Traces of Ethane C2H4 & Acetylen C2H2 in new / not yet energized transformer .

[ralawneh]

We have three transformers kept at site for more than 3 years not energised and when DGA samples taken we noticed traces of Ethane C2H4 ( 117 ppm ) & Acetylene C2H2 ( 3 ppm ) , what cloud be the reasons ? any risk to energise transformers ? is it necessary to change oil ? We are thinking to energise and monitor and take another DGA samples after 2 weeks any risk ?

 

[prc]

In a stored transformer there is no chance of acetylene formation.It has to be investigated.any topping up done with oil ?
Any way before energistaion,important to check BDV and water content of oil, hot oil filtertaion at leasy for 3 days, checking water ppm at the end of filteration by taking hot oil sample.

 

[unclebob]

I guess someone at the lab isn't using ''laboratory good practices''...

 

[cranky108]

What size are the transformers? Larger transformers are filled with oil after they are welded. However many smaller transformers are welded after they are filled.

So if these are small transformers, it might be from the final welding.

 

[prc]

Transformer engineers always advise- Never weld on an empty transformer, but only under oil filling.

 

[ralawneh]

I would like to thank all for the valuable comments .
Regarding doubt in sampling these values are after repeating sampling, we are very familiar with DGA sampling so no doubt on this subject.
The size of transformers as follows:
1. 2000 kVA 34.5 kv/480 V Sealed type transformer we found Acetylene in the three samples.
3ppm , 3ppm , 2.5 ppm
2. Other transformer rating 2500 kVA , 4.16kV/480V conservator type transformer with breather we found only Ethane C2H6 (sorry for initial mistake I mentioned in the beginning , It is not C2H4 the gas found is C2H6 )
158 ppm , 96 ppm , 117ppm

No welding done on units .

Transformers located / installed in Petrochemical company “ethylene and polyethylene plant”
Is there any possibility that this could be the reason? The gas are coming from outside environment since transformer is conservator type? If yes how we can solve this issue?

 

[prc]

Nothing to do. In first case, since only acetylene and no other fault gas, may not be a cause for concern. Any on-load tap-changer with it? If so, any chance for oil leaking from that chamber?In case ambient air has ethane gas content, it can get dissolved. Even otherwise, that much gas content is not a cause for worry since no other fault gas is present.

 

[cranky108]

Even being outside the transformers can breath in the outside air. So it might have taken in gas from the enviroment.

These aren't small, but also aren't big.

We have found gas in new sealed transformers, but only because they were small, and the welding to seal them was done as a last step in there manufacture. We no longer measure them as they are of low cost to replace.
Larger transformers maybe shipped empty, and vacuum filled at the site.

With these not being energized, they may have taken water, which will work on the paper.