Current Limiting In Combination With Voltage Ramp Or Torque Control Starting Mode - Siemens Sirius 3RW44 System Manual

6.2.4 Current limiting in combination with voltage ramp or torque control starting mode

Current limit value
Run-up recognition
Typical applications for current limiting
SIRIUS 3RW44 manual
GWA 4NEB 535 2195-02 DS 01
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 limit value on the soft starter.
The current limiting can be activated if voltage ramp+currrent limiting or torque
control+current limiting have been selected as 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 defined breakaway pulse is superimposed on the
current limiting during the breakaway time.
As a factor of the motor rated current, the current limit value is set to the
maximum current required during the starting procedure. If the set current limit
value is reached, the motor voltage is lowered (or controlled) by the soft starter
such that the current will not exceed the set current limit value. The configured
current limit value must be selected high enough that enough torque can be
created in the motor in order to bring the drive into the rated area of operation. A
typical value is 3-4 times the value of the rated operating current (I
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 will close and the thyristors are
bridged.
Motor current
I
I
Direct on-line
starting
Motor
Beginning deter-
mined by specified
starting mode, in this
case breakaway pulse
I
Soft starter
adjustable current
limit value
Beginning deter-
mined by specified
starting mode, in this
case voltage ramp
I
e Motor
Fig. 6-5: Current limiting with soft starter
Used in applications with large centrifugal mass (mass reactance) and hence the
long starting times, e.g. large fans in order to lighten the load on the supply
network.
Device functions
) of the
e
Motor speed
n
n
e Motor
6-9