Siemens SIMATIC ET 200pro - Figure 8-10: Phase Control of the Mains Voltage by Means of Semiconductor Elements on the Soft Starter Sdsste; Srsste

SIMATIC – ET 200pro motor starter
GWA 4NEB 950 5661-02 DS 04
8-19
Soft starter sDSSte / sRSSte (soft start function activated)
In the case of a soft starter, the motor voltage is raised by phase control within
a start-up time from an adjustable start voltage to the rated motor voltage. As
the motor current is proportionally to the motor voltage, the start current is
reduced by the factor of the set start voltage.
The following graphic shows the function principle of the soft starter sDSSte /
sRSSte:
Figure 8-10: Phase control of the mains voltage by means of semiconductor elements on the soft
starter sDSSte / sRSSte
Example:
Start voltage 50 % of U
e
=> start current equals 50% of the motor start-up cur-
rent with direct start-up.
The motor torque is also reduced on a soft starter. This is why there is no longer
a switch-on jolt on a soft-started motor.
The following applies to the relationship: motor torque proportional to the
square of the motor voltage.
U
L1- L3
ϕ
M
3 ~
L2
L1
L3
α
α
α
α
G1
U
L2- L3