IEC 62535:2008

IEC 62535
Edition 1.0 2008-10
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Insulating liquids – Test method for detection of potentially corrosive sulphur in
used and unused insulating oil

Liquides isolants – Méthode d’essai pour la détection du soufre potentiellement
corrosif dans les huiles usagées et neuves

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IEC 62535
Edition 1.0 2008-10
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Insulating liquids – Test method for detection of potentially corrosive sulphur in
used and unused insulating oil

Liquides isolants – Méthode d’essai pour la détection du soufre potentiellement
corrosif dans les huiles usagées et neuves

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
P
CODE PRIX
ICS 29.040.10 ISBN 978-2-88910-756-8
– 2 – 62535 © IEC:2008
CONTENTS
FOREWORD.3
INTRODUCTION.5
1 Scope.6
2 Normative references .6
3 Terms and definitions .6
4 Sampling .7
5 Procedure .7
5.1 Principle.7
5.2 Apparatus and materials.7
5.3 Method.8
6 Inspection and interpretation .8
6.1 General .8
6.2 Copper .9
6.3 Paper .9
6.4 Result .9
7 Repeatability and reproducibility.9
8 Report .10
Annex A (informative) Copper strip method to detect corrosive and potentially
corrosive sulphur in oil.11
Annex B (informative) Analysis for copper sulphide on insulating paper by scanning
electron microscope-energy dispersive X-ray spectrometry (SEM/EDX) .14
Bibliography.16

62535 © IEC:2008 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INSULATING LIQUIDS –
TEST METHOD FOR DETECTION OF POTENTIALLY CORROSIVE
SULPHUR IN USED AND UNUSED INSULATING 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,
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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
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Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
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between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
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5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible 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.
International Standard IEC 62535 has been prepared by IEC technical committee 10: Fluids
for electrotechnical applications.
The text of this standard is based on the following documents:
FDIS Report on voting
10/746/FDIS 10/749/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

– 4 – 62535 © IEC:2008
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site 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.
62535 © IEC:2008 – 5 –
INTRODUCTION
In recent years, several failures of transformers and reactors due to copper sulphide
formation in/on the cellulose insulation have been reported worldwide. The tendency of
transformer oils to form copper sulphide in the presence of copper is seen as one of the major
contributing factors.
The most common reason for such failures is arcing between adjacent disks or conductors of
a winding, due to the formation of deposits of copper sulphide on the cellulosic insulating
paper.
It has been demonstrated that existing test methods for corrosive sulphur, ASTM D1275
method A and DIN 51353, are unable to detect oils having potentially corrosive behaviour.
For this reason, IEC technical committee 10 has prepared this International Standard for the
detection of potentially corrosive sulphur in mineral insulating oils. The wrapped conductor
test method is suitable for used and unused mineral oils.
This test method is based on a study performed by Conseil International des Grands Réseaux
Electriques (CIGRE) working group A2.32 [1] .
Health and safety
This International Standard does not purport to address all the safety problems associated
with its use. It is the responsibility of the user of the standard 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 standard should be handled with due regard to
personal 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 standard involve the use of processes that could lead to a
hazardous situation. Attention is drawn to the relevant standard for guidance.
Environment
This standard 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.

– 6 – 62535 © IEC:2008
INSULATING LIQUIDS –
TEST METHOD FOR DETECTION OF POTENTIALLY CORROSIVE
SULPHUR IN USED AND UNUSED INSULATING OIL

