Issues with transformer ester oils

[norcalnewb]

Hello. I was recently told by a colleague in Europe that transformer manufacturers in Europe are not recommending ester oils, either natural or synthetic, on new units. Supposedly, there are some issues people are seeing. This seems a little different than I have heard. Are there long term problems developing with these oils?

 

[FPelec]

We’ve been using autotransformers insulated with natural ester (from various suppliers) since 2016, with tens of units currently in operation, and we haven’t encountered any major issues. These are typically 400 kV, 250 MVA units.
It’s important to note that these transformers were specifically designed to work with natural ester — not makeshift solutions where a transformer (and its components, such as OLTC and bushings) originally designed for mineral oil is simply filled with natural ester, as some manufacturers may propose.
This is a CESI powerpoint on the topic, although not very recent,that also outlines certain details of the manufacturing process, particularly paper impregnation:
https://www.cesi.it/app/uploads/202...ower-Transformers-in-Natural-Esters-Terna.pdf