Insulating liquids can be characterised using interfacial tension measurements. In this standard, insulating liquids are measured at the interface against water using a tensiometer and the ring method. This measurement gives an indication about the ageing process of the liquid.

IEC 62961: Application and Use

Insulating liquids can be characterised using interfacial tension measurements against water. In the case of insulating liquids, the interfacial tension can be used to describe the ageing process of the liquid.

The IEC 62961 is related to the ASTM D 971 and the EN 14210. The ASTM D 971 only stipulates a single measurement. To achieve a more robust result, the EN 14210 could be used, which proposes repeated measurements until a static value is achieved. However, this standard requires a long measurement time. The IEC 62961 wants to reach a compromise between those two standards by measuring the interfacial tension at a surface age of 180 seconds.

IEC 62961: Experimentation

Apparatus

For this measurement, the following apparatus is needed:

• a tensiometer
• a sample vessel platform which can be moved up and down
• a balance to measure the force exerted on the ring
• a ring: a platinum/iridium ring; thickness maximum: 0,4 mm, mean circumference: 60 mm
• glass vessel with a minimum diameter of 60 mm

All Force Tensiometers of the DCAT series from DataPhysics Instruments comply with this standard.

Procedure

• Follow the cleaning routine for vessels and ring
• Use bi-distilled or deionised water
• Set the balance to zero after the ring is attached
• Conduct a measurement only with water to ensure that the apparatus and sample is cleaned properly
• Again, fill the sample vessel with water. Submerge the ring. Slowly overlay the water with the insulating liquid.
• Start the measurement after 180 seconds.

The IEC 62961 is in use since 2018.

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