Acetylene Appeared After Maintenance and Transformer Testing

Thanks, i will go filtration, retest and continues monitoring

Arcing is not the only way to manufacture acetylene in a paper insulated transformer. Overload of the transformer can generate acetylene. The following quote from

https://www.morganschaffer.com/page-article-dga-power.html

Acetylene stands out from the rest as being important at any detectable concentration. In the progression of a thermal fault, this critical gas is formed only at the more extreme temperatures, starting with localized overheating above 700°C. In such cases, the acetylene concentration is typically less than 10% of the ethylene concentration. When the acetylene makes up a higher proportion of the hydrocarbon gases, a critical arcing fault is likely present. The statistics suggest a normal concentration is <5 ppm, which includes the contribution of non-critical thermal faults in aged transformers. However, even 1 ppm of acetylene would be considered a possible serious indicator if found in a new transformer, or when first observed during the service life.

The transformer manufacturer can certainly comment. What was the outcome of the telephone calls on the topic, please?

Thanks, i will go filtration, retest and continues monitoring

Do NOT yet filter the oil until you find out what caused the acetylene. It is an indicator of arcing taking place under the oil. Acetylene takes a lot of energy to form from the hydrocarbons of the insulating oil. The fact that it has not increased in the past month only means that the arcing has not continued, but it doesn't mean that it won't happen again.

Do you have past (recent) test results to verify that the acetylene was not there already? That is the first thing you must confirm.

During testing, was the DETC operated? If the contacts of the DETC were not well settled at the chosen tap, arcing can occur. Make sure the tap setting is firmly locked.

Was any other internal work done during the testing outage? Were any connections in the tank disturbed? Did the testing apply any voltage to the transformer windings that might have been above their insulation ratings, so that there could have been a flash-over? Was there any other unusual event when the transformer was reenergized?

Filtering the oil will eliminate any evidence of what may have happened. You should also look at the ratios of the other combustible gases to the acetylene (Rogers Ratios), which could give you clues to any other conditions that may have caused it. Check out the site below for a ratio tool. Only filter the oil after you are satisfied that the cause has been corrected. And THEN take a new sample to give yourself a baseline for future comparison.

Rogers Ratios calculator

I too think so. The priority should be given to find out what caused 'arcing'.

Since the OP mentioned only testing was done, whether Tap changer was operated during testing (when the current is flowing) should certainly be looked in to. This is relevant if the tap changer is off-circuit type.

It's not just whether there was current flowing during testing. Rather, if the tap changer setting was changed (such as to test winding resistance or ratio on each of the taps), and the contacts didn't make cleanly after resetting to the desired tap, then operation of the transformer afterward could cause arcing at the DETC contacts. I have seen that myself. The springs that put tension on the DETC contacts are not that stiff, and a sloppy detent can cause the contacts not to "make" well. But we'll see if the OP comes back with any additional info...

Thanks to all for informative comments, FYI, the history records of oil sampling did not record any appearance of Acetylene before. “We are conducting oil sample test on a yearly basis"

The Acetylene appeared only after last transformer testing conducted on last November 2018-"Off line test every three year basis"

During last test, the DETC -5 taps- was changed for testing of resistance and ratio in all taps.

The oil sampled again after back in service, and since back in service, oil sample was collected for testing, the test repeated three times over one month and the PPM of Acetylene was almost fixed and tends to decrease....

I doubt this happened because of DETC.

Based on those facts, I opt to filter and test and monitoring for weekly sampling for according actions.

I preferred to postpone taking the Tr. to outside workshop until confirm acetylene is not because of DETC.

The <...acetylene...> is a gas, and cannot be removed by using a <...filter...>; filtration will only remove solids from fluids.