Natural esters - Guidelines for maintenance and use in electrical equipment

IEC 62975:2021 provides procedures and guidelines that are intended for the use and maintenance of natural ester liquid in sealed transformers and other electrical equipment.
This document is applicable to natural esters, originally supplied conforming to IEC 62770 and other applicable standards (e.g. ASTM D6871) in transformers, switchgear and electrical apparatus where liquid sampling is practical and where the normal operating conditions specified in the equipment specifications apply.
At present, there is a limited amount of information available for electrical equipment other than transformers.
This document is also intended to assist the power equipment operator to evaluate the condition of the natural ester and maintain it in a serviceable condition. It also provides a common basis for the preparation of more specific and complete local codes of practice.
The document includes recommendations on tests and evaluation procedures and outlines methods for reconditioning and reclaiming the liquid, when necessary.

Esters naturels - Lignes directrices pour la maintenance et l’utilisation dans les matériels électriques

IEC 62975:2021 fournit des procédures et des lignes directrices destinées à l’utilisation et à la maintenance d’un liquide à base d'esters naturels présent dans les transformateurs hermétiques et autres matériels électriques.
Le présent document s'applique aux esters naturels, conformes à l’origine à l’IEC 62770 et aux autres normes applicables (par exemple, l’ASTM D6871) et présents dans les transformateurs, les appareillages de connexion et appareils électriques pour lesquels l'échantillonnage de liquide est possible, et avec lesquels les conditions normales de fonctionnement définies dans les spécifications des matériels s’appliquent.
Actuellement, les informations disponibles concernant les matériels électriques autres que les transformateurs sont limitées.
Le présent document est également destiné à aider l’opérateur d’un matériel électrique à évaluer l’état de l’ester naturel et à le maintenir dans un état d’utilisation. Il fournit également une base commune à l’élaboration de codes de bonnes pratiques locaux plus spécifiques et plus exhaustifs.
Le présent document comprend des recommandations concernant les essais et les procédures d'évaluation, et présente des méthodes de retraitement et de régénération de l’ester liquide si nécessaire.

General Information

Status
Published
Publication Date
04-Jan-2021
Current Stage
PPUB - Publication issued
Completion Date
05-Jan-2021
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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
IEC 62975:2021-01(en-fr)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
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

Warning! Make sure that you obtained this publication from an authorized distributor.

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 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

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IEC 62975:2021 © IEC 2021 – 3 –

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

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

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– 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,

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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is

indispensable for the correct application of this publication.

9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of

patent rights. IEC shall not be held responsible for identifying any or all such patent rights.

International Standard IEC 62975 has been prepared by IEC technical committee 10: Fluids

for electrotechnical applications.
The text of this International Standard is based on the following documents:
FDIS Report on voting
10/1123/FDIS 10/1126/RVD

Full information on the voting for the approval of this International Standard can be found in

the report on voting indicated in the above table.

This document has been drafted in accordance with the ISO/IEC Directives, Part 2.

---------------------- Page: 6 ----------------------
IEC 62975:2021 © IEC 2021 – 5 –

The committee has decided that the contents of this document will remain unchanged until the

stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to

the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates

that it contains colours which are considered to be useful for the correct

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colour printer.
---------------------- Page: 7 ----------------------
– 6 – IEC 62975:2021 © IEC 2021
INTRODUCTION

Natural esters are increasingly being used in transformers and electrical equipment employed

in electrical power generation, transmission, distribution and industrial applications.

The use of natural esters is recommended for equipment where the liquid does not remain in

continuous contact with ambient air, such as hermetically sealed units, units with closed

conservators equipped with a rubber bag (bladder) or external expansion elements (external

bag), units with a headspace having either a nitrogen blanket or a confined volume of air

(distribution transformers).

Monitoring and maintaining liquid quality are essential to ensure the reliable operation of

natural ester filled electrical equipment. Codes of practice for this purpose have been

established by electrical power authorities, power companies and industries in many

countries. A review of current experience reveals a wide variation of procedures and criteria.

It is possible, however, to compare the value and significance of standardized liquid tests and

to recommend uniform criteria for the evaluation of test data.

