Insulating liquids - Quantitative determination of methanol and ethanol in insulating liquids

IEC TR 63025:2021(E) specifies two test methods for methanol and ethanol determination in insulating liquids.
Methanol (MeOH) and ethanol (EtOH) are two light alcohols generated during the degradation process of cellulosic materials. They are soluble in insulating liquids so they can be regarded as ageing tracers whose concentrations in oil reflect the degradation of insulating cellulosic materials in liquid-impregnated transformers.

General Information

Status
Published
Publication Date
11-Jul-2021
Current Stage
PPUB - Publication issued
Completion Date
12-Jul-2021
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IEC TR 63025
Edition 1.0 2021-07
TECHNICAL
REPORT
colour
inside
Insulating liquids – Quantitative determination of methanol and ethanol in
insulating liquids
IEC TR 63025:2021-07(en)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC TR 63025
Edition 1.0 2021-07
TECHNICAL
REPORT
colour
inside
Insulating liquids – Quantitative determination of methanol and ethanol in
insulating liquids
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.040.10 ISBN 978-2-8322-9990-6

Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – IEC TR 63025:2021 © IEC 2021
CONTENTS

FOREWORD ........................................................................................................................... 4

INTRODUCTION ..................................................................................................................... 6

1 Scope .............................................................................................................................. 8

2 Normative references ...................................................................................................... 8

3 Terms and definitions ...................................................................................................... 8

4 Symbols and abbreviated terms ....................................................................................... 9

5 Sampling ....................................................................................................................... 10

6 Principle of the methods ................................................................................................ 10

7 Method A – HS-GC-MS .................................................................................................. 10

7.1 General ................................................................................................................. 10

7.2 Apparatus ............................................................................................................. 10

7.2.1 Analytical balance ......................................................................................... 10

7.2.2 Headspace sampler ....................................................................................... 10

7.2.3 Gas chromatograph coupled with mass spectrometry detector ....................... 11

7.3 Reagents and materials ........................................................................................ 11

7.3.1 Laboratory equipment and glassware ............................................................. 11

7.3.2 Standard chemicals ....................................................................................... 11

7.3.3 GC carrier gases ........................................................................................... 12

7.4 Preparation of standard solutions .......................................................................... 12

7.4.1 General ......................................................................................................... 12

7.4.2 Degassed insulating liquid ............................................................................. 12

7.4.3 Internal standard stock solution ..................................................................... 12

7.4.4 Standard solutions of methanol and ethanol .................................................. 13

7.5 Sample preparation ............................................................................................... 14

7.6 Headspace sampler parameters ............................................................................ 15

7.7 Gas chromatograph parameters ............................................................................ 15

7.7.1 Injector .......................................................................................................... 15

7.7.2 Carrier gas .................................................................................................... 15

7.7.3 Temperature ramp ......................................................................................... 15

7.8 Mass spectrometer parameters ............................................................................. 16

7.9 Analysis procedure ............................................................................................... 16

7.10 Internal standard calibration .................................................................................. 17

7.10.1 General ......................................................................................................... 17

7.10.2 Response factor determination ...................................................................... 18

7.11 Expression of the results ....................................................................................... 18

8 Method B – HS-GC-FID ................................................................................................. 18

8.1 General ................................................................................................................. 18

8.2 Apparatus ............................................................................................................. 18

8.2.1 Analytical balance ......................................................................................... 18

8.2.2 Headspace sampler ....................................................................................... 18

8.2.3 Gas chromatograph with flame ionization detector ......................................... 19

8.3 Reagents and materials ........................................................................................ 19

8.3.1 Laboratory equipment and glassware ............................................................. 19

8.3.2 Standard chemicals ....................................................................................... 19

8.3.3 GC carrier gases ........................................................................................... 19

8.4 Preparation of standard solutions .......................................................................... 20

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IEC TR 63025:2021 © IEC 2021 – 3 –

8.4.1 General ......................................................................................................... 20

8.4.2 Degassed insulating liquid ............................................................................. 20

8.4.3 Standard solutions of methanol and ethanol .................................................. 20

8.5 Sample preparation ............................................................................................... 21

8.6 Headspace sampler parameters ............................................................................ 21

8.7 Gas chromatograph parameters ............................................................................ 22

8.7.1 Injector .......................................................................................................... 22

8.7.2 Carrier gas .................................................................................................... 22

