IEC 60567:2023
(Main)Oil-filled electrical equipment - Sampling of free gases and analysis of free and dissolved gases in mineral oils and other insulating liquids - Guidance
Oil-filled electrical equipment - Sampling of free gases and analysis of free and dissolved gases in mineral oils and other insulating liquids - Guidance
IEC 60567:2023 deals with the techniques for sampling free gases from gas-collecting relays from power transformers. Three methods of sampling free gases are described. The techniques for sampling oil from oil-filled equipment such as power and instrument transformers, reactors, bushings, oil-filled cables and oil-filled tank-type capacitors are no longer covered by this document, but are instead described in IEC 60475:2022, 4.2. Before analysing the gases dissolved in oil, they are first extracted from the oil. Three basic methods are described, one using extraction by vacuum (Toepler and partial degassing), another by displacement of the dissolved gases by bubbling the carrier gas through the oil sample (stripping) and the last one by partition of gases between the oil sample and a small volume of the carrier gas (headspace). The gases are analysed quantitatively after extraction by gas chromatography; a method of analysis is described. Free gases from gas-collecting relays are analysed without preliminary treatment.
Matériels électriques immergés - Échantillonnage de gaz libres et analyse des gaz libres et dissous dans les huiles minérales et d'autres liquides isolants - Recommandations
L'IEC 60567:2023 traite des techniques d'échantillonnage de gaz libres au niveau des relais de protection des transformateurs de puissance. Trois méthodes d'échantillonnage des gaz libres sont décrites. Les techniques d'échantillonnage de l'huile dans les matériels immergés dans l'huile, tels que les transformateurs de puissance et de mesure, les bobines d'inductances, les traversées de transformateurs, les câbles à huile fluide et les condensateurs de puissance ne sont plus couverts par le présent document, mais se trouvent dorénavant dans l'IEC 60475:2022, 4.2. Avant d'analyser les gaz dissous dans l'huile, ils sont en premier lieu extraits de l'huile. Trois méthodes de base sont décrites, l'une utilisant l'extraction sous vide (Toepler et dégazage partiel), une autre par déplacement des gaz dissous par barbotage d'un gaz vecteur dans l'échantillon d'huile (entraînement) et la dernière par partition des gaz entre l'échantillon d'huile et un faible volume du gaz vecteur (espace de tête). Après extraction, l'analyse quantitative des gaz s'effectue par chromatographie en phase gazeuse; une méthode d'analyse est décrite. Les gaz libres prélevés au niveau des relais de protection sont analysés sans traitement préalable.
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IEC 60567 ®
Edition 5.0 2023-12
COMMENTED VERSION
INTERNATIONAL
STANDARD
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Oil-filled electrical equipment – Sampling of free gases and analysis of free and
dissolved gases in mineral oils and other insulating liquids – Guidance
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IEC 60567 ®
Edition 5.0 2023-12
COMMENTED VERSION
INTERNATIONAL
STANDARD
colour
inside
Oil-filled electrical equipment – Sampling of free gases and analysis of free and
dissolved gases in mineral oils and other insulating liquids – Guidance
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.040.10 ISBN 978-2-8322-7996-0
– 2 – IEC 60567:2023 CMV © IEC 2023
CONTENTS
FOREWORD .5
INTRODUCTION .7
1 Scope .9
2 Normative references .9
3 Terms, definitions, symbols and abbreviated terms . 10
3.1 Terms and definitions . 10
3.2 Symbols and abbreviated terms . 10
3.2.1 Symbols . 10
3.2.2 Abbreviated terms . 10
4 Sampling of gases from gas-collecting (Buchholz) relays . 11
4.1 General remarks . 11
4.2 Sampling of free gases by syringe . 11
4.2.1 Sampling equipment . 11
4.2.2 Sampling procedure . 12
4.3 Sampling of free gases by displacement of oil . 13
4.4 Sampling of free gases by vacuum . 13
4.5 Sampling of oil from oil filled equipment . 15
5 Labelling of gas samples . 15
6 Sampling, labelling and transferring of oil from oil-filled equipment . 16
6.1 Sampling and labelling of oil . 16
6.2 Transfer of oil for DGA analysis . 16
6.2.1 General . 16
6.2.2 Transfer from oil syringes . 16
6.2.3 Transfer from ampoules . 16
6.2.4 Transfer from flexible metal bottles . 17
6.2.5 Transfer from glass and rigid metal bottles . 17
7 Preparation of gas-in-oil standards . 17
7.1 General remarks . 17
7.2 First method: preparation of a large volume of gas-in-oil standard . 17
7.2.1 Equipment . 17
7.2.2 Procedure . 18
7.2.3 Calculation . 20
7.3 Second method: preparation of gas-in-oil standards in a syringe or a vial . 20
7.3.1 General . 20
7.3.2 Equipment . 22
7.3.3 Procedure . 22
8 Extraction of gases from oil . 22
8.1 General remarks . 22
8.2 Multi-cycle vacuum extraction using Toepler pump apparatus . 23
8.2.1 General . 23
8.2.2 Toepler pump extraction apparatus . 23
8.2.3 Extraction procedure . 26
8.3 Vacuum extraction by partial degassing method . 27
8.3.1 General remarks . 27
8.3.2 Partial degassing apparatus . 27
8.3.3 Extraction procedure . 28
8.4 Stripping extraction method . 28
8.4.1 General . 28
8.4.2 Stripping apparatus . 28
8.4.3 Outline of procedure . 31
8.5 Headspace method . 32
8.5.1 Principle of the method . 32
8.5.2 Headspace extraction apparatus . 33
8.5.3 Headspace extraction procedure . 37
8.5.4 Calibration of the headspace extractor . 41
9 Gas analysis by gas-solid chromatography . 43
9.1 General remarks . 43
9.2 Outline of suitable methods using Table 4 . 45
9.3 Apparatus. 45
9.3.1 Gas chromatograph . 45
9.3.2 Columns . 47
9.3.3 Carrier gas . 47
9.3.4 Detectors . 47
9.3.5 Methanator . 47
9.3.6 Cold trap . 47
9.3.7 Integrator and recorder . 47
9.4 Preparation of apparatus. 48
9.5 Analysis . 48
9.6 Calibration of the chromatograph . 48
9.7 Calculations . 49
10 Quality control . 49
10.1 Verification of the entire analytical system . 49
10.2 Limits of detection and quantification . 50
10.3 Repeatability, reproducibility and accuracy . 51
10.3.1 General remark . 51
10.3.2 Repeatability . 51
10.3.3 Reproducibility . 51
10.3.4 Accuracy . 52
11 Report of results . 52
Annex A (informative) Correction for incomplete gas extraction in partial degassing
method by calculation. 54
Annex B (informative) Mercury-free and shake test versions of the standard extraction
methods.
