purifying transformers on line 4

[simisteven]

I have generally accepted that distribution transformers can have the oil purified/regenerated online subject to certain limits of oil condition.
Recently I have been advised that this practice is risky.
I would like to know what is the general practice and school of thought in other places

 

[oldfieldguy]

Given the choice, I'd do offline.

Online can be done, but if I remember correctly, my former employer's oil crew wanted at least 300 gallons of oil capacity.

Risky? Yes, especially for old transformers where the unusual oil circulation patterns may disturb sludge and other materials, but this is usually a small risk that must be assumed if conditions do not allow off-line work.

old field guy

 

[Sanchez01]

Ideally, you would have an online oil purification system installed, I have seen some for LTC cabinet and I am sure that exists for the whole xfmr too.

I don't agree with the online purification not because of the potential danger involved, but because you are getting rid of the symptoms not the issue. If you have an arcing inside
the transformer and you see acetylene in the oil, you would want to investigate the issue more, not keep on purifying the oil to get rid of acetylene (which takes a while to go away b.t.w).

But if you have decided to do it, I don't see any issue as long as this is done with enough prudence and preparation.

 

[potteryshard]

As I remember discussions on this topic, the risk associated with processing transformer oil while on line is essentially inversely proportional to the rate at which the oil is processed.

The greater the amount of oil per unit time is pumped into the transformer, and especially greater the velocity at which the oil in injected back into the tank the greater the risks are that the incoming oil will dislodge sediment, that the oil will entrain air as it splashes in turn causing corona, and that static electrification might occur.

The consensus seemed to be that a small processing unit of, say 5 to 10 gpm would present little risk, but anything much above that would present increasing levels of risk.

This seemed to suggest overall that it could be more cost effective to purchase a small low-volume unit and leave it attached to the transformer for several months with periodic checks than hire a process crew and trailer to visit.

There are some small filter-based units which will do a reasonable job if left long enough and filters changed at reasonable intervals. I've also spotted some tiny vacuum coalescing (sp?) units which might be a slick way to process several transformers if left on a each unit long enough.

I suspect that the big trailer-mounted units will always do a faster processing job, and will probably always do a better job, but an outage is required. If oil must be processed while on line, going small seemed to be the safest.

 

[mgtrp]

I don't agree with the online purification not because of the potential danger involved, but because you are getting rid of the symptoms not the issue. If you have an arcing inside
the transformer and you see acetylene in the oil, you would want to investigate the issue more, not keep on purifying the oil to get rid of acetylene (which takes a while to go away b.t.w).

The purpose of transformer oil reclamation is not to remove the acetylene. Reclamation is done to remove the by-products of the normal ageing process - by-products which, if not removed, will increase the rate of insulation ageing.

 

[prc]

There are two distinct processes for transformers-

Reconditioning: Removing moisture,particles and air from oil to get better BDV.Done by filtering and passing the oil through a vacuum chamber.


Reclamation: In addition to above processes oil is passed through a bed of special catalytic filters( eg Fullers Earth)to remove from oil acids ,polar compounds etc resulting from oxidation and ageing of oil.Resulting oil will have better power factor,oxidation stability and interfacial tension

Both the above can be done on-line and off line.Off -line is safer and fast and should be preferred tn-line requires expertise and special equipment and instruments.