scope:

This guide recommends tests and evaluation procedures, as well as criteria and methods of maintenance, for natural ester-based transformer insulating fluids. These base fluids are also known as vegetable seed oils. Methods of reconditioning natural ester-based insulating fluids are also described. Where instructions given by the transformer or fluid manufacturer differ from those given in this guide, the manufacturer's instructions are to be given preference.

Purpose

There is growing interest in and usage of natural ester dielectric coolants for transformer applications. These fluids are currently being used in the range of small distribution class transformers to medium power transformers. They are being applied in new equipment and for retrofilling existing equipment. It is important that a guide be developed to assist the transformer operator in maintaining the fluid in serviceable condition. This guide, therefore, recommends standard tests and evaluation procedures, methods of reconditioning and reclaiming natural ester fluids, and the analysis results at which reprocessing becomes necessary. It will also address the routines for restoring resistance to oxidation, where desired, by the addition of inhibitors.