Mineral oil-filled electrical equipment - Application of dissolved gas analysis (DGA) to factory tests on electrical equipment

IEC 61181:2007+A1:2012 Specifies oil-sampling procedures, analysis requirements and procedures, and recommends sensitivity, repeatability and accuracy criteria for the application of dissolved gas analysis (DGA) to factory testing of new power transformers, reactors and instrument transformers filled with mineral insulating oil when DGA testing has been specified. The most effective and useful application of DGA techniques to factory testing is during the performance of long-term tests, typically temperature-rise (heat run) and overloading tests on power transformers and reactors, also impulse tests on instrument transformers. DGA may also be valuable for over-excitation tests run over an extended period of time. Experience with DGA results, before and after short-time dielectric tests, indicates that DGA is normally less sensitive than electrical and acoustic methods for detecting partial discharges. However, DGA will indicate when these partial discharges become harmful to the insulation and may be detected by inspection [2]. This edition includes the following significant technical changes with respect to the previous edition:
a) the specific procedures used during factory tests (sampling location, sampling frequency, gas extraction and chromatographic analysis in the laboratory) are described in more detail;
b) information is provided in Annex A concerning the residual gas contents recommended before thermal tests on power transformers, typical gas values observed during the tests and cases where gas formation during the tests was followed by problems in the transformers;
c) typical values observed during chopped lightning-impulse tests on instrument transformers are indicated in Annex B. This consolidated version consists of the second edition (2007) and its amendment 1 (2012). Therefore, no need to order amendment in addition to this publication.

Matériels électriques imprégnés d'huile minérale - Application de l'analyse des gaz dissous (AGD) lors d'essais en usine de matériels électriques

La CEI 61181:2007+A1:2012 Spécifie les modes opératoires d'échantillonnage des huiles, les exigences analytiques et les procédures, et recommande les critères de sensibilité, de répétabilité et de précision pour l'application de l'analyse des gaz dissous (AGD) aux essais en usine des transformateurs de puissance neufs, des bobines d'inductance et des transformateurs de mesure, dans le cas où le cahier des charges prévoit des essais d'analyse des gaz dissous (AGD). L'application des techniques d'AGD la plus utile et la plus efficace, au cours des essais en usine, est celle pratiquée pendant les essais de fonctionnement de longue durée, particulièrement les essais de surcharge et d'échauffement des transformateurs de puissance et des bobines d'inductance, ainsi que les essais au choc de foudre sur les transformateurs de mesure. L'analyse des gaz dissous peut être aussi valable pour les essais de surexcitation effectués pendant une période de temps prolongée. L'expérience acquise avec les résultats de l'AGD, avant et après les essais diélectriques de courte durée, montre que, l'analyse des gaz dissous, est moins sensible que les méthodes électriques et acoustiques pour la détection des décharges partielles. Cependant, l'AGD indiquera quand ces décharges deviennent dangereuses pour l'isolation et peuvent être détectées par inspection [2]. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
a) les procédures spécifiques utilisées pendant les essais en usine (points et fréquence d'échantillonnage, extraction des gaz et analyse chromatographique en laboratoire) sont décrites avec plus de détails;
b) l'Annexe A fournit des informations sur les teneurs en gaz résiduelles qui sont recommandées avant les essais thermiques sur les transformateurs de puissance, sur les valeurs typiques de gaz observées pendant les essais, et sur les cas où la formation de gaz pendant les essais a été suivie de problèmes dans les transformateurs;
c) l'Annexe B indique les valeurs typiques observées pendant les essais en choc de foudre coupé sur les transformateurs de mesure.  Cette version consolidée comprend la deuxième édition (2007) et son amendement 1 (2012). Il n'est donc pas nécessaire de commander l'amendement avec cette publication.

