Introduction
2.1 Basic physical principles of the three-phase asynchronous motor and operating principle of the soft starter
3RW44 soft starters
Manual, 03/2017, NEB535219502000/RS-AB/008
15
Example
SIEMENS 1LG4253AA motor (55 kW)
Rated data at 400 V
P
e
:
55 kW
I
e
:
100 A
I
direct starting
:
approx. 700 A
M
e
:
355 Nm
Example:
n
e
:
1480 rpm
M
direct starting
:
approx. 700 Nm
Set starting voltage:
50 % (½ of line voltage)
=> I
starting
½ of direct-on-line starting switch-on current (approx. 350 A)
=> M
starting
¼ of direct-on-line starting torque (approx. 175 Nm)
The diagrams below show the starting current and torque characteristics for a three-phase
asynchronous motor in combination with a soft starter:
Figure 2-3
Reduced current characteristic of a three-phase asynchronous motor during startup with
a SIRIUS 3RW44 soft starter
