Insulating oil - Determination of fibre contamination by the counting method using a microscope

This standard describes the method of determining fibre contamination of mineral insulating oil used in electrotechnical equipment by counting the number of fibres on the surface of a membrane filter

Isolieröl - Bestimmung der Faserverunreinigungen mittels eines Zählverfahrens mit einem Mikroskop

Huiles isolantes - Détermination de la contamination par fibres par la méthode du comptage avec utilisation d'un microscope

Insulating oil - Determination of fibre contamination by the counting method using a microscope

General Information

Status
Published
Publication Date
26-Sep-2001
Current Stage
6060 - Document made available
Completion Date
27-Sep-2001

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EN 50353:2002
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2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Insulating oil - Determination of fibre contamination by the counting method using a microscopeIsolieröl - Bestimmung der Faserverunreinigungen mittels eines Zählverfahrens mit einem MikroskopHuiles isolantes - Détermination de la contamination par fibres par la méthode du comptage avec utilisation d'un microscopeInsulating oil - Determination of fibre contamination by the counting method using a microscope29.040.10Izolacijska oljaInsulating oilsICS:Ta slovenski standard je istoveten z:EN 50353:2001SIST EN 50353:2002en01-maj-2002SIST EN 50353:2002SLOVENSKI

STANDARD
SIST EN 50353:2002

EUROPEAN STANDARDEN 50353NORME EUROPÉENNEEUROPÄISCHE NORMSeptember 2001CENELECEuropean Committee for Electrotechnical StandardizationComité Européen de Normalisation ElectrotechniqueEuropäisches Komitee für Elektrotechnische NormungCentral Secretariat: rue de Stassart 35, B - 1050 Brussels© 2001 CENELEC -All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.Ref. No. EN 50353:2001 EICS 29.040.20English versionInsulating oil -Determination of fibre contamination bythe counting method using a microscopeHuiles isolantes -Détermination de la contaminationpar fibres par la méthode du comptageavec utilisation d'un microscopeIsolieröl -Bestimmung der Faserverunreinigungenmittels eines Zählverfahrens mit einemMikroskopThis European Standard was approved by CENELEC on 2000-12-01. CENELEC members are bound tocomply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration.Up-to-date lists and bibliographical references concerning such national standards may be obtained onapplication to the Central Secretariat or to any CENELEC member.This European Standard exists in three official versions (English, French, German). A version in any otherlanguage made by translation under the responsibility of a CENELEC member into its own language andnotified to the Central Secretariat has the same status as the official versions.CENELEC members are the national electrotechnical committees of Austria, Belgium, Czech Republic,Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway,Portugal, Spain, Sweden, Switzerland and United Kingdom.SIST EN 50353:2002

EN 50353:2001- 2 -ContentsPageForeword........................................................................................................................3Introduction.....................................................................................................................41 Scope........................................................................................................................42 Normative references...............................................................................................43 Terms and definitions...............................................................................................44 Principle...................................................................................................................55 Reagents.................................................................................................................56 Apparatus................................................................................................................57 Cleaning procedure.................................................................................................68 Sampling....................................................................................................................79 Filtration procedure..................................................................................................710 Microscope calibration.............................................................................................811 Fibre counting and sizing procedure........................................................................912 Calculation and expression of results.......................................................................1013 Precision..................................................................................................................1014 Test report...............................................................................................................10Figure 1 - Schematic representation of a suitable filtration apparatus.............................11Annex A (normative)

Method for low fibre concentrations..............................................12A.1 Reagents.................................................................................................................12A.2 Apparatus................................................................................................................12A.3 Initial set-up and cleaning........................................................................................13A.4 Sampling, and filtration of oil sample........................................................................13A.5 Blank tests...............................................................................................................14A.6 Counting method.....................................................................................................14A.7 Calculation and expression of results.......................................................................15A.8 Precision..................................................................................................................15A.9 Test report...............................................................................................................15Figure A.1 — Schematic representation of a suitable filtration apparatus forlow fibre concentrations..................................................................................................16SIST EN 50353:2002

- 3 -EN 50353:2001ForewordThis European Standard was prepared by the CENELEC BTWG 99-1, Insulating oil.The text of the draft was submitted to the Unique Acceptance Procedure and was approvedby CENELEC as EN 50353 on 2000-12-01.The following dates were fixed:-latest date by which the EN has to be implementedat national level by publication of an identicalnational standard or by endorsement(dop)2002-04-01-latest date by which the national standards conflictingwith the EN have to be withdrawn(dow)2004-01-01Annexes designated "normative" are part of the body of the standard.In this standard, annex A is normative.Warning

