Insulating Fluids in Distribution and Power Transformers

Standardization News

Insulating Fluids in Distribution and Power Transformers

ASTM’s committee on electrical insulating liquids and gases (D27) is developing a proposed standard for insulating fluids in distribution and power transformers.

According to ASTM International member Edward Casserly, because insulating fluids can oxidize over time, the liquids are formulated with antioxidants that act as inhibitors to minimize oxidation that is detrimental to cooling efficiency and electrical insulation.

The proposed standard (WK81449) will cover natural and synthetic esters that are used as insulating fluids. The standard will be useful in the following ways:

  • Manufacturers that produce insulating liquid will be able to use the proposed standard for quality assurance/quality control compliance;
  • Transformer manufacturers that buy insulating liquids, fill the transformers, and sell to the utilities, to ensure compliance with the standards and customer requirements;
  • End-user utilities will use the standard to obtain maintenance information needed over the lifetime of transformers; and,
  • Laboratories contracted by utilities will use the standard to determine the identity of the inhibitors, as well as the concentration.

This effort directly relates to the United Nations Sustainable Development Goal #12 on responsible consumption and production.

“Natural esters are renewable and sustainable with a negative carbon footprint,” says Casserly. “Both the natural and synthetic esters are non-toxic, non-hazardous, and biodegradable and are less likely to damage the soil or water if spilled.”  

ASTM welcomes participation in the development of its standards. Become a member at

“We are looking for support from the liquid manufacturers, utilities, transformer manufacturers, and service laboratories to develop a standard that all can use,” says Casserly.

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