Configuration
12.3 ON time and switching frequency
SIRIUS 3RW30 / 3RW40
92 Manual, 10/2018, NEB535199502000/RS-AB/005
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 127)). If these values are
exceeded, a larger soft starter may have to be selected.
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
s
= ramp-up time [s]
t
b
= operating time [s]
t
p
= idle time [s]
The following diagram illustrates this process.
Figure 12-1 ON time
The maximum permissible switching frequency must not be exceeded because the devices
could be damaged due to thermal overloading.
The switching frequency of the 3RW402. to 3RW404. 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 95).
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