8.7.3 Temperature ramp ......................................................................................... 22

8.7.4 FID parameters .............................................................................................. 22

8.8 Analysis procedure ............................................................................................... 22

8.9 Calibration ............................................................................................................ 23

8.10 Expression of the results ....................................................................................... 23

9 Test report ..................................................................................................................... 23

10 Precision ....................................................................................................................... 24

10.1 Verification of the entire analytical system ............................................................ 24

10.2 General ................................................................................................................. 24

10.3 Detection limits of Method A and Method B ........................................................... 24

10.4 Repeatability ......................................................................................................... 24

10.5 Reproducibility ...................................................................................................... 25

Bibliography .......................................................................................................................... 26

Figure 1 – Comparison of methanol and 2-furfural production in mineral oil versus

cellulose scission number ....................................................................................................... 7

Figure 2 –Typical chromatogram with selected ion (m/z = 31) mass spectrum ....................... 17

Figure 3 – Typical GC-FID chromatogram ............................................................................. 23

Table 1 –Method A – Example of GC temperature ramp parameters ..................................... 16

Table 2 – Method A – m/z values of internal standard ions .................................................... 16

Table 3 – Method B – Examples of FID parameters reported in literature .............................. 22

Table 4 – Detection limits of Method A and Method B, in mineral oil ..................................... 24

Table 5 – Repeatability (r) in % for Method A (HS-GC-MS), in mineral oil ............................. 24

Table 6 – Reproducibility (R) in % for Method A (HS-GC-MS), in mineral oil .......................... 25

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– 4 – IEC TR 63025:2021 © IEC 2021
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INSULATING LIQUIDS – QUANTITATIVE DETERMINATION OF
METHANOL AND ETHANOL IN INSULATING LIQUIDS
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

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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.

IEC TR 63025 has been prepared by IEC technical committee 10: Fluids for electrotechnical

applications. It is a Technical Report.
The text of this Technical Report is based on the following documents:
Draft Report on voting
10/1112/DTR 10/1131/RVDTR

Full information on the voting for its approval can be found in the report on voting indicated in

the above table.
The language used for the development of this Technical Report is English.

This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in

accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available

at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are

described in greater detail at www.iec.ch/standardsdev/publications.
---------------------- Page: 6 ----------------------
IEC TR 63025:2021 © IEC 2021 – 5 –

The committee has decided that the contents of this document will remain unchanged until the

stability date indicated on the IEC website under webstore.iec.ch in the data related to the

specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.

IMPORTANT – The "colour inside" logo on the cover page of this document indicates

that it contains colours which are considered to be useful for the correct understanding

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

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– 6 – IEC TR 63025:2021 © IEC 2021
INTRODUCTION

It has been demonstrated over several years that the ageing of impregnated paper in insulating

liquid, which results in cellulose degradation, produces molecules of light alcohols, methanol

(MeOH) and ethanol (EtOH). In laboratory experiments, a good correlation has been established

between the increase of the methanol content in insulating liquid and the decrease of the degree

of polymerization of the cellulose, irrespective of the type of paper, standard kraft or thermally

upgraded. Further, at the early stages of paper ageing, i.e. of cellulose degradation, the

methanol content is always higher than that of furanic compounds (mainly 2-furfural), so this

behaviour suggests that methanol could be a relevant in-oil marker to detect early paper ageing

in transformers and to assess its evolution (see Figure 1).

Ethanol is a second light alcohol of interest that these methods would be able to detect.

It should be emphasized that in a real transformer the situation is much more complicated than

in laboratory setups, so the relationship between in situ paper degradation and tracer

concentration (MeOH, EtOH, as well as 2-FAL) is much more complex and hard to establish.

In order to address the growing interest of industry in using these alcohols as tracers of

cellulosic material ageing in operating equipment, there is a need for the development of a

document describing analytical methods to quantify methanol and ethanol in the different types

of insulating liquids. The objective is for one of these methods to remain as simple and

affordable as possible, and for the other to be more sophisticated and more accurate.

The principle of this Technical Report was brought up and discussed during the IEC TC 10

plenary meeting held in Vienna in November 2013. A project team was set up to prepare test

methods for the unambiguous quantitative determination of methanol and ethanol in unused

and used insulating liquids.
WARNING – Health and safety

This document does not purport to address all the safety problems associated with its use. It is

the responsibility of the user of this document 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 document should be handled with due regard

to personal hygiene. Direct contact with eyes may cause slight irritation. In the case of eye

contact, irrigation with copious quantities of clean running water should be carried out and

medical advice sought.