Annex B (informative) Alternative gas extraction methods . 58
B.1 Mercury-free versions of the vacuum extraction methods . 58
B.1.1 Mercury-free version of the Toepler method . 58
B.1.2 Mercury-free version of the partial degassing method . 58
B.2 Syringe versions of the headspace method . 58
B.2.1 Shake test method . 58
B.2.2 Mechanical oscillation method . 60
Annex C (informative) Preparation of air-saturated standards . 61
Annex D (informative) Correction for gas bubbles in syringes and air gap in rigid
bottles . 62
Annex E (informative) Procedure for comparing gas monitor readings to laboratory
results . 63
– 4 – IEC 60567:2023 CMV © IEC 2023
Annex F (normative) Insulating liquids based on synthetic and natural esters and
silicones . 64
Bibliography . 66
List of comments . 67
Figure 1 – Sampling of gas by syringe . 12
Figure 2 – Sampling of free gases by oil displacement . 13
Figure 3 – Sampling of free gases by vacuum . 15
Figure 4 – First method of preparing gas-in-oil standards . 19
Figure 5 – Second method for preparing gas-in-oil standards . 21
Figure 6 – Example of a Toepler pump extraction apparatus . 25
Figure 7 – Types of glass strippers . 29
Figure 8 – Stainless steel stripper . 30
Figure 9 – Schematic arrangement for connecting an oil stripper to a gas
chromatograph . 31
Figure 10 – Schematic representation of headspace sampler. 32
Figure 11 – Vial filled with water . 34
Figure 12 – Revolving table . 36
Figure 13 – Schematic arrangement for gas chromatography . 46
Figure B.1 – Schematic representation of methods in Annex B .
Figure B.1 – Schematic representation of mercury-free Toepler method . 59
Figure B.2 – Schematic representation of mercury-free partial degassing method . 59
Figure B.3 – Schematic representation of shake test method . 59
Figure B.4 – Schematic representations of mechanical oscillation method . 60
Table 1 – Information required for gas samples . 16
Table 2 – Examples of headspace operating conditions . 37
Table 3 – Examples of headspace partition coefficients at 70 °C in mineral insulating oil . 43
Table 4 – Examples of gas chromatographic operating conditions . 44
Table 5 – Required limits of detection in oil . 50
Table 6 – Examples of accuracy of extraction methods . 52
Table A.1 – Examples of solubility coefficients a (at 25 °C) reported by
i
CIGRE TF D1.01.15 in 2006 . 54
Table C.1 – Examples of solubility values of air for different oil types . 61
Table C.2 – Examples of temperature variations for oxygen and nitrogen solubility in
mineral oil . 61
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
OIL-FILLED ELECTRICAL EQUIPMENT –
SAMPLING OF FREE GASES AND ANALYSIS
OF FREE AND DISSOLVED GASES IN MINERAL OILS
AND OTHER INSULATING LIQUIDS – GUIDANCE
FOREWORD
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This commented version (CMV) of the official standard IEC 60567:2023 edition 5.0 allows
the user to identify the changes made to the previous IEC 60567:2011 edition 4.0.
Furthermore, comments from IEC TC 10 experts are provided to explain the reasons of
the most relevant changes, or to clarify any part of the content.
A vertical bar appears in the margin wherever a change has been made. Additions are in
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This publication contains the CMV and the official standard. The full list of comments is
available at the end of the CMV.
– 6 – IEC 60567:2023 CMV © IEC 2023
IEC 60567 has been prepared by IEC technical committee 10: Fluids for electrotechnical
applications. It is an International Standard.
This fifth edition cancels and replaces the fourth edition published in 2011. This edition
constitutes a technical revision. 1
This edition includes the following significant technical changes with respect to the previous
edition:
a) a new normative Annex F relating to DGA analysis of insulating liquids other than mineral
oils (esters and silicones) has been added;
b) Clause 4 to Clause 11 and informative Annex A to Annex E remain devoted to mineral oils;
c) two new mercury-free gas extraction methods are described in Annex B (low pressure
vacuum extraction and mechanical oscillation).
The text of this International Standard is based on the following documents:
Draft Report on voting
10/1207/FDIS 10/1211/RVD
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 International Standard 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/publications.
The committee has decided that the contents of this document will remain unchanged until the
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specific document. At this date, the document will be
• reconfirmed,
• withdrawn, or
• revised.
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.
INTRODUCTION
Gases may can be formed in oil-filled electrical equipment due to natural ageing but also, to a
much greater extent, as a result of faults.
Operation with a fault may can seriously damage the equipment, and it is valuable to be able
to detect the fault at an early stage of development.
Where a fault is not severe, the gases formed will normally dissolve in the oil, with a small
proportion eventually diffusing from the liquid into any gas phase above it. Extracting dissolved
gas from a sample of the oil and determining the amount and composition of this gas is a means
of detecting such faults, and the type and severity of any fault may can often be inferred from
the composition of the gas and the rate at which it is formed.
In the case of a sufficiently severe fault, free gas will pass through the oil and collect in the gas-
collecting (Buchholz) relay if fitted; if necessary, this gas may be analysed to assist in
determining the type of fault that has generated it. The composition of gases within the bubbles
changes as they move through the oil towards the gas-collecting relay.
