Debris on Transformer Base Tank 1

[anggapra]

Hi,

Recently, there was a failure in one of our transformers in the field.

Based on the relay protection records, there was an LL fault in the transformer and confirmed after untaking the transformer that there was a fault between 2 phases in its Deenergized Tap changer.

Debris was found inside the transformer base tank, as shown in the photo below. I would like to ask for your opinion: where do you think this debris originated from? Could it be due to corrosion in the winding? Because there are no signs of corrosion on the internal base tank.

Thanks

 

[waross]

Look for signs of overheating.
Then look for charred Micarta or insulating board adjacent to the heating.
We had a distribution transformer fail.
The root cause was a loose connection external to the tank on one of the connection lugs.
The heat generated by the loose connection heated up the lug insulation internal to the tank.
The charred material came loose and started to circulate with the oil.
As the charred material had a high carbon content, an internal flash-over soon followed.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[prc]

Using a magnifying glass, please see what type of material it is. Whether paper or burnt part of tap-changer( phenolic sheet) or sludge from varnish. There is any varnishing of windings, inside the tank or core? Uncured varnish can create this type of slime when reacted with oil.

 

[anggapra]

Thank you for your response, Waross and PRC. I believe the debris resembles rust scale and sand, but I couldn't find any signs of rust or overheating on the tank, terminals, or windings.

After bypassing the DETC, the TTR and WRM readings are good. However, there appears to be a deformation in the top yoke.

 

[prc]

The debris may be from poor tank cleaning before assembly. The top yoke deformation is not a problem. it is from the poor assembly at the factory.

 

[anggapra]

Is it possible that this debris circulating inside the tank then leading to the fault at the tap changer?

 

[prc]

Since the transformer is not forced cooled and the debris was not seen anywhere else, I am not suspecting such a failure mode.

 

[stevenal]

Was the DETC recently operated? Was the debris located below the DETC?

 

[anggapra]

prc, "After closer observation, smaller-sized debris is also visible on the core."

stevenal, the DETC hasn't been operated for years

 

[prc]

What you have seen in the core is normal. It cannot be termed as debris.