Dear Sir,

interfacial tension tell you about abilty of dissolving water in oil. Higher
interfacial tension decrease quantity of dissolved water in transformer oil.
Influence of ageing products, i.e. polar molecules is dominant. IFT for new,
unused transformer oil at 20 C is > 35 mN/m (IEC 60296), but recomendations of
DOBLE and IEEE is > 40 mN/m (40 dyn/cm).
IEC 60422 (for used oil) define IFT < 22 mN/m as poor condition, 22-28 mN/m as
fair condition and > 28 mN/m as good condition.

p.s. Sorry for my bad English

Kind regards,
Dejan Pantic, Eng.
General Manager