Siemens SIRIUS 3RW40, Manual

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Product description
3.2 Basic physical principles of a three-phase induction motor
SIRIUS 3RW30 / 3RW40
16
Manual, 01/2010, 535 1995-02 DS01
Starting current
Three-phase induction motors have a high direct starting current I
starting
. Depending on the
motor type, this current can be between three and fifteen times as high as the rated
operational current. Seven or eight times the motor's rated current can be assumed as a
typical value.
Disadvantage
This results in the following disadvantage:
• Higher load on the electrical supply system. The supply system must therefore be
dimensioned for this higher power during the motor startup.
Figure 3-1 Typical starting current characteristic of a three-phase induction motor
Starting torque
The starting torque and the breakdown torque can usually be assumed to be between two
and four times the rated torque. From the point of view of the load machine, this means that
the starting and acceleration forces exert a higher mechanical load on the machine and the
product being conveyed compared to nominal operation.
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