Buchholz Alarm
Buchholz Alarm
(OP)
in 400 MVA transformer we get every night first stage alarm at , we noticed that the alarm comes when the ambient temperature is low and unit load is low. we susbect air ingress during low temperature time when both oil and air temperature are at thier lowest value.
we performed DGA for the oil and the result was as follow
Gas ppm
H2 82
O2 5980
N2 91848
CO2 8199
C2H4 Ethylene 38
C2H6 Ethane 185
C2H2 Acetylene 0
C3H8 & C3H6
Propane & Propene 183
CH4 Methane 149
CO Carbon Monoxide 1337
we are searching for any source of air ingress through leaking gaskets on the oil pipes and coolers.
Any feed back experience please. any available procedure
Thanks
we performed DGA for the oil and the result was as follow
Gas ppm
H2 82
O2 5980
N2 91848
CO2 8199
C2H4 Ethylene 38
C2H6 Ethane 185
C2H2 Acetylene 0
C3H8 & C3H6
Propane & Propene 183
CH4 Methane 149
CO Carbon Monoxide 1337
we are searching for any source of air ingress through leaking gaskets on the oil pipes and coolers.
Any feed back experience please. any available procedure
Thanks






RE: Buchholz Alarm
DGA levels are of far greater use when considered as a trend than as a spot value. That said, some of the values are unusually high - methane, ethane, hydrogen certainly are. What does the trend information tell you? anything rising rapidly? When was the oil last processed?
----------------------------------
If we learn from our mistakes I'm getting a great education!
RE: Buchholz Alarm
i think the conservator is higher than the BUCHLOZ, the level of the conservator is from 50 to 60%.
we checked the upper limit for methane, ethane, hydrogen they are within limits,
any other reasons ?
thanks
RE: Buchholz Alarm
Gas ppm
H2 8
O2 18987
N2 82141
CO2 2488
C2H4 Ethylene 10
C2H6 Ethane 47
C2H2 Acetylene 0
C3H8 & C3H6
Propane & Propene 46
CH4 Methane 37
CO Carbon Monoxide 383
thanks again
RE: Buchholz Alarm
Since the trip contact is not closing low oil level cannot be the reason.
Please check the silical breather and its breather pipe line for any blocking.Then such phenomena can occur.
RE: Buchholz Alarm
the conservator tank is equiped with air bag connected to the silicaal breather. fyi we used to vent the BUCHHLOZ we we get the first alarm then it dissapear and no trip happens.if we did not vent it with the first alarm, is it going to trip after sometime?
Thanks again
RE: Buchholz Alarm
we removed the oil cup at the inlet of the silica gel breather and replace the oil there was nothing abnormal,how can we check if the breather is blocked?
RE: Buchholz Alarm
Trust the conservator -breather is an open breathing type and not with air cell.Some of the occasions that I noticed breather pipe blocking were 1) Compacting of gel in breather and thereby air blocking 2) Insects building up in oil cup inlet 3) Simple errors in erection-closing the pipe with a full dia gasket at one of the pipe joints etc.
I dont think the problem is due to air sucking by oil pump.If so it should have happened always.
As you may be knowing transformer oil can contain air up to 8-10 % of its volume.For every 10 C fall in oil temperature,oil volume shrinks by 0.8%.So if breather pipe is closed, during temperature drop,a vacuum will be created over the oil level in conservator which in turn allows the dissolved air in oil to escape out as bubbles.
To your question, the situation will not cause a trip.But it is not a good condition to allow to continue.Bubbling can happen between two winding discs which can trigger a voltgae breakdown. I have seen such failures.
Best way to check whether breathing is happening freely or not is to watch the oil cup during a temperature change.You must find air bubbling in or out through the oil seal.If it is not happening,check for air blocking anywhere in pipe by disassembling and blowing air.
RE: Buchholz Alarm
i would like to give some data about our transformer, it is equiped by 7 pumps and 7 horizintal coolers located above the transformer, the conservator tank contains air bag connected to the silical breather,
yesterday we noticed one of the coolers dropping very little oil, we isolated inlet and outlet valves the situation didnt improve much.
to put back again this cooler in service, is there any risk of big quantity of air to enter the transformer and triggering of BUCHOLZ?.
cuz i want to understand what you mean by (I dont think the problem is due to air sucking by oil pump.If so it should have happened always)
for my understanding , is there some points on the cooling system that its pressure varies from positive to vacuum pressure during low load and low ambient temperature?
Thanks again for your support
RE: Buchholz Alarm
You can stop the leak in cooler using some epoxy compound and then put it in to use.In such cooler banks there will always be a spare cooler so that you can use transformer without one cooler also.
Since you said transformer is with air cell there cannot be any free breathing.You have to check first if there is any air outside the air cell.Normally it should be full of oil.Please check the plain window sight glass in conservator to check the oil level out side the conservator.
RE: Buchholz Alarm
we always operate at this level also the other unit is the same, i will look for this plain window
if the air bag has hole, is it going to block the breathing? cuz i couldn't see any bubbles in the oil cup after removing the silica gel and connect again for one complete day.
RE: Buchholz Alarm
Another alternative is a rubber diaphragm at the middle of conservator.In all these cases air must move in and out through.As per your statement it is not happening.Please look carefully why it is not happening.Someplace, it is bypassing breather?
Anyway the physics can be only as I explained-I hope so. Please investigate carefully and will be happy if you inform success.
RE: Buchholz Alarm
RE: Buchholz Alarm
RE: Buchholz Alarm
"Since the trip contact is not closing low oil level cannot be the reason."
I think you are too quick to dismiss the obvious.
Normally the alarm is connected to the upper contact because this is where the gas accumulates. The lower float with the surge plate is used for the trip, and therefore the upper float will detect a low oil level by detecting the presence of gas (air in this case) in the Buchholz before the transformer trips. If you ignore the alarm and let more oil leak out, or if the temperature drops a little further, then the transformer will trip when the lower float drops. I strongly suspect this is what is happening here - seen it too often not to recognise the symptoms!
Conservator level indicators are often worse than useless, especially the pad cell type with a remote indicator when used in conjunction with a bladder in the tank. When oil level is abnormally low the bladder rests on the indicator mechanism giving a false indication. The best level indicators are sightglass types.
----------------------------------
If we learn from our mistakes I'm getting a great education!
RE: Buchholz Alarm
You had said that trip will work when the relay is empty of oil.In this case trip is not operating so I concluded that low oil level may not be the reason.In the example I quoted from Texas,both alarm and trip operated.The air cell blocked the relay pipe end in the conservator due to sudden surge of oil back in to transformer tank. Oil in the pipe was emptied due to contraction of oil with temperature.
In India we always provide a plain oil sight window opposite to magnetic oil level guage to monitor the condition of air cell and also to see whether there is any air leakage in to conservator.On healthy condition, oil sight window should show full always.
RE: Buchholz Alarm
----------------------------------
If we learn from our mistakes I'm getting a great education!
RE: Buchholz Alarm
RE: Buchholz Alarm