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

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