Oil tests below 0C

[samair99]

Which oil analysis test is invalid below 0 degrees C?
-moisture
-interfacial tension
-furans
-specific gravity

[SecondGen]

Which oil analysis test is invalid below 0 degrees C?
-moisture
-interfacial tension
-furans
-specific gravity

Here is some info I found regarding oil testing in cold temperatures:


While mineral oil maintains lower viscosity in cold temperatures, its ability to hold water is very low, potentially weakening the dielectric strength significantly.

At subzero temperatures, mineral oil can only tolerate a few parts per million of water before it becomes saturated. Subsequently, the dielectric strength of saturated mineral oil (not to mention free water) is poor.

Energizing a very cold mineral oil filled transformer at full load yields a significant risk of dielectric failure. The cold start procedure enables the transformer to warm slowly in order for the free water to dissolve within the mineral oil.

https://www.envirotempfluids.com/products/envirotemp-fr3-dielectric-fluid/cold-temp/



In extremely cold climates, specific gravity can be used to determine whether ice, resulting from freezing of water in oil-filled apparatus, will float on the oil. Such a condition possibly may result in flashover of conductors extending above the oil level.

https://www.ecmweb.com/content/analyzing-transformer-insulating-fluid

Based on the above I'd say specific gravity can be eliminated, my best choice would be moisture content.