SIST EN IEC 61203:2025
(Main)Synthetic esters - Guidelines for maintenance and use in electrical equipment
Synthetic esters - Guidelines for maintenance and use in electrical equipment
IEC 61203:2025 This document provides procedures and supervision for the use and maintenance of synthetic esters in transformers and other electrical equipment. This document includes recommendations on tests and evaluation procedures and outlines methods for reconditioning and reclaiming the liquid, when necessary
Synthetische organische Ester für elektrotechnische Zwecke - Leitlinie zur Wartung von Transformator-Estern in Betriebsmitteln
Esters organiques de synthèse à usages électriques - Guide de maintenance des esters pour transformateurs dans les matériels
IEC 61203:2025 Le présent document décrit les procédures et la surveillance pour l'utilisation et la maintenance des esters synthétiques dans les transformateurs et d'autres matériels électriques. Le présent document inclut des recommandations sur les essais et les procédures d'évaluation et indique des procédés de retraitement et de régénération du liquide, si nécessaire.
Sintetični estri - Smernice za vzdrževanje in uporabo v električni opremi
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
01-september-2025
Nadomešča:
SIST EN 61203:1997
Sintetični estri - Smernice za vzdrževanje in uporabo v električni opremi
Synthetic esters - Guidelines for maintenance and use in electrical equipment
Synthetische organische Ester für elektrotechnische Zwecke - Leitlinie zur Wartung von
Transformator-Estern in Betriebsmitteln
Esters organiques de synthèse à usages
électriques - Guide de maintenance des esters pour transformateurs dans
les matériels
Ta slovenski standard je istoveten z: EN IEC 61203:2025
ICS:
29.035.20 Plastični in gumeni izolacijski Plastics and rubber insulating
materiali materials
29.180 Transformatorji. Dušilke Transformers. Reactors
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EUROPEAN STANDARD EN IEC 61203
NORME EUROPÉENNE
EUROPÄISCHE NORM July 2025
ICS 29.040.10; 29.180 Supersedes EN 61203:1994
English Version
Synthetic organic esters - Guidelines for maintenance and use in
electrical equipment
(IEC 61203:2025)
Esters organiques synthétiques - Lignes directrices pour la Synthetische organische Ester - Leitlinien für
maintenance et l'utilisation dans les matériels électriques Instandhaltung und Betrieb in elektrischen Betriebsmitteln
(IEC 61203:2025) (IEC 61203:2025)
This European Standard was approved by CENELEC on 2025-06-25. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Türkiye and the United Kingdom.
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2025 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 61203:2025 E
European foreword
The text of document 10/1259/FDIS, future edition 2 of IEC 61203, prepared by TC 10 "Fluids for
electrotechnical applications" was submitted to the IEC-CENELEC parallel vote and approved by
CENELEC as EN IEC 61203:2025.
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2026-07-31
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2028-07-31
document have to be withdrawn
This document supersedes EN 61203:1994 and all of its amendments and corrigenda (if any).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
Endorsement notice
The text of the International Standard IEC 61203:2025 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standard indicated:
IEC 60422 NOTE Approved as EN IEC 60422
IEC 61619 NOTE Approved as EN 61619
IEC 61039 NOTE Approved as EN IEC 61039
1 2
IEC 63177 NOTE Approved as EN IEC 63177
Under preparation. Stage at the time of publication: IEC FDIS 63177:2024.
Under preparation. Stage at the time of publication: FprEN IEC 63177:2024.
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments)
applies.
NOTE 1 Where an International Publication has been modified by common modifications, indicated by (mod),
the relevant EN/HD applies.
NOTE 2 Up-to-date information on the latest versions of the European Standards listed in this annex is available
here: www.cencenelec.eu.
