Guidance on the interpretation of carbon dioxide and 2-furfuraldehyde as markers of paper thermal degradation in insulating mineral oil

IEC TR 62874:2015 is a Technical Report which provides guidance for the estimation of consumed thermal life of transformers' cellulosic insulators, through the analysis of some compound dissolved in the insulating mineral oil. A comparison between analytical results of 2-furfural (2-FAL) and carbon oxides and their correspondent typical values estimated for different families of equipment gives information on the estimated thermal degradation of papers.

Guide pour l'interprétation du dioxyde de carbone et du 2-furfuraldéhyde comme marqueurs de la dégradation thermique du papier dans de l'huile minérale isolante

L'IEC TR 62874:2015, qui est un rapport technique, est destiné à estimer la vie thermique consommée de l'isolation cellulosique d'un transformateur, grâce à l'analyse de certains composés dissous dans l'huile minérale isolante. Une comparaison entre les résultats d'analyse de 2-furfural (2-FAL) et d oxyde de carbone et de leurs valeurs types correspondantes estimées pour différentes familles d'équipement donne des informations sur la dégradation thermique estimée des papiers.

General Information

Status
Published
Publication Date
04-May-2015
Current Stage
PPUB - Publication issued
Start Date
05-May-2015
Completion Date
05-May-2015
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IEC TR 62874
Edition 1.0 2015-05
TECHNICAL
REPORT
RAPPORT
TECHNIQUE
Guidance on the interpretation of carbon dioxide and 2-furfuraldehyde as
markers of paper thermal degradation in insulating mineral oil
Guide pour l’interprétation du dioxyde de carbone et du 2-furfuraldéhyde
comme marqueurs de la dégradation thermique du papier dans de l’huile
minérale isolante
IEC TR 62874:2015-05(en-fr)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC TR 62874
Edition 1.0 2015-05
TECHNICAL
REPORT
RAPPORT
TECHNIQUE
Guidance on the interpretation of carbon dioxide and 2-furfuraldehyde as
markers of paper thermal degradation in insulating mineral oil
Guide pour l’interprétation du dioxyde de carbone et du 2-furfuraldéhyde
comme marqueurs de la dégradation thermique du papier dans de l’huile
minérale isolante
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.040.10 ISBN 978-2-8322-3085-5

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 TR 62874:2015 © IEC 2015
CONTENTS

FOREWORD ........................................................................................................................... 4

INTRODUCTION ..................................................................................................................... 6

1 Scope .............................................................................................................................. 7

2 Normative references ...................................................................................................... 7

3 Significance ..................................................................................................................... 8

3.1 General ................................................................................................................... 8

3.2 Thermal and mechanical degradation of paper ........................................................ 8

3.2.1 General ........................................................................................................... 8

3.2.2 Impact of temperature ...................................................................................... 8

3.2.3 Impact of humidity and oxygen ........................................................................ 9

3.3 Symptoms of paper ageing in insulating oil ........................................................... 10

3.3.1 General ......................................................................................................... 10

3.3.2 Volatile by-products ....................................................................................... 11

3.3.3 Soluble by-products ....................................................................................... 11

3.3.4 Insoluble by-products .................................................................................... 11

3.4 Operational parameters influencing paper thermal ageing ..................................... 11

3.5 Role of oil type and condition ................................................................................ 12

3.6 Fault conditions that may affect thermal ageing .................................................... 12

3.7 Maintenance operations that may affect thermal ageing indicators ........................ 13

3.7.1 General ......................................................................................................... 13

3.7.2 Effects of oil reconditioning ............................................................................ 13

3.7.3 Effects of oil reclamation ............................................................................... 13

3.7.4 Effects of oil change ...................................................................................... 13

4 Monitoring protocol ........................................................................................................ 14

4.1 General ................................................................................................................. 14

4.2 Parameters ........................................................................................................... 14

