Siemens SIRIUS 3RW40, Manual

Page: 104 / 212

Commissioning
12.4 Commissioning the 3RW40
SIRIUS 3RW30 / 3RW40
104
Manual, 01/2010, 535 1995-02 DS01
protection also refers to this set value if it is active. For the permissible settings referred to the
required motor overload trip class, refer to chapter Motor current settings [Page 107].
12.4.8 Setting the current limiting value
xI
e
potentiometer
The current limiting value is set with the xI
e
potentiometer to the maximum required starting
current as a factor of the set rated motor current (I
e
).
Example
• I
e
potentiometer set to 100 A
• xI
e
potentiometer set to 5 => current limiting 500 A.
As soon as the selected current limiting value is reached, the motor voltage is reduced or
controlled by the soft starter to prevent the current from exceeding the limit. Since the starting
current is asymmetrical, the set current corresponds to the arithmetic mean value for the
three phases.
If the current limiting value is set to the equivalent of 100 A, the starting currents might be
approx. 80 A in L1, 120 A in L2, and 100 A in L3 (refer to chapter Starting current asymmetry
[Page 21]).
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.
The current limiting function is always active because it is required by the intrinsic device
protection. If the current limiting potentiometer is set to the clockwise stop (maximum), the
starting current is limited to five times the set rated motor current.
12.4.9 Ramp-up detection
The SIRIUS soft starter has a motor ramp-up detection function that is always active
regardless of the start mode. If it detects a motor startup, the motor voltage is immediately
increased to 100 % of the mains voltage. The thyristors of the soft starter are bridged by the
bypass contacts integrated in the device and the successful startup is indicated by means of
the BYPASS output and the STATE / BYPASSED LED.