Oil Transformer top up 7

[Emadshaaban1987]

Hi
Due to plant condition we are attempting for oil top up of ABB power transformer 35MVA in energizing state .
the planned procedure is remove the breather pipe in top of the conservator and force the oil to flow unit reaching the predetermined level.
The questions are;
Is there any risk of triggering the buchholz relay ?
Are there any safety risks ?

 

[davidbeach]

Yes, and Yes.

Deenergize and do it right.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[electricpete]

David has the best advice.

I'll just talk through what I see are some of the concerns. I'm not intending to tell you how to do anything, just food for your own thought in thinking about why we might do things certain ways. You're on your own to make responsible decisions.

I worked on transformers for awhile during the 90's. Some of that is a little fuzzy, but I don't ever remember adding oil to any transformer without (deenergizing and) draining then refilling under vacuum. As I recall for conservator transformers, we isolated the conservator before draining the main tank and if conservator level was low we added oil to the conservator while it was isolated.

There are a few different types of conservators. Obviously if there's a bladder in there, you probably don't want to add oil into a breather space above the bladder. It's not designed to work that way... among other things your bladder could sink and block the port to the transformer tank.

I would be worried about the risk of air bubbles trapped in the oil that cause a problem when you energize the thing. It may seem unlikely bubbles could make their way from conservator to tank but you never know. If you following normal procedures of deenergizing the transformer then there would be a wait period before you energize (maybe with pumps running) to help make sure there were no bubbles in the tank.

Also obviously if the transformer has exposed bushings you have to keep your people and equipment far enough away from those.

The transformer OEM may have some recommended procedures to consult. Your organization may have some procedures. If you are not following a well thought out procedure from someone that knows what they're doing that's sometimes a cue that you're out on a limb and you need to be extra careful.

=====================================
(2B)+(2B)' ?

 

[RRaghunath]

'Risk of triggering the Buchholz relay' - Unlikely as the oil being added is not going to pass through the Buchholz relay.
I agree it has risks otherwise and to to my knowledge no transformer manufacturer recommends it.

 

[low1]

Strange, it's our standard operating procedure to top up transformers while on line. Open the vent cap and throttle the flow into the conservator tank, ensuring pressure isn't being built up. The only time we ever had an issue was when a crew didn't open the proper vent and caused the unit to trip off on pressure rise.

 

[Palletjack]

I assume you mean the oil level in the conservator is at min level but the XF is full and the port isn’t clogged..Surely the level isn’t below the relay.

Why is it low? Is it leaking or just low from drawing off oil for testing? If it’s the latter I would say it’s time for a transformer test anyway if you’ve drawn that much oil.
Deenergize, test, and fill it up correctly.

 

[Emadshaaban1987]

Thanks folks for your helpful feedback.

low1 (Electrical) ...... Can you please send me your standard procedure plan and does it approved by the manufacture .

Palletjack (Electrical)........ the oil level has reduced because of the oil remains in side Oil treatment machine during recycling ,then this issue has finger out recently .

 

[waross]

the oil level has reduced because of the oil remains in side Oil treatment machine during recycling ,then this issue has finger out recently .

Is it possible to safely and cleanly add oil through the recycling machine?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[thermionic1]

I have heard of some oil processing services that would do on-line processing of oil, which isn't too far from just filling it. I would not want to be the operator of the machine or the one who authorized its use if something went wrong.

 

[Palletjack]

Is it possible to safely and cleanly add oil through the recycling machine?

Kind of what I’m wondering..

 

[bacon4life]

I do not have detailed instructions since the valving sequence is specific to each transformer. There is definitely a risk of tripping on buchholz or sudden pressure if the incorrect sequence of valves is used.

Also consider the pressure relief device (PRD). A substation crew told me about the PRD activating and spraying oil everywhere when they were adding oil to a transformer LTC compartment. It turned out the air breather was designed for small rates of airflow, and could not handle the airflow caused by filling at normal oil flow rates.

When specifying transformers, it can be useful to include a requirement that the conservator and LTC conservator are large enough to allow routine oil sampling for at least 20 years. In addition to the actual oil sample, the extra volume in the conservators should account for flushing the piping to obtain a representative sample. On a 230 kV transformer, the oil piping volume that needs flushing before sampling can exceed 10 liters.

Online filtration could certainly be considered a kind of recycling. I could see loosing a small amount of oil each time the filter is changed out. It can take dozens of hydrophilic filter changeouts to appreciable lower the water content of the transformer.

 

[low1]

Palletjack, yes, oil level in conservator tank low, main tank still full (above bushing turrets and gas relay piping). In our case, these are generator step up transformers for ~100MW units on a tailrace deck in Northern Manitoba. Significant heat cycling when online/offline. This has always been hard on seals, and we have constant issues with minor leaks (over time... years).

On our transformers (newer Hyundai units), there is piping at ground level, clearly labelled "Fill", "Drain" and "Vent". These transformers are also equipped with Messko breathers. To fill (top up), we ensure the bung/plug is removed from the vent line and valving is open, connect oil pump to "fill" line and throttle valving to fill at an appropriate rate. Qualitrol pressure devices are set to operate protection at 7.5psi, I believe. Transformers also have PRD, although discharge piping is directed down into the containment in the event of a "mishap". I've topped up dozens of transformers online without any issues. We had to top up our spare transformer this fall, and as it was a slightly different design with unclear labelling, we separated the piping to the Messko breather as well to avoid issues with oil contamination in the event we were wrong in our assumptions of the proper vent piping. This transformer is not in service, so it was of little consequence anyway.

 

[waross]

Be extremely careful of contaminants when connecting lines and/or opening valves that may have had the atmospheric side open.
Improper filling may lead to Buchholz trip.
Contamination may lead to a damaged transformer.
It doesn't take much conductive contamination to initiate an internal flashover.

Bill
--------------------
"Why not the best?"
Jimmy Carter