Siemens SIRIUS 3RW40 - Configuration; 12.1 Configuration in general

SIRIUS 3RW30 / 3RW40
Manual, 10/2018, NEB535199502000/RS-AB/005
85
Configuration
12
12.1
Configuration in general
The SIRIUS 3RW30 and 3RW40 electronic soft starters are designed for normal starting. A
larger size may need to be selected for longer ramp-up times or a higher starting frequency.
An appropriately dimensioned SIRIUS 3RW40 or 3RW44 soft starter should be chosen for
startup processes with motor ramp-up times > 20 s.
The motor feeder between the soft starter and motor must not contain any capacitive
elements (such as compensation systems). Active filters must not be operated in
combination with soft starters.
All elements of the main circuit (such as fuses and switching devices) must be dimensioned
for direct starting and according to the on-site short-circuit conditions, and ordered
separately.
The harmonic component load of the starting current must be taken into consideration when
selecting motor starter protectors (trip selection).
Note
Voltage dips generally occur in all start modes (direct starting, wye
-delta starting, soft
starting) when a three
-phase motor is switched on. The infeed transformer must always be
dimensioned so that the voltage dip at the motor startup remains w
ithin the permissible
tolerance. If the infeed transformer is insufficiently dimensioned, the control voltage should
be supplied from a separate circuit (independently of the main voltage) in order to prevent
the voltage dip from disconnecting the 3RW.
Note
All elements of the main circuit (such as fuses, motor starter protectors, and switching
devices) must be dimensioned for direct starting and according to the on
-site short-circuit
conditions, and ordered separately.
If wye
-delta starters are exchanged for soft starters in an existing system, you should check
the fuse ratings in the feeder in order to avoid false tripping. This is particularly important in
connection with heavy
-duty starting or if the fuse that is installed has already been operated
close to the thermal tripping limit with the wye
-delta assembly.
For recommended fuse and motor starter protector ratings for the feeder with soft starter,
refer to chapter
Technical data (Page 127).