Figure 8-11: Current And Torque Characteristics When A Soft Starter Is Used - Siemens SIMATIC ET 200pro Quick Manual

Example:
Starting voltage 50% of U
start.
Advantages:
• Low space requirement in the control cabinet
• No circuits (e.g. filters) necessary to comply with interference suppression
regulations
• Low assembly overhead
• Easy commissioning
• In comparison with star-delta starters, only 3 motor feed lines
• Local setting options enable rapid adaptation to the system.
Disadvantages:
• No longer speed adjustment possible.
• Low torque with reduced voltage
I
start-up
start-up
0.7 x
start-up
0.5 x

Figure 8-11: Current and torque characteristics when a soft starter is used

Direct starter sDSte / sRSte (soft start function deactivated)
Direct switching (instant switching) applies power to the motor without delay
and reaches its maximum torque within a very short time.
Advantage: very high switching frequency
Disadvantage:high load on the connection lines and mechanical motor bearings
8-20
=> start torque 25% of the start torque with direct
e
100% U
mains
M
70% U
mains
50% U
mains
M
M
n
n
syn
M
100% U
start-up
start-up
0.49 x
start-up
0.25 x
SIMATIC - ET 200pro motor starter
GWA 4NEB 950 5661-02 DS 04
mains
70% U
mains
50% U
mains
n n
syn