On Time And Switching Frequency - Siemens SIRIUS 3RW30 Manual

11.3

ON time and switching frequency

Based on the rated motor current and the startup class, the SIRIUS 3RW30 and 3RW40 soft
starters are dimensioned for a maximum permissible switching frequency in combination with
a relative ON time (refer to chapter Technical data [Page 121]). If these values are exceeded,
a larger soft starter may have to be selected.
ON time
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:
where:
OT = ON time [%]
t = ramp-up time [s]
s
t = operating time [s]
b
t = idle time [s]
p
The following diagram illustrates this process.
Figure 11-1
Switching frequency
The maximum permissible switching frequency must not be exceeded because the devices
could be damaged due to thermal overloading.
Optional additional fan
The switching frequency of the 3RW40 2. to 3RW40 4. soft starters can be increased by
installing an optional additional fan. For information about factors and how to determine the
maximum switching frequency if an additional fan is installed, refer to chapter Calculating the
permissible switching frequency [Page 81].
SIRIUS 3RW30 / 3RW40
Manual, 01/2010, 535 1995-02 DS01
ON time
11.3 ON time and switching frequency
Configuration
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