Publication Year Title EN/HD Year
IEC 60156 - Insulating liquids - Determination of the breakdown EN IEC 60156 -
voltage at power frequency - Test method
IEC 60247 - Insulating liquids - Measurement of relative EN 60247 -
permittivity, dielectric dissipation factor (tan d) and
d.c. resistivity
IEC 60475 - Method of sampling insulating liquids EN IEC 60475 -
IEC 60666 - Detection and determination of specified additives in EN 60666 -
mineral insulating oils
IEC 60814 - Insulating liquids - Oil-impregnated paper and EN 60814 -
pressboard - Determination of water by automatic
coulometric Karl Fischer titration
IEC 60970 - Insulating liquids - Methods for counting and sizing EN 60970 -
particles
IEC 61099 - Insulating liquids - Specifications for unused EN 61099 -
synthetic organic esters for electrical purposes
IEC 61125 - Insulating liquids - Test methods for oxidation EN IEC 61125 -
stability - Test method for evaluating the oxidation
stability of insulating liquids in the delivered state
IEC 62021-3 - Insulating liquids - Determination of acidity - Part 3: EN 62021-3 -
Test methods for non-mineral insulating oils
IEC 62535 - Insulating liquids - Test method for detection of EN 62535 -
potentially corrosive sulphur in used and unused
insulating oil
IEC 62961 - Insulating liquids - Test methods for the EN IEC 62961 -
determination of interfacial tension of insulating
liquids - Determination with the ring method
ISO 2049 - Petroleum products_- Determination of colour - -
(ASTM_scale)
ISO 2211 - Liquid chemical products - Measurement of colour in - -
Hazen units (platinum-cobalt scale)
Publication Year Title EN/HD Year
ISO 2592 - Petroleum products - Determination of flash and fire - -
points - Cleveland open cup method
ISO 3016 - Petroleum and related products from natural or EN ISO 3016 -
synthetic sources - Determination of pour point
ISO 3104 - Petroleum products - Transparent and opaque EN ISO 3104 -
liquids - Determination of kinematic viscosity and
calculation of dynamic viscosity
ISO 3675 - Crude petroleum and liquid petroleum products - EN ISO 3675 -
Laboratory determination of density - Hydrometer
method
ISO 4406 - Hydraulic fluid power - Fluids_- Method for coding - -
the level of contamination by solid particles
ISO 5661 - Petroleum products - Hydrocarbon liquids - - -
Determination of refractive index
ISO 12185 - Crude petroleum, petroleum products and related EN ISO 12185 -
products - Determination of density - Laboratory
density meter with an oscillating U-tube sensor
ASTM D 92 - Standard Test Method for Flash and Fire Points by - -
Cleveland Open Cup Tester
ASTM D 97 - Standard Test Method for Pour Point of Petroleum - -
Products
ASTM D1275 - Standard test method for corrosive sulfur in electrical - -
insulating liquids
ASTM D1500 - Standard Test Method for ASTM Color of Petroleum - -
Products (ASTM Colour Scale)
ASTM D 5950 - Standard Test Method for Pour Point of Petroleum - -
Products (Automatic Tilt Method)
ASTM D 6922 - Standard Test Method for Determination of - -
Homogeneity and Miscibility in Automotive Engine
Oils
ASTM D 7042 - Standard Test Method for Dynamic Viscosity and - -
Density of Liquids by Stabinger Viscometer (and the
Calculation of Kinematic Viscosity)
ASTM D 7155 - Standard Practice for Evaluating Compatibility of - -
Mixtures of Turbine Lubricating Oils
ASTM D 7752 - Standard Practice for Evaluating Compatibility of - -
Mixtures of Hydraulic Liquids
DIN 51353 - Testing of insulating oils; detection of corrosive - -
sulfur; silver strip test
DIN 51423-1 - Testing of mineral oils - Part 1: Measurement of the - -
relative refractive index with the precision
refractometer
IEC 61203 ®
Edition 2.0 2025-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Synthetic organic esters – Guidelines for maintenance and use in electrical
equipment
Esters organiques synthétiques – Lignes directrices pour la maintenance et
l'utilisation dans les matériels électriques
ICS 29.040.10, 29.180 ISBN 978-2-8327-0396-0
IEC 61203:2025-05(en-fr)
– 2 – IEC 61203:2025 © IEC 2025
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 9
4 Categories of equipment . 9
5 In-service synthetic ester diagnostic tests . 10
6 Evaluation of synthetic esters in new equipment . 11
7 Evaluation of synthetic esters in equipment in service . 12
7.1 General . 12
7.2 Frequency of examination . 12
7.3 Testing procedures . 13
7.3.1 Field tests . 13
7.3.2 Laboratory tests . 14
7.4 Classification of in-service synthetic esters . 14
8 General requirements for corrective actions . 19
9 Interpretation of results. 19
9.1 Water content . 19
9.2 Colour and appearance . 19
9.3 Breakdown voltage (BDV) . 20
9.4 Viscosity . 20
9.5 Acidity. 20
9.6 Dielectric dissipation factor (DDF) and resistivity . 21
9.7 Fire point . 21
9.8 Interfacial tension (IFT) . 21
9.9 Density . 21
9.10 Pour point . 22
9.11 Additives . 22
9.12 Particle (identification, counting and sizing) . 22
9.13 Compatibility and miscibility of synthetic esters . 23
9.14 Oxidation stability . 24
9.15 Refractive index . 24
9.16 Potentially corrosive sulfur . 24
10 Sampling of synthetic esters from equipment . 24
Annex A (informative) Water and synthetic esters . 25
A.1 General . 25
A.2 Water content . 25
A.2.1 General . 25
A.2.2 Water in synthetic esters . 25
A.3 Moistu
...
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