User Manual

Product description
3.3 Functional principle of the SIRIUS 3RW30 and 3RW40 soft starters
SIRIUS 3RW30 / 3RW40
Manual, 10/2010, 535199502000 DS 03
19
The diagrams below show the starting current and torque characteristics for a three-phase
induction motor in combination with a soft starter:
0RWRUFXUUHQW
,
,
'LUHFW
RQOLQH
VWDUWLQJ
,
6RIWVWDUWHU
,
1RP
Q
1RP
0RWRUVSHHG
Q
Figure 3-3 Reduced current characteristic of a three-phase induction motor during starting with a
SIRIUS 3RW30 or 3RW40 soft starter




0RWRUWRUTXH
0
0

'LUHFW
RQOLQH
VWDUWLQJ
0
1RP
0
6RIWVWDUW
YROWDJHUDPS
0
/RDGHJSXPS
Q
1RP
0RWRUVSHHG
Q
Figure 3-4 Reduced torque characteristic of a three-phase induction motor during starting with a
SIRIUS 3RW30 or 3RW40 soft starter
Soft start /soft stop
This means that, since the motor voltage is controlled by the electronic soft starter during the
startup process, the consumed starting current and the starting torque generated in the
motor are also controlled.
The same principle is applied during the stop process. This ensures that the torque
generated in the motor is gradually reduced, so that the application can stop smoothly (the
soft stop function is only supported by the 3RW40).
The frequency remains constant during this process and corresponds to the mains
frequency, in contrast to frequency controlled starting and stopping of a frequency converter.