1 Scope
This International Standard specifies a test method for detection of potentially corrosive
sulphur in used and unused mineral insulating oil.
Most recent failures due to corrosive sulphur are related to the formation of copper sulphide
deposits in and on the surface of winding cellulosic paper.
The test method uses a copper conductor, wrapped with one layer of paper, immersed in the
oil and heated to evaluate the capability of the oil to yield copper sulphide and transfer it to
paper layers.
The growth of copper sulphide on bare copper may cause the presence of conductive
particulates in the oil, which can act as nuclei for electrical discharge and may lead to a fault.
Other test methods exist using a bare copper strip immersed in oil and heated to detect the
corrosive behaviour of oil against copper. ASTM D1275 Method B is also used for this test
and a modified procedure using low oil volumes is included in Annex A.
Tests with and without paper are considered as complementary and may lead to different
results.
2 Normative references
The following referenced documents are indispensable for the application 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 60475, Method of sampling liquid dielectrics
IEC 60554-3-1, Specification for cellulosic papers for electrical purposes – Part 3:
Specifications for individual materials – Sheet 1: General purpose electrical paper
ASTM D1275, Methods A and B: Standard test method for corrosive sulfur in electrical
insulating oils
ASTM D130, Standard test method for corrosiveness to copper from petroleum products by
copper strip test
DIN 51353, Testing of insulating oils; detection of corrosive sulfur; silver strip test
EN 13601, Copper and copper alloys. Copper rod, bar and wire for general electrical
purposes
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

62535 © IEC:2008 – 7 –
3.1
potentially corrosive sulphur
organo-sulphur compounds present in transformer oils that may cause copper sulphide
formation.
NOTE Some of these compounds may be initially corrosive, or become corrosive under certain operating
conditions
4 Sampling
Samples shall be taken, following the procedure given in IEC 60475. Ensure that the test
portion is representative by thoroughly mixing.
5 Procedure
5.1 Principle
A piece of copper conductor wrapped with Kraft paper is immersed in the oil and subjected to
heating for 72 h at 150 °C in a sealed glass headspace vial.
The copper is examined for indications of discolouration and the paper is examined for the
presence of copper sulphide deposits.
5.2 Apparatus and materials
The following apparatus and materials shall be used:
– Glass headspace vial as used for chromatography, capacity approximately 20 ml, with a
nominal diameter of 22,5 mm to 23 mm.
NOTE 1 Vials are commonly available from suppliers of chromatography consumables and from instrument
manufacturers.
– PTFE-faced silicone septum and aluminium cap for sealing the vial.
– Crimping tool.
– Heating chamber or oven capable of being maintained at 150 °C ± 2 °C.
– Flat, unvarnished, paper-wrapped copper conductor obtained from a transformer
manufacturer or winding supplier. Dimension of the flat copper: approximately 7,5 mm x
1,5 mm (or with a surface area corresponding to these dimensions). Wrapping paper width
10 mm to 14 mm. The most suitable have proven to be flat conductors having four layers
of wrapped paper. The paper adjacent to copper should be wound gap to gap (the gap
+1,00
should be in the tolerance mm, the negative value means overlapping). This is the
−0,2
layer used with the copper conductor for the test itself. The rest of the paper layers have
only a mechanical and protective function during transport and storage.
NOTE 2 Possible sources of supply are :
– Asta Elektrodraht GmbH & Co. (Austria)
– Essex Nexans L+K GmbH, (Germany)
– Siemens AG, Trafowerk Nuremberg (Germany).2