4.2.1 Basic monitoring ............................................................................................ 14

4.2.2 Complementary monitoring ............................................................................ 14

4.3 Recommended testing frequencies ....................................................................... 14

5 Typical values of paper ageing symptoms ...................................................................... 15

5.1 General ................................................................................................................. 15

5.2 Families of equipment ........................................................................................... 15

6 Estimation of paper thermal degradation and ageing rate .............................................. 16

6.1 General approach ................................................................................................. 16

6.2 Practice ................................................................................................................ 16

7 Actions .......................................................................................................................... 17

Annex A (informative) Typical values tables ......................................................................... 19

A.1 General warning ................................................................................................... 19

A.2 2-FAL typical values ............................................................................................. 19

A.2.1 General ......................................................................................................... 19

A.2.2 Family: GSU (generation step-up units) ......................................................... 19

A.2.3 Family: network transmission units ................................................................ 20

A.2.4 Family: large distribution units ....................................................................... 20

A.2.5 Family: industrial distribution units ................................................................. 20

A.2.6 Family: LVDC units ........................................................................................ 21

---------------------- Page: 4 ----------------------
IEC TR 62874:2015 © IEC 2015 – 3 –

A.3 Carbon dioxide typical values................................................................................ 21

A.3.1 General ......................................................................................................... 21

A.3.2 Family: GSU (generation step-up units) ......................................................... 21

A.3.3 Family: network transmission units ................................................................ 21

A.3.4 Family: large distribution units ....................................................................... 22

A.3.5 Family: industrial distribution units ................................................................. 22

A.3.6 Family: LVDC units ........................................................................................ 22

Bibliography .......................................................................................................................... 23

Figure 1 – Schematic diagram showing rate of ageing k, depending on different ageing

mechanisms ............................................................................................................................ 9

Figure 2 – Relationship between mechanical properties of insulating paper and paper

degree of polymerization (DP) [5] .......................................................................................... 10

Figure 3 – Example of flow-chart for the estimation of paper degradation conditions ............ 17

Table A.1 – 2-FAL typical values for GSU transformers, filled with uninhibited mineral

oil (based on a population of 1 860 units) .............................................................................. 19

Table A.2 – 2-FAL typical values for GSU transformers, filled with inhibited mineral oil

(based on a population of 176 units) ..................................................................................... 19

Table A.3 – 2-FAL typical values for network transmission transformers, filled with

uninhibited mineral oil (based on a population of 2 845 units) ............................................... 20

Table A.4 – 2-FAL typical values for large distribution transformers, with open

breathing conservator, filled with uninhibited mineral oil (based on a population of

7 107 units) ........................................................................................................................... 20

Table A.5 – 2-FAL typical values for large distribution transformers, with sealed

conservator, filled with uninhibited mineral oil (based on a population of 288 units) ............. 20

Table A.6 – 2-FAL typical values for industrial distribution transformers, filled with

uninhibited mineral oil (based on a population of 3 885 units) ............................................... 20

Table A.7 – 2-FAL typical values for LVDC transformers, filled with uninhibited mineral

oil (based on a population of 360 units) ................................................................................ 21

Table A.8 – CO typical values for GSU and excitation transformers, filled with

uninhibited mineral oil (based on a population of 1 098 units) ............................................... 21

Table A.9 – CO typical values for network transmission transformers, filled with

uninhibited mineral oil (based on a population of 435 units) .................................................. 21

Table A.10 – CO typical values for large distribution transformers, filled with

uninhibited mineral oil (based on a population of 7 291 units) ............................................... 22

Table A.11 – CO typical values for industrial distribution transformers, filled with

uninhibited mineral oil (based on a population of 4 556 units) ............................................... 22

Table A.12 – CO typical values for LVDC transformers, filled with uninhibited mineral

oil (based on a population of 273 units) ................................................................................ 22

---------------------- Page: 5 ----------------------
– 4 – IEC TR 62874:2015 © IEC 2015
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
GUIDANCE ON THE INTERPRETATION OF CARBON DIOXIDE
AND 2-FURFURALDEHYDE AS MARKERS OF PAPER THERMAL
DEGRADATION IN INSULATING MINERAL OIL
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 organizations.