This can be put to good use, as information on the rate of gas production may can often be
inferred by comparing the composition of the free gases collected with the concentrations
remaining dissolved in the liquid.
The interpretation of the gas analyses is the subject of IEC 60599.
These techniques are valuable at all stages in the life of oil-filled equipment. During acceptance
tests on transformers in the factory, comparison of gas-in-oil analyses before, during and after
a heat run test can show if any hot-spots are present, and similarly analysis after dielectric
testing can add to information regarding the presence of partial discharges or sparking. During
operation in the field, the periodic removal of an oil sample and analysis of the gas content
serve to monitor the condition of transformers and other oil-filled equipment.
The importance of these techniques has led to the preparation of this document, to the
procedures used for the sampling, from oil-filled electrical equipment, of gases and oils
containing gases, and for subsequent analysis.
NOTE Methods described in this document apply to insulating oils, since experience to date has been almost
entirely with such oils. The methods may can also be applied to other insulating liquids, in some cases with
modifications.
General caution, health, safety and environmental protection
WARNING – 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 oils which are the subject of this document should be handled with due regard
to personal hygiene. Direct contact with the eyes may can cause 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 can lead to a hazardous situation. Attention is drawn to the relevant
standard for guidance.
Mercury presents an environmental and health hazard. Any spillage should immediately be
removed and be properly disposed of. Consult local regulations Regulatory requirements for
mercury use and handling can apply. Mercury-free methods may be requested in some
countries.
– 8 – IEC 60567:2023 CMV © IEC 2023
Environment
WARNING – This document is applicable to insulating oils, chemicals and used sample
containers.
Attention is drawn to the fact that, at the time of writing of this document, many insulating oils
in service are known to be contaminated to some degree by polychlorinated biphenyls (PCBs).
If this is the case, safety countermeasures should be taken to avoid risks to workers, the public
and the environment during the life of the equipment, by strictly controlling spills and emissions.
Disposal or decontamination of these oils should be carried out strictly according to local
regulations can be subject to regulatory requirements. Every precaution should be taken to
prevent the release of any type of insulating oil into the environment, including those partially
biodegradable with time.
OIL-FILLED ELECTRICAL EQUIPMENT –
SAMPLING OF FREE GASES AND ANALYSIS
OF FREE AND DISSOLVED GASES IN MINERAL OILS
AND OTHER INSULATING LIQUIDS – GUIDANCE
1 Scope
This document deals with the techniques for sampling free gases from gas-collecting relays
from power transformers. Three methods of sampling free gases are described.
The techniques for sampling oil from oil-filled equipment such as power and instrument
transformers, reactors, bushings, oil-filled cables and oil-filled tank-type capacitors are no
longer covered by this document, but are instead described in IEC 60475:20112022, 4.2.
Before analysing the gases dissolved in oil, they are first extracted from the oil. Three basic
methods are described, one using extraction by vacuum (Toepler and partial degassing),
another by displacement of the dissolved gases by bubbling the carrier gas through the oil
sample (stripping) and the last one by partition of gases between the oil sample and a small
volume of the carrier gas (headspace). The gases are analysed quantitatively after extraction
by gas chromatography; a method of analysis is described. Free gases from gas-collecting
relays are analysed without preliminary treatment.
The preferred method for ensuring the performance of the gas extraction and analysis
equipment, considered together as a single system, is to degas samples of oil prepared in the
laboratory and containing known concentrations of gases ("gas-in-oil standards") and
quantitatively analyse the gases extracted. Two methods of preparing gas-in-oil standards are
described.
For daily calibration checks of the chromatograph, it is convenient to use a standard gas mixture
containing a suitable known amount of each of the gas components to be in a similar ratio to
the common ratios of the gases extracted from transformer oils.
The techniques described take account, on the one hand, of the problems peculiar to analyses
associated with acceptance testing in the factory, where gas contents of oil are generally very
low and, on the other hand, of the problems imposed by monitoring equipment in the field,
where transport of samples may can be by un-pressurized air freight and where considerable
differences in ambient temperature may can exist between the plant and the examining
laboratory.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 60296, Fluids for electrotechnical applications – Unused Mineral insulating oils for
transformers and switchgear Mineral insulating oils for electrical equipment
IEC 60475:20112022, Method of sampling insulating liquids
IEC 60599, Mineral oil-impregnated electrical equipment in service – Guide to the interpretation
of dissolved and free gases analysis
– 10 – IEC 60567:2023 CMV © IEC 2023
ISO 5725 (all parts), Accuracy (trueness and precision) of measurement methods and results
ISO 5725-1, Accuracy (trueness and precision) of measurement methods and results – Part 1:
General principles and definitions
ASTM D2780, Standard Test Method for Solubility of Fixed Gases in Liquids
3 Terms, definitions, symbols and abbreviated terms
3.1 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.2 Symbols and abbreviated terms
3.2.1 Symbols
The symbols used in 8.5.2 are:
V total volume of the vial
V volume of the gas phase in the vial
G
V volume of the oil phase in the vial
L
C concentration of gas (i) in the gas phase of vial, obtained by GC (gas chromatography)
G
0*
concentration of gas (i) in the oil sample, obtained directly from C using calibration
C
L G
curves with gas-in-oil standards
P, t atmospheric pressure and temperature when the oil sample was analysed (P in kPa;
t in °C)
P , t atmospheric pressure and temperature when the gas-in-oil standard, or the gas
s s
standard, was analysed (P in kPa; t in °C)
s s
K partition coefficient of gas (i), for the calculation of using gas standards
C
L
concentration of gas (i) in the oil sample
C
L
3.2.2 Abbreviated terms
DGA dissolved gas analysis
FID flame ionization detector
GC gas chromatography
GILS gas-in-liquid standards
GIOS gas-in-oil standards
HID helium ionization detector
ID inner diameter
NIST National Institute of Standards and Technology
OD outer diameter
anger
OLTC on-load tap-ch
PLOT porous large open tubular
PTFE polytetrafluoroethylene
TCD thermal conductivity detector
4 Sampling of gases from gas-collecting (Buchholz) relays
4.1 General remarks
It is important to bear in mind that receiving a qualitative and a representative sample is crucial
for obtaining a reliable diagnosis of the electrical equipment. Even the most sophisticated
extraction or diagnosis methods cannot overcome faulty samples.
