Current Limiting In Combination With The Voltage Ramp Or Torque Control Starting Mode - Siemens SIRIUS 3RW44 User Manual

6.2.4 Current Limiting in Combination with the Voltage Ramp or Torque Control Starting Mode

Current limiting value
Run-up recognition
Typical applications for current limiting
SIRIUS 3RW44 manual
GWA 4NEB 535 2195-02 DS 06
The starter continuously measures the phase current (motor current) using the
integrated current transformer.
During motor run-up, it is possible to set a current limiting value on the soft
starter.
The current limiting can be activated if "Voltage ramp+current limiting" or
"Torque control+current limiting" has been selected as the starting mode and a
value has been entered in the relevant parameter.
During the starting procedure, the phase current is limited to the set value until it
falls below this value. A set breakaway pulse is superimposed on the current
limiting during the breakaway time.
As a factor of the motor rated current, the current limiting value is set to the
maximum current required during the starting procedure. If the set current
limiting value is reached, the motor voltage is lowered (or regulated) by the soft
starter in such a way that the current will not exceed the set current limiting
value. The set current limiting value must be at least selected high enough for
enough torque to be created in the motor to bring the drive into rated operation.
A typical value can be 3 to 4 times the value of the rated operating current (I
the motor.
The soft starter features an internal run-up recognition. If a completed motor run-
up is recognized, the motor voltage is immediately increased to 100 % of the line
voltage. The internal bypass contacts close and the thyristors are bridged.
Motor current
Beginning determined
by specified starting
mode, in this case
breakaway pulse
Beginning determined
by specified starting
mode, in this case
voltage ramp
Figure 6-5: Current limiting with soft starter
Used in applications with a large centrifugal mass (mass reactance) and hence
long starting times, e.g. large fans, in order to lighten the load on the supply
network.
Device Functions
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