34 Technical description 8100_A
Caution! During commissioning always check that the no-load current does not
exceed the rated motor current. If necessary, the current consumption
during idle running can be reduced by increasing the VIf nominal
frequency and therefore the VIf characteristic.
7.2.5 VOLTAGEBOOST UminC016
The Umin parameter must be adapted to the asynchronous motor used, otherwise
the motor may be damaged due to overheat. We can say from experience that self-
ventilated standard asynchronous motors of insulation class B can be operated with
their rated current in the lower frequency range (fd=0...25Hz) for a short time.
Adapt the Uminparameter as foliows:
- Connect r.m.s current meter to one motor phase
-Run the motor without load at fd = 5Hz
- Set Umin:
a) For short-time operation in the lower frequency range, set Uminsuch that the
motor current does not exceed its rated value (lMotor:s INMotor)
b) For continuous operation in the lower frequency range, set Uminsuch that the
motor current does not exceed 80% of its rated value (lMotor :s 0,8 . IN Motor) or
use a force-ventilated motor or a motor with higher insulation class and set Umin
as under a).
An internal compensation of the DC bus voltage compensates for changes in the
mains voltage so that these must not be considered when setting the VIf rated
frequency.
7.2.6 RESPONSE THRESHOLD QMIN C017
The amin signal shows if the field frequency (in open-Ioop operation) or the actual
value of the PI-controller (in closed-Ioop operation) is smaller than or equal to the
frequency set under CO17. The amin signal can be assigned to a digital output
terminal using codes C116, C117.
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