Some of the tests specified in this document involve the use of processes that could lead to a

hazardous situation. Attention is drawn to the relevant standard for guidance.
WARNING – Environment

This document involves mineral oils, ester liquids, chemicals and used sample containers. The

disposal of these items should be carried out in accordance with current national legislation

with regard to their impacts on the environment. Every precaution should be taken to prevent

the release into the environment of the chemicals used during the test.
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IEC TR 63025:2021 © IEC 2021 – 7 –
a) Clupak HD75 specimens
b) Manning 220 mannitherm D specimens
Key

NS: number of scissions, inversely proportional to the polymerization degree (DPv)

a): standard kraft paper
b): thermally upgraded paper

NOTE See Jalbert J., Gilbert R., Tétreault P., Morin B. and Lessard-Déziel D. (2007) in the Bibliography.

Figure 1 – Comparison of methanol and 2-furfural production in mineral oil
versus cellulose scission number
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– 8 – IEC TR 63025:2021 © IEC 2021
INSULATING LIQUIDS – QUANTITATIVE DETERMINATION OF
METHANOL AND ETHANOL IN INSULATING LIQUIDS
1 Scope

This document specifies two test methods for methanol and ethanol determination in insulating

liquids.

Methanol (MeOH) and ethanol (EtOH) are two light alcohols generated during the degradation

process of cellulosic materials. They are soluble in insulating liquids so they can be regarded

as ageing tracers whose concentrations in oil reflect the degradation of insulating cellulosic

materials in liquid-impregnated transformers.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following

addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
flame ionization detector

device in which hydrocarbons are burned in a hydrogen-air flame and the electrical current

caused by the resulting ions is measured between two electrodes

Note 1 to entry: The flame ionization detector is used in gas chromatography mainly to detect hydrocarbon

compounds.
[SOURCE: ISO 14532:2014, 2.4.8, modified – "detector" replaced with "device".]
3.2
gas chromatograph

device used to determine complex mixture components that can be vaporized without

decomposition then separated by differential migration with a carrier gas through a stationary

phase in a column
Note 1 to entry: The method used is called "gas chromatography" (GC).

[SOURCE: IEC 62697-1:2012, 3.1.14, modified – "used for separating volatile and semi-volatile

compounds in mixtures" replaced with "used to determine complex mixture components",

"through differential migration" replaced with "then separated by differential migration" and "a

stationary phase" and Note 1 to entry added.]
3.3
headspace extraction

procedure for collecting the volatile compounds emitted by a specimen enclosed in an airtight

vial under controlled conditions
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IEC TR 63025:2021 © IEC 2021 – 9 –

Note 1 to entry: The gaseous phase is assumed to contain the volatile compounds in equilibrium with that present

in the specimen in the vial (via Henry’s partition coefficient).

[SOURCE: ISO 8873-3:2007, 3.7, modified – In the term "analysis" replaced with "extraction",

definition revised and note replaced with the Note to entry.]
3.4
internal standard

compound, different from target analytes but as similar as possible in its properties (structure,

polarity, etc.) and analytical response, which is added in the tested sample in a known amount

and detected simultaneously with the analytes

Note 1 to entry: A defined volume of the internal standard solution is added to both the sample and calibration

solution such that they both contain an identical concentration.
[SOURCE: IEC 62697-1:2012, 3.1.12, modified – Definition revised.]
3.5
mass spectrometer

instrument used for ionizing neutral chemical species, separating ions according to their mass

to charge ratio (m/z) and then detecting selected ions

Note 1 to entry: It permits determining concentrations of target analytes in complex mixtures such as insulating

liquids.
Note 2 to entry: The method used is called "mass spectrometry" (MS).

[SOURCE: IEC 62697-1:2012, 3.1.15, modified – "(m/z) and then detecting selected ions"

added, in the Note 1 to entry "compounds" replaced with "analytes" and Note 2 to entry added.]

4 Symbols and abbreviated terms

For the purposes of this document, the following symbols and abbreviated terms are used.

