Dear Ashish,

I attached some data concerning the thermal conductivity and a talk (I found, sorry in german) concerning the properties of transformer oil.

Yours

R. Mitdank

The thermal conductivity of transformer oil reduces with age. Some of the vegetable oils have better thermal conductivity but higher oxidation stability which is not desirable. This leads to faster oxidation of the vegetable oil as compared to the conventional oil. However, the properties of vegetable oils vary considerably from each other, so it is diffivult to make a generalized statement. If you can pick a particular oil, then assessment would be easy. Thermogravimetric analysis (TGA) can also be performed to understand the degrdation of a particular oil with temeprature.

Below are some links for reference:

https://www.hindawi.com/journals/jchem/2019/4567973/

https://ieeexplore.ieee.org/document/8728166

https://ieeexplore.ieee.org/document/8813220

Article Thermal stability of a vegetable oil-based thermal fluid at ...

I hope this helps.

Thanks