Siemens SIRIUS 3RW44 - On-Time and Switching Frequency

Configuration Instructions
SIRIUS 3RW44 manual
GWA 4NEB 535 2195-02 DS 02
2-5
2.3 On-time and Switching Frequency
In terms of motor rated current and normal/heavy starting, the 3RW44 soft
starters are dimensioned for a maximum permissible switching frequency in
combination with a relative on-time. Please also refer to Chapter 9.3.2 "Technical
Data Power Electronics". If these values are exceeded, you may have to select a
larger soft starter.
On-time OT The relative on-time OT in % corresponds to the relationship between the load
duration and the switching-cycle period of loads that are frequently switched on
and off.
The on-time OT can be calculated using the following formula:
Explanation of the formula:
OT On-time [%]
t
s
Starting time [s]
t
o
Operating time [s]
t
i
Idle time [s]
The following graphic illustrates the procedure.
Fig. 2-1: On-time OT
Switching frequency To prevent thermal overloading of the devices, the maximum permissible
switching frequency must be adhered to under all circumstances.
OT
t
s
t
o
+
t
s
t
o
t
i
++
------------------------=
I
e
t
t
s
t
o
t
i