IEEE IEEESTANDARDSASSOCIATION IEEE Guide for Acceptance and Maintenance of Natural Ester Insulating Liquid in Transformers IEEE Power and Energy Society Sponsored by the Transformers Committee IEEE IEEEStdC57.147TM-2018 3ParkAvenue (Revision of IEEE Std C57.147-2008) New York, NY 10016-5997 USA IEEEStdC57.147TM-2018 (Revision of IEEE Std C57.147-2008) IEEE Guide for Acceptance and Maintenance of Natural Ester Insulating Liquid in Transformers Sponsor Transformers Committee of the IEEEPowerand EnergySociety Approved 15 February 2018 IEEE-SA Standards Board Abstract:Assistancetoequipmentmanufacturersandservicecompaniestoevaluatethesuitability of unused natural ester insulating liquids being received from suppliers is provided in this guide. Information for transformer operators in evaluating and maintaining natural ester insulating liquids in serviceable condition is also provided. Keywords: dielectric coolant, high fire point liquid, IEEE C57.147TM, insulating liquid, less- flammable liquid, natural ester liquid, transformer, vegetable oil The Institute of Electrical and Electronics Engineers, Inc. 3 Park Avenue, New York, NY 10016-5997, USA Copyright 2018 by The Institute of Electrical and Electronics Engineers, Inc. All rights reserved. Published 19 July 2018. Printed in the United States of America. IEEE is a registered trademark in the U.S. Patent & Trademark Office, owned by The Institute of Electrical and Electronics Engineers Incorporated. PDF: ISBN 978-1-5044-4919-9 STD23135 Print: ISBN 978-1-5044-4920-5 STDPD23135 IEEE prohibits discrimination,harassment, and bullying. For more information, visit http:/www.ieee.org/web/aboutus/whatis/policies/p9-26.html. of the publisher.