Siemens 3RW44 - ON Time and Switching Frequency

Configuration instructions
3.3 ON time and switching frequency
3RW44 soft starters
Manual, 03/2017, NEB535219502000/RS-AB/008
25
3.3
ON time and switching frequency
Based on the rated motor current and the startup class, the 3RW44 soft starters are
dimensioned for a maximum permissible switching frequency in combination with a relative
ON time. See also Chapter Technical data of the power unit (Page 259). A larger soft starter
may have to be selected if these values are exceeded.
ON time motor OT
The relative ON time in % is the ratio between the load duration and the cycle duration for
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 diagram illustrates this process.
Figure 3-1 ON time motor OT
Switching frequency
The maximum permissible switching frequency must not be exceeded because the devices
could be damaged due to thermal overloading.