Gas samples from relays should be taken from the equipment with the minimum delay after gas
accumulation has been signalled. Changes in composition caused by the selective re-
absorption of components may can occur if free gases are left in contact with oil.
Certain precautions are necessary when taking gas samples. The connection between the
sampling device and the sampling vessel shall avoid the ingress of air. Temporary connections
should be as short as possible. Any rubber or plastic tubing used should have been proved to
be impermeable to gases.
Gas samples should shall be properly labelled (see Clause 5) and analysed without undue delay
to minimize hydrogen loss from the syringe used for gas sampling (e.g. within a maximum period
of one week).
Oxygen, if present in the gas, may can react with any oil drawn out with the sample. Reaction
is delayed by excluding light from the sample, for example, by wrapping the vessel in aluminium
foil or suitable opaque material.
4.4, the syringe method is recommended. The
Of the three methods described in 4.2, 4.3 and
other two methods are alternatives to be used exclusively in case of serious hindrance.
Sampling into a sampling tube by liquid displacement using transformer oil as a sealing liquid
is simple, but require to take into account the different solubilities of the gas components may
need to be taken into account if the gas quantity is such that some oil remains in the tube.
The vacuum method requires skill to avoid contaminating the sample by leakage of air into the
system. It is particularly true where the gas to be sampled may can be at less than atmospheric
pressure (e.g. some sealed transformers).
4.2 Sampling of free gases by syringe
4.2.1 Sampling equipment
NOTE Numbers in brackets refer to those circled numbers in the relevant figure.
See Figure 1. The equipment shall be as follows:
a) Impermeable oil-resistant plastic or rubber tubing (3) provided with a connector to fit onto a
suitable sampling connection of the gas-collecting relay. To avoid cross-contamination, the
tubing should be used only once.
b) Gas-tight syringes of suitable volume (1) (25 ml to 250 ml). Medical or veterinary quality
glass syringes with ground-in plungers may be suitable; alternatively, syringes with oil-proof
seals may be used. The syringe should be fitted with a cock enabling it to be sealed. It is
often convenient to use the same syringes for both gas sampling and for oil sampling (see
IEC 60475:20112022, 4.2.2).
The gas tightness of a glass syringe used for gas sampling may be tested by storing an oil
sample containing a measurable quantity of hydrogen for at least two weeks and analysing
– 12 – IEC 60567:2023 CMV © IEC 2023
aliquots for hydrogen at the beginning and end of the period. An acceptable syringe will
permit losses of hydrogen of less than 2,5 % per week. General experience suggests that
all-glass syringes leak less than those using plastic seals. Improvement of the gas tightness
may be obtained by the use of a lubricant such as a light grease or transformer oil.
It is a good practice to test the integrity of syringes and valve system before the sampling.
A recommended procedure is given in IEC 60475:20112022, Annex B.
c) Transport containers should be designed to hold the syringe firmly in place during transport,
but allow the syringe plunger freedom to move, and prevent its tip from contacting the
container, whatever its position during transportation.
Key
1 syringe
2 stopcock
3 rubber connecting tubing
4 three-way valve
5 equipment sampling valve
6 gas-collecting relay valve
7 waste vessel
Figure 1 – Sampling of gas by syringe
4.2.2 Sampling procedure
The apparatus is connected as shown in Figure 1. The connections should be as short as
possible and filled with oil at the start of sampling.
The sampling valve (5) is opened. If sampling from a gas-collecting relay on a transformer fitted
with a conservator, a positive pressure will exist; the three-way valve (4) is carefully turned to
position A and the oil in the connecting tubing (3) allowed to flow to waste (7). When gas reaches
the three-way valve (4), the latter is turned to position B to connect the pre-lubricated syringe
(1). The stopcock (2) is then opened and the syringe allowed to fill under the hydrostatic
pressure, taking care that its plunger is not expelled. When a sufficient sample has been taken,
the stopcock (2) and sampling valve (5) are closed and the apparatus is disconnected.
The oil in the syringe is expelled by inverting the syringe and applying gentle pressure to the
plunger.
Label carefully the sample (see Clause 5).
4.3 Sampling of free gases by displacement of oil
This method is reliable only where the gas sample is at or above atmospheric pressure. The
apparatus is shown in Figure 2.
The sampling tube (5), typically of 100 ml capacity, is preferably of glass since the operator can
then see how much oil remains in it during gas sampling. The sampling tube is filled with oil
from the transformer on site. Before being used as described below, the connecting tube (3)
should also be filled with oil.
The open end of the connecting tube (3) is fitted onto the gas-sampling valve (2). The sampling
valve and inlet stopcock of the sampling tube are opened. The sampling tube is inclined so that
its closed end is the lowest point. The outlet stopcock on the sampling tube is then opened,
allowing oil to run out to waste (6), drawing first any oil from the connection between relay and
sampling valve, and the gas from the relay, into the sampling tube.
Sampling is complete when the gas-collecting relay is completely filled with oil or when nearly
all oil has gone from the sampling tube.
Both stopcocks (4) on the sampling tube and the sampling valve (2) are closed and then the
connections removed.
Key
1 gas collecting relay valve
2 equipment sampling valve
3 oil-resistant connecting tubing
4 stopcock
5 sampling tube
6 waste vessel
Figure 2 – Sampling of free gases by oil displacement
4.4 Sampling of free gases by vacuum
The apparatus is connected as shown in Figure 3. With the equipment sampling valve closed,
stopcocks (1), (2) and (10) open, and the three-way valve (4) turned to position A, the vacuum
pump (12) is allowed to evacuate the connecting tubing, the trap and the sampling vessel.
– 14 – IEC 60567:2023 CMV © IEC 2023
A satisfactory vacuum will be below 100 Pa. The system should be checked for leaks by closing
the pump suction stopcock (10) and observing that no appreciable change in vacuum occurs.