If a certain amount of liquid deterioration (by degradation or contamination) is exceeded,

there is inevitably some erosion of safety margins and the question of the risk of premature

failure should be considered. While the quantification of the risk can be very difficult, a first

step involves the identification of potential effects of increased deterioration. The philosophy

underlying this document is to furnish users with as broad a base of understanding of liquid

quality deterioration as is available, so that they can make informed decisions on inspection

and maintenance practices.

Unused natural ester liquids are sustainable resources and are readily available. Natural

esters are, by most regulations, deemed to be regulated and/or controlled waste. If spills

occur, the user should refer to the regulations applicable to their specific location and

requirements set by their local authorities.

This document, while technically sound, is mainly intended to serve as a common basis for

the preparation of more specific and complete codes of practice by users in the light of local

circumstances. Sound engineering judgement should be exerted in seeking the best
compromise between technical requirements and economic factors.

Application of natural ester liquids in large power transformers at this time is still relatively

limited after 20 years although a very large number of units is operating. While the collection

of operating data has allowed for the development of this document, care should be used

when applying the recommended values. Manufacturers of natural ester liquids should be

contacted with specific questions or concerns.

WARNING – This document does not purport to address all the safety problems associated

with its use. It is the responsibility of the user of this document to establish appropriate health

and safety practices and determine the applicability of regulatory limitations prior to use.

The natural esters which are the subject of this document should be handled in compliance

with local regulations and supplier’s safety datasheets.

This document is applicable to natural esters, chemicals and used sample containers. The

disposal of these items should be carried out according to local regulations regarding their

impact on the environment.
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IEC 62975:2021 © IEC 2021 – 7 –
NATURAL ESTERS – GUIDELINES FOR
MAINTENANCE AND USE IN ELECTRICAL EQUIPMENT
1 Scope

This document provides procedures and guidelines that are intended for the use and

maintenance of natural ester liquid in sealed transformers and other electrical equipment.

This document is applicable to natural esters, originally supplied conforming to IEC 62770

and other applicable standards (e.g. ASTM D6871 [1] ) in transformers, switchgear and

electrical apparatus where liquid sampling is practical and where the normal operating

conditions specified in the equipment specifications apply.

At present, there is a limited amount of information available for electrical equipment other

than transformers.

This document is also intended to assist the power equipment operator to evaluate the

condition of the natural ester and maintain it in a serviceable condition. It also provides a

common basis for the preparation of more specific and complete local codes of practice.

The document includes recommendations on tests and evaluation procedures and outlines

methods for reconditioning and reclaiming the liquid, when necessary.
2 Normative references

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.

IEC 60156, Insulating liquids – Determination of the breakdown voltage at power frequency –

Test method

IEC 60247, Insulating liquids – Measurement of relative permittivity, dielectric dissipation

factor (tan δ) and d.c. resistivity

IEC 60422:2013, Mineral insulating oils in electrical equipment – Supervision and

maintenance guidance
IEC 60475, Method of sampling insulating liquids

IEC 60567, Oil-filled electrical equipment – Sampling of gases and analysis of free and

dissolved gases – Guidance

IEC 60666, Detection and determination of specified additives in mineral insulating oils

IEC 60814, Insulating liquids – Oil-impregnated paper and pressboard – Determination of

water by automatic coulometric Karl Fischer titration
IEC 60970, Insulating liquids – Methods for counting and sizing particles
___________
Numbers in square brackets refer to the bibliography.
---------------------- Page: 9 ----------------------
– 8 – IEC 62975:2021 © IEC 2021

IEC 61125, Insulating liquids – Test methods for oxidation 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: Test methods for non-

mineral insulating oils

IEC 62770, Fluids for electrotechnical applications – Unused natural esters for transformers

and similar electrical equipment

IEC 62961, Insulating liquids – Test methods for the determination of interfacial tension of

insulating liquids – Determination with the ring method
ISO 2049, Petroleum products – Determination of colour (ASTM scale)