This European Standard calls for the use of substances and/or procedures thatmay be injurious to health if adequate precautions are not taken. It refers only to technicalsuitability and does not absolve the user from legal obligations relating to health and safety atany stage.__________SIST EN 50353:2002

EN 50353:2001- 4 -IntroductionIt is generally recognized that fibres and other particles have a detrimental effect on thedielectric strength of insulating oil. It has long been a requirement to include in specificationsfor insulating liquids that the fluid be clear and free from visible particulate matter orsediment. This Standard provides the methodology for testing for contamination by fibres andconsists of filtering a known volume of the insulating liquid under vacuum assisted conditionsthrough a membrane filter to collect contaminants on the filter surface. The membrane isthen examined microscopically to count and size the fibres.1

ScopeThis European Standard specifies two methods for determining the fibre contamination ofmineral insulating oil used in electrotechnical equipment, based on filtering a sample of oiland examining and counting the number of fibres on the surface of the filter using an opticalmicroscope. Fibres down to 100 µm in length can be sized and counted by these methods.The methods are applicable both to unused oils and to oils in service.The method specified in the main text is applicable to oil samples taken from barrelled oil orfrom electrotechnical equipment in service, in which the fibre concentration is expected to berelatively high. The alternative method specified in annex A is applicable to samples takenfrom new oil in bulk containers, or from large transformers which have not been operatedmuch since they were filled, in which the fibre concentration is expected to be relatively low.NOTE

These methods are also suitable for other insulating liquids such as silicones and synthetic esters.2

Normative referencesThis European Standard incorporates by dated or undated reference, provisions from otherstandards. These normative references are cited at the appropriate places in the text and thepublications are listed hereafter. For dated references, subsequent amendments to orrevisions of any of these publications apply to this European Standard only whenincorporated in it by amendment or revision. For undated references the latest edition of thepublication referred to applies.IEC 60475Method of sampling liquid dielectricsISO 5598Fluid power systems and components - Vocabulary3

Terms and definitionsFor the purposes of this European Standard, the terms and definitions given in ISO 5598 andthe following apply.3.1blank countcount of the number of fibres introduced from other sources, such as reagents or cleaning ofglassware3.2effective filtration areaarea of a membrane filter open to flow during filtration of the fluidSIST EN 50353:2002

- 5 -EN 50353:2001NOTE

For commercially obtainable gridded membrane filters of diameter 37 mm, this is generally accepted as100 grid squares of dimension 3,1 mm, with a nominal area of 960 mm2.3.3detectable fibrefibre longer than 100 µm with a length-to-width ratio greater than or equal to 5:1NOTE

For the purposes of this standard, detectable fibres are defined as longer than 100 µm becauseexperience has shown that only these fibres cause severe degradation of dielectric strength in practical situations.4

PrincipleA known volume of insulating oil is filtered, using vacuum assistance, through a membranefilter to separate contaminants from the sample liquid and deposit them on the surface of themembrane filter. The contamination is examined microscopically to size and count any fibrespresent.5

ReagentsNOTE
These chemicals are used for cleaning and rinsing the apparatus.5.1
Liquid detergent, without solid residue.5.2
Distilled or de-mineralized water.5.3
2-propanol, acetone-free.5.4
Solvent

- petroleum ether, boiling range 100oC to 120oC preferred, but heptane, hexaneand cyclohexane are suitable alternatives.WARNING - Petroleum ether and many of its alternatives are highly flammable solventswhich have low flash points. It is essential that appropriate safety measures are observedduring use of these solvents. Only small quantities (e.g. not greater than about 100 ml)should be used on the workbench and larger quantities should be handled in a fumecupboard to avoid the inhalation of fumes from these solvents.6

ApparatusNOTE
An example of suitable apparatus is shown in Figure 1.6.1

Membrane filter holder, consisting of the following components:-a glass funnel of 250 ml capacity, with a loosely fitting glass cap;− a clamping device;− a suitable base to support the membrane filter (e.g. a glass frit).NOTE

If problems are experienced due to build-up of electrostatic charge on the filter during filtration, it may benecessary to use an earthed metal anti-static base to support the membrane filter.6.2

Membrane filters, with a pore diameter of 1,2 µm or less. Gridded filters shall be usedfor manual counting and ungridded filters shall be used if an automatic counting system is tobe employed (see 6.8).SIST EN 50353:2002

