On-Time And Switching Frequency - Siemens SIRIUS 3RW44 Manual

2.3

On-time and Switching Frequency

On-time OT
Switching frequency
SIRIUS 3RW44 manual
GWA 4NEB 535 2195-02 DS 02
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 Chapter 9.3.2 "Technical
Data Power Electronics". If these values are exceeded, you may have to select a
larger soft starter.
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 [%]
t Starting time [s]
s
t Operating time [s]
o
t Idle time [s]
i
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 to under all circumstances.
t +
s
OT = ----------------------- -
t + t
s o
t
i
Configuration Instructions
t
o
+ t
i
t
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