Symptoms (analysis)
The main symptom of “C4” criticality is linked to the presence of:
metals dissolved in insulating liquids (e.g. copper) (ASTM D7151)
There are other co-factors useful for completing the diagnostic picture:
Appearance (ISO 2049)
Colour (ISO 2049)
Particles (IEC 60970)
Dielectric dissipation factor – tan delta (IEC 60247)
CDT test (Copper Deposition Tendency Test) (internal method)
Total acidity – TAN (IEC 62021-1 or IEC 62021-2)
Additives: Passivators (BTA, Irgamet 39, Irgament 30); oxidation inhibitors (DBPC, DBP)
Oil fingerprint (internal method)
M.C. Bruzzoniti, R.M. De Carlo, C. Sarzanini, R. Maina, V. Tumiatti, Stability and Reactivity of Sulfur Compounds against Copper in Insulating Mineral Oil: Definition of a Corrosiveness Ranking, Ind. Eng. Chem. Res., 2014, DOI: dx.doi.org/10.1021/ie4032814
