Insulating liquids - Methods for counting and sizing particles

This standard describes the sampling procedures and methods for the determination of particle concentration and size distribution. Three methods are specified. One uses an automatic particle size analyser, working on the light interruption principle. The other two use an optical microscope, in either the transmitted light or incident light mode, to count particles collected on the surface of a membrane filter. The optical microscope methods are described in ISO 4407. All three methods are applicable to both used and unused insulating liquids. Annex A contains an alternative sampling procedure using a syringe and Annex B reports a reference for the calibration of automatic particle counters.

Isolierflüssigkeiten - Verfahren zur Bestimmung der Anzahl und Größen von Teilchen

Isolants liquides - Méthodes de détermination du nombre et de la taille des particules

Décrit les procédures de prélèvement et les méthodes pour déterminer la concentration des particules et la répartition selon leur taille. Trois méthodes sont recommandées. L'une d'entre elles utilise un analyseur automatique de particules, dont le principe repose sur l'interruption d'un faisceau lumineux. Les deux autres utilisent un microscope optique, en mode soit de lumière transmise soit de lumière incidente, pour compter les particules retenues à la surface d'une membrane filtrante. Les méthodes au microscope optique sont décrites dans l'ISO 4407. Ces trois méthodes sont applicables tant aux isolants liquides usagés qu'aux isolants liquides neufs. L'Annexe A comporte une autre procédure d'échantillonnage utilisant une seringue et l'Annexe B indique une référence pour l'étalonnage des compteurs automatiques de particules. Les principales modifications techniques par rapport à l'édition précédente sont les suivantes: - nouvelles procédures d'étalonnage pour les analyseurs automatiques de particules; - code de contamination à trois chiffres; - nouvelle procédure pour le pré-traitement d'échantillons quand la méthode des compteurs de particules automatisés est utilisée.

Izolacijske tekočine – Metode za štetje in ugotavljanje velikosti delcev (IEC 60970:2007)

General Information

Status
Published
Publication Date
23-Oct-2007
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
10-Oct-2007
Due Date
15-Dec-2007
Completion Date
24-Oct-2007

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SLOVENSKI STANDARD
SIST EN 60970:2007
01-december-2007
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Insulating liquids - Methods for counting and sizing particles

Isolierflüssigkeiten - Verfahren zur Bestimmung der Anzahl und Größen von Teilchen

Isolants liquides - Méthodes de détermination du nombre et de la taille des particules

Ta slovenski standard je istoveten z: EN 60970:2007
ICS:
17.220.99 Drugi standardi v zvezi z Other standards related to
elektriko in magnetizmom electricity and magnetism
29.040.01 Izolacijski fluidi na splošno Insulating fluids in general
SIST EN 60970:2007 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN 60970:2007
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SIST EN 60970:2007
EUROPEAN STANDARD
EN 60970
NORME EUROPÉENNE
August 2007
EUROPÄISCHE NORM
ICS 17.220.99. 29.040.10
English version
Insulating liquids -
Methods for counting and sizing particles
(IEC 60970:2007)
Isolants liquides - Isolierflüssigkeiten -
Méthodes de détermination du nombre Verfahren zur Bestimmung der Anzahl
et de la taille des particules und Größen von Teilchen
(CEI 60970:2007) (IEC 60970:2007)

This European Standard was approved by CENELEC on 2007-08-01. CENELEC members are bound to comply

with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard

the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on

application to the Central Secretariat or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other

language made by translation under the responsibility of a CENELEC member into its own language and notified

to the Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Cyprus, the

Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,

Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,

Sweden, Switzerland and the United Kingdom.
CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
Central Secretariat: rue de Stassart 35, B - 1050 Brussels

© 2007 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.

Ref. No. EN 60970:2007 E
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SIST EN 60970:2007
EN 60970:2007 - 2 -
Foreword

The text of document 10/695/FDIS, future edition 2 of IEC 60970, prepared by IEC TC 10, Fluids for

electrotechnical applications, was submitted to the IEC-CENELEC parallel vote and was approved by

CENELEC as EN 60970 on 2007-08-01.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2008-05-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2010-08-01
Annex ZA has been added by CENELEC.
__________
Endorsement notice

The text of the International Standard IEC 60970:2007 was approved by CENELEC as a European

Standard without any modification.

In the official version, for Bibliography, the following notes have to be added for the standards indicated:

IEC 60422 NOTE Harmonized as EN 60422:2006 (not modified).
ISO 4402 NOTE Harmonized as EN ISO 14402:1999 (not modified).
_________
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SIST EN 60970:2007
- 3 - EN 60970:2007
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

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.