General Information

Status
Published
Publication Date
25-Mar-2012
Current Stage
PPUB - Publication issued
Start Date
26-Mar-2012
Completion Date
26-Mar-2012
Ref Project

Buy Standard

Standard
IEC 61181:2007+AMD1:2012 CSV - Mineral oil-filled electrical equipment - Application of dissolved gas analysis (DGA) to factory tests on electrical equipment
English and French language
29 pages
sale 15% off
Preview
sale 15% off
Preview

Standards Content (sample)

IEC 61181
Edition 2.1 2012-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Mineral oil-filled electrical equipment – Application of dissolved gas analysis
(DGA) to factory tests on electrical equipment
Matériels électriques imprégnés d’huile minérale – Application de l’analyse des
gaz dissous (AGD) lors d’essais en usine de matériels électriques
IEC 61181:2007+A1:2012
---------------------- Page: 1 ----------------------
THIS PUBLICATION IS COPYRIGHT PROTECTED
Copyright © 2012 IEC, Geneva, Switzerland

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form

or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from

either IEC or IEC's member National Committee in the country of the requester.

If you have any questions about IEC copyright or have an enquiry about obtaining additional rights to this publication,

please contact the address below or your local IEC member National Committee for further information.

Droits de reproduction réservés. Sauf indication contraire, aucune partie de cette publication ne peut être reproduite ni

utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie et les

microfilms, sans l'accord écrit de la CEI ou du Comité national de la CEI du pays du demandeur.

Si vous avez des questions sur le copyright de la CEI ou si vous désirez obtenir des droits supplémentaires sur cette

publication, utilisez les coordonnées ci-après ou contactez le Comité national de la CEI de votre pays de résidence.

IEC Central Office Tel.: +41 22 919 02 11
3, rue de Varembé Fax: +41 22 919 03 00
CH-1211 Geneva 20 info@iec.ch
Switzerland www.iec.ch
About the IEC

The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes

International Standards for all electrical, electronic and related technologies.
About IEC publications

The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the

latest edition, a corrigenda or an amendment might have been published.
Useful links:

IEC publications search - www.iec.ch/searchpub Electropedia - www.electropedia.org

The advanced search enables you to find IEC publications The world's leading online dictionary of electronic and

by a variety of criteria (reference number, text, technical electrical terms containing more than 30 000 terms and

committee,…). definitions in English and French, with equivalent terms in

It also gives information on projects, replaced and additional languages. Also known as the International

withdrawn publications. Electrotechnical Vocabulary (IEV) on-line.

IEC Just Published - webstore.iec.ch/justpublished Customer Service Centre - webstore.iec.ch/csc

Stay up to date on all new IEC publications. Just Published If you wish to give us your feedback on this publication

details all new publications released. Available on-line and or need further assistance, please contact the

also once a month by email. Customer Service Centre: csc@iec.ch.
A propos de la CEI

La Commission Electrotechnique Internationale (CEI) est la première organisation mondiale qui élabore et publie des

Normes internationales pour tout ce qui a trait à l'électricité, à l'électronique et aux technologies apparentées.

A propos des publications CEI

Le contenu technique des publications de la CEI est constamment revu. Veuillez vous assurer que vous possédez

l’édition la plus récente, un corrigendum ou amendement peut avoir été publié.
Liens utiles:

Recherche de publications CEI - www.iec.ch/searchpub Electropedia - www.electropedia.org

La recherche avancée vous permet de trouver des Le premier dictionnaire en ligne au monde de termes

publications CEI en utilisant différents critères (numéro de électroniques et électriques. Il contient plus de 30 000

référence, texte, comité d’études,…). termes et définitions en anglais et en français, ainsi que

Elle donne aussi des informations sur les projets et les les termes équivalents dans les langues additionnelles.

publications remplacées ou retirées. Egalement appelé Vocabulaire Electrotechnique

International (VEI) en ligne.
Just Published CEI - webstore.iec.ch/justpublished
Service Clients - webstore.iec.ch/csc
Restez informé sur les nouvelles publications de la CEI.

