Natural esters, also known as vegetable oils, can be used as an alternative to mineral oil as an insulating liquid in power transformers and other electrical equipment. A proposed new ASTM International standard will provide the electrical power industry with a relatively straightforward test for oxidation stability of natural esters.
The proposed standard is WK21616, Test Method for Oxidation Induction Time of Natural Ester Insulating Fluids by Regular Differential Scanning Calorimetry (DSC).
“The history of dielectric insulating fluids developed with mineral oil as the main liquid dielectric,” says ASTM member Kevin Rapp, senior chemist, Cargill Industrial Specialties. “Electrical power industry experience and the majority of knowledge has been devoted to mineral oil, which has a chemical composition much different than natural esters. Thus, many of the oxidation test methods developed for mineral oils cannot be applied to natural ester fluids.”
The DSC oxidation induction time method as described in WK21616 takes between two and three hours, is a direct oxidation measurement using a very small sample size and does not use hazardous laboratory chemicals that require disposal.
Once it has been approved, WK21616 will find use among fluid and equipment manufacturers, specifiers, end users and testing laboratories that currently have no standard method for measuring oxidation stability of natural ester dielectric fluids.
WK21616 was developed by Subcommittee D27.15 on Planning Resource and Development and was recently assigned to Subcommittee D27.06 on Chemical Methods. Both subcommittees are part of ASTM International Committee D27 on Electrical Insulating Liquids and Gases. The subcommittee invites all interested parties, particularly those who use DSC equipment, to take part in the ongoing development of WK21616.