– Kraft paper according to IEC 60554-3-1:
– Density: 0,70 to 0,85 g/cm
– Thickness: 0,060 mm to 0,100 mm
___________
2 This information is given for the convenience of the users of this International Standard and does not constitute
an endorsement by the IEC.
– 8 – 62535 © IEC:2008
– Air permeability M or H
– Conductivity: < 4 mS/m
– Free nitrogen content: 0 %
– Cu-ETP according to EN 13601, (old material code: E-Cu58):
– Material code: CW 004A
– Oxygen content: < 0,04 % (w/w)
– Cu: 99,90 %
– Solvent for rinsing:
– Cyclohexane or heptane, analytical grade.
5.3 Method
Pour 50 ml of oil into a beaker of 100 ml and leave in the open air for 60 min (protected from
sunlight).
Transfer 15 ml of this oil into the headspace vial. The precision given by a measuring cylinder
is adequate, as is use of a headspace vial pre-marked at 15 ml.
Cut the conductor in 30 mm ± 3 mm lengths. Unwrap the outer layers of the copper conductor
and leave only one layer in contact with the copper. Do not touch paper or copper with fingers
during this and subsequent operations and ensure that all tools are pre-cleaned with solvent.
Place the wrapped flat conductor inside the headspace vial and close it with the septum
(PTFE face towards the oil) and close the cap using a crimping tool. The crimped cap should
be sufficiently tight such that hand rotating of the cap on the vial is not possible.
NOTE It is essential that, if a butyl rubber septum is used, the PTFE face seals correctly to the glass vial. The hot
oil must have no access to the butyl rubber, which contains sulphur.
Place in a heating chamber for 72 h ± 30 min at 150 °C ± 2 °C.
After the vial has cooled, remove the cap and take out the wrapped conductor. Tweezers
should always used to handle the conductor and the paper.
Unwrap the paper for evaluation of the copper surface.
Rinse the copper conductor with cyclohexane or heptane, and allow to dry for 2 min in air.
Prior to evaluation, degrease the paper by immersion in 50 ml of solvent in a beaker for 1 min.
Repeat the degreasing twice in fresh solvent and allow the paper to dry for at least 5 min until
all solvent is evaporated.
Carry out the test in duplicate.
Carry out a blank test, in order to ensure that all materials used are sulphur free. The blank
test should be carried out with a white oil or other oil containing less than 5 mg/kg sulphur.
Such a test will also assist in detecting changes to the copper.
6 Inspection and interpretation
6.1 General
All inspections should be carried out under very good light conditions. Bright daylight or
strong fluorescent lighting has been proven to be satisfactory. It is important to view objects
with light from different angles.

62535 © IEC:2008 – 9 –
Both the copper and the paper shall be inspected for signs of sulphide formation. The results
from the duplicate tests must show the same discolouration.
6.2 Copper
Examine all surfaces of the copper for discolouration and note the appearance and colour.
The result is positive if the copper strip has one of the following colours: graphite grey, dark
brown or black. All other colours are considered a negative result.
6.3 Paper
Examine both the inside and outside surfaces of the paper strip. A magnifying glass (approx.
5 × magnification) can be helpful.
Copper sulphide deposition on the paper appears metallic, from clearly shiny to almost
lustreless, often with a lead- or tin-like appearance. It can also have the appearance of silver,
brass or bronze. The metal-like surface of sulphide can have an overlay of blue and/or purple
due to interference phenomena. Other discolourations (i.e. by-products of paper ageing and
oil deterioration) shall not to be taken as copper sulphide formation.
Copper sulphide may be formed both on the outside as well as the inside of the paper. Even
though sulphide may be formed anywhere, particular attention should be paid to edges and
inside bends. Note that deposits localized at some edges may come from copper
mechanically transferred to the paper while cutting the conductor. Sometimes the paper
surface is smoothed at the edges by the cutting tool. If any shiny appearance of the paper is
limited to such edges, it shall not be considered a positive result unless confirmed to be
sulphide.
Although copper sulphide formation is often clearly evident even when the paper is
discoloured, it may possibly be obscured by strong discoloration. SEM-EDX, or alternative
methods to determine total copper and sulphur content of the paper may be used to assist the
interpretation. An example of a method using SEM-EDX to evaluate the presence of copper
sulphide deposits on paper is described in Annex B.
In case of doubt concerning the composition of the precipitate, the result cannot be
considered as corrosive unless the precipitate is positively identified as copper sulphide.
X-ray diffraction or determination of copper and sulphur content of the paper may also give
guidance. It is also highly recommended in those cases to analyse for both copper and
sulphur on paper from an unused test specimen.
6.4 Result
If, for both of the duplicate samples, a positive result is found for copper, or paper, or both,
the oil shall be reported as potentially corrosive. If, for both samples, a negative result is
obtained for both copper and paper, the oil shall be reported as non-corrosive.
If the results for the duplicate sample are different, the test shall be repeated.
NOTE If there are any doubts in the interpretation of the results of inspection of paper, the composition of
precipitate should be analysed by other methods (for example by SEM-EDX). If the precipitate is identified as
copper sulphide, the oil must be reported as potentially corrosive.
7 Repeatability and reproducibility
Repeatability: according to inter-laboratory tests carried out by CIGRE WG A2.32, duplicate
results had 100 % agreement.
– 10 – 62535 © IEC:2008
Reproducibility: according to inter-laboratory tests carried out by CIGRE WG A2.32, 2
laboratories out of 16 had different results. In these cases the oils differed from the original
delivered batches.
8 Report
The test report shall contain at least the following information:
• testing laboratory;
• the type and identification of the product tested;
• a reference to this International Standard;
• the result of the test (see 6.4);
• any deviation, by agreement or otherwise, from the procedure specified;
• the date of the test.
62535 © IEC:2008 – 11 –
Annex A
(informative)
Copper strip method to detect corrosive and
potentially corrosive sulphur in oil

