Regular Buchholz Tripping

Dear Gunjan, u should filtrate your transformer oil continue tell when ur BDV reached above 60 KV. YOUR oil should be circulate 7 times in Centerifuge machine on 80 degree temp . We can face same problem and found no more plm. Finally we apply this and now normal running.

while filtration of oil, temperature was around 70C to 75C. how hard we tried we couldn't increase the BDV. Could it be because of ageing of transformer oil?

The NEW oil should not age that much in 6 months that it breaks down or degenerates if it was new oil you put into the NEW transformer.

You said it was a new install, or did you use an old transformer from another location and install it somewhere else?

Please detail all the facts!

-> transformer is not new, it was in operation and then stored with oil since 9 to 12 months earlier then it was shipped to our plant. During shipped we didn't emptied the tank, we just disconnected the fins and conservator tanks, the main tank was full of oil. Later after installation and fitting of accessories we top upped the oil by filtration.

You must analyze the gas removed from the Buchholz relay. If it is air, then you are simply seeing air bubbles from recent installation working their way out. This problem would most likely occur on a continuous basis, which is not what you are seeing.

If it is CO2 and CO, then you may have arcing between turns or turn to ground. This process will give you instant gas generation, which is what you see.

Yes, Gas trapping in the buchholz is not continuous, however it might be possible that gas bubbles get trapped and accumulated inside the tank and only goes to buchholz after volume of gas becomes large enough.

and currently we don't have facility to analyse the gas trapped in the buchholz. if it is because of interturn faults of ground faults then megger should have low value. But i don't find any abnormality in resistance per phases as well as megger values.

You said..

currently we don't have facility to analyse the gas trapped in the buchholz.

No one does... the testing equipment is rather expensive and if you only have a few Tx's then it will be money badly spent, you send it to an external lab to be tested

If you are getting gas in the BHR, then how often does someone inspect it?

You said

however it might be possible that gas bubbles get trapped and accumulated inside the tank and only goes to buchholz after volume of gas becomes large enough.

YES that is exactly how the BHR works.. you should know this

Good answer because you steer him in the right direction and give him home work, the only way to learn, well done.

-> transformer is not new, it was in operation and then stored with oil since 9 to 12 months earlier then it was shipped to our plant. During shipped we didn't emptied the tank, we just disconnected the fins and conservator tanks, the main tank was full of oil. Later after installation and fitting of accessories we top upped the oil by filtration.

-> my suspect was ageing of transformer has weaken the oil enough, so even the electric field strength is enough for decomposing the oil. Is it possible?

-> there are no any alarm signal, rather the buchholz directly give the trip command.

OIL does not decompose, it gets wet, or absorbs moisture.

If you had a failure within the Tx windings, then it would cascade and blow the windings, trust me you would know about it! I've seen high power Tx's explode!

You need to first take a sample and get it FULLY tested. Then based on the results you decide what to do with your oil.

Your air problem is of your own making, by removing the fins and moving the Tx you've introduced air into the main tank and the windings.

AS for other trips... you are asking me.. in your original post you said..

Hello Everyone

I am working as an electrical engineer in a hydro power plant with installed capacity 70 MW. Apart from main power transformers, our plant have a 12.5 MVA transformer for local residence power

You have stated that you are an engineer.. work it out yourself or find someone that can do the job.

"..The oil within the Tx will ONLY produce gas if there is a short circuit within the windings...", not true due to the word "ONLY". There are many mechanisms inside a transformer that lead to the production of gases that will find their way into a Bucholz, a short circuit is just one of them.

The type, rate of production, and quantity produced (as a percentage of all gases), gives many clues as to the myriad sources of dissolved gases. Aside from short circuits (which usually manifest themselves through protective relaying action after the loud boom), there are many sources which can be detected by routine DGA (Dissolved Gas Analysis) long before the transformer is rendered useless. These include; Partial Discharge (PD); overheating in connections, conductors, laminations, insulation, support structures, etc.; normal aging of internals and oil, etc. The exact combination and/or ratio of gases helps in pinpointing exactly what is causing the gassing.

Another thing that to watch for is the type of Bucholz and how it is set up. Some are set to trip, but most are set to alarm. There may be two sets of contacts, one for slow production, another for fast production of gases.

you are correct that gasses can be produced from a range of other conditions within the Tx, however, the OP IMHO, is not all he makes out to be. So I tried K.I.S.S!

Actually in dissolved gas analysis of transformer oil or DGA of transformer oil test, the gases in oil are extracted from oil and analyze the quantity of gasses in a specific amount of oil. By observing percentages of different gasses present in the oil, one can predict the internal condition of transformer.

Generally the gasses found in the oil in service are hydrogen (H2), methane(CH4), Ethane (C2H6), ethylene(C2H4), acetylene (C2H3), carbon monoxide (CO), carbon dioxide (CO2), nitrogen(N2) and oxygen(O2).

