Siemens SIRIUS 3RW44 - On-Time and Switching Frequency

Configuration Instructions
SIRIUS 3RW44 manual
GWA 4NEB 535 2195-02 DS 06
2-5
2.3 On-time and Switching Frequency
In terms of motor rated current and normal or 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 10.3.2
"Technical Data Power Unit". 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 cycle duration 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
b
Operating time [s]
t
p
Idle time [s]
The following graph illustrates the procedure.
Figure 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
b
+
t
s
t
b
t
p
++
--------------------------=
I
e
t
t
s
t
b
t
p