A.0 Introduction
This procedure describes a downsized corrosion test for which only a 15 ml oil sample is
needed, based on ASTM D1275 method B.
A.1 Principle
A cleaned strip of copper is immersed in a degassed portion of oil under investigation and
subjected to heating for 48 h at 150 °C in a sealed container.
The test is carried out by immersing the copper strip in 15 ml of oil into a sealed glass
headspace vial, under the same heating regime as in method B of ASTM D1275. The copper
is examined for indications of corrosion and interpretation of the results is the same as for
method B of that standard.
A.2 Reagents, apparatus and materials
A.2.1 Reagents
Acetone, analytical grade, sulphur-free.
Nitrogen gas or argon gas, oxygen free.
A.2.2 Apparatus and materials
The following apparatus and materials shall be used.
Bath
Heating chamber or oven capable of being maintained at 150 °C ± 2 °C.
Copper foil
>99,9 % pure, and 0,127 mm to 0,254 mm in thickness.
Polishing material
240-grit silicon carbide paper or cloth, and also 230-mesh silicon carbide grains and
pharmaceutical absorbent cotton.
Copper strips
Cut a strip of copper foil 6 mm by 25 mm and remove blemishes from surfaces with the 240-
grit silicon carbide paper. Strips may be stored in acetone at this point for future use.
Carry out final polishing of the strip by removing it from the acetone, holding it in the fingers
protected with ashless filter paper or nitrile gloves, and rubbing with 230-mesh silicon carbide
grains picked up from a glass plate with a pad of absorbent cotton moistened with a drop of
acetone. Wipe the strip with fresh pads of cotton and subsequently handle only with stainless

