Transformer Trip on Ground Fault

Is the presence of these element is due to arching inside the transformer?

Yes this is the most likely cause, with the earth fault trip due to the transformer oil dielectric properties being compromised due to oil contamination.

Any other possible cause?

If you had a filter and/or seal failure that allowed moisture to mix with the oil that could explain some of what you are seeing, but you discounted that due to your finding of little moisture contamination in the oil.

Short answer, looks like arc discharge (or possibly excessive heating) due to a failed joint or connection. Carefully inspect your transformer before putting it back into service.

Your transformer may have some internal faults occur. Hydrogen inside your transformer oil concentration increases due to the breakdown of your transformer oil. Your transformer oil is Hydrocarbon base. When there is a faults in the transformer, heat is generated and your transformer oil chemically breakdown to hydrogen and carbon. That why your hydrogen is increase

Most transformers are filled with mineral oil because of it chemical stability and high natural dielectric strength. Being that, it is a hydrocarbon material, the principal molecular makeup of transformer oil is Hydrogen and Carbon in their various forms. All transformers oils breakdown naturally over time. The main enemies of transformer oil are oxygen, water and excessive heat.

Whenever transformer oil is exposed to thermal of electrical faults, the natural breakdown process is greatly speeded up. During breakdown on the oil, certain hydrocarbon based gasses are produced in small quantity. The magnitude of the fault and surrounding materials will determine which gasses are produced.

A good example of this process is in the case of Corona. Corona inside the transformer is a very low energy discharge. The presence of Corona will ionize the oil surrounding the fault and release hydrogen in detectable amounts. Since Corona is a low energy condition and Hydrogen is the easiest gas to produce as it requires the least amount of energy, If your DGA test that reveals higher than normal Hydrogen in the oil, with no other elevated gasses, would point to a Corona condition occurring inside the transformer.

Therefore, it is better to get an expert to double check your transformer oil and the transformer winding insulation before you energize it.

that's right for all analysis, but to more of analysis you can dissipasi factor (tandel), this metode importen to measure medium between component transformer, can't higher 1%. the result may be paper damage or lead to bushing and maybe the bushing is a main caused.

At this stage, you need to do a full range of tests on your transformer . I would suggest that you publish the result full range of DGA tests( acetylene, CO, CO2,,,), tandelta, and winding resistance on all tap positions. How old is the transformer anyway? Is it sheltered or outdoors, free breathing to atmophere or bladder type.

I had a similiar problem once , it turned out that one of my tap position had severely arced contacts which would have resulted when we had a system fault which did not clear very fast.

We only found out after we did a winding resistance test on all tap positions.

Our solution was to filter the oil and put back in service avoiding use of that tap position.