8 3RW3 semiconductor motor control unit (soft starter) - Siemens ...
8 3RW3 semiconductor motor control unit (soft starter) - Siemens ...
8 3RW3 semiconductor motor control unit (soft starter) - Siemens ...
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<strong>3RW3</strong> <strong>semiconductor</strong> <strong>motor</strong> <strong>control</strong> <strong>unit</strong><br />
8.2.1 Physical principles<br />
Starting current<br />
Three-phase current asynchronous <strong>motor</strong>s have a high inrush current<br />
I (starting) . This inrush current can be between three and fifteen times as high<br />
as the rated operational current, depending on the type of <strong>motor</strong>. A figure<br />
between seven and eight times the rated operational current can be postulated<br />
as typical.<br />
I<br />
I starting<br />
I rated<br />
n rated n syn n<br />
I 0 (no-load)<br />
M<br />
M starting<br />
M saddle<br />
M <strong>motor</strong><br />
M cusp<br />
M <strong>motor</strong><br />
M load<br />
M accel<br />
M rated<br />
M load<br />
n rated n syn<br />
n<br />
Fig. 8-2: Typical current and torque curve of a three-phase asynchronous <strong>motor</strong><br />
Important<br />
This starting current must be taken into consideration in the design of the<br />
supply network, among other things by adapting the supply (high heat development)<br />
and the fusing (inadvertent tripping of the fuses).<br />
Reducing the starting<br />
current<br />
There are various ways of reducing the starting current:<br />
• By star-delta <strong>starter</strong><br />
• By frequency converter<br />
• By <strong>soft</strong> <strong>starter</strong><br />
SIRIUS System Manual<br />
8-6 GWA 4NEB 430 0999-02c
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