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Having issues with 3 phase industrial motor... looking for ideas

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tautech:
One more consideration for a lathe motor, until the headstock oil warms with a little running the load on the motor can be higher than normal especially it the headstock gears are set to high speeds.
In this case selecting lower gearbox speeds overcomes startup issues.

Gregg:
I have seen the same symptoms caused by a bad connection to one of the phases.  The motor will run OK without the VFD because the grid doesn't care if the load is imbalanced, but the VFD sees it as a problem.  What I have seen several times is poor crimp connections to the ring terminals of the motor leads, where the crimps were covered by the lead numbers at the factory. 

dom0:

--- Quote from: Gregg on October 16, 2019, 05:10:04 am ---I have seen the same symptoms caused by a bad connection to one of the phases.  The motor will run OK without the VFD because the grid doesn't care if the load is imbalanced, but the VFD sees it as a problem.

--- End quote ---

With VFD the VFD itself provides the necessary motor circuit breaker functionality, but without VFD it would be unwise to connect a big motor without MCB to mains. MCB will also trip on unbalanced load, since a three phase motor missing a phase may not start properly and at zero speed current is very high.

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