Over a time equal to that which will be taken for sampling, the pressure should not increase by
more than 100 Pa. Similarly, the stopcock (1) on the sampling tube should be vacuum tight to
the same degree over several weeks.
If the connecting tubing between the equipment sampling valve (5) and the gas-collecting relay
is filled with oil, the three-way valve (4) is turned to position B. The equipment sampling valve
(5) is carefully opened and oil allowed to flow into the trap (9). When the end of the oil stream
is observed to reach the three-way valve (4), it is turned to position D to evacuate the oil from
it. Thereafter, valve (4) is turned to position C. When sampling is complete, stopcock (1) is
closed first, then the equipment sampling valve (5) closed and the apparatus disconnected.
If the connecting tubing between the equipment and the sampling valve is empty of oil, the
procedure for draining oil is omitted and the three-way valve (4) used in position C after
evacuating and testing that the apparatus is leak tight.
Key
1 vacuum tight stopcock
2 vacuum tight stopcock
3 rubber connecting tubing
4 vacuum tight three-way valve
5 equipment sampling valve
6 gas collecting relay valve
8 vacuum gauge
9 trap
10 vacuum tight stopcock
12 vacuum pump
28 sampling tube
Figure 3 – Sampling of free gases by vacuum
4.5 Sampling of oil from oil filled equipment
See IEC 60475:20112022, 4.2.
5 Labelling of gas samples
Gas samples should shall be properly labelled before dispatch to the laboratory.
The following information, as shown in Table 1, is necessary (whenever it is known).
– 16 – IEC 60567:2023 CMV © IEC 2023
Table 1 – Information required for gas samples
Transformer Sampling
Customer Sampling date and time following a gas alarm
Location Sampling point
Identification number Sampling person
Manufacturer Reason for analysis
General type (power, instrument or Transformer non-energized, off-load
industrial) energized or on-load
Rated MVA
Voltage ratio
Type and location of OLTC
Date of commissioning
Oil
Type of oil (mineral or non-mineral) Weight (or volume) of oil
Product name Date of last oil treatment
The following additional information is desirable:
– ambient temperature, reading of MVA or load current or percentage load, operation of
pumps, mode of communication of its tap-changer with the main tank, oil preservation
system (conservator, nitrogen blanket, etc.), and any changes in operational conditions or
any maintenance carried out since last sampling;
– time of sampling where more than one sample is taken.
6 Sampling, labelling and transferring of oil from oil-filled equipment
6.1 Sampling and labelling of oil
Consult IEC 60475:20112022, 4.2 to
...
IEC 60567 ®
Edition 5.0 2023-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Oil-filled electrical equipment – Sampling of free gases and analysis of free and
dissolved gases in mineral oils and other insulating liquids – Guidance
Matériels électriques immergés – Échantillonnage de gaz libres et analyse des
gaz libres et dissous dans les huiles minérales et d'autres liquides isolants –
Recommandations
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IEC 60567 ®
Edition 5.0 2023-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Oil-filled electrical equipment – Sampling of free gases and analysis of free and
dissolved gases in mineral oils and other insulating liquids – Guidance
Matériels électriques immergés – Échantillonnage de gaz libres et analyse des
gaz libres et dissous dans les huiles minérales et d'autres liquides isolants –
Recommandations
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.040.10 ISBN 978-2-8322-7960-1
– 2 – IEC 60567:2023 © IEC 2023
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 9
2 Normative references . 9
3 Terms, definitions, symbols and abbreviated terms . 10
3.1 Terms and definitions . 10
3.2 Symbols and abbreviated terms . 10
3.2.1 Symbols . 10
3.2.2 Abbreviated terms . 10
4 Sampling of gases from gas-collecting relays . 11
4.1 General remarks . 11
4.2 Sampling of free gases by syringe . 11
4.2.1 Sampling equipment . 11
4.2.2 Sampling procedure . 12
4.3 Sampling of free gases by displacement of oil . 13
4.4 Sampling of free gases by vacuum . 13
4.5 Sampling of oil from oil filled equipment . 15
5 Labelling of gas samples . 15
6 Sampling, labelling and transferring of oil from oil-filled equipment . 15
6.1 Sampling and labelling of oil . 15
6.2 Transfer of oil for DGA analysis . 15
6.2.1 General . 15
6.2.2 Transfer from oil syringes . 15
6.2.3 Transfer from ampoules . 16
6.2.4 Transfer from flexible metal bottles . 16
6.2.5 Transfer from glass and rigid metal bottles . 16
7 Preparation of gas-in-oil standards . 16
7.1 General remarks . 16
7.2 First method: preparation of a large volume of gas-in-oil standard . 16
7.2.1 Equipment . 16
7.2.2 Procedure . 17
7.2.3 Calculation . 19
7.3 Second method: preparation of gas-in-oil standards in a syringe or a vial . 19
7.3.1 General . 19
7.3.2 Equipment . 21
7.3.3 Procedure . 21
8 Extraction of gases from oil . 21
8.1 General remarks . 21
8.2 Multi-cycle vacuum extraction using Toepler pump apparatus . 22
8.2.1 General . 22
8.2.2 Toepler pump extraction apparatus . 22
8.2.3 Extraction procedure . 25
8.3 Vacuum extraction by partial degassing method . 26
8.3.1 General remarks . 26
8.3.2 Partial degassing apparatus . 26
8.3.3 Extraction procedure . 27
8.4 Stripping extraction method . 27
8.4.1 General . 27
8.4.2 Stripping apparatus . 27
8.4.3 Outline of procedure . 30
8.5 Headspace method . 31
8.5.1 Principle of the method . 31
8.5.2 Headspace extraction apparatus . 32
8.5.3 Headspace extraction procedure . 36
8.5.4 Calibration of the headspace extractor . 40
9 Gas analysis by gas-solid chromatography . 42
9.1 General remarks . 42
9.2 Outline of suitable methods using Table 4 . 44
9.3 Apparatus . 44
9.3.1 Gas chromatograph . 44
9.3.2 Columns . 46
9.3.3 Carrier gas . 46
9.3.4 Detectors . 46
9.3.5 Methanator . 46
9.3.6 Cold trap . 46
9.3.7 Integrator and recorder . 46
9.4 Preparation of apparatus . 47
9.5 Analysis . 47
9.6 Calibration of the chromatograph . 47
9.7 Calculations . 48
10 Quality control . 48
10.1 Verification of the entire analytical system . 48
10.2 Limits of detection and quantification . 49
10.3 Repeatability, reproducibility and accuracy . 50
10.3.1 General remark . 50
10.3.2 Repeatability . 50
10.3.3 Reproducibility . 50
