This International Standard describes specifications and test methods for unused natural ester in transformers and similar oil impregnated electrical equipment in which a liquids required as an insulating and heat transfer medium. Use of natural ester is not recommended for electrical equipment that is open to atmosphere. It applies to natural esters delivered to an agreed upon point at a set time period. In this standard the term “natural esters” applies to insulating fluids for transformers and similar electrical equipment with suitable iodegradability and environmental compatibility. Such natural esters are vegetable oils obtained from seeds and oils obtained from other suitable biological materials. These esters are comprised of triglycerides.