EN 50353:2001- 6 -NOTE 1

It is essential that a type of filter is selected which is known to be compatible with the oil sample andwith the solvents which are to be used (see clause 5).NOTE 2

Black membranes may be helpful for the purpose of counting, by improving the visibility of fibres wheremost of them are translucent, transparent or white in colour.6.3

Vacuum flask (for waste filtrate), glass, with side arm, of 1 l capacity and capable ofaccepting the membrane filter holder (6.1).6.4

Vacuum pump, capable of establishing a vacuum to assist the flow of oil through themembrane.NOTE

A condensing trap may be used to protect the vacuum pump from vapours.6.5

Filtered-solvent dispenser, comprising a pressure-operated system which dischargesthe solvent through an in-line membrane filter with a pore diameter of 1,2 µm or less.NOTE

The type of filter selected shall be compatible with the solvents used (see clause 5).6.6

Tweezers, stainless steel, flat ended, un-serrated.6.7
Petri dishes, glass, with cover.6.8

Microscope, capable of producing magnifications of ×50, equipped with fine and coarsefocus controls, having an eyepiece graticule, and fitted with a mechanical stage so that theeffective filtration area of the filter can be scanned.NOTE

The microscope may be fitted with an image analysis system if automatic determination of fibre sizedistribution is required.6.9

Stage micrometer, graduated in 0,1 mm and 0,01 mm divisions, with its calibrationtraceable to national standards.6.10

External lamp, of variable intensity, if the microscope does not include an inbuilt lightsource.6.11

Sample bottles, minimum capacity 250 ml, cylindrical, wide-mouthed, clear glass with anon-fibre-shedding, oil-tight closure.7

Cleaning procedureClean the filtration apparatus, tweezers and petri dishes, and the sample bottles andclosures as follows:a)wash the glassware, and the tweezers, in warm tap water/liquid detergent solution;b) rinse three times with distilled or de-mineralized water;c) rinse with filtered 2-propanol to remove water;d) rinse with filtered petroleum ether, using a spirally directed jet where possible;e) suspend the funnel in suitable sized beaker, wash down with petroleum ether and thencover;f) leave a little solvent in each sample bottle and cap with a pre-cleaned closure.NOTE

Solvent evaporation slightly pressurises the bottle and therefore excludes contamination when the bottleis opened.SIST EN 50353:2002

- 7 -EN 50353:20018

SamplingClean the sampling equipment in accordance with clause 7.Ensure that the sampling equipment is free from fibrous contamination by flushing with the oilbeing sampled.Extract a sample (of minimum volume 250 ml) of the insulating oil from the reservoir/container in accordance with the method laid down in IEC 60475.NOTE

The fibre count of an oil sample from any item of electrotechnical equipment can depend on the samplingpoint, the time elapsed since filling, the oil circulation rate and/or the time the oil is left to stand. Circulation of oil inthe tank of the electrical equipment before taking the samples can be expected to yield more consistent fibrecount results.Storage of the samples will generally lead to sedimentation and coalescence of fibres andparticles. Therefore, the analysis should be undertaken as soon as possible after sampling. Ithas been established that analysis of a sub-sample from a sample container may produceinaccurate results. Therefore the total contents of the sample container shall be used for thetest.9

Filtration procedure9.1

GeneralA blank test, to determine the blank count, in accordance with 9.3, shall be carried out beforethe filtration of each batch of oil samples (see 9.2). If the batch of oil samples is so large thatthe analysis takes more than a week, a blank test, to determine the blank count, shall becarried out once a week.It is essential to minimize fibre contamination during filtration and counting. Therefore, it isrecommended that these procedures are carried out in either:a)a laminar flow cabinet; orb)a clean room reserved specifically for microscopy, in which no activities likely to generatefibres are carried out.Precautions should also be taken to minimize fibre shedding from the operators’ clothing. It isrecommended that operators should wear non fibre-shedding overclothes and should covertheir hair.NOTE

The material of these overclothes shall not pose high risk for the wearer in case of fire.9.2

Filtration of oil sample9.2.1

Using cleaned tweezers, remove a membrane filter from its container, inspect it (usingthe microscope) to ensure that it is fibre-free and place it, grid side up, centrally on thescreen of the filter holder base. Carefully install and clamp the funnel in position. Do notremove the cap from the funnel opening until ready to start filtration.9.2.2

Connect the vacuum pump to the side arm of the vacuum flask.9.2.3
After noting any details (sample identity etc.
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