MV 4160v motor imbalance protection

[vetlover]

I am in search of some form of conditioning/protection that may assist in cleaning up a voltage imbalance being incurred on a medium voltage 4160v motor starter. There is an additional load on the incoming power from downstream that is causing phase imbalance enough to vibrate and burn out motors for this compressor station. I plan to set PT's and a Fluke 434 power analyzer to record the imbalance and prove how bold it is. I plan a 1 week study, then I need to be able to make suggestions for remidying the issue. Any suggestions?

 

[TurbineGen]

I could be wrong, but if you have a voltage imbalance at your starter, the problem sounds like a power factor issue, or your lines might be undersized and are suffering voltage drop. In any case, we need more information. What is the additional load on the line? What is the load on the motor? What are the length and size of the conductors? Voltage phase shift present? How great is the voltage imbalance? Does it get worse as load increases? These should come from your study. Once we have some of this information, we can help you select a fix.

------------------------------------------------------------------------
If it is broken, fix it. If it isn't broken, I'll soon fix that.

 

[vetlover]

I appreciate your response. I will be visiting the site the first week of December. Please look for my update when I return, I will try to answer your questions. I really appreciate the consideration. The one confirmation I can make is that a small coal mine has come on line below it. I am sure there are some surging motor loads from it. I will get all motor information.

 

[dpc]

If possible, check the incoming utility voltage to see if it is relatively balanced. Most voltage imbalance issues are caused by unequal loading on the phases, or some bad connections somewhere. Check the currents in all three phases without the motor running to see if there is a load imbalance. For motor loads, small levels of voltage imbalance will cause large current imbalance in the motor, but generally not vibration problems. If you are actually having vibration issues, I'd look elsewhere first for a cause.

 

[vetlover]

Gentlemen,
I have new information. The original issue was resolved in a wiring problem, but there is one issue left. On occasion, there are rectifiers being shorted in the motor VFD. This is a Toshiba unit,900hp compressor, 4160v with a 1.15 SF. I found a recloser on site with the following being monitored. The incoming is 12,470v and I viewed ABC 7520v,7423v,7422v, seems A is a bit high? Also, my Power Factor was right at .76. KW on ABC was 256,267,254 with 782 total. What I have found out is that the utility is now admitting that there is capacitor switching occurring in a distribution yard close to this unit, coincidentally occurring close to the times of the rectifier loss. Even though that is very brief, would you not think this transient overvoltage could be occuring and taking out these rectifiers? A ringwave effect or even a surge charge? If so, do you think a harmonic filter or a TVSS might assist. Any thoughts appreciated, thanks for quick responses.