Siemens SIMATIC ET 200pro - Figure 8-11: Current and Torque Characteristics When a Soft Starter Is Used

SIMATIC - ET 200pro motor starter
8-20 GWA 4NEB 950 5661-02 DS 04
Example:
Starting voltage 50% of U
e
=> start torque 25% of the start torque with direct
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
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
n
n
syn
M
start-up
M
M
start-up
M
start-up
100% U
mains
70% U
mains
50% U
mains
0.49 x
0.25 x
n
n
syn
s
tart-up
I
s
tart-up
0.7 x
s
tart-up
0.5 x
100% U
mains
70% U
mains
50% U
mains