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

2.3

On-time and Switching Frequency

On-time OT
Switching frequency
SIRIUS 3RW44 manual
GWA 4NEB 535 2195-02 DS 06
In terms of motor rated current and normal or 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 10.3.2
"Technical Data Power Unit". 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 cycle duration 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]
b
t Idle time [s]
p
The following graph illustrates the procedure.
I
e
t t
s b
Figure 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 + t
s b
OT = ------------------------- -
t + t +
s b
t
p
Configuration Instructions
t
p
t
2-5