ISO 2592, Petroleum products – Determination of flash and fire points – Cleveland open cup

method

ISO 3016, Petroleum and related products from natural or synthetic sources – Determination

of pour point

ISO 3104, Petroleum products – Transparent and opaque liquids – Determination of kinematic

viscosity and calculation of dynamic viscosity

ISO 3675, Crude petroleum and liquid petroleum products -- Laboratory determination of

density – Hydrometer method

ISO 12185, Crude Petroleum and petroleum products – Determination of density – Oscillating

U-tube method

ISO 21018-3, Hydraulic fluid power – Monitoring the level of particulate contamination of the

fluid – Part 3: Use of the filter blockage technique

ASTM D92, Standard Test Method for Flash and Fire Points by Cleveland Open Cup Tester

ASTM D1500, Standard Test Method for ASTM Color of Petroleum Products (ASTM Color

Scale)

ASTM D1544, Standard Test Method for Color of Transparent Liquids (Gardner Color Scale)

ASTM D3455, Standard Test Methods for Compatibility of Construction Material with Electrical

Insulating Oil of Petroleum Origin

ASTM D6922, Standard Test Method for Determination of Homogeneity and Miscibility in

Automotive Engine Oils
ASTM D7042, Standard Test Method for Dynamic Viscosity and Density of Liquids by
Stabinger Viscometer (and the Calculation of Kinematic Viscosity)

ASTM D7155, Standard Practice for Evaluating Compatibility of Mixtures of Turbine

Lubricating Oils

ASTM D7647, Standard Test Method for Automatic Particle Counting of Lubricating and

Hydraulic Fluids Using Dilution Techniques to Eliminate the Contribution of Water and

Interfering Soft Particles by Light Extinction

ASTM D7752, Standard Practice for Evaluating Compatibility of Mixtures of Hydraulic Fluids

---------------------- Page: 10 ----------------------
IEC 62975:2021 © IEC 2021 – 9 –
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following

addresses:
– IEC Electropedia: available at http://www.electropedia.org/
– ISO Online browsing platform: available at http://www.iso.org.obp
NOTE ASTM and IEEE terminology are given in:

– ASTM D2864, Standard Terminology Relating to Electrical Insulating Liquids and Gases [2],

– IEEE C57.12.80, Standard Terminology for Power and Distribution Transformers [3].

3.1
local regulations
regulations pertinent to the particular process in the country concerned

Note 1 to entry: These regulations may be defined by local, regional or national legislation or even by the owner

or operator of the equipment itself. They are always to be considered as the most stringent of any combination

thereof. It is the responsibility of each user of this document to familiarize themselves with the regulations

applicable to their situation. These regulations shall refer to operational, environmental or health and safety issues.

A detailed risk assessment will usually be required.
3.2
routine tests (Group 1)

minimum tests required to monitor the liquid and to ensure that it is suitable for continued

service

Note 1 to entry: If the results obtained from these tests do not exceed recommended action limits, usually no

further tests are considered necessary until the next regular period for inspection but, under certain perceived

conditions, complementary tests may be deemed prudent.
3.3
complementary tests (Group 2)

additional tests, which may be performed to obtain further specific information about the

quality of the natural ester, and may be performed to assist in the evaluation of the natural

ester for continued use in service
3.4
special investigative tests (Group 3)

tests performed mainly to determine the suitability of the natural ester for the type of

equipment in use and to ensure compliance with environmental and operational
considerations
4 Categories of equipment

In order to consider the different user requirements, equipment has been placed in various

categories as shown in Table 1.

For practical and economic reasons, some electrical utilities may decide that their small

transformers up to 1 MVA and 36 kV are not included in this classification. It is possible that

routine monitoring programmes are not considered economical for this type of equipment.

Where a monitoring programme is required for these transformers, the guidelines given for

category C should be adequate.
---------------------- Page: 11 ----------------------
– 10 – IEC 62975:2021 © IEC 2021
Table 1 – Categories of equipment
Category Type of equipment

Category O Power transformers / reactors with a nominal system voltage of 400 kV and above.

Category A Power transformers / reactors with a nominal system voltage above 170 kV and below 400 kV.

Also, power transformers of any ra
...

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