Case Study on failing motors due to high neutral current

[2banee]

I remember browsing a thread that talked about a case study detailing the existence of high neutral current within an industrial building that caused multiple motors to subsequently fail. Does anyone remember the thread or could provide me with that study? I think it was started by a member from Australia. Please advise.
Thanks

 

[busbar]

Looks like you've ruled out harmonic content.

The impulse description sounds like a chattering contactor, but that doesn’t answer why all have periodic problems.

I’d move the logger directly to the subject compressor’s terminals and watch.

Simple AC millivolt-drop tests within the equipment may be in order.

 

[DanDel]

Cliffordball, did you check the current imbalance while the motors are running?

 

[jbartos]

Suggestion: The higher waveform magnitudes (spikes) approximately as mentioned in Cliffordball Aug. 19, 2003, i.e. 25 times may be related to a short resonance or a transition over the resonance. The inrush currents are normally noticeably smaller in the magnitude.

 

[reactive]

Is there by any chance PFC connected to the motor terminals i.e. downstream of the contactor ?

The 25x transient is a big worry and sounds like some kind of restriking problem at first glance.

Is it possible for you to measure the recovery voltage transient across the contactor at quite high speed?

 

[Shortstub]

I believe the thread you remembered covered ungrounded systems... "The Physics Of Ungrounded Systems"