Lenze 8400 motec - Manual (Page 104)

5 Motor control (MCTRL)
5.5 V/f characteristic control (VFCplus)
104 Lenze · 8400 motec · Reference manual · DMS 4.1 EN · 08/2013 · TD05
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5.5.3.4 Torque limitation
The previous chapter, " Optimising the Imax controller ", describes how the drive can be protected
from overload. During commissioning, these settings are carried out once and remain unchanged
afterwards. However, it is often necessary to limit the torque to a lower value for plant or process
reasons.
• To avoid overload in the drive train, the torque in motor mode can be limited via the
nTorqueMotLimit_a process input signal, and the torque in generator mode can be limited via
the nTorqueGenLimit_a process input signal:
V/f characteristic control (VFC)
The accuracy of the torque limitation is limited because the actual torque (
C00056/2 ) is only
calculated from the slip speed measured indirectly via the motor current.
V/f control (VFC + encoder)
The slip speed of the motor is available at the slip controller output. This leads to a high accuracy for
the actual torque ( C00056/2 ) and the torque limitation.
Identifier
DIS code | data type
Information/possible settings
nTorqueMotLimit_a
C00830/4 | INT
Torque limitation in motor mode
• Scaling: 16384 ≡ 100 % M
max
( C00057 )
• Setting range: 0 … +199.99 %
nTorqueGenLimit_a
C00830/5 | INT
Torque limitation in generator mode
• Scaling: 16384 ≡ 100 % M
max
( C00057 )
• Setting range: 0 … +199.99 %

Note!
• The actual torque ( C00056/2 ) is directly calculated from the current slip speed of the
machine. This requires correct entry of the motor data.  Motor selection/Motor data
( 82)
• To avoid instabilities during operation with active slip compensation, the torque limit
values are internally processed as absolute values.
• If slip compensation is deactivated ( C00021 = 0), indirect torque limitation
(differential signal between apparent motor current and nTorqueMotLimit_a or
nTorqueGenLimit_a) occurs. Above the no-load current of the motor, the accuracy of
the indirect torque limitation is limited.