NOTE When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD

applies.
Publication Year Title EN/HD Year
- - Insulating oil - Determination of fibre EN 50353 -
contamination by the counting method using
a microscope
IEC 60475 - Method of sampling liquid dielectrics - -
ISO 4406 - Hydraulic fluid power - Fluids - Method for - -
coding the level of contamination by solid
particles
ISO 4407 - Hydraulic fluid power - Fluid contamination - - -
Determination of particulate contamination by
the counting method using an optical
microscope
ISO 5884 - Aerospace - Fluid systems and components - - -
Methods for system sampling and measuring
the solid particle contamination of hydraulic
fluids
Undated reference.
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SIST EN 60970:2007
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SIST EN 60970:2007
INTERNATIONAL IEC
STANDARD
CEI
60970
NORME
Second edition
INTERNATIONALE
Deuxième édition
2007-07
Insulating liquids – Methods for counting and
sizing particles
Isolants liquides – Méthodes de détermination du
nombre et de la taille des particules
PRICE CODE
CODE PRIX
Commission Electrotechnique Internationale
International Electrotechnical Commission
МеждународнаяЭлектротехническаяКомиссия
For price, see current catalogue
Pour prix, voir catalogue en vigueur
---------------------- Page: 7 ----------------------
SIST EN 60970:2007
– 2 – 60970 © IEC:2007
CONTENTS

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

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

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

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

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

4 Significance......................................................................................................................7

5 Comparison and limitation of the methods ........................................................................7

6 Types and identification of particles..................................................................................8

7 Sampling ..........................................................................................................................8

7.1 General remarks......................................................................................................8

7.2 Sampling vessels ....................................................................................................9

7.3 Cleaning of sampling bottles ...................................................................................9

7.4 General directions for sampling ...............................................................................9

7.5 Sampling procedure ..............................................................................................10

7.6 Labelling of samples..............................................................................................10

7.6.1 Samples from tanks ...................................................................................10

7.6.2 Samples from electrical equipment ............................................................10

8 Preparation of the samples for analysis ..........................................................................10

9 Method A – Automatic particle size analyzer...................................................................11

9.1 Summary of method ..............................................................................................11

9.2 Apparatus and auxiliary materials..........................................................................11

9.3 Calibration procedures ..........................................................................................11

9.4 Preparation of the apparatus for counting..............................................................12

9.5 Preparation of sample before counting ..................................................................12

9.6 Preparation of sample for counting ........................................................................12

9.7 Counting procedures .............................................................................................12

9.8 Report ...................................................................................................................13

9.9 Precision ...............................................................................................................13

9.10 Repeatability .........................................................................................................13

9.11 Reproducibility ......................................................................................................13

10 Method B – Optical microscopy ......................................................................................14

10.1 Principle................................................................................................................14

10.2 Procedure by transmitted light ...............................................................................14

10.3 Procedure by incident light ....................................................................................14

Annex A (informative) Use of syringes as sampling vessels .................................................15

Annex B (informative) Calibration of the automatic particle counters ....................................17

Bibliography..........................................................................................................................18

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SIST EN 60970:2007
60970 © IEC:2007 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INSULATING LIQUIDS – METHODS FOR COUNTING AND SIZING
PARTICLES
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 provides no marking procedure to indicate its approval and cannot be rendered responsible for any

equipment declared to be in conformity with an IEC Publication.

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.

International Standard IEC 60970 has been prepared by IEC technical committee 10: Fluids

for electrotechnical applications.

This second edition cancels and replaces the first edition published in 1989. This edition

constitutes a technical revision.

The significant technical changes with respect to the previous edition are as follows:

– new calibration procedures for automated laser particle;
– three figures contamination code;

– new procedure of sample pre-treatment when automated laser counter method are used.

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SIST EN 60970:2007
– 4 – 60970 © IEC:2007
The text of this standard is based on the following documents:
FDIS Report on voting
10/695/FDIS 10/714/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.

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.
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SIST EN 60970:2007
60970 © IEC:2007 – 5 –
INTRODUCTION

The first edition of this standard was published in 1989, and confirmed in 1996. The present

edition has been found necessary for consistency with the new ISO 4406:1999, in which

calibration procedures for automated particles counters have been changed from ACFTD

standard to ISO-MTD standard. Specific procedures for sample preparation are described in

more detail when automated particle counters are used. Results and ISO Code reporting are

consistent with ISO 4406:1999 standard. Repeatability and reproducibility data are reported.

It has been demonstrated that particle contamination of insulating liquids used in electrical

equipment have been responsible for major faults [1] . Particle analysis is recommended (as

complementary test) by IEC 60422[3] for power transformers with nominal voltage above

170 kV[2].

Particle counting and sizing is usually carried out using automated counters; the calibration

standard for these counters was changed in 1999. The ISO reporting code has also been

changed from a two-figure to a three-figure code. This code gives information on three

classes of cumulative counting: particles/ml with ∅ > 4 μm, particles/ml with ∅ > 6 μm,

particles/ml with ∅ > 14 μm. Particle analysis with automated particle counters has been

thoroughly investigated to verify factors influencing the results and to optimize the analysis

procedure. Reference figures for repeatability and Reproducibility are reported, for particle

counting and for ISO Class.

