Incorrect Motor Operation - Danfoss VLT Series Service Manual

3.2.2 Incorrect Motor Operation

Occasionally, a fault can occur where the motor will continue
to run, but not in the correct manner. The symptoms and
causes may vary considerably. Many of the possible problems
are listed below by symptom along with recommended
procedures for determining their causes.
Wrong Speed/Unit Will Not Respond To Command
Possible incorrect reference (speed command).
Ensure that the unit is programmed correctly according to the
reference signal being used, and that all reference limits are
set correctly as well. Perform Input Terminal Signal Test in
section 5 to check for faulty reference signals.
Motor Speed Unstable
Possible incorrect parameter settings, faulty current feedback
circuit, loss of motor (output) phase.
Check settings of all motor parameters, including all motor
compensation settings (Slip Compensation, Load
Compensation, etc.) For Closed Loop operation, check PID
settings. Perform Input Terminal Signal Test in section 5 to
check for faulty reference signals. Perform Output Phase
Imbalance Test in section 5 to check for loss of motor phase.
Motor Runs Rough
Possible over magnetization (incorrect motor settings), or an
IGBT misfiring. Note: Motor may also stall when loaded or the
drive may trip occasionally on Alarm 13.
Check setting of all motor parameters. Perform Output Phase
Imbalance Test in section 5.
If output voltage is unbalanced, perform Gate Drive Signal Test
in section 5.
Motor Draws High Current but Cannot Start
Possible open winding in motor or open connection to motor.
Perform Output Phase Imbalance Test in section 5 to ensure
drive is providing correct output (see Motor Runs Rough above).
Check motor for open windings. Check all motor wiring
connections.
Motor Will Not Brake
Possible fault in brake circuit. Possible incorrect setting in brake
parameters. Ramp down time too short. Note: May be
accompanied by an alarm or warning message.
Check all brake parameters and ramp down time (parameters
208, 400, 401, 402).
Perform Brake Check in section 5.
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