2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international

consensus of opinion on the relevant subjects since each technical committee has representation from all

interested IEC National Committees.

3) IEC Publications have the form of recommendations for international use and are accepted by IEC National

Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC

Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any

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6) All users should ensure that they have the latest edition of this publication.

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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.

The main task of IEC technical committees is to prepare International Standards. However, a

technical committee may propose the publication of a Technical Report when it has collected

data of a different kind from that which is normally published as an International Standard, for

example "state of the art".

IEC TR 62874, which is a Technical Report, has been prepared by IEC technical committee

10: Fluids for electrotechnical applications.

This bilingual version (2016-01) corresponds to the English version, published in 2015-05.

The text of this Technical Report is based on the following documents:
---------------------- Page: 6 ----------------------
IEC TR 62874:2015 © IEC 2015 – 5 –
Enquiry draft Report on voting
10/903/DTR 10/917A/RVC

Full information on the voting for the approval of this Technical Report can be found in the

report on voting indicated in the above table.
The French version of this Technical Report has note been voted upon.

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

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

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

related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
---------------------- Page: 7 ----------------------
– 6 – IEC TR 62874:2015 © IEC 2015
INTRODUCTION

The cellulosic solid insulation of transformers and other electrical apparatus is subject to

thermal degradation during their operational lifetime. This results in a progressive loss of

paper’s mechanical properties, such as tensile strength, which are related to the duration of

the technical life of the equipment [3,4] .

During its thermal degradation process (also called “ageing” in this Technical Report),

cellulose forms several by-products, some of which may be detected by means of insulating

oil’s chemical analysis [1,2]. The concentration and rate of increase of those by-products can

be used as a tool to estimate the progress of paper thermal degradation in transformers and

other electrical apparata in service.

For this reason, IEC technical committee 10 has prepared this Technical Report for the

monitoring of insulating oil parameters related to cellulose ageing and the interpretation of

results, as a guidance to the thermal degradation evaluation of insulating paper.

This Technical Report is based on the evaluation of cellulose ageing by-products content in

insulating oil, and their rate of formation during the life of the oil-immersed electrical

equipment. Statistical reference values reported in Annex A of this Technical Report are

based on data collected by TC10. The final report of CIGRE WG D1.01.TF13 [7] was taken as

a source of information concerning mechanisms and parameters influencing the formation of

furanic compounds.

NOTE Methods for the estimation of actual degree of polymerization (DP) values of paper, which are widely

available in literature, were not applied within this Technical Report. This is due to the fact that a number of

different models have been developed and reported, and they often lead to different results. Moreover, the

applicability of those models has not been sufficiently proven by comparison with field experience to be included

into an IEC standard.
Health and safety

This Technical Report does not purport to address all the safety problems associated with its

use. It is the responsibility of the user of the Technical Report to establish appropriate health

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

The mineral oils which are the subject of this Technical Report should be handled with due

regard to personal safety and hygiene. Direct contact with eyes may cause slight irritation. In

the case of eye contact, irrigation with copious quantities of clean running water should be

carried out and medical advice sought.

Some of the tests specified in this Technical Report involve the use of processes that could

lead to a hazardous situation. Attention is drawn to the relevant standard for guidance.

Environment

This Technical Report involves mineral oils, chemicals and used sample containers. The

disposal of these items should be carried out in accordance with current national legislation

with regard to the impact on the environment. Every precaution should be taken to prevent the

release into the environment of mineral oil.
___________
Figures in square brackets refer to the Bibliography.
---------------------- Page: 8 ----------------------
IEC TR 62874:2015 © IEC 2015 – 7 –
GUIDANCE ON THE INTERPRETATION OF CARBON DIOXIDE
AND 2-FURFURALDEHYDE AS MARKERS OF PAPER THERMAL
DEGRADATION IN INSULATING MINERAL OIL
1 Scope

IEC TR 62874, which is a Technical Report, provides guidance for the estimation of

consumed thermal life of transformers' cellulosic insulators, through the analysis of some

compound dissolved in the insulating mineral oil. A comparison between analytical results of

2-furfural (2-FAL) and carbon oxides and their correspondent typical values estimated for

different families of equipment gives information on the estimated thermal degradation of

papers.