– 12 – 62535 © IEC:2008
steel forceps (do not touch with the fingers). Rub in the direction of the long axis of the strip.
Clean all metal dust and abrasive from the strip, using successive clean cotton pads until a
fresh pad remains unsoiled.
Bend the clean strip in a V-shape at approximately a 30° angle and wash successively in
acetone, distilled water, and again in acetone. Dry in an oven for 3 min to 5 min at a
temperature of betweeen 80 °C and 100 °C and immediately immerse the copper strip in the
prepared test specimen of oil.
Do not use compressed air or an inert gas to dry the copper strip.
Glass headspace vial
A 20 ml glass headspace vial (as used for chromatography), with a nominal diameter of
22,5 mm or 23 mm and a height of 75,5 mm, fitted with a crimp cap and a butyl rubber/PTFE
septum.
NOTE 1 Vials are commonly available from suppliers of chromatography consumables and from instrument
manufacturers.
NOTE 2 A butyl rubber septum with a PTFE layer facing the oil is preferred since it ensures a better seal to
prevent ingress of oxygen. Although it contains corrosive sulphur, it has not been found to interfere with this test.
A.3 Procedure
A.3.1 General
Tests should be run in duplicate.
Carry out a blank test in order to ensure that materials have no influence on the test. The
blank test should be carried out with a white oil or other oil containing less than 5 mg/kg
sulphur.
A.3.2 Sample preparation
Place the bent copper strip into a headspace vial. Bubble nitrogen or argon through the oil in
the vial, by means of a glass tube connected to a reduction or needle valve of gas supply
(rubber tubes connection must be sulphur free) for 10 min. Take about 20 ml of this oxygen
free oil in a glass gas-tight syringe using stainless steel needle.
NOTE 1 Syringes described in IEC 60567[2] for DGA sampling are suitable.
Using a glove box or other suitable apparatus with an inert atmosphere (nitrogen or argon),
add 15 ml ± 0,1 ml of oil to the vial. Seal with a butyl rubber septum and a cap, using a
crimping tool. The crimp cap should be sufficiently tight that hand rotating of the cap on the
vial is not possible.
NOTE 2 The revolving table, described in IEC 60567, is suitable for sample preparation under inert gas.
A.3.3 Analysis
Place the crimped vial in an oven set at 150 °C.
Remove the vial after heating for 48 h ± 30 min at 150 °C ± 2 °C and allow to cool.
Using clean tweezers, take the copper strip from the vial and wash with acetone or other
suitable solvent to remove all of the oil and allow it to air dry. Do not use pressurized air to
dry the copper strip.
62535 © IEC:2008 – 13 –
NOTE If the oil visibly darkens during testing then most likely oxygen has entered the vial and oxidized the oil. In
this case, the test procedure is compromised and must be repeated.
A.4 Interpretation of results
Classification of corrosive or non-corrosive shall be made using ASTM copper strip corrosion
standards as referred to in test method ASTM D130.
To inspect, hold the test strip in such a manner that light reflected from it at an angle of
approximately 45° will be observed.
If the results for the duplicate samples are different, the test shall be repeated. Classify the oil
as corrosive if the strip classification is ≥ 4a.
A.5 Report
The test report shall contain at least the following information:
• testing laboratory;
• the type and identification of the product tested;
• a reference to this International Standard and to the method used;
• the result of the test (see A.4) as: Corrosive or Non corrosive;
• tarnish level according to test method ASTM D130;
• any deviation, by agreement or otherwise, from this procedure;
• the date of the test.
– 14 – 62535 © IEC:2008
Annex B
(informative)
Analysis for copper sulphide on insulating paper by
scanning electron microscope-energy dispersive
X-ray spectrometry (SEM/EDX)
B.1 Field of application
This method gives guidance to analyse deposits on insulating papers following tests for
potentially corrosive sulphur.
Due to different test equipment, these guidelines may need to be adapted for individual
equipment.
B.2 Principle
A paper is analysed by SEM-EDX. If copper sulphide is present in a significant amount it is
easily detected.
B.3 Apparatus and materials (examples)
An example of parameters used in a typical, commercially available SEM-EDX instrument is:
• Working distance (WD) = 19 mm
• Variable pressure mode, chamber pressure at 30 Pa
• 20 kV accelerating voltage
• 1 nA probe current
• Standard element cobalt
• Backscattered electron detector
Other equipment may have different settings according to manufacturer’s recommendations.
The correction method used for calculation of the percentage of atoms may also influence
what choice of settings shall be used.
32 mm aluminium stubs.
Double-sided conducting adhesive pad.
B.4 Sampling
Samples are made up from the papers obtained after performing the “wrapped-conductor
corrosion test”, and prepared for visual inspection as described in 6.3.
B.5 Procedure
Fix the paper with a double-sided conducting adhesive pad on a stub. The parameters of the
SEM-EDX are set using manufacturer’s recommendations as described in B.3.