10.3.4 Accuracy . 51
11 Report of results . 51
Annex A (informative) Correction for incomplete gas extraction in partial degassing
method by calculation . 53
Annex B (informative) Alternative gas extraction methods . 54
B.1 Mercury-free versions of the vacuum extraction methods . 54
B.1.1 Mercury-free version of the Toepler method . 54
B.1.2 Mercury-free version of the partial degassing method . 54
B.2 Syringe versions of the headspace method . 54
B.2.1 Shake test method . 54
B.2.2 Mechanical oscillation method . 56
Annex C (informative) Preparation of air-saturated standards . 57
Annex D (informative) Correction for gas bubbles in syringes and air gap in rigid
bottles . 58
Annex E (informative) Procedure for comparing gas monitor readings to laboratory
results . 59
Annex F (normative) Insulating liquids based on synthetic and natural esters and
silicones . 60
– 4 – IEC 60567:2023 © IEC 2023
Bibliography . 62
Figure 1 – Sampling of gas by syringe . 12
Figure 2 – Sampling of free gases by oil displacement . 13
Figure 3 – Sampling of free gases by vacuum . 14
Figure 4 – First method of preparing gas-in-oil standards. 18
Figure 5 – Second method for preparing gas-in-oil standards . 20
Figure 6 – Example of a Toepler pump extraction apparatus . 24
Figure 7 – Types of glass strippers . 28
Figure 8 – Stainless steel stripper . 29
Figure 9 – Schematic arrangement for connecting an oil stripper to a gas
chromatograph . 30
Figure 10 – Schematic representation of headspace sampler . 31
Figure 11 – Vial filled with water . 33
Figure 12 – Revolving table . 35
Figure 13 – Schematic arrangement for gas chromatography . 45
Figure B.1 – Schematic representation of mercury-free Toepler method . 55
Figure B.2 – Schematic representation of mercury-free partial degassing method . 55
Figure B.3 – Schematic representation of shake test method . 55
Figure B.4 – Schematic representations of mechanical oscillation method . 56
Table 1 – Information required for gas samples . 15
Table 2 – Examples of headspace operating conditions . 36
Table 3 – Examples of headspace partition coefficients at 70 °C in mineral insulating oil . 42
Table 4 – Examples of gas chromatographic operating conditions . 43
Table 5 – Required limits of detection in oil . 49
Table 6 – Examples of accuracy of extraction methods . 51
Table A.1 – Examples of solubility coefficients a (at 25 °C) reported by
i
CIGRE TF D1.01.15 in 2006 . 53
Table C.1 – Examples of solubility values of air for different oil types . 57
Table C.2 – Examples of temperature variations for oxygen and nitrogen solubility in
mineral oil . 57
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
OIL-FILLED ELECTRICAL EQUIPMENT –
SAMPLING OF FREE GASES AND ANALYSIS
OF FREE AND DISSOLVED GASES IN MINERAL OILS
AND OTHER INSULATING LIQUIDS – GUIDANCE
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
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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) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in
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shall not be held responsible for identifying any or all such patent rights.
IEC 60567 has been prepared by IEC technical committee 10: Fluids for electrotechnical
applications. It is an International Standard.
This fifth edition cancels and replaces the fourth edition published in 2011. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) a new normative Annex F relating to DGA analysis of insulating liquids other than mineral
oils (esters and silicones) has been added;
b) Clause 4 to Clause 11 and informative Annex A to Annex E remain devoted to mineral oils;
– 6 – IEC 60567:2023 © IEC 2023
c) two new mercury-free gas extraction methods are described in Annex B (low pressure
vacuum extraction and mechanical oscillation).
The text of this International Standard is based on the following documents:
Draft Report on voting
10/1207/FDIS 10/1211/RVD
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 International Standard 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/publications.
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, or
• revised.
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.
INTRODUCTION
Gases can be formed in oil-filled electrical equipment due to natural ageing but also, to a much
greater extent, as a result of faults.
Operation with a fault can seriously damage the equipment, and it is valuable to be able to
detect the fault at an early stage of development.
Where a fault is not severe, the gases formed will normally dissolve in the oil, with a small
proportion eventually diffusing from the liquid into any gas phase above it. Extracting dissolved
gas from a sample of the oil and determining the amount and composition of this gas is a means
of detecting such faults, and the type and severity of any fault can often be inferred from the
composition of the gas and the rate at which it is formed.
In the case of a sufficiently severe fault, free gas will pass through the oil and collect in the gas-
collecting (Buchholz) relay if fitted; if necessary, this gas may be analysed to assist in
determining the type of fault that has generated it. The composition of gases within the bubbles
changes as they move through the oil towards the gas-collecting relay.
This can be put to good use, as information on the rate of gas production can often be inferred
by comparing the composition of the free gases collected with the concentrations remaining
dissolved in the liquid.
The interpretation of the gas analyses is the subject of IEC 60599.
These techniques are valuable at all stages in the life of oil-filled equipment. During acceptance
tests on transformers in the factory, comparison of gas-in-oil analyses before, during and after
a heat run test can show if any hot-spots are present, and similarly analysis after dielectric
testing can add to information regarding the presence of partial discharges or sparking. During
operation in the field, the periodic removal of an oil sample and analysis of the gas content
serve to monitor the condition of transformers and other oil-filled equipment.
The importance of these techniques has led to the preparation of this document, to the
procedures used for the sampling, from oil-filled electrical equipment, of gases and oils
containing gases, and for subsequent analysis.
