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IEC 62975
Edition 1.0 2021-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Natural esters – Guidelines for maintenance and use in electrical equipment
Esters naturels – Lignes directrices pour la maintenance et l’utilisation dans les
matériels électriques
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IEC 62975
Edition 1.0 2021-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Natural esters – Guidelines for maintenance and use in electrical equipment
Esters naturels – Lignes directrices pour la maintenance et l’utilisation dans les
matériels électriques
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.040.10 ISBN 978-2-8322-9222-8
– 2 – IEC 62975:2021 © IEC 2021
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 natural ester diagnostic tests . 10
6 Evaluation of natural esters in new equipment . 11
7 Evaluation of natural ester in equipment in service . 12
7.1 General . 12
7.2 Frequency of examination . 13
7.3 Testing procedures . 14
7.3.1 Field tests . 14
7.3.2 Laboratory tests . 14
7.4 Classification of in-service natural esters . 14
8 General requirements for corrective actions . 19
9 Interpretation of results. 19
9.1 General . 19
9.2 Colour and appearance . 19
9.3 Breakdown voltage . 19
9.4 Viscosity . 20
9.5 Acidity. 20
9.6 Dielectric dissipation factor (DDF) and resistivity . 20
9.7 Dissolved gas-in-oil. 21
9.8 Flash and fire points . 21
9.9 Interfacial tension (IFT) . 21
9.10 Density . 22
9.11 Pour point . 22
9.12 Additives . 22
9.13 Particle count . 22
9.14 Compatibility and miscibility of natural esters . 22
9.15 Oxidation stability . 23
9.16 Polymerization . 23
10 Sampling of natural esters from equipment . 24
Annex A (informative) Water and natural ester liquids . 25
A.1 General . 25
A.2 Water content . 25
A.2.1 General . 25
A.2.2 Water in natural esters . 25
A.3 Moisture equilibrium between liquid and solid insulation . 27
Annex B (informative) Replacement and treatments of natural esters in transformers . 30
B.1 Transformer retrofilling with natural esters . 30
B.2 Reconditioning and reclaiming . 31
B.2.1 General . 31
B.2.2 Reconditioning . 31
B.2.3 Reclaiming . 32
Annex C (informative) Use of natural ester liquids with on-load tap-changers (OLTCs) . 33
Bibliography . 35
Figure A.1 – Moisture saturation values between liquids versus temperature [10] . 27
Figure A.2 – Example of water (high concentrations) equilibrium curves for paper and
natural ester [11] . 28
Figure A.3 – Example of water (medium concentrations) equilibrium curves for paper
and liquid [11] . 29
Figure A.4 – Example of water (low concentrations) equilibrium curves for paper and
liquid [11] . 29
Table 1 – Categories of equipment . 10
Table 2 – Diagnostic tests for in-service natural esters . 11
Table 3 – Recommended limits for natural esters properties after filling in new
electrical transformers and reactors prior to energization . 12
a
Table 4 – Recommended frequency of testing . 14
Table 5 – Recommended limits for in service natural esters in transformers . 15
Table A.1 – Typical values for A and B for different insulating liquids [10] . 26
Table A.2 – Guidelines for interpreting data expressed in relative saturation . 27
– 4 – IEC 62975:2021 © IEC 2021
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
NATURAL ESTERS – GUIDELINES FOR
MAINTENANCE AND USE IN ELECTRICAL EQUIPMENT
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two org
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