Just Published détaille les nouvelles publications parues. Si vous désirez nous donner des commentaires sur

Disponible en ligne et aussi une fois par mois par email. cette publication ou si vous avez des questions

contactez-nous: csc@iec.ch.
---------------------- Page: 2 ----------------------
IEC 61181
Edition 2.1 2012-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Mineral oil-filled electrical equipment – Application of dissolved gas analysis
(DGA) to factory tests on electrical equipment
Matériels électriques imprégnés d’huile minérale – Application de l’analyse des
gaz dissous (AGD) lors d’essais en usine de matériels électriques
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX
ICS 29.040 ISBN 978-2-8322-0051-3

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 – 61181  IEC:2007+A1:2012
CONTENTS

FOREWORD ........................................................................................................................... 3

INTRODUCTION ..................................................................................................................... 5

1 Scope ............................................................................................................................... 6

2 Normative references ....................................................................................................... 6

3 General caution, health, safety and environmental protection ........................................... 6

4 Oil sampling ..................................................................................................................... 7

4.1 General ................................................................................................................... 7

4.2 Sample containers ................................................................................................... 7

4.3 Sampling location .................................................................................................... 7

4.4 Sampling frequency ................................................................................................. 7

4.5 Sample labelling ...................................................................................................... 8

4.6 Sample storage ....................................................................................................... 8

4.7 Disposal of waste oil ............................................................................................... 8

5 Factors affecting gassing rate during thermal tests ........................................................... 8

6 Dissolved gas extraction and analysis .............................................................................. 9

7 Report ............................................................................................................................ 10

Annex A (informative) Gas formation rates during thermal tests on power transformers ....... 11

Annex B (informative) Gas formation rates during chopped-lightning impulse tests on

instrument transformers [6] ................................................................................................... 13

Bibliography .......................................................................................................................... 14

Table 1 – Required detection limits for factory tests ................................................................ 9

Table A.1 – Ranges of 90 % typical rates of gas formation in modern, mineral oil- filled

power transformers during thermal tests, in µl/l/h .................................................................. 11

Table A.2 – Survey of cases followed by problems in core-type, mineral oil- filled

power transformers, for various rates of gas formation observed during the thermal

tests, (values in µl/l/h)........................................................................................................... 12

Table B.1 – 90 % typical gas concentration increases observed between the beginning

and the end of chopped lightning-impulse tests on instrument transformers .......................... 13

---------------------- Page: 4 ----------------------
61181  IEC:2007+A1:2012 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MINERAL OIL-FILLED ELECTRICAL EQUIPMENT –
APPLICATION OF DISSOLVED GAS ANALYSIS (DGA)
TO FACTORY TESTS ON 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 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

misinterpretation by any end user.

4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications

transparently to the maximum extent possible in their national and regional publications. Any divergence

between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in

the latter.

5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity

assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any

services carried out by independent certification bodies.

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

7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and

members of its technical committees and IEC National Committees for any personal injury, property damage or

other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and

expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC

Publications.

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.

This consolidated version of IEC 61181 consists of the second edition (2007)
[documents 10/675/FDIS and 10/688/RVD] and its amendment 1 (2012) [documents
10/881/FDIS and 10/886/RVD]. It bears the edition number 2.1.

The technical content is therefore identical to the base edition and its amendment and

has been prepared for user convenience. A vertical line in the margin shows where the

base publication has been modified by amendment 1. Additions and deletions are
displayed in red, with deletions being struck through.
---------------------- Page: 5 ----------------------
– 4 – 61181  IEC:2007+A1:2012

International Standard IEC 61181 has been prepared by IEC technical committee 10: Fluids

for electrotechnical applications.

This edition includes the following significant technical changes with respect to the previous

edition:

a) the specific procedures used during factory tests (sampling location, sampling frequency,

gas extraction and chromatographic analysis in the laboratory) are described in more

detail;

b) information is provided in Annex A concerning the residual gas contents recommended

before thermal tests on power transformers, typical gas values observed during the tests

and cases where gas formation during the tests was followed by problems in the
transformers;

c) typical values observed during chopped lightning-impulse tests on instrument transformers

are indicated in Annex B.

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

The committee has decided that the contents of the base publication and its amendments will

remain unchanged until the stability 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.

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 understanding

of its contents. Users should therefore print this publication using a colour printer.

