impulse short-circuit current I
P
of the system
components that occur during a short-circuit.
You can find more information in Chapter Use in the motor protection area (Page 74).
3.3.2 Subdivision according to power ranges
VL160X circuit breakers
The most important components of the VL160X circuit breakers are the three current paths
with the incoming and outgoing terminals. The fixed and movable contacts are arranged in
such a way as to guarantee magnetic repulsion of the contacts. In conjunction with the arc
splitter chambers, a dynamic impedance is created that causes a current limitation through
the reduction in the harmful effects of I
2
t and the I
p
energy resulting from short-circuits.
The overcurrent trip unit is a thermomagnetic device installed at the factory. It is equipped
with fixed or adjustable overload releases and a fixed short-circuit release in each pole.
To the right and left of the centrally positioned toggle handle of every SENTRON VL circuit
breaker is a double-insulated accessories compartment for installing auxiliary switches or
alarm switches as well as voltage and undervoltage releases.