Device functions
7.7 Intrinsic device protection
3RW44 soft starters
Manual, 03/2017, NEB535219502000/RS-AB/008
139
7.7
Intrinsic device protection
7.7.1
Intrinsic device protection
The soft starter has integrated intrinsic device protection that prevents thermal overloading of
the thyristors.
This is realized on the one hand by current measurement using transformers in the three
phases and additionally by temperature measurement using thermal sensors on the thyristor
heat sink.
A message is generated on the soft starter if a permanently set warning threshold is
exceeded. If the internal permanently set switch-off value is exceeded, the soft starter will
switch off automatically.
After tripping, a fixed 30 s recovery time must be observed before the starter can be started
again.
If protection against voltage failure is activated, and the control supply voltage fails during a
trip, the current tripping state of the thermal motor model and the current recovery time are
stored in the soft starter. When the control supply voltage is restored, the current tripping
state of the thermal intrinsic device protection prior to the power failure are likewise
automatically restored.
SITOR semiconductor fuses must be connected upstream to protect the thyristors against
short-circuits (e.g. in case of cable damage or an interturn fault in the motor). You will find
applicable selection tables in chapter Feeder component layout (standard circuit) (Page 270)
and in chapter Feeder component layout (inside-delta circuit) (Page 275).
Note
If the soft starter is switched off via a motor protection or inherent device protection tripping,
the action cannot be acknowledged using the "Trip Reset" function until the displayed
cooling time has expired.