How to improve the cooling of 2000 kVA ONAN transformer

[dhia33]

I have a transformer with ONAN cooling (natural ventilation like figure) and 2000 kVA that works always near full capacity, in summer it over heats above the limit. to improve the cooling and prevent reaching the oil temperature limit. I decided to place an exhaust fan and an inlet fan like exactly the figure. the exhaust fans are usually used but I want to know if it is ok to place a fun under the transformer to blow air directly to the radiator knowing that it was originally designed as ONAN and not ONAF.

 

[i=p/u]

Maybe try reduce load

 

[plugsandsparks]

Best to contact manufacturer, if you give them the KVA you are consistently drawing and the ambient temp around the transformer, they , hopefully will suggest best ways of cooling.

 

[Pete999]

I have a transformer with ONAN cooling (natural ventilation like figure) and 2000 kVA that works always near full capacity, in summer it over heats above the limit. to improve the cooling and prevent reaching the oil temperature limit. I decided to place an exhaust fan and an inlet fan like exactly the figure. the exhaust fans are usually used but I want to know if it is ok to place a fun under the transformer to blow air directly to the radiator knowing that it was originally designed as ONAN and not ONAF.

Has the radiator(cooling coil) been cleaned any debris removed etc?

 

[Andy-1960]

I am currently looking at the same problem on a transformer here in the UK, customer has already installed fans but to little effect, we have just installed a data logger to look at the harmonic load on the transformer which we feel may be the cause of the issue.
With all of the solid state switching devices now being installed (VSD’s, LED lighting, switch mode power supplies, etc) it all adds up and the harmonics created will cause the transformer to overheat, even if the transformer appears to be running below capacity.
The solution then is to install an active filter to neutralise the harmonics.

 

[R-fur]

Have you checked the oil level? If the oil level drops to the where the cooling tubes are, then over heating will occur.

 

[R-fur]

Also check the Ph of the oil, overheating causes the oil to become acidic which causes breakdown of the insulation.

 

[dhia33]

Thank you everyone for your answers

Concerning the load it can't be reduced, in fact it is increasing after installing new equipment
The cooling coil is clean and the oil is checked and it is changed when needed (the transformer is maintained every tow years approximately ).
The overheating occurs when turning on some equipment that are not usually working 24 hrs, and when it is summer (30 to 35 °C are common for outside temperature and it can be 40 °C for many days ). So the only solution is forced ventilation.
I will try to contact the manufacturer and I will look to the active filter solution, although the people in charge are looking to improve just the cooling. Finally I wanted to ask if fans are added, can they cause problems or damage in any way ?

 

[Moley]

Looking at the drawing you attached it looks like a corrugated tank and not radiators? Is that a conservator tank on the top? Hopefully if it is (not really clear in that picture) it'll have a bucholz between to con tank and body so it should trip if the level gets low so you can rule out low oil levels. If it's not got a con tank and it's a sealed unit then be very careful. I've had to deal with corrugated tank transformers that have buckled through over heating. You say you have the Tx maintained. What sort of DGA results are you getting? The only real fix for what you have is to either reduce the load of fit a higher rated transformer with external radiators and WTI controlled fans.

 

[dhia33]

Looking at the drawing you attached it looks like a corrugated tank and not radiators? Is that a conservator tank on the top? Hopefully if it is (not really clear in that picture) it'll have a bucholz between to con tank and body so it should trip if the level gets low so you can rule out low oil levels. If it's not got a con tank and it's a sealed unit then be very careful. I've had to deal with corrugated tank transformers that have buckled through over heating. You say you have the Tx maintained. What sort of DGA results are you getting? The only real fix for what you have is to either reduce the load of fit a higher rated transformer with external radiators and WTI controlled fans.

Hi Moley , it has DGPT2 protection that shows oil level. I don't know if they did DGA tests.

 

[Pete999]

Hi Moley , it has DGPT2 protection that shows oil level. I don't know if they did DGA tests.

Which begs the question are there any records of oil changes or tests? could be if the windings nave overheated the oil could be compromised electrically

 

[Moley]

Looking at that picture it's not a corrugated tank, it has rads and it has a con tank which should allow it to breathe so ignore my comment about the tank buckling. I can't see any reason why cooling fans can't be fitted. Only comment I would make is how they are going to be operated as I doubt if it's got a WTI with fan on/off contacts. I would recommend a DGA test just to confirm everything is okay with the oil. Can also show up any faults that may be on their way. What make is the Tx?

 

[dhia33]

Which begs the question are there any records of oil changes or tests? could be if the windings nave overheated the oil could be compromised electrically

Hi Pete I will check and search for any records.

 

[dhia33]

Looking at that picture it's not a corrugated tank, it has rads and it has a con tank which should allow it to breathe so ignore my comment about the tank buckling. I can't see any reason why cooling fans can't be fitted. Only comment I would make is how they are going to be operated as I doubt if it's got a WTI with fan on/off contacts. I would recommend a DGA test just to confirm everything is okay with the oil. Can also show up any faults that may be on their way. What make is the Tx?

I was thinking of using a raspberry pi with pt100 sensors to measure the room temperature and the tank temp and command the fans and the exhaust automatically. The transformer brand is SACEM

 

[Moley]

Are there pockets on the Tx to mount the PT100? If so are they for winding or oil temps or both?