IEC 62961-18

Insulating liquids – Test methods for the determination of interfacial tension of insulating liquids – Determination with the ring method

Standard for measuring the quality of insulating oils which are used for electrical transducers. Interfacial tension (IFT) of transformer oils has been used for a long time as a criterion for ageing evaluation. 

Trying to find a compromise between the older ASTM D971 standard – a less accurate but fast measuring method – and the EN 14210 standard – a highly accurate but time consuming measuring method – the IEC 62961 was published. Required by the new standard, the measurement is carried out after a surface age of approximately 180 (±30) seconds in order to obtain a value that provides a realistic expression of the interfacial tension while keeping the measurement time at a minimum. 

This change in measurement time especially increases the accuracy when distinguishing differently aged insulating synthetic and natural esters.