---------------------- Page: 6 ----------------------
61181  IEC:2007+A1:2012 – 5 –
INTRODUCTION

IEC technical committee 10, responsible for IEC 61181, has prepared guidelines for

performing DGA measurements during factory testing on equipment filled with mineral

insulating oil in order to ensure consistency in the industry and improve the confidence with

which the results will be used.

DGA is used routinely as a standard quality control procedure during and after factory tests

on electrical equipment, for example during temperature-rise and chopped lightning-impulse

tests, to indicate that a design meets specified requirements. Due to the small quantities of

gases generated during factory tests, specific requirements are necessary for the sampling

and analysis of oil samples and the interpretation of results.

Acceptance criteria are beyond the scope of TC 10. Attention is drawn, however, to the fact

do not apply any more to transformers
that the guidelines issued by CIGRE in 1993-1995 [1]

manufactured today, the design of which having been improved. Examples of values actually

observed today are indicated in Annexes A and B.
———————
Figures in square brackets refer to the bibliography.
---------------------- Page: 7 ----------------------
– 6 – 61181  IEC:2007+A1:2012
MINERAL OIL-FILLED ELECTRICAL EQUIPMENT –
APPLICATION OF DISSOLVED GAS ANALYSIS (DGA)
TO FACTORY TESTS ON ELECTRICAL EQUIPMENT
1 Scope

This International Standard specifies oil-sampling procedures, analysis requirements and

procedures, and recommends sensitivity, repeatability and accuracy criteria for the application

of dissolved gas analysis (DGA) to factory testing of new power transformers, reactors and

instrument transformers filled with mineral insulating oil when DGA testing has been specified.

The most effective and useful application of DGA techniques to factory testing is during the

performance of long-term tests, typically temperature-rise (heat run) and overloading tests on

power transformers and reactors, also impulse tests on instrument transformers. DGA may

also be valuable for over-excitation tests run over an extended period of time.

Experience with DGA results, before and after short-time dielectric tests, indicates that DGA

is normally less sensitive than electrical and acoustic methods for detecting partial

discharges. However, DGA will indicate when these partial discharges become harmful to the

insulation and may be detected by inspection [2].
2 Normative references

The following referenced document is 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 60567: Guide for the sampling of gases and of oil from oil-filled electrical equipment and

for the analysis of free and dissolved gases
IEC 60475:2011, Method of sampling insulating liquids

IEC 60567:2011, Oil-filled electrical equipment – Sampling of gases and analysis of free and

dissolved gases – Guidance
3 General caution, health, safety and environmental protection

This 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 insulating oils which are the subject of this standard should be handled with due

regard to personal hygiene. Direct contact with the eyes may cause 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.

This standard is applicable to mineral insulating oils and used sample containers, the disposal

or decontamination of which must be done according to local regulations. Every precaution

should be taken to prevent release of mineral oil into the environment.
---------------------- Page: 8 ----------------------
61181  IEC:2007+A1:2012 – 7 –
4 Oil sampling
4.1 General

Sampling of oil shall be carried out using apparatus and methods complying with IEC 60567

60475:2011.

It is recommended that samples be taken by qualified personnel, trained to operate in

accordance with IEC 60567 60475:2011.
Samples shall be taken in duplicate (test sample and spare sample).
4.2 Sample containers

The most appropriate container is a gas-tight glass syringe of suitable capacity and fitted with

a three-way sampling cock. For storage and transportation, stainless steel caps may also be

used.
Alternative sample containers conforming to IEC 60567 60475:2011 are acceptable.
4.3 Sampling location

Oil samples shall be representative of the bulk of the oil in the equipment. In power

transformers, oil samples shall be taken from the main oil stream (e.g. at the ground level of

the pipes circulating the oil through the radiators, when the pump is in operation, or using a

metal pipe to bring the oil from the top oil valve to the ground). Points outside the main oil

stream (e.g. from the bottom valve of the tank) shall be disregarded. For instrument

transformers, follow the indications of manufacturers.

When using syringes, draining of at least 2 l of oil is recommended before sampling (when

using bottles, twice the volume of the bottle or 5 l). When using bottles, a piece of oil-

compatible tubing should be used from the oil valve to the bottom of the bottle, and the bottle

filled with oil from the bottom up.