62535 © IEC:2008 – 15 –
To control the apparatus, run a standard element (usually cobalt) under a stable beam in the
conditions in which the analysis is to be carried out.
Move the paper to find bright deposits on it, in backscattered detector mode. The paper areas
overhanging the stubs are not analysed. Zoom in on some of these deposits and analyse
them. After analysis of at least 3 and a maximum of 5 of the deposits, finalise the analysis.
If the result is not clear enough, analyse further deposits until confidence is achieved. This
may differ form paper to paper and is related to the number and kind of deposits.
It is strongly recommended to analyse reference materials, including unused papers and
papers tested with oil types that failed in the field. A reference can be prepared by rubbing
some Cu S into the same kind of paper as used in the test.
B.6 Interpretation and report of results
With SEM-EDX, the presence of significant amounts of copper sulphide should give clearly
visible x-ray fluorescence signals of copper and sulphur (e.g. at 0,94 keV and 2,3 keV,
respectively) in a ratio of 1,5:1 to 2,5:1 together with a minimum of 2 atom % sulphur and
4 atom % copper. The atomic percentage is usually calculated by the software of the SEM-
EDX.
Even on unused paper, traces of sulphur and some copper is detectable; for this reason a
minimum atomic percentage of sulphur and copper is required. Determination of atomic
percentage is influenced by various parameters, such as correction method, analysis depth,
etc.
– 16 – 62535 © IEC:2008
Bibliography
[1] CIGRE Progress report WG A2.32:2006, Copper sulphide in transformer insulation (only
available in English)
[2] IEC 60567, Oil filled electrical equipment – Sampling of gases and of oil for analysis of
free and dissolved gases – Guidance

___________
– 18 – 62535 © CEI:2008
SOMMAIRE
AVANT-PROPOS.19
INTRODUCTION.21
1 Domaine d'application .22
2 Références normatives.22
3 Termes et définitions .23
4 Échantillonnage.23
5 Mode opératoire .23
5.1 Principe.23
5.2 Appareillage et matériaux.23
5.3 Méthode .24
6 Examen et interprétation .25
6.1 Généralités.25
6.2 Cuivre .25
6.3 Papier .25
6.4 Résultats.26
7 Répétabilité et reproductibilité .26
8 Rapport .26
Annexe A (informative) Méthode de la bande de cuivre pour détecter le soufre corrosif
et potentiellement corrosif dans l'huile .27
Annexe B (informative) Analyse du sulfure de cuivre sur du papier isolant par
microscope à balayage électronique-spectrométrie X à dispersion d’énergie
(SEM/EDX) .30
Bibliographie.32

62535 © CEI:2008 – 19 –
COMMISSION ÉLECTROTECHNIQUE INTERNATIONALE
____________
LIQUIDES ISOLANTS –
MÉTHODE D’ESSAI POUR LA DÉTECTION DU SOUFRE
POTENTIELLEMENT CORROSIF DANS LES HUILES
USAGÉES ET NEUVES
AVANT-PROPOS
1) La Commission Electrotechnique Internationale (CEI) est une organisation mondiale de normalisation
composée de l'ensemble des comités électrotechniques nationaux (Comités nationaux de la CEI). La CEI a
pour objet de favoriser la coopération internationale pour toutes les questions de normalisation dans les
domaines de l'électricité et de l'électronique. A cet effet, la CEI – entre autres activités – publie des Normes
internationales, des Spécifications techniques, des Rapports techniques, des Spécifications accessibles au
public (PAS) et des Guides (ci-après dénommés "Publication(s) de la CEI"). Leur élaboration est confiée à des
comités d'études, aux travaux desquels tout Comité national intéressé par le sujet traité peut participer. Les
organisations internationales, gouvernementales et non gouvernementales, en liaison avec la CEI, participent
également aux travaux. La CEI collabore étroitement avec l'Organisation Internationale de Normalisation (ISO),
selon des conditions fixées par accord entre les deux organisations.
2) Les décisions ou accords officiels de la CEI concernant les questions techniques représentent, dans la mesure
du possible, un accord international sur les sujets étudiés, étant donné que les Comités nationaux de la CEI
intéressés sont représentés dans chaque comité d’études.
3) Les Publications de la CEI se présentent sous la forme de recommandations internationales et sont agréées
comme telles par les Comités nationaux de la CEI. Tous les efforts raisonnables sont entrepris afin que la CEI
s'assure de l'exactitude du contenu technique de ses publications; la CEI ne peut pas être tenue responsable
de l'éventuelle mauvaise utilisation ou interprétation qui en est faite par un quelconque utilisateur final.
4) Dans le but d'encourager l'uniformité internationale, les Comités nationaux de la CEI s'engagent, dans toute la
mesure possible, à appliquer de façon transparente les Publications de la CEI dans leurs publications
nationales et régionales. Toutes divergences entre toutes Publications de la CEI et toutes publications
nationales ou régionales correspondantes doivent être indiquées en termes clairs dans ces dernières.
5) La CEI n’a prévu aucune procédure de marquage valant indication d’approbation et n'engage pas sa
responsabilité pour les équipements déclarés conformes à une de ses Publications.
6) Tous les utilisateurs doivent s'assurer qu'ils sont en possession de la dernière édition de cette publication.
7) Aucune responsabilité ne doit être imputée à la CEI, à ses administrateurs, employés, auxiliaires ou
mandataires, y compris ses experts particuliers et les membres de ses comités d'études et des Comités
nationaux de la CEI, pour tout préjudice causé en cas de dommages corporels et matériels, ou de tout autre
dommage de quelque nature que ce soit, directe ou indirecte, ou pour supporter les coûts (y compris les frais
de justice) et les dépenses découlant de la publication ou de l'utilisation de cette Publication de la CEI ou de
toute autre Publication de la CEI, ou au crédit qui lui est accordé.
8) L'attention est attirée sur les références normatives citées dans cette publication. L'utilisation de publications
référencées est obligatoire pour une application correcte de la présente publication.
9) L’attention est attirée sur le fait que certains des éléments de la présente Publication de la CEI peuvent faire
l’objet de droits de propriété intellectuelle ou de droits analogues. La CEI ne saurait être tenue pour
responsable de ne pas avoir identifié de tels droits de propriété et de ne pas avoir signalé leur existence.
La Norme internationale CEI 62535 a été établie par le comité d'études 10 de la CEI: Fluides
pour applications électrotechniques.
Le texte de cette norme est issu des documents suivants:
FDIS Rapport de vote
10/746/FDIS 10/749/RVD
Le rapport de vote indiqué dans le tableau ci-dessus donne toute information sur le vote ayant
abouti à l'approbation de cette norme.
Cette publication a été rédigée selon les Directives ISO/CEI, Partie 2.

