The limit value of transformer oil interfacial tension is 19mN/m.
There are two possible reasons for the change in the interfacial tension of transformer oil: the transformer oil is seriously aging, soluble or sedimentary sludge is deposited in the oil, and the oil is polluted.
For transformer oil with excessive interfacial tension, the following countermeasures should be taken: take measures in conjunction with the determination of acid value and sludge, perform regeneration treatment or replace with new transformer oil.