Physical Principles; Figure 8-1: Typical Current And Torque Curve Of A Three-Phase Asynchronous Motor - Siemens sirius System Manual

3RW3 semiconductor motor control unit

8.2.1 Physical principles

Starting current
Reducing the starting
current
8-6
Three-phase current asynchronous motors have a high inrush current I
. This inrush current can be between three and fifteen times as high as
ting)
the rated operational current, depending on the type of motor. A figure bet-
ween seven and eight times the rated operational current can be postulated
as typical.
I
I
starting
I
rated
I
0 (no-load)
M
M
starting
M
saddle

Figure 8-1: Typical current and torque curve of a three-phase asynchronous motor

Important
This starting current must be taken into consideration in the design of the
supply network, among other things by adapting the supply (high heat deve-
lopment) and the fusing (inadvertent tripping of the fuses).
There are various ways of reducing the starting current:
• By star-delta starter
• By frequency converter
• By soft starter
n
M
cusp
M
accel
M
motor
M
load
n
n
rated syn
M
motor
M
load
M
rated
n n
n
rated syn
SIRIUS System Manual
GWA 4NEB 430 0999-02b
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