NOTE Methods described in this document apply to insulating oils, since experience to date has been almost
entirely with such oils. The methods can also be applied to other insulating liquids, in some cases with modifications.
General caution, health, safety and environmental protection
WARNING – 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 oils which are the subject of this document should be handled with due regard
to personal hygiene. Direct contact with the eyes can cause 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
can lead to a hazardous situation. Attention is drawn to the relevant standard for guidance.
Mercury presents an environmental and health hazard. Any spillage should immediately be
removed and be properly disposed of. Regulatory requirements for mercury use and handling
can apply. Mercury-free methods may be requested in some countries.
– 8 – IEC 60567:2023 © IEC 2023
Environment
WARNING – This document is applicable to insulating oils, chemicals and used sample
containers.
Attention is drawn to the fact that, at the time of writing of this document, many insulating oils
in service are known to be contaminated to some degree by polychlorinated biphenyls (PCBs).
If this is the case, safety countermeasures should be taken to avoid risks to workers, the public
and the environment during the life of the equipment, by strictly controlling spills and emissions.
Disposal or decontamination of these oils can be subject to regulatory requirements. Every
precaution should be taken to prevent the release of any type of insulating oil into the
environment, including those partially biodegradable with time.
OIL-FILLED ELECTRICAL EQUIPMENT –
SAMPLING OF FREE GASES AND ANALYSIS
OF FREE AND DISSOLVED GASES IN MINERAL OILS
AND OTHER INSULATING LIQUIDS – GUIDANCE
1 Scope
This document deals with the techniques for sampling free gases from gas-collecting relays
from power transformers. Three methods of sampling free gases are described.
The techniques for sampling oil from oil-filled equipment such as power and instrument
transformers, reactors, bushings, oil-filled cables and oil-filled tank-type capacitors are no
longer covered by this document, but are instead described in IEC 60475:2022, 4.2.
Before analysing the gases dissolved in oil, they are first extracted from the oil. Three basic
methods are described, one using extraction by vacuum (Toepler and partial degassing),
another by displacement of the dissolved gases by bubbling the carrier gas through the oil
sample (stripping) and the last one by partition of gases between the oil sample and a small
volume of the carrier gas (headspace). The gases are analysed quantitatively after extraction
by gas chromatography; a method of analysis is described. Free gases from gas-collecting
relays are analysed without preliminary treatment.
The preferred method for ensuring the performance of the gas extraction and analysis
equipment, considered together as a single system, is to degas samples of oil prepared in the
laboratory and containing known concentrations of gases ("gas-in-oil standards") and
quantitatively analyse the gases extracted. Two methods of preparing gas-in-oil standards are
described.
For daily calibration checks of the chromatograph, it is convenient to use a standard gas mixture
containing a suitable known amount of each of the gas components to be in a similar ratio to
the common ratios of the gases extracted from transformer oils.
The techniques described take account, on the one hand, of the problems peculiar to analyses
associated with acceptance testing in the factory, where gas contents of oil are generally very
low and, on the other hand, of the problems imposed by monitoring equipment in the field,
where transport of samples can be by un-pressurized air freight and where considerable
differences in ambient temperature can exist between the plant and the examining laboratory.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 60296, Fluids for electrotechnical applications – Mineral insulating oils for electrical
equipment
IEC 60475:2022, Method of sampling insulating liquids
ISO 5725-1, Accuracy (trueness and precision) of measurement methods and results – Part 1:
General principles and definitions
– 10 – IEC 60567:2023 © IEC 2023
3 Terms, definitions, symbols and abbreviated terms
3.1 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.2 Symbols and abbreviated terms
3.2.1 Symbols
The symbols used in 8.5.2 are:
V total volume of the vial
V volume of the gas phase in the vial
G
V volume of the oil phase in the vial
L
C concentration of gas (i) in the gas phase of vial, obtained by GC (gas chromatography)
G
0*
concentration of gas (i) in the oil sample, obtained directly from C using calibration
C
L G
curves with gas-in-oil standards
P, t atmospheric pressure and temperature when the oil sample was analysed (P in kPa;
t in °C)
P , t atmospheric pressure and temperature when the gas-in-oil standard, or the gas
s s
standard, was analysed (P in kPa; t in °C)
s s
K partition coefficient of gas (i), for the calculation of C using gas standards
L
C concentration of gas (i) in the oil sample
L
3.2.2 Abbreviated terms
DGA dissolved gas analysis
FID flame ionization detector
GC gas chromatography
GILS gas-in-liquid standards
GIOS gas-in-oil standards
HID helium ionization detector
ID inner diameter
NIST National Institute of Standards and Technology
OD outer diameter
OLTC on-load tap-changer
PLOT porous large open tubular
PTFE polytetrafluoroethylene
TCD thermal conductivity detector
4 Sampling of gases from gas-collecting relays
4.1 General remarks
It is important to bear in mind that receiving a qualitative and a representative sample is crucial
for obtaining a reliable diagnosis of the electrical equipment. Even the most sophisticated
extraction or diagnosis methods cannot overcome faulty samples.
Gas samples from relays should be taken from the equipment with the minimum delay after gas
accumulation has been signalled. Changes in composition caused by the selective re-
absorption of components can occur if free gases are left in contact with oil.
Certain precautions are necessary when taking gas samples. The connection between the
sampling device and the sampling vessel shall avoid the ingress of air. Temporary connections
should be as short as possible. Any rubber or plastic tubing used should have been proved to
be impermeable to gases.
Gas samples shall be properly labelled (see Clause 5) and analysed without undue delay to
minimize hydrogen loss from the syringe used for gas sampling (e.g. within a maximum period
of one week).
Oxygen, if present in the gas, can react with any oil drawn out with the sample. Reaction is
delayed by excluding light from the sample, for example, by wrapping the vessel in aluminium
foil or suitable opaque material.
Of the three methods described in 4.2, 4.3 and 4.4, the syringe method is recommended. The
other two methods are alternatives to be used exclusively in case of serious hindrance.
