On-Time And Switching Frequency - Siemens Sirius 3RW44 System Manual

2.3

On-time and switching frequency

On-time OT
Switching frequency
SIRIUS 3RW44 manual
GWA 4NEB 535 2195-02 DS 01
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 Section 9.3.2 Technical
data power component. If these values are exceeded, a larger soft starter
dimension may need to be selected.
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 [%]
ts Starting time [s]
to Operating time [s]
ti Idle time [s]
The following graphic illustrates the procedure.
I
e
t t
s o
Fig. 2-1: On-time OT
To prevent thermal overloading of the devices, the maximum permissible
switching frequency must be adhered under all circumstances.
t +
s
ED = -------------------------------- -
t + t
s b
t
i
Configuration instructions
t
b
+ t
p
t
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