Device functions
7.2 Startup modes
3RW44 soft starters
Manual, 03/2017, NEB535219502000/RS-AB/008
125
Typical applications for breakaway pulses
Typical applications for breakaway pulses are load machines with inverse torque behavior,
e.g. crushers and mills.
Note
A breakaway pulse that is set too high may lead to the "Current measurement range
exceeded" error message.
Remedy: use a larger starter dimension or a lower breakaway voltage.
Set the breakaway pulse only when it is really required (e.g. for mills and crushers).
A wrongly set breakaway pulse, e.g. for pumps, may lead to the "Incorrect start conditions"
error message.
7.2.4
Current limitation in combination with the voltage ramp or torque control startup
mode
The starter measures the phase current (motor current) continuously with the help of
integrated current transformers.
A current limiting value can be set on the soft starter while the motor is starting up.
Current limiting can be activated when "voltage ramp + current limiting" or "torque c
current limiting" has been selected as the startup mode and a value has been entered in the
applicable parameter.
During starting, the phase current is limited to the set value until this value is undershot. A
set breakaway pulse is superimposed on the current limitation during the breakaway time.
Current limiting value
The current limiting value is set as a factor of the rated motor current to the maximum current
required during startup. Once the selected current limiting value has been reached, the
motor voltage is reduced or controlled by the soft starter to prevent the current from
exceeding the set current limiting value. The set current limiting value must be high enough
to ensure that the torque generated in the motor is sufficient to accelerate the motor to
nominal speed. Three to four times the value of the motor's rated operational current (I
e
) can
be assumed as typical here.