NOTE These provisions are not applicable to electrical equipment of small oil volume.

4.4 Sampling frequency
4.4.1 Thermal tests on power transformers

Irrespective of the type and duration of the test, oil samples for DGA shall be taken before the

test begins and after the conclusion of the test.

Intermediate samples may be taken during the test depending on its duration and nature as

they may be essential to improve the precision of the data and the reliability of their

evaluation. Practices to that respect vary widely, and it is left to the user to decide the number

of samples to be taken.

Oil sampling at the followings stages of the thermal tests has been found useful:

– after filling the transformer with degassed oil (for quality control of the drying and filling

process);

– one day to one week later, depending on the transformer (when impregnation of oil in

paper is completed);
– before start of thermal test;

– every 2 h during the tests, or at different test intervals depending on test duration and

transformer design;
– at the end of test only;
---------------------- Page: 9 ----------------------
– 8 – 61181  IEC:2007+A1:2012

– 24 h or more after the test is completed (to allow for equilibrium to be completed);

– some users recommend analysis of the duplicate and intermediate samples only if found

necessary later.

If the cooling system of the unit under test includes oil pumps, they should be operated 2 h

before the first oil sample is taken and kept running until the last oil sample is taken, except

for any period the test conditions require the pumps to be turned off.

NOTE In the case of dielectric tests on power transformers, oil sampling may be performed:

− before first HV test.
− after all dielectric tests.
4.4.2 Impulse tests on instrument transformers

An oil sample shall be taken before the chopped lightning-impulse test. A second oil sample

shall be taken 72 h after the test to assure the diffusion of the small quantities of gas

generated during the test.

NOTE 1 During dielectric tests, the oil in an instrument transformer is virtually stationary and even convective

movement is restricted. Consequently, the diffusion of small quantities of gas generated to the sampling point may

take a considerable time. It is essential that the manufacturer and purchaser reach an agreement on the time the

last sample should be taken.

NOTE 2 Between the beginning and the end of impulse tests, instrument transformers should not be subjected to

other tests.
4.5 Sample labelling

Oil samples should be properly labelled before dispatch to the laboratory with the following

minimum information:
– identification of equipment;
– date and time of sampling;
– nature of factory test;
– sampling point;
– top oil temperature.
4.6 Sample storage

To prevent oxidation, the samples shall be shielded from direct light by wrapping the

container in aluminium foil or by storing in an opaque enclosure.
4.7 Disposal of waste oil
Waste oil shall be disposed of according to local regulations.
5 Factors affecting gassing rate during thermal tests

Gas measurements are used to detect the effect of abnormal temperatures in windings, leads,

magnetic circuit, structural elements, or from abnormal leakage flux. The design of these

transformer parts therefore has an influence on gas production rate. Other important design

aspects that may affect production rate are:

– oil to cellulose mass ratio: if there is less oil to absorb the gas produced, higher gassing

rates will be observed;
– paper type or quality (thermally upgraded or not, Nomex);
– oil type or brand (stray gassing tendency);
– in some transformers: paints, glues, stainless steel and other materials;
---------------------- Page: 10 ----------------------
61181  IEC:2007+A1:2012 – 9 –
– cooling method and cooling efficiency;
– test duration.

Gassing rate is strongly dependent on temperature and air content. It should be noted that

there is always some gassing, although very low, during all thermal tests.

Oxygen concentration is normally low since the oil is initially degassed. Sometimes the oil can

be oxygenated to a given range of concentrations, such as 8 000 µl/l to 12 000 µl/l, to

increase gas formation. In case of a nitrogen-cushioned transformer, considerable amounts of

gases may diffuse from the oil.
6 Dissolved gas extraction and analysis
Gases dissolved in oil should be extracted and analysed by gas chromatography in

accordance with IEC 60567:2011, with the detection limits of the overall determination

indicated in Table 1.
Table 1 – Required detection limits for factory tests
Concentrations
Gas
µl/l µmol/l
Hydrogen 2 0,08
Hydrocarbons 0,1 0,004
Carbon monoxide 5 0,2
Carbon dioxide 10 0,4
Oxygen 500 21
Nitrogen 2000 84

Oil samples should be analysed as soon as possible after being taken and in no case later

than seven days afterwards.
The recommended methods of gas extraction for factory tests, as indicated in

IEC 60567:2011, are the Toepler and partial degassing methods, including their Mercury Free

versions, since they allow a higher gas extraction efficiency at the low gas concentration

levels observed during factory tests. Head space may be used if a sufficient sensitivity and

accuracy can be reached.

