DIN EN IEC 62770:2025-05

This International Standard describes specifications and test methods for unused natural esters in transformers and similar liquid-impregnated electrical equipment in which a liquid is required as an insulating and heat transfer medium. In this standard the term “natural esters” applies to insulating liquids for transformers and similar electrical equipment with suitable biodegradability and lower environmental impact. Such natural esters are vegetable oils obtained from seeds and oils obtained from other suitable biological materials and delivered to an agreed point, at a set date. These oils are comprised of triglycerides. Natural esters with additives are within the scope of this document. Because of their different chemical composition, natural esters differ from insulating mineral oils and other insulating liquids that have high fire points, such as synthetic esters or silicone fluids. Natural ester-derived insulating liquids with low viscosity have been introduced but are not covered by this document. IEC 63012 covers these liquids. This document is applicable only to unused natural esters. Reclaimed natural esters and natural esters blended with other insulating liquids are beyond the scope of this document. The standard differs from DIN EN 62770 (VDE 0370-70):2014-10 as follows: a) an introduction to IEC 63012, which describes other fluids not covered by this document, and IEC 63012 has been published in 2019 following the first edition of IEC 62770 (2013); b) a new Table 1 with explanations of terms has been added; c) the requirements for appearance and color have been consolidated; d) pour point: information on the significance of LCSET with notes on the behavior of natural esters at low temperatures; e) additives: a new agreed wording to explain additives has been added; f) fire and flash points are now determined only by the Cleveland open-cup method, as the Pensky-Martens closed-cup method has been identified as problematic for natural esters; g) water toxicity has been given special emphasis; h) Annex B has been removed, as it is no longer required following the publication of IEC 63012.