WYE Transformer & AC Drive Issues

[rrecce]

Hello, I am a long time lurker and a new member currently trying to wrap my head around some issues a electrical contractor left us with out in the field.

We are using a 12,470Y : 3,160Y transformer connected to a motor drive: http://i.imgur.com/PKwAEg1.png

Initially, the building contractor mis-wired the primary side of the transformer as L3, L2, L1 and it was later corrected to L1, L2, L3, but we are not sure where the contractor made the wiring swap. It could have been at the switchgear, the primary, or even somewhere after the transformer. What happens if the swap was after the transformer? This would be easily evident from a voltage/current imbalance in the secondary?


We can get the drive and motor working, but have some intermittent issues. It seems that the drive output Phase 2 current is lagging the Phase 1 current by around 30 deg. See image:http://i.imgur.com/UIQUMNA.png


Does anyone have any insight or be willing to answer a few basic questions regarding this Y-Y transformer wiring?

Thanks!

 

[Jraef]

The only insight I can offer is that any problem on the output, from the VFD to the motor, has zero to do with anything on the input side. The VFD has no direct connection from line to load, it only uses the line power as a raw material to create DC, so input phase rotation makes no difference whatsoever. The only thing that can happen from an input phase current imbalance is to stress the diodes that have to carry more current than the others. Once it is converted to DC, nothing that happens on the line side has any direct affect.

So what that means is that if you have an output phase current imbalance, that is a sign of either damage to the motor windings, one of the motor leads / terminations are bad, or the VFD output transistors are failing.