Hi - what tests should be performed on the oil for transformers?

Dissolved gas?
Viscosity?
Acid no?
PQ?
Metals?
Additives?
Water?
Colour?

Thanks. Mike.

As usual it depends. I would rank them roughly most important to least important as follows:

I would say water and DGA are most important. Water is a common problem, DGA is very helpful for diagnostic of a wide range of problems.

Color should normally be checked simply because it is so easy.

Dielectric strength - particularly important for new oils before putting them into the equipment. Checks the basic dielectric function of the oil which can suffer from water or contaminants (water is certainly the most common).

Interfacial tension - checks for long-term oil degradation. (I think an earlier warning than acid number).

Acid number - checks for long-term oil degradation.

Additives - check with your oil supplier. Some oils lacking natural oxidation resistance have oxidation inhibitors added and you may want to check the concentration on an infrequent basis.

Metals - not a common check for transforemrs. We did use it once for generator stepup transformers (a very critical transformer) where we suspected pump bearing problems putting brass particles into the oil.

Viscosity - I don't think this is checked for transformers.

PQ = ?

Note - I added IFT and dielectric strength which are very common transformer tests not included in your list.

Of course if you are sending your oil samples out for analysis, you might want to check what your lab recommends, and what they offer as a package.