When using partial degassing, the following adaptations for factory tests are recommended:

– use a gas burette of smaller volume;

– run a blank (with no oil injected) to check for vacuum leaks in the extraction system;

– use an extraction system dedicated to factory tests (to avoid contamination by routine oil

samples containing high levels of fault gases);

– if this is not possible, perform a full extraction procedure on a sample of degassed oil

before running the factory test samples;

– if a better precision is desired, use a larger volume of oil (e.g., a 50 ml or 100 ml syringe).

---------------------- Page: 11 ----------------------
– 10 – 61181  IEC:2007+A1:2012
When using Toepler method, the following adaptations are recommended:

– if it is known before gas extraction that the oil used has been well degassed (total volume

< 1 %), introduce a measured volume (e.g. 1 ml to 2 ml) of argon into the oil syringe (to

increase the precision on the reading of the total gas measured in the burette);

– if after gas extraction the extracted gas volume is too small for precise quantification,

introduce e.g. 1 ml or 1,5 ml of argon to the extracted gas, so that there is sufficient gas

volume to carry out the analysis;

– alternatively, when the total gas volume is too small to obtain a reading on the burette,

lower the mercury level and take a reading at reduced pressure, then correct to
atmospheric pressure;

– flush with air then put under vacuum (to decontaminate the extraction system from

previous analyses). A full extraction procedure on a sample of degassed oil may also be

used where the apparatus may be contaminated from routine samples;

– an alternative procedure consists in increasing the volume of oil used (typically, twice the

amount used for routine analysis).

The use of high sensitivity capillary columns, as in example 2 of Table 3 4 of IEC 60567:2011

is recommended.

In addition to adequate sensitivity levels, a very good repeatability r is necessary to prevent

misinterpretation of results. Consequently, it is essential for all samples to be analysed by the

same laboratory, by highly-trained qualified personnel, and within a short period of time. It is

also recommended that the laboratory repeatability be regularly monitored. A required criteria

for repeatability at low gas concentrations, as indicated in IEC 60567:2011, is:
r ≤ S
where S is the required detection limit.

The objective of the DGA determinations is the detection of very small differences between oil

samples. A calculated difference is significant only if it is larger than the repeatability (for

analyses performed within a short period of time, e.g., one day), or than the reproducibility or

by default the accuracy (for analyses performed over a longer period of time), as indicated in

9.3 of IEC 60567:2011.

The required accuracy, deduced from round robin tests performed by IEC TC 10 at low gas

levels (1 µl/l to 3 µl/l of the hydrocarbons, 2,5 µl/l of H , 5 µl/l of CO and 40 µl/l of CO ), is

2 2
±44 %.
7 Report
The report should include the following information:
– testing laboratory;
– identification of equipment tested;
– sampling location;

– DGA results on each sample, in µl/l or µmol/l (total volume of gas, oxygen and nitrogen

may conveniently be expressed in percent of oil volume);
– rate of generation of gases in µl/l/h.
---------------------- Page: 12 ----------------------
61181  IEC:2007+A1:2012 – 11 –
Annex A
(informative)
Gas formation rates during thermal tests on power transformers

Because of the small gas quantities formed during factory tests, the oil used in the equipment

tested is usually degassed to eliminate any gases previously present that might interfere with

test diagnoses. Typical residual air contents recommended are < 0,5 % in large power

transformers (>100 MVA), <1 % in medium power transformers (between 20 MVA and
100 MVA) and up to 2 % in
...

Questions, Comments and Discussion

Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.