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How do you troubleshoot unbalanced motor currents on the output of a drive?

Issue:

How do you troubleshoot unbalanced motor currents on the output of a drive?

Product Line:
ATV

 

Environment:
All

Cause:
Wiring

Resolution:If the unit has bypass, run the motor across the line, measure and write down the phase to phase voltages on the line side of the contactor and the load side.  Also, measure and write down the individual motor currents in each phase. 
Repeat the exact same test while running the motor from the drive at rated speed. 
Next, roll ALL three motor leads, and run the exact same test again writing down the measurements.
If the unbalanced currents follow the motor leads, suspect a problem with motor.
If the unbalanced currents remain constant with relationship to the contactor phase, suspect problem with drive, bypass scheme, or iso / bypass contactors. Knowing the actual voltages measured on the line and load side of the contactors is crucial to further troubleshooting. 
The same technique applies to all drive products - Altivar Drives and Class 8839. The same principle also applies if no output contactors are used in conjunction with the drive.



 
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