Inherent Protection - Siemens SIRIUS 3RW44 System Manual

6.7

Inherent Protection

SIRIUS 3RW44 System Manual
GWA 4NEB 535 2195-02 DS 04
The soft starter has integrated device protection to prevent the thyristors from
becoming thermally overloaded.
This is achieved via current measurement using converters in the three phases
and by measuring the temperature with thermosensors at the thyristor heatsink.
If a fixed warning threshold is exceeded, a message is issued by the soft starter.
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 a shorted coil in the motor), SITOR semiconductor
fuses must be connected upstream. You can find the corresponding selection
tables in Chapter 10.3.6 "Branch Component Circuitry (Standard or Inline
Circuit)" and in Chapter 10.3.7 "Branch Component Layout (Inside Delta
Circuit)".
Notice
If the soft starter is switched off via a motor protection or device protection
tripping, the action cannot be acknowledged using the "Trip reset" function until
the displayed cooling time has expired.
Device Functions
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