Most commonly used method of determining the content of these gases in oil, is using a Vacuum Gas Extraction Apparatus and Gas Chronographs. By this apparatus first gasses are extracted from oil by stirring it under vacuum. These extracted gasses are then introduced in gas Chronographs for measurement of each component.

Generally it is found that hydrogen and methane are produced in large quantity if internal temperature of power transformer rises up to 150°C to 300°C due to abnormal thermal stresses. If temperature goes above 300°C, ethylene(C2H4) are produced in large quantity. At the temperature is higher than 700°C large amount of hydrogen(H2) and ethylene(C2H4) are produced.

Ethylene(C2H4) is indication of very high temperature hot spot inside electrical transformer. If during DGA test of transformer oil, CO and CO2 are found in large quantity it is predicted that there is breakdown of proper insulation.

Furfural Test or Furfuraldehyde Analysis of Transformer Oil
Transformer core and winding have mainly paper insulation. Base of paper is cellulose. The Cellulose has a structure of long chain of molecules. As the paper becomes aged, these long chains are broken into number of shorter parts. This phenomenon we often observe in our home. The pages of very old books become very much brittle. In transformer, the aging affect of paper insulation is accelerated due to oxidation occurs in oil. When insulating paper becomes mechanically weak, it can not withstand the mechanical stresses applied during electrical short circuit and leads to electrical breakdown.

It is therefore necessary to monitor the condition of paper insulation inside a power transformer.

It is not possible to bring out a piece of paper insulation from a transformer in service for testing purpose. But we are lucky enough, that there is a testing technique developed, where we can examine the condition of paper insulation without touching it.

The method is called Furfuradehyde analysis or Furfural test.

Although by dissolved gas analysis one can predict the condition of the paper insulation primarily, but it is not very sensitive method. There is a guide line in IEC-599, where it is told that if the ratio of CO2 and CO in DGA results is more than 11, it is predicted that the condition of paper insulation inside the transformer is not good. A healthy cellulose insulation gives that ratio in a range of 4 to 11. But still it is not a very sensitive way of monitoring the condition of paper insulation. Because CO2 and CO gases also produced during oil breakdown and sometimes the ratio may misleads the prediction.

When oil is soaked into paper, it is damaged by heat and some unique oil soluble compounds are realized and dissolved in the oil along with CO2 and CO. These compounds belong to the Furfuraldehyde group. These are some times called Furfural for short. Among all Furfurals compounds 2- Furfural is the most predominant. These Furfural family compound can only be released from destructive heating of cellulose or paper.

Furfuraldehyde analysis is very sensitive as because damage of few grams of paper is noticeable in the oil even of a very large size transformer. It is a very significant diagnostic test. It is best test for assessing life of transformer. The rate of rise of percentage of Furfurals products in oil, with respect to time, is used for assessing the condition and remaining life of paper insulation in power transformer.

Also.... it is not wise to have BHR that will only trip a Tx for the slightest amount of gas, as power interuptions are costly and annoy customers, as I'm guessing is the case here with the OP. I was taught that weekly/monthly checks on the BHR might produce a small amount of gas that would be captured, and as it amassed or more was released by the Tx for whatever reason, it would trigger an alarm, not a trip. The 'Trip' would be caused by a breakdown of the windings causing a massive release of gas within the TX that would rush to the highest point and in doing so activate the trip in the BHR.

Hope that has cleared it up for you?

The only thing "unclear" to me is why you felt compelled to copy other people's work without attribution (no less a blog that also does the same thing), and try to make it appear as if it were your own. At least quote from, and give credit to, some of the well known authorities on the subject.

Also, stating something unequivocally ("...ONLY...") and then contradicting yourself hardly contributes to confidence in the answer. I like to believe that the next reader of any thread can learn something useful that he can pass along without the fear that his peers say, "Where did you learn that incorrect/misleading piece of information?"

As far as tripping goes, as I previously stated that it's usually an "alarming" relay, secondary to primary relaying such as Differential and Sudden Pressure (SPR) Relays, although some Bucholz's do have a similar "rapid rise" functionality.

Is that the "ONLY" thing you can latch onto?

I have NOT contradicted myself, I have for you, explained my motives for my post with your favorite word "ONLY", and while I don't have to explain myself, it is obvious that you did not understand why I did it.

It is quite obvious that your understanding is VERY different to mine of the workings of a BHR. While I say potatoes you say pot tat toes.

Lighten up.. regardless of what we say, the OP won't get it.. and that's my point! Thinking about it, neither will you!

You may rule out one by one from the following:

2.If this transformer is having a on-load tap auto changer it may be put off for some time and tripping can be watched. Or if it has manual just change over to next level of voltage preferably higher one and the problem may go as it is not expected that looseness may be there in all position.

1.The gas being released may be tested by chemist and take action accordingly. if it shows any sign of spark related gas then only option is take shut down at the earliest and save your transformer.

3. I hope that commissioning has be done properly. if it is not , oil filtration may help.