SIST EN 60970:2007

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
1)
- - Insulating oil - Determination of fibre EN 50353 -
contamination by the counting method using
a microscope


1)
IEC 60475 - Method of sampling liquid dielectrics - -


1)
ISO 4406 - Hydraulic fluid power - Fluids - Method for - -
coding the level of contamination by solid
particles


1)
ISO 4407 - Hydraulic fluid power - Fluid contamination - - -
Determination of particulate contamination by
the counting method using an optical
microscope


1)
ISO 5884 - Aerospace - Fluid systems and components - - -
Methods for system sampling and measuring
the solid particle contamination of hydraulic
fluids





1)
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
R
CODE PRIX
Commission Electrotechnique Internationale
International Electrotechnical Commission
МеждународнаяЭлектротехническаяКомиссия
For price, see current catalogue
Pour prix, voir catalogue en vigueur

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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
1
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.

___________
1
Figures in square brackets refer to the bibliography.

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SIST EN 60970:2007
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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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