Inherent Protection - Siemens Sirius 3RW44 System Manual

Device functions
6.7

Inherent protection

6-22
The soft starter has integrated device protection to prevent the thyristors
becoming thermally overloaded.
This is achieved via a current measurement using converters in the three phases
and by measuring the temperature with thermosensors on the thyristor
heatsink.
If a fixed warning threshold is exceeded, a message to the soft starter is
generated. If the fixed tripping value is exceeded, the soft starter switches off
automatically.
After a trip has occurred, a fixed 30-second pre-charge time must be kept before
the starter can be restarted.
If protection against voltage failure is active and the control supply voltage
breaks down while a trip is pending, the current trip condition of the thermal
motor model and the current pre-charge time are stored in the soft starter.
When the control supply voltage returns, the trip condition of the thermal
inherent protection before voltage failure will be restored.
In order to protect the thyristors from being destroyed by short circuits (e.g. in
the event of cable damage or shorted coil in the motor), SITOR semiconductor
fuses must be connected upstream. You can find the corresponding selection
tables in Chapter 9.3.6 Branch component layout (standard circuit) and in
Chapter 9.3.7 Branch component layout (inside delta circuit).
SIRIUS 3RW44 manual
GWA 4NEB 535 2195-02 DS 01