Sampling into a sampling tube by liquid displacement using transformer oil as a sealing liquid
is simple, but require to take into account the different solubilities of the gas components if the
gas quantity is such that some oil remains in the tube.
The vacuum method requires skill to avoid contaminating the sample by leakage of air into the
system. It is particularly true where the gas to be sampled can be at less than atmospheric
pressure (e.g. some sealed transformers).
4.2 Sampling of free gases by syringe
4.2.1 Sampling equipment
NOTE Numbers in brackets refer to those circled numbers in the relevant figure.
See Figure 1. The equipment shall be as follows:
a) Impermeable oil-resistant plastic or rubber tubing (3) provided with a connector to fit onto a
suitable sampling connection of the gas-collecting relay. To avoid cross-contamination, the
tubing should be used only once.
b) Gas-tight syringes of suitable volume (1) (25 ml to 250 ml). Medical or veterinary quality
glass syringes with ground-in plungers may be suitable; alternatively, syringes with oil-proof
seals may be used. The syringe should be fitted with a cock enabling it to be sealed. It is
often convenient to use the same syringes for both gas sampling and for oil sampling (see
IEC 60475:2022, 4.2.2).
The gas tightness of a glass syringe used for gas sampling may be tested by storing an oil
sample containing a measurable quantity of hydrogen for at least two weeks and analysing
aliquots for hydrogen at the beginning and end of the period. An acceptable syringe will
permit losses of hydrogen of less than 2,5 % per week. General experience suggests that
all-glass syringes leak less than those using plastic seals. Improvement of the gas tightness
may be obtained by the use of a lubricant such as a light grease or transformer oil.
– 12 – IEC 60567:2023 © IEC 2023
It is a good practice to test the integrity of syringes and valve system before the sampling.
A recommended procedure is given in IEC 60475:2022, Annex B.
c) Transport containers should be designed to hold the syringe firmly in place during transport,
but allow the syringe plunger freedom to move, and prevent its tip from contacting the
container, whatever its position during transportation.
Key
1 syringe
2 stopcock
3 rubber connecting tubing
4 three-way valve
5 equipment sampling valve
6 gas-collecting relay valve
7 waste vessel
Figure 1 – Sampling of gas by syringe
4.2.2 Sampling procedure
The apparatus is connected as shown in Figure 1. The connections should be as short as
possible and filled with oil at the start of sampling.
The sampling valve (5) is opened. If sampling from a gas-collecting relay on a transformer fitted
with a conservator, a positive pressure will exist; the three-way valve (4) is carefully turned to
position A and the oil in the connecting tubing (3) allowed to flow to waste (7). When gas reaches
the three-way valve (4), the latter is turned to position B to connect the pre-lubricated syringe
(1). The stopcock (2) is then opened and the syringe allowed to fill under the hydrostatic
pressure, taking care that its plunger is not expelled. When a sufficient sample has been taken,
the stopcock (2) and sampling valve (5) are closed and the apparatus is disconnected.
The oil in the syringe is expelled by inverting the syringe and applying gentle pressure to the
plunger.
Label carefully the sample (see Clause 5).
4.3 Sampling of free gases by displacement of oil
This method is reliable only where the gas sample is at or above atmospheric pressure. The
apparatus is shown in Figure 2.
The sampling tube (5), typically of 100 ml capacity, is preferably of glass since the operator can
then see how much oil remains in it during gas sampling. The sampling tube is filled with oil
from the transformer on site. Before being used as described below, the connecting tube (3)
should also be filled with oil.
The open end of the connecting tube (3) is fitted onto the gas-sampling valve (2). The sampling
valve and inlet stopcock of the sampling tube are opened. The sampling tube is inclined so that
its closed end is the lowest point. The outlet stopcock on the sampling tube is then opened,
allowing oil to run out to waste (6), drawing first any oil from the connection between relay and
sampling valve, and the gas from the relay, into the sampling tube.
Sampling is complete when the gas-collecting relay is completely filled with oil or when nearly
all oil has gone from the sampling tube.
Both stopcocks (4) on the sampling tube and the sampling valve (2) are closed and then the
connections removed.
Key
1 gas collecting relay valve
2 equipment sampling valve
3 oil-resistant connecting tubing
4 stopcock
5 sampling tube
6 waste vessel
Figure 2 – Sampling of free gases by oil displacement
4.4 Sampling of free gases by vacuum
The apparatus is connected as shown in Figure 3. With the equipment sampling valve closed,
stopcocks (1), (2) and (10) open, and the three-way valve (4) turned to position A, the vacuum
pump (12) is allowed to evacuate the connecting tubing, the trap and the sampling vessel.
– 14 – IEC 60567:2023 © IEC 2023
A satisfactory vacuum will be below 100 Pa. The system should be checked for leaks by closing
the pump suction stopcock (10) and observing that no appreciable change in vacuum occurs.
Over a time equal to that which will be taken for sampling, the pressure should not increase by
more than 100 Pa. Similarly, the stopcock (1) on the sampling tube should be vacuum tight to
the same degree over several weeks.
If the connecting tubing between the equipment sampling valve (5) and the gas-collecting relay
is filled with oil, the three-way valve (4) is turned to position B. The equipment sampling valve
(5) is carefully opened and oil allowed to flow into the trap (9). When the end of the oil stream
is observed to reach the three-way valve (4), it is turned to position D to evacuate the oil from
it. Thereafter, valve (4) is turned to position C. When sampling is complete, stopcock (1) is
closed first, then the equipment sampling valve (5) closed and the apparatus disconnected.
If the connecting tubing between the equipment and the sampling valve is empty of oil, the
procedure for draining oil is omitted and the three-way valve (4) used in position C after
evacuating and testing that the apparatus is leak tight.
Key
1 vacuum tight stopcock
2 vacuum tight stopcock
3 rubber connecting tubing
4 vacuum tight three-way valve
5 equipment sampling valve
6 gas collecting relay valve
8 vacuum gauge
9 trap
10 vacuum tight stopcock
12 vacuum pump
28 sampling tube
Figure 3 – Sampling of free gases by vacuum
4.5 Sampling of oil from
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