DMSO dimethyl sulfoxid
ethanol (CH -CH -OH)
EtOH
3 2
FID flame ionization detector
GC gas chromatography / gas chromatograph
HS headspace (vial/extraction/sampler)
gas chromatograph, with headspace sampler, coupled with
HS-CG-MS
a mass spectrometer detector (Method A)
gas chromatograph, with headspace sampler, coupled with
HS-CG-FID
a flame ionization detector (Method B)
IS internal standard
methanol (CH -OH)
MeOH
MS mass spectrometer (detector)
PLOT porous layer open tubular
PTFE polytetrafluoroethylene
RT retention time
RF response factor
SIM selected-ion monitoring
TIC total ion current
TOGA total oil gas analysis
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– 10 – IEC TR 63025:2021 © IEC 2021
5 Sampling

Insulating liquid is sampled in a glass syringe following the procedure given in IEC 60475:2011,

4.2.2 that provides guidance for the sampling of insulating liquids for dissolved gas analysis.

A representative sample requires a sufficient purge of the injection system of the apparatus, to

ensure that the stagnant insulating liquid in the valve is eliminated.

NOTE Sampling is preferably performed in a glass syringe or suitable aluminium can or glass bottle filled to the top

according to DGA sampling practices specified in IEC 60475:2011, 4.2.1.5.
6 Principle of the methods

The analysis requires extraction of MeOH and EtOH from an insulating liquid sample in a closed

vial with free space, and then injection of the gaseous phase into a chromatograph. MeOH and

EtOH are separated from the other volatile constituents of the sample through a suitable

capillary column, and detected at the outlet of the column using a mass spectrometer or a flame

ionization detector.

Their quantification is done using external calibration curves or by the internal standard

technique.
The two elected methods are:

• Method A: gas chromatography with headspace sampler, coupled with a mass spectrometer

detector (HS-GC-MS), and

• Method B: gas chromatography with headspace sampler, coupled with a flame ionization

detector (HS-GC-FID):
The MeOH quantification limit is around 10 µg · kg with both methods.
NOTE Method B can be less sensitive in the case of heavily aged liquids.
7 Method A – HS-GC-MS
7.1 General
Differences between gas chromatographs, headspace samplers and mass spectrometer

detectors from different manufacturers make it impractical to specify detailed operating

conditions. Refer to the manufacturer's instructions for instrument setup to allow optimized

separation and detection of MeOH and EtOH.
7.2 Apparatus
7.2.1 Analytical balance
A balance with a precision at 4 gram decimal (0,000 1 g) or better is used.
7.2.2 Headspace sampler

HS sampler equipped with an oven capable of heating the HS vials up to 90 °C, running with

mechanical shaking. Its injection loop and transfer line are connected to the injection port of

the gas chromatograph.
Injection volume is in the range of 250 µl to 1 000 µl.
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IEC TR 63025:2021 © IEC 2021 – 11 –
7.2.3 Gas chromatograph coupled with mass spectrometry detector
A gas chromatograph equipped with a mass spectrometry detector is used.

A split/splitless injector can be used but other injection techniques are suitable (e.g. on-column).

The use of a porous layer open tubular (PLOT) GC column is preferred to achieve adequate

peak separation and to achieve good detection limits. A capillary column for light alcohols, 10 m

to 60 m long, low bleeding, giving the appropriate separation of the analytes and potential

interferents is opted for.

NOTE 624-type capillary columns were found suitable for the purpose. Other columns can be used if appropriate

peak separation is obtained.

A single quadrupole MS detector is sufficient to obtain the required quantification limit, however

devices which demonstrate similar or better quantification limits can also be used (e.g. high

resolution mass spectrometer, tandem mass spectrometer, ion trap).
7.3 Reagents and materials
7.3.1 Laboratory equipment and glassware

The vessels and accessories used for the tests are cleaned and prepared with analytical grade

solvents.

NOTE 1 To ensure that all glassware and accessories are free from MeOH and EtOH, they can be heated in an

oven at 100 °C for 1 h to 2 h and brought back to room temperature prior to their use.

• headspace glass vials of 20 ml nominal capacity, with crimp- or screw-type caps and

polytetrafluoroethylene (PTFE) faced butyl septa;
NOTE 2 Vials and septa fulfilling the IEC 60567 requirements are suitable.
NOTE 3 Other volumes of vials are suitable (e.g. 10 ml).
• crimping system;
• Class A volumetric flasks;
• standard flask with stopper, in a precision c
...

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