Interfacial tension of insulating liquids against water has been used for a long time as a criterion for aging evaluation. Interfacial tension measurement provides a sensitive method to detect small amounts of soluble polar contaminants and products of oxidation. The high interfacial tension between new mineral insulating oil and water, indicate the absence of the most unwanted polar contaminants.
The latest revision for the ASTM D971 Standard test method for interfacial tension of oil against water by ring method dates back to 2012. The ASTM D971 standard describes the testing procedure that is based on the measurement of interfacial tension at the non-equilibrium conditions. The measurement is done 60 seconds after the interface between oil and water has been formed. This allows rather short measurement times but can lead to inaccurate measurements as the surface active species present in the oil doesn't have time to adsorb at the interface.
The new IEC standard is about the be released to tackle the issue. This will pose some new requirements for your measurement device. Are you ready for the change?
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The new standard IEC 62961 for the transformer oil quality testing has just been released. In this blog post, the main differences between the old ASTM D971 and the new IEC 62961 standard are discussed.