Transformer oil gas analysis

[panthripu]

I am surprised by sudden increase in the level of acetylene in one of our transformer. Since years we are regularly monitoring the DGA and have never come across any gas more than set limits of IEEE. The acetylene contents has gone around 50ppm within last four months.The transformer is for arc furnace application ( with onload tap changer) and still in working conditions. The winding resistance and TTR shows normal results.Documents and papers on internet tells that this gas is generated due to arcing inside the transformer along with hydrogen. I dont see any noticable increase in other gases like H2 or CO or CO2.This increase has been notices after recent oil filtration and manintenance of diverter switch of tapchanger by manufacturer of tap changer. I suspect that something has gone wrong during these activities but dont know what ?
The total dissloved combustible gases content very much below limit of 720ppm (IEEE).
I would like the experts here for their opinion for further actions .

 

[Sahib]

If your transformer is provided with Bucholz relay, it would sound alarm when there is any gradual accumulation of gas like acetylene in it due to any incipient fault in the transformer. otherwise it is difficult to guess what is happening in the transformer. Perhaps it is normal as you stated

The total dissloved combustible gases content very much below limit of 720ppm (IEEE).
.

 

[Sahib]

But keep on doing DGA on the transformer more frequently. If the dissolved acetylene gas level is increasing and exceeds 70 ppm, You may consider removable of the transfomer from service for further inspection and fault rectification to avoid any ctastrophic failure of the transformer in service.

 

[kingpb]

An incipient fault or developing fault, usually causes slow formation of gas.
Examples are:

• Current flow through defective supporting and insulating structures;
• Defective joints at winding terminals causing heating;
• Minor tap changer troubles; and
• Core faults.

Failure to take corrective action will undoubtedly result in a catastrophic equipment failure as the fault progresses.

 

[Phil Corso]

Panthripu...

Is the Tap assembly located within the main tank or in a separate enclosure?

Regards, Phil corso

 

[panthripu]

tapchanger assembley

tapchanger assembley

The tap changer assembly is inside the main tank , however the diverter switch for it is in seperate chamber. Can any problem in diverter switch may lead to arcing in the contact of tapchanger assembly ? or is it possible that something went wrong during the recent filteration of transfomer oil?

 

[Phil Corso]

Panthripu...

Thus far sounds like cross-contamination! Were separate DGA's performed on the maint-tank, and the diverter-switch enclosure?

Can you provide the DGA results before the start of work, and upon completion! Include all constituents!

Regards, Phil