Danfoss VLT Series Service Manual page 18

Section Two
SYMPTOM/CAUSE CHARTS
SYMPTOM
5. Motor Runs Unloaded But Stalls
When Loaded. (Motor may run
rough and VLT may trip.)
6. Unbalanced Input Phase Currents
Note: Slight variations in phase
currents are normal. Variations
greater than 5% require
investigation.
7. Unbalanced Motor Phase Currents
Note: Slight variations in phase
currents are normal. Variations
greater than 5% require
investigation.
2 - 10
POSSIBLE CAUSES
Current Limit set too low
One half of one inverter phase missing. Test output phase balance.
Input line voltage unbalanced
Faulty connection on input wiring
Fault in plant power transformer
Input Rectifier module faulty (open diode).
Open motor winding
Faulty motor connection
Fault in inverter section (see Symptom No. 6.)