Installation, Connection and Branch Layout
SIRIUS 3RW44 manual
GWA 4NEB 535 2195-02 DS 06
3-9
3.3 Protection of the Soft Starter against Short-Circuits
(Utilization class 2)
The soft starter has integrated thyristor protection against overloading. In the
event of a short-circuit, e.g. due to a defect in the windings of the motor or a
short-circuit via the motor supply cable, this internal thyristor protection function
is not sufficient. Special semiconductor fuses, e.g. SITOR fuses from SIEMENS,
must be used for this purpose.
(Refer to Chapter 10.3 "Technical Data" for the fuse assignment)
Figure 3-7: Schematic circuit diagram of branch with semiconductor fuses
Note
Chapter 10.3.7 "Branch Component Layout (Standard Circuit)" indicates fuses
for minimum and maximum dimensionings.
Minimum dimensioning: The fuse is optimized for the I²t value of the thyristor. If
the thyristor is cold (ambient temperature) and the starting procedure lasts a
maximum of 20 s with 3.5 times the rated device current, the fuse does not yet
trip.
Maximum dimensioning: The fuse does not trip and the thyristor is not damaged
even if the maximum permissible current for the thyristor is flowing.
Maximum dimensioning is recommended for heavy starting.
012_Standardschaltung und Sitor Zeichnung mit Bildern.vsd
U1 V1 W1
V2
U2W2
U1 V1 W1
W2 U2
V2
L1
L2
L3
PE
3/N/PE~ 50 Hz 400 V
Q1
G1
M1
F3
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