Annex A provides information about sampling with syringes. Annex B reports a reference for

ISO MTD calibration procedure.
___________
Figures in square brackets refer to the bibliography.
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SIST EN 60970:2007
– 6 – 60970 © IEC:2007
INSULATING LIQUIDS – METHODS FOR COUNTING AND SIZING
PARTICLES
1 Scope

This standard describes the sampling procedures and methods for the determination of

particle concentration and size distribution.

Three methods are specified. One uses an automatic particle size analyser, working on the

light interruption principle. The other two use an optical microscope, in either the transmitted

light or incident light mode, to count particles collected on the surface of a membrane filter.

The optical microscope methods are described in ISO 4407.
All three methods are applicable to both used and unused insulating liquids.

Annex A contains an alternative sampling procedure using a syringe and Annex B reports a

reference for the calibration of automatic particle counters.

NOTE 1 The methods are not intended to measure particulate matter in liquids containing sludge. While analysing

solid content on oils containing sludge refers to method for sediment and sludge determination in IEC 60422,

Annex C.

NOTE 2 The methods specified are only applicable to measurements related to a limited range of size and

number.
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

ISO 4406: Hydraulic fluid power – Fluids – Method for coding the level of contamination by

solid particles

ISO 4407: Hydraulic fluid power – Fluid contamination – Determination of particulate

contamination by the counting method using an optical microscope
ISO 5884: Aerospace – Fluid systems and components – Methods for sampling and
measuring the solid particle contamination of hydraulic fluids

EN 50353: Insulating oil – Determination of fibre contamination by the counting method using

a microscope
3 General caution, health, safety and environmental protection

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 insulating liquids 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

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SIST EN 60970:2007
60970 © IEC:2007 – 7 –

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 insulating liquids 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.
4 Significance

It is well known that particles have a detrimental effect on the dielectric strength of insulating

liquids. It has long been the practice to include in specifications of insulating liquids the

requirement that the fluid be clear and free of visible particulate matter. However, there has

been no standard method for quantitative estimates, so that practices have differed. This

standard gives standard procedures for the test.

Filtration of insulating liquids is an established practice in the electrical industry. The

procedure described may serve to assess the performance of the filter system. The results

obtained are dependent upon the method used. With the automatic counter the measured

values also depend on the calibration procedure and in particular on the calibration material.

It is therefore essential that the methods of analysis and the calibration standards are

specified when quoting results.

The particle content of a sample may depend on different transformer parameters as well as

the condition of the oil itself.

Storage may affect the sample, due to sedimentation and/or coalescence of particles. Shaking

of the sample before analysis will be necessary.
5 Comparison and limitation of the methods

Automatic particle counters using the light interruption principle are quick and easy to use, but

the following points should be borne in mind:

– With some liquids it may be necessary to modify their viscosity to comply with the

operating parameters of the instrument.

– It is necessary to choose a sensor head suitable for counting in the size range required.

No single head can count both very small particles (<2 µm) and very large particles

(>200 µm).

– The instrument records the light interruption area of the particle and from this calculates

the diameter of a sphere having the equivalent area or the longer axis of a specified

ellipsoid with the same area, as established by ISO 4407. When measurements are

carried out with automatic particle counters, the reported sizes are expressed as μm(c) to

indicate that the particle size has been calculated from the observed cross-sectional area.

Particle sizes from optical microscope counting are expressed as μm. The relationship

between the two units is described in ISO 4406:
• 6 μm(c) corresponds to 5 μm
• 14 μm(c) corresponds to 15 μm.

– Automatic counters give no information as to the shape of the particles, and this

constitutes a limitation with respect to the recognition of fibres. Their narrow and

elongated shape results in a slight light obscuration and consequently in a very small

equivalent sphere diameter. The results obtained can be different from those obtained by

microscope counting. When it is important to evaluate the concentration of fibres,

automatic counters cannot perform this task adequately.

– When air-saturated or over-saturated liquids are shaken manually or in a shaking machine,

or given high-energy ultrasonic treatment, finely dispersed micro-bubbles may be formed

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SIST EN 60970:2007
– 8 – 60970 © IEC:2007

in the liquid. In the optical system of the automatic counter, these micro-bubbles will be

counted as solid particles.

– These difficulties are avoided when using either of the optical microscopic methods. In

addition, optical microscopy may give some information about the types of particles

present. These methods are, however, much more time-consuming and operator
dependent and may be very difficult to count particles of less than 5 µm.
6 Types and identification of particles
The origins of particles found in insulating liquids are manifold.

