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Topic Title: Partial Discharge Testing - OLPD
Topic Summary: Any advice
Created On: 09 February 2017 07:09 PM
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 09 February 2017 07:09 PM
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Joined: 03 October 2006

Hi I'm aware of Partial Discharge testing being performed as a very effective online condition monitoring technique used in conjunction with other techniques such as oil and gas analysis. However I'm by no means an expert!

Just wondered what anyones experiences are regarding say, 6.6Kv, 11Kv transformers, motors etc. If baselined and trended would you be still wanting to carry out periodic dielectric testing / pressure testing at set intervals?

Or does a good condition monitoring scheme monitored at suitable intervals and checked by a cm specialist, dependent on the results, warrant suitable monitoring to highlight any problems?

Andrew McGeachie
Eur Ing, CEng MIET
 09 February 2017 07:59 PM
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Dielectric (HiPot) testing on a regular basis can cause more problems by stressing the equipment.

The reports of my death are greatly exaggerated.
 09 February 2017 11:02 PM
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I'm not a power transformer person per-se, but the day job sometimes has me HV testing things like antenna insulators, so some of what follows is probably not useful in the cases you describe.
Given that partial discharges can cause slow creeping damage, for example by forming ozone in air bubbles in insulation, that then chemically attacks, I'd be wary of introducing deliberate overstress in components to look for it.
Monitoring for partial discharge, under normal load conditions, is the electrical equivalent of listening for the twangs and creaks in the ship, by looking for sudden discontinuities in the current waveform (when there is in effect a brief flashover between regions within the insulation, but it does not make a continuous conductive path to the surface). It is a good measure for telling you that something is happening, but like the arc fault detector, you can't easily say what - it may be benign, or teetering just one more click from a spectacular failure. (at 50hz, I;d expect to see short duration spikes or 'clicks' at more or less the same point on the sine wave on successive cycles)
At best I would suggest that it is one more weapon in the armoury, giving some extra confidence about fitness for service, not a replacement for scheduled inspection or maintenance.
It might be possible with many identical components, known to always fail in the same way, to accurately predict hours to failure, but I doubt it.

regards Mike

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