Insulating liquids - Determination of the breakdown voltage at power frequency - Test method

IEC 60156:2018 is now available as IEC 60156:2018 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.
IEC 60156:2018 specifies the method for determining the dielectric breakdown voltage of insulating liquids at power frequency. The test procedure is performed in a specified apparatus, where the oil sample is subjected to an increasing AC electrical field until breakdown occurs. The method applies to all types of insulating liquids of nominal viscosity up to 350 mm2/s at 40 °C. It is appropriate both for acceptance testing on unused liquids at the time of their delivery and for establishing the condition of samples taken in monitoring and maintenance of equipment. This third edition cancels and replaces the second edition published in 1995. This edition constitutes a technical revision and, mainly, confirms the content of the previous edition even if some advances are included. The test method has not been changed for practical reason due to the very large number of instrumentation disseminated around the world, even if the use of stirring is now recommended.

Isolants liquides - Détermination de la tension de claquage à fréquence industrielle - Méthode d’essai

IEC 60156:2018 est disponible sous forme de IEC 60156:2018 RLV qui contient la Norme internationale et sa version Redline, illustrant les modifications du contenu technique depuis l'édition précédente.
L'IEC 60156:2018 spécifie la méthode de détermination de la tension de claquage diélectrique des isolants liquides à fréquence industrielle. La procédure d’essai est réalisée dans un appareil spécifié dans lequel l’échantillon d’huile est soumis à un champ électrique alternatif croissant jusqu’à l’obtention du claquage. La méthode est applicable à tous les types d’isolants liquides de viscosité nominale allant jusqu’à 350 mm2/s à 40 °C. Elle convient aussi bien pour les essais de réception de liquides neufs à la livraison que pour définir l’état des échantillons prélevés lors de la surveillance et de la maintenance des matériels. Cette troisième édition annule et remplace la deuxième édition parue en 1995. Cette édition constitue une révision technique et valide essentiellement le contenu de l’édition précédente même si elle comporte certaines améliorations. La méthode d’essai n’a pas été modifiée pour des raisons pratiques et du fait du très grand nombre de dispositifs de mesure utilisés au niveau international, même si l’emploi de l’agitateur est maintenant recommandé.

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Status
Published
Publication Date
16-Aug-2018
Current Stage
PPUB - Publication issued
Completion Date
17-Aug-2018
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IEