Insulating liquids - Oil-impregnated paper and pressboard - Determination of water by automatic coulometric Karl Fischer titration

Describes methods for the determination of water in insulating liquids and in oil-impregnated cellulosic insulation with coulmetrically generated Karl Fischer reagent.

Isolierflüssigkeiten - Ölimprägniertes Papier und ölimprägnierter Presspan - Bestimmung von Wasser durch automatische coulometrische Karl-Fischer-Titration

Isolants liquides - Cartons et papiers imprégnés d'huile - Détermination de la teneur en eau par titrage coulométrique de Karl Fischer automatique

Décrit des méthodes de détermination de la teneur en eau des isolants liquides et des isolants cellulosiques imprégnés d'huile, par la méthode de titrage coulométrique de Karl Fischer.

Insulating liquids - Oil-impregnated paper and pressboard - Determination of water by automatic coulometric Karl Fischer titration (IEC 60814:1997)

General Information

Status
Published
Publication Date
31-Dec-1998
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
01-Jan-1999
Due Date
01-Jan-1999
Completion Date
01-Jan-1999

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SLOVENSKI STANDARD
SIST EN 60814:1999
01-januar-1999

Insulating liquids - Oil-impregnated paper and pressboard - Determination of water

by automatic coulometric Karl Fischer titration (IEC 60814:1997)

Insulating liquids - Oil-impregnated paper and pressboard - Determination of water by

automatic coulometric Karl Fischer titration

Isolierflüssigkeiten - Ölimprägniertes Papier und ölimprägnierter Presspan - Bestimmung

von Wasser durch automatische coulometrische Karl-Fischer-Titration

Isolants liquides - Cartons et papiers imprégnés d'huile - Détermination de la teneur en

eau par titrage coulométrique de Karl Fischer automatique
Ta slovenski standard je istoveten z: EN 60814:1997
ICS:
29.040.10 Izolacijska olja Insulating oils
SIST EN 60814:1999 en

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

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SIST EN 60814:1999
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SIST EN 60814:1999
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SIST EN 60814:1999
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SIST EN 60814:1999
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SIST EN 60814:1999
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SIST EN 60814:1999
NORME
CEI
INTERNATIONALE
IEC
60814
INTERNATIONAL
Deuxième édition
STANDARD
Second edition
1997-08
Isolants liquides – Cartons et papiers
imprégnés d'huile –
Détermination de la teneur en eau par titrage
coulométrique de Karl Fischer automatique
Insulating liquids – Oil-impregnated paper
and pressboard –
Determination of water by automatic
coulometric Karl Fischer titration
 IEC 1997 Droits de reproduction réservés  Copyright - all rights reserved

Aucune partie de cette publication ne peut être reproduite ni No part of this publication may be reproduced or utilized in

utilisée sous quelque forme que ce soit et par aucun any form or by any means, electronic or mechanical,

procédé, électronique ou mécanique, y compris la photo- including photocopying and microfilm, without permission in

copie et les microfilms, sans l'accord écrit de l'éditeur. writing from the publisher.

International Electrotechnical Commission 3, rue de Varembé Geneva, Switzerland
Telefax: +41 22 919 0300 e-mail: inmail@iec.ch IEC web site http: //www.iec.ch
CODE PRIX
Commission Electrotechnique Internationale
PRICE CODE
International Electrotechnical Commission
Pour prix, voir catalogue en vigueur
For price, see current catalogue
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SIST EN 60814:1999
60814 © IEC:1997 – 3 –
CONTENTS
Page

FOREWORD ................................................................................................................................... 5

Clause

1 General....................................................................................................................................... 7

1.1 Scope................................................................................................................................ 7

1.2 Normative references........................................................................................................7

2 Direct titration for low viscosity liquids ........................................................................................ 7

2.1 Field of application ............................................................................................................ 7

2.2 Chemistry.......................................................................................................................... 9

2.3 Apparatus.......................................................................................................................... 9

2.4 Reagents and auxiliary materials ...................................................................................... 13

2.5 Preparation of the apparatus............................................................................................. 13

2.6 Sampling methods............................................................................................................13

2.7 Procedure.......................................................................................................................... 15

2.8 Calculation of the result..................................................................................................... 15

2.9 Report............................................................................................................................... 15

2.10 Precision........................................................................................................................... 17

3 Evaporative stripping method for high viscosity liquids .............................................................. 17

3.1 Field of application ............................................................................................................ 17

3.2 Outline of the method........................................................................................................ 17

3.3 Apparatus and reagents.................................................................................................... 17

3.4 Procedure.......................................................................................................................... 19

3.5 Calculation of water content.............................................................................................. 19

3.6 Report............................................................................................................................... 19

4 Determination of water in oil-impregnated paper and pressboard ............................................. 21

4.1 Field of application ............................................................................................................ 21

4.2 Determination of water after previous extraction with methanol ....................................... 21

4.3 Determination by direct titration......................................................................................... 23

4.4 Evaporative stripping method............................................................................................ 25

Figures

1 Block diagram of automatic titrator............................................................................................. 29

2 Suitable titration vessel assembly .............................................................................................. 31

3 Block diagram of automatic titrator and evaporation stripping unit ............................................ 33

4 Evaporator glass vessel with heater........................................................................................... 35

5 Methanol container and extraction tube ..................................................................................... 37

Annex A – Method for sampling of oil-impregnated paper and pressboard .................................... 39

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SIST EN 60814:1999
60814 © IEC:1997 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
_________
INSULATING LIQUIDS – OIL-IMPREGNATED PAPER AND PRESSBOARD –
DETERMINATION OF WATER BY AUTOMATIC COULOMETRIC
KARL FISCHER TITRATION
FOREWORD

1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising

all national electrotechnical committees (IEC National Committees). The object of the 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, the IEC publishes International Standards. 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. The 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 the 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 National Committees.

3) The documents produced have the form of recommendations for international use and are published in the form

of standards, technical reports or guides and they are accepted by the National Committees in that sense.

4) In order to promote international unification, IEC National Committees undertake to apply IEC International

Standards transparently to the maximum extent possible in their national and regional standards. Any

divergence between the IEC Standard and the corresponding national or regional standard shall be clearly

indicated in the latter.

5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any

equipment declared to be in conformity with one of its standards.

6) Attention is drawn to the possibility that some of the elements of this International Standard may be the subject

of patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.

International Standard IEC 60814 has been prepared by IEC technical committee 10: Fluids for

electrotechnical applications.

This second edition of IEC 60814 cancels and replaces the first edition published in 1985 of

which it constitutes a technical revision.
It also cancels IEC 60733, published in 1982.
The text of this standard is based on the following documents:
FDIS Report on voting
10/406/FDIS 10/422/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.
Annex A is for information only.
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SIST EN 60814:1999
60814 © IEC:1997 – 7 –
INSULATING LIQUIDS – OIL-IMPREGNATED PAPER AND PRESSBOARD –
DETERMINATION OF WATER BY AUTOMATIC COULOMETRIC
KARL FISCHER TITRATION
1 General
1.1 Scope

This International Standard describes methods for the determination of water in insulating

liquids and in oil-impregnated cellulosic insulation with coulometrically generated Karl Fischer

reagent.

The method in clause 2 is applicable to water concentrations above 2 mg/kg in liquids having

viscosity of less than 100 mm /s at 40 °C.

The test method in clause 3, where water is extracted by means of a nitrogen stream, is the

preferred method for insulating liquids of viscosity higher than 100 mm /s.

Clause 4 describes methods for the determination of water content in oil-impregnated paper

and pressboard over the range 0,1 % to 20 % by mass.
1.2 Normative references

The following normative documents contain provisions which, through reference in this text,

constitute provisions of this International Standard. At the time of publication, the editions

indicated were valid. All normative documents are subject to revision, and parties to

agreements based on this International Standard are encouraged to investigate the possibility

of applying the most recent editions of the normative documents indicated below. Members of

IEC and ISO maintain registers of currently valid International Standards.
IEC 60475: 1974, Method of sampling liquid dielectrics

IEC 60567: 1992, Guide for the sampling of gases and of oil from oil-filled electrical equipment

and for the analysis of free and dissolved gases

ISO 595-1: 1986, Reusable all-glass or metal-and-glass syringes for medical use – Part 1:

Dimensions

ISO 595-2: 1987, Reusable all-glass or metal-and-glass syringes for medical use – Part 2:

Design, performance requirements and tests
2 Direct titration for low viscosity liquids
2.1 Field of application

This method is applicable to water concentrations above 2 mg/kg in liquids having viscosity up

to 100 mm /s at 40 °C. The precision data given in 2.10 apply only to new liquids.

NOTES

1 For liquids in service, the accuracy of the method may be affected by the presence of contaminants and

degradation products.

2 The method has been designed to be particularly suitable to hydrocarbon and ester liquids. With other

liquids, particularly silicone fluids, methanol free reagents must be used.
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SIST EN 60814:1999
60814 © IEC:1997 – 9 –
2.2 Chemistry

The reactions occurring in a Karl Fischer titration are known to be complex, but are essentially

of water with iodine, sulphur dioxide, an organic base and an alcohol in an organic solvent. The

original Karl Fischer reagent used pyridine and methanol, and the reactions may be expressed

as:
H O + I + SO + 3C H N → 2C H N.HI + C H N.SO (1)
2 2 2 5 5 5 5 5 5 3
C H N.SO + CH OH → C H NH.SO .CH (2)
5 5 3 3 5 5 4 3

Other base-alcohol combinations are possible and may be necessary for titrations on some

insulating liquids.

In coulometric Karl Fischer titration, the sample is mixed with a base/alcohol solution of iodide

ion and sulphur dioxide. Iodine is generated electrolytically and reacts with water in a similar

way to that shown in reactions (1) and (2). Iodine is generated in proportion to the quantity of

electricity according to Faraday's law, as shown by the following reaction:
2 I – 2 e → I (3)

One mole of iodine reacts with one mole of water stoichiometrically as shown in reactions (1)

so that 1 mg of water is equivalent to 10,72 C (number of coulombs). Based on this principle it

is possible to determine the amount of water directly from the quantity of electricity (number of

coulombs) required for the electrolysis.
2.3 Apparatus
2.3.1 Principle of operation

The titration vessel has the configuration of an electrolysis cell with two compartments

connected by a porous diaphragm. The anodic compartment contains the mixture of reagent-

solvent and sample (anodic solution), the cathodic compartment (generator assembly) contains

anhydrous reagent (cathodic solution). On both sides of the diaphragm are located the

electrolysis electrodes.
NOTE – Titrators without the porous diaphragm may be used.

Iodine generated by the electrolysis, as shown in reaction (3), reacts with the water in a similar

way to the Karl Fischer reactions (1) and (2). The end-point of the reaction is detected by a pair

of platinum electrodes immersed in the anodic solution. At the end of the titration, excess

iodine depolarizes the dual platinum electrodes, giving a change in the current/voltage ratio

which is used to activate the end-point indicator and to stop the current integrator.

The current integrator integrates the current consumed during the electrolysis, calculates the

water equivalent according to Faraday's law, and finally displays it in micrograms of water.

2.3.2 Description of the apparatus

Commercial coulometric Karl Fischer titrators use proprietary circuitry. The following

description of one suitable form of apparatus is given for illustrative purposes only.

The block diagram shown in figure 1 illustrates the apparatus and includes the components

detailed below.
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SIST EN 60814:1999
60814 © IEC:1997 – 11 –
2.3.2.1 Titration vessel assembly

An example of a suitable titration vessel assembly is shown in figure 2. However, the

changes in instrument technology are such that radically different designs may become

available which comply with the technical requirements of this standard. The exemplified

apparatus consists of:

– a flanged glass reaction vessel (a) with sample injection plug (b) and drain cock (c)

(optional);

– a polytetrafluoroethylene lid (d), flanged to match the titration vessel, with three holes to

receive the electrodes and drying tube;

– a generator assembly (combined electrolysis cell) (e) consisting of a glass tube closed at

its lower end by a diaphragm and equipped with platinum electrodes on each side of the

diaphragm;

NOTE – The diaphragm may consist of ion exchange membrane, fritted disc, ceramic filter or other system to

prevent diffusion of both solutions, while allowing enough current for electrolysis.

– detector electrodes: dual platinum electrodes for measurement of potential or current (f);

– a polytetrafluoroethylene coated stirrer bar (g);

– drying tubes (h) to protect the titration vessel and the generator assembly from

atmospheric moisture;

– silicone rubber septa to seal the injection port. It is recommended that crosscuts should

be made in the septa before use, to enable blunt, square-ended needles to be used for

sample injection (see 2.4.2 d)). Septa should be replaced as required to prevent air leakage

as indicated by excessive instrument drift.
2.3.2.2 Detection circuit

DC constant voltage or a.c. constant current is supplied to the detector electrodes (dual

platinum measuring electrodes) so that the end-point may be detected from the change of the

polarized current or voltage.
2.3.2.3 Current regulator circuit

This circuit controls the electrolysis according to the signal from the detector circuit.

2.3.2.4 DC power supply
DC power supply for electrolysis.
2.3.2.5 End-point indicator
Indicates when the end-point has been reached.
2.3.2.6 Current integrator

Measures the quantity of electricity consumed by the electrolysis cell during the titration, then

calculates and displays the quantity of water, in micrograms, corresponding to it.

NOTE – Some instruments have built-in calculation facilities, and display the water concentration for a specific

sample quantity.
2.3.2.7 Electromagnetic stirrer

Electromagnetic stirrer, capable of maintaining a constant speed sufficient to ensure adequate

dispersion. (The content of the titration vessel will not in general be a single phase, since most

insulating liquids are not completely miscible with the reagent liquids.)
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SIST EN 60814:1999
60814 © IEC:1997 – 13 –
2.4 Reagents and auxiliary materials

WARNING – Certain reagents may be detrimental to health and must be handled with proper

care.
2.4.1 Reagents

Prepared reagents are commercially available, but care is needed that the reagent is suitable

for the particular type of instrument used and the insulating liquid under test.

Interfering reactions may take place between methanol based reagents and some silicone

compounds. In addition, similar reactions may take place with aldehydes, some ketones, and

conjugated unsaturated organic acids, which may be present in oils as degradation products or

contaminants. In these cases, reagents not based on methanol are recommended.

NOTE – Some insulating liquids may require the use of additional or alternative solvents.

2.4.2 Auxiliary materials
a) Neutralizing solution, methanol containing approximately 20 mg water/cm .

b) Desiccant, for example, anhydrous magnesium perchlorate or self-indicating silicagel.

c) Lubricant grease: Polytetrafluoroethylene based or fluorinated hydrocarbon types.

Commercially supplied greases to this description have been found satisfactory.
3 3

d) Glass syringes for sample measurement and introduction. 10 cm and 5 cm syringes in

accordance with ISO 595, with needles of suitable length and diameter. Needles of length

100 mm and bore 1 mm have been found satisfactory for general use. Blunt, square-ended

needles are preferred, in order to minimize damage to the septa.
2.5 Preparation of the apparatus

Prepare and assemble the apparatus, install the reagents and carry out the stabilization

procedure in accordance with the manufacturer's instructions.
2.6 Sampling methods

If samples taken are intended for additional tests to water content the water analysis shall be

carried out first.
2.6.1 Routine sampling

For routine tests, the sampling methods described in clause 2 and 3.1 of IEC 60475 shall be

used. Sample bottles shall be dried by heating in an oven for 16 h to 24 h at 115 °C ± 5 °C.

2.6.2 Recommended sampling

For better accuracy, and particularly where the moisture content is very low, the procedures

described in clause 4 of IEC 60567 shall be used. Sample bottles shall be prepared as

specified in 2.7.1. The syringes and needles shall be dismantled, dried for at least 8 h at

115 °C ± 5 °C, cooled in a desiccator with anhydrous silica gel, and kept in the desiccator until

required.

NOTE – The accuracy of the determination can be adversely affected by the taking of composite or average

samples, which is not recommended.
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SIST EN 60814:1999
60814 © IEC:1997 – 15 –
2.6.3 Storage

Samples for water analysis shall at no time be exposed to direct sunlight. Between the time of

collection and analysis, the samples should be kept in the dark, and the time between

collection and analysis should be not greater than seven days.
2.7 Procedure
a) With samples which have been collected in bottles

Clean and dry in a well-ventilated oven at 115 °C ± 5 °C a glass syringe and needle of a

suitable size. Allow to cool in a desiccator. Fill the syringe with the insulating liquid, keeping

the tip of the needle well below the surface of the liquid. Re-close the glass bottle

immediately. Holding the syringe vertically with the needle uppermost, discharge all air

bubbles. Discharge the contents of the syringe to waste. Refill the syringe and weigh to the

nearest 0,1 g.
With samples which have been collected in a syringe

Discharge approximately 2 cm to flush out the needle and weigh the syringe to the

nearest 0,1 g.

The sample size is governed by the expected range of moisture content. However, the

optimum sample size has been found to be 5 cm for most types of insulating liquids, new

and used, with water contents of between 2 mg/kg and 100 mg/kg.

b) Operate the instrument controls to start the electrolysis according to the manufacturer’s

instructions and quickly inject a suitable quantity of sample into the titration vessel through

the septum. The tip of the needle shall not be allowed to touch the surface of the reagent.

Re-weigh the syringe and record the mass M, in grams, of sample injected.

Ensure that the oil is thoroughly mixed with the solvent. The speed of the stirrer shall not be

changed after the instrument has self-equilibrated or during the titration.

c) Read out the quantity of water titrated, m, (expressed in micrograms (μg)) from the

display when the titration is completed.

d) Carry out a duplicate determination by rinsing the syringe twice in the oil sample and

refilling and weighing as in step a). Carry out steps b) and c).

e) After several determinations, a considerable quantity of insulating liquid may have

accumulated. Remove the excess of liquid in accordance with the manufacturer's

instructions, which should also be followed with respect to the relative levels of the anode

and cathode reagents and re-stabilization of the instrument.

After several withdrawals, the titration vessel and generator electrode should be recharged with

fresh solutions and the stabilization procedure repeated.
2.8 Calculation of the result
water content (mg/kg) =
where
m is the quantity of water titrated in micrograms (μg);
M is the mass of insulating liquid in grams (g).
2.9 Report

The water content of the insulating liquid sample is the mean of the duplicate determinations,

expressed to the nearest integer in milligrams per kilogram (mg/kg).
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SIST EN 60814:1999
60814 © IEC:1997 – 17 –
2.10 Precision

NOTE – Precision data have been established for hydrocarbon based insulating liquids.

2.10.1 Repeatability

Duplicate determinations carried out by one operator should be considered suspect at the 95 %

confidence level if they differ by more than 0,60 x mg/kg, where x is the average of the

duplicate determinations.
2.10.2 Reproducibility

When two laboratories carry out tests on identical test material, each shall produce duplicate

results and report their mean.

The two means should be considered suspect at the 95 % confidence level if they differ by

more than 1,50 x mg/kg, where x is the average of the two means.
3 Evaporative stripping method for high viscosity liquids
3.1 Field of application

This method is designed for the determination of water in unused insulating liquids having

viscosity greater than 100 mm /s at 40 °C. This method is mainly applicable to water concen-

tration above 2 mg/kg.

NOTE – Alternatively, high viscosity liquids may also be analyzed for water content by the method in clause 2

after dilution with a suitable solvent. Precision for a dilution procedure will be affected by the degree of dilution

and the water content and viscosity of the chosen solvent.
3.2 Outline of the method

A known amount of the insulating liquid is heated in a closed vessel located next to the Karl

Fischer apparatus. The water evolved is quantitatively transferred into the titration vessel by a

stream of dry nitrogen gas where coulometric titration is performed.
3.3 Apparatus and reagents

The block diagram of the apparatus is illustrated in figure 3 and consists of the following items:

– titrator: automatic coulometric Karl Fischer (see 2.3);

– evaporator: glass vessel, 100 ml capacity; nitrogen inlet tube, 1,25 mm inside diameter

(see figure 4);
– heater: clear, transparent electro-conductive glass heater;
– temperature controller: automatic control, accuracy ± 2 °C;
– carrier gas: nitrogen gas, commercial grade, less than 10 μl/l water;

– desiccants for carrier gas: one silica gel column plus two phosphorus pentoxide columns;

– reagents as listed in 2.4.

NOTE – When interfering compounds are present, the need for suitable reagents in the titrator is of equal

importance as for direct sample injection.
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SIST EN 60814:1999
60814 © IEC:1997 – 19 –
3.4 Procedure
a) Operate the Karl Fischer titrator as per procedures specified in 2.5.

b) Inject a sufficient volume (approximately 10 cm ) of base oil into the evaporator vessel

via the septum of the injection plug so as to immerse the tip of the nitrogen inlet tube to

permit bubbling of the gas. This base oil may be the insulating liquid to be tested or any

other miscible oil which does not react with the sample and of similar viscosity at the

operating temperature to the oil being analyzed.

c) Set the temperature of the evaporator unit to 130 °C ± 5 °C and allow the temperature

to stabilize. Purge the whole system with dry nitrogen gas at a flow rate of 50 cm /min

to 200 cm /min to thoroughly dry the base oil as indicated by a low and stable reading of

background current.

d) Turn on the titration switch. Run two blanks of 10 min each on this initial base oil by

following steps f) and g) of the procedure. If the two blanks are within 5 μg of water, take the

average blank value (m ). If the two blanks differ by more than 5 μg of water, further drying

of the base oil may be needed.

e) Introduce a suitable quantity of the insulating liquid (M) into the evaporator vessel using a

syringe (minimum needle size: 2 mm inside diameter) or other suitable sampler. Weigh the

syringe before and after liquid injection to obtain the accurate mass of sample. Use a 10 g

sample for water contents greater than 10 mg/kg and a 20 g ± 5 g sample for water contents

less than 10 mg/kg.

f) Turn off titration switch on main unit, or otherwise inhibit titration, for a 10 min period to

allow moisture released in the evaporator to accumulate in the titration cell.

g) After 10 min, turn on the titration switch and allow to titrate to the end-point.

h) Read the quantity of water titrated (m ) from the Karl Fischer apparatus.

NOTE – When the water contents are higher than 50 mg/kg and/or the mass of sample is 10 g, there is the

possibility that complete evaporation of the water has not taken place. In such cases, the analysis should be

repeated as in steps e) to h) but using an increased titration delay time and/or a lower amount of oil. With some

designs of titrator this purpose can be achieved by setting the delay time sufficiently long.

i) It is good practice to confirm stable operating conditions by carrying out another blank

determination for a 10 min period. If the value determined is within 5 μg of the original blank

value m , no further titration is needed.
j) Carry out a duplicate determination.

NOTE – In the case of routine tests steps d) and i) may be omitted and in steps f) and g) the 10 min may be

reduced to 1 min.
3.5 Calculation of water content
For each individual determination, calculate the water content as follows:
mm−
water content (mg/kg) =
where
m is the average blank reading in micrograms (μg);
m is the mass of water titrated during sample analysis in micrograms (μg);
M is the mass of the sample in grams (g).
3.6 Report

The water content of the insulating liquid sample is expressed as the average of duplicate

determinations to the nearest integer in milligrams per kilogram.
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SIST EN 60814:1999
60814 © IEC:1997 – 21 –
4 Determination of water in oil-impregnated paper and pressboard
4.1 Field of application

These methods apply to the determination of the water content in oil-impregnated cellulosic

insulation materials. Three procedures are described:

– with the procedure in 4.2, water is first extracted with absolute methanol and the

determination carried out on the extract;

– with the procedure in 4.3, water extraction takes place directly in the titration vessel

(see note);

NOTE – This procedure is restricted to cellulosic material of thickness up to approximately 1 mm because an

oil-impregnated sample of higher thickness can never be completely extracted within the normal duration of a

determ
...

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