The ageing rate of insulating papers can be evaluated, in short time ranges (e.g. 1 year), by

regularly monitoring 2-FAL and carbon oxides content in the oil and by comparing them to

typical rates of increase.

A statistical approach for the estimation of paper thermal degradation, and the evaluation of

ageing rate is given.

Typical values for concentrations and rates of increase of the parameters related to paper

ageing were extrapolated from a statistical database collected, and are reported in Annex A.

They may be used as a rough guide, but they should not be considered as threshold values.

This Technical Report is only applicable to transformers and reactors filled with insulating

mineral oils and insulated with Kraft paper. The approaches and procedures specified should

be taken as a practical guidance to investigate the thermal degradation of cellulosic

insulation, and not as an algorithm to calculate the actual degree of polymerization (DP) of

papers.

The paper thermal life evaluation protocol described in this Technical Report applies to

mineral oil impregnated transformers and reactors, insulated with Kraft paper. Any equipment

filled with insulating liquids other than mineral oil (i.e. esters, silicones) or insulated with solid

materials other than Kraft paper (i.e. TUP – thermally upgraded Kraft paper, synthetic

polymers) is outside of the scope of this Technical Report.

This Technical Report is applicable to equipment that has been submitted to a regular

monitoring practice during the service, and for which maintenance and fault history is known.

2 Normative references

The following documents, in whole or in part, are normatively referenced in this document and

are indispensable for its application. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any
amendments) applies.
None.
---------------------- Page: 9 ----------------------
– 8 – IEC TR 62874:2015 © IEC 2015
3 Significance
3.1 General

This Technical Report describes a statistical approach to paper thermal life evaluation. This

means that all typical values are obtained from populations of transformers belonging to the

same family for technical characteristics and application (see Annex A).

The approach used to collect statistical data, described in 6.1, can be applied by utilities or

owners having a large population of units, to calculate individual reference values related to a

specific family of transformers or reactors. This is very important because different population

of transformers (i.e. operating in different climates or under different operational conditions)

may have different typical values.

NOTE For an extensive survey on furanic compounds as markers for diagnosis of paper insulation degradation,

see CIGRE Brochure 494/2012 [7].
3.2 Thermal and mechanical degradation of paper
3.2.1 General

There are main factors: design and materials, contaminants in the insulation system and

operational conditions, that will determine the ageing of a transformer [1,2]. For the solid

insulation – paper and pressboard – it means a combination of mechanical and dielectric

performance, which are interlinked and synergetic. For a transformer, in the context of

thermal ageing, it is the mechanical strength of the paper that matters. The ageing of paper

results in a decreased mechanical strength and is assumed to reduce the ability of the

transformer to withstand short circuit stress. This, however, has not been statistically

demonstrated, yet.

Tensile strength, elongation and folding strength all decay with time, and more quickly at

higher temperatures.

The mechanical performance of cellulosic insulation is given in terms of tensile index or

degree of polymerization (DP), which are strongly influenced by ageing. The DP value is an

average value of chain lengths of the cellulose molecules given as a number of glucose rings

in a cellulose chain. It is measured through measurement of the viscosity of a paper solution,

according to IEC 60450 [8].

It is more convenient to perform DP than tensile index, because of the limited amount of

paper accessible for tests; therefore it is widely used for the evaluation of the cellulosic

ageing status.
There are three main processes of degradation:
– hydrolysis;
– oxidation;
– pyrolysis.
3.2.2 Impact of temperature

Temperature affects the rate of degradation. This fact is reflected in IEC 60076-7 [3] and

IEE
...

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