In new, unenergized, equipment the insulating liquid may contain cellulose fibres plus

particles from the manufacturing process. These could include iron, aluminium, brass, welding

cinder and sandblasting materials.

Insulating liquids in working transformers, at both normal and overload temperatures, slowly

acquire soot and sludge particles. Localised overheating over 500 ºC could be a source of

carbon. The carbon particles produced in the OLTC diverter may migrate by leakage,

accidents or human error into the bulk fluid compartment and contaminate the full charge.

A typical source of metallic particles is from pump bearing wear, although corrosion and

arcing on metallic components may also produce particles.

Cellulose lint, sand, dust and particles of varnish, plastic or rubber can also be found in the

fluid of transformers in service.

A knowledge of which particle types are present in the insulating liquid can, in certain cases,

help in assessing the conditions of the equipment, in diagnosing a fault or indicating a risk of

failure. The most dangerous particles are the conductive ones (metals, carbon, wet fibres,

etc.). Particle identification and counting have been found to be necessary procedures of

condition monitoring (CIGRE brochures 157[1] and 227[2]).

Certain particles may be identified by filtering a sample through a membrane filter and

examining the residue under a microscope (EN 50353). At this stage some fibres can be

identified using the dispersion staining technique and a number of metals by means of spot

tests or micro chemical methods. Metallic particles can be better identified and quantified by

instrumental analytical methods such as atomic absorption spectroscopy (AAS), induced

coupled plasma (ICP-AES), and wet chemical analysis. A detailed description of methods for

the identification of particles is, however, outside the scope of this standard.
7 Sampling
7.1 General remarks

The sample taken should only be used for the particle count determination. Further analysis

may be done on the residual sample, but after the particle count determination.

The particle content of a sample is also dependant on the sampling point, time elapsed since

the transformer was filled, the circulation rate and the time that the transformer has been left

to stand prior to sampling.

With used liquids, oxidation products which are soluble at operating temperatures may

precipitate when the sample is allowed to stand at room temperature for a prolonged period.

This process, which is dependent upon the service age of the liquid, the time between

sampling and analysis and the storage temperature, can affect the particle count.

For the above mentioned reasons, sampling is the main source of spreading of results.

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SIST EN 60970:2007
60970 © IEC:2007 – 9 –
7.2 Sampling vessels

The sampling vessels recommended in this standard are cylindrical, flat-bottomed, wide-

necked, clear glass bottles fitted with a polypropylene threaded cap forming a seal with the

bottle without the use of any inserts.

When an automatic particle size analyzer is used, the volume sampled shall be enough to

allow a proper rinsing of the instrument’s dead volume and measuring cell before the analysis.

For microscopy, the bottles shall have at least 100 cm³ capacity and be permanently marked

to indicate 100 cm³ sample size.

An alternative method for insulating liquids in service using syringes as sampling vessels is

given in Annex A.
7.3 Cleaning of sampling bottles

It is recommended that the bottles be cleaned to achieve a blank count of less than 200

particles above 5 µm per 100 cm³. The test should be performed on the filtered solvent used

in the last stage of the cleaning process.

A cleaning method is given for guidance, but other methods can be used provided they

achieve a similar or greater degree of cleanliness.
a) Wash with warm water containing a detergent
b Rinse with warm water and drain
c) Rinse thoroughly with 0,45 µm membrane filtered acetone to remove water

d) Rinse with 0,45 µm membrane filtered petroleum ether 40 °C to 70 °C or with another

suitable solvent. Leave 1 cm³ or 2 cm³ of solvent in the bottle and close the bottle.

If ultrasonic agitation is used before counting particles, the cleaning procedure must include

ultrasonic treatment. Reject the procedure outlined in stage c) and instead place the sample

bottle, filled with 0,45 µm membrane filtered acetone, in an ultrasonic bath for 1 min.

A residue of solvent in the bottle creates a positive pressure in the bottle helping to prevent

contamination from the atmosphere when opening the bottle.

Warning: Attention is called to national regulations associated with the use of solvents.

The use of purchased sample bottles cleaned in accordance with ISO 5884 is allowed.

7.4 General directions for sampling

It is difficult to obtain representative samples from a drum. If sampling is found to be

necessary, the procedure given in Annex A may be used or, alternatively, the procedures

given in IEC 60475. In the case of sealed power transformers and instrument transformers or

similar equipment with small liquid volume, the manufacturer’s instructions on sampling

procedure and quantity shall be followed. A sample from a transformer should preferably be

taken during fluid circulation or immediately afterwards. The analysis obtained may depend on

the sampling point selected. Confirmatory or follow-up samples should therefore always be

taken from the same point.
Every precaution shall be taken when sampling not to contaminate the sample.

Outdoor sampling of insulating liquids in rain, fog, snowfall or high wind is only permitted if all

precautions are taken to avoid contamination of the samples. In this special case the use of a

cover is necessary.
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