– 20 – 62535 © CEI:2008
Le comité a décidé que le contenu de cette publication ne sera pas modifié avant la date de
maintenance indiquée sur le site web de la CEI sous «http://webstore.iec.ch» dans les
données relatives à la publication recherchée. A cette date, la publication sera
• reconduite ;
• supprimée ;
• remplacée par une édition révisée ; ou
• amendée.
62535 © CEI:2008 – 21 –
INTRODUCTION
Au cours de ces dernières années, plusieurs défaillances de transformateurs et de bobines
d’inductance ont été signalées à travers le monde, en raison de la formation de sulfure de
cuivre dans/sur l’isolation en cellulose. La tendance des huiles de transformateur à la
formation de sulfure de cuivre en présence de cuivre est perçue comme un des facteurs
majeurs en cause.
La raison la plus courante de telles défaillances est l’apparition d’un arc (électrique) entre les
disques ou les conducteurs adjacents d'un enroulement en raison de la formation de dépôts
de sulfure de cuivre sur le papier isolant cellulosique.
Il a été démontré que les méthodes d’essai existantes relatives au soufre corrosif, ASTM
D1275 méthode A et DIN 51353, sont incapables de détecter des huiles dont le comportement
est potentiellement corrosif.
C’est pourquoi, le comité d’études 10 de la CEI a élaboré la présente Norme internationale
relative à la détection du soufre potentiellement corrosif dans les huiles minérales isolantes.
La méthode d'essai du conducteur guipé convient pour les huiles minérales usagées et
neuves.
Cette méthode d’essai est fondée sur une étude réalisée par le groupe de travail A2.32 du
Conseil International des Grands Réseaux Electriques (CIGRE) [1] .
Santé et sécurité
La présente Norme internationale n’est pas censée aborder tous les problèmes de sécurité
associés à son utilisation. Il incombe à l’utilisateur de la norme d’établir les pratiques
sanitaires et de sécurité appropriées et de déterminer l’applicabilité des limites
réglementaires avant utilisation.
Il est recommandé de manipuler les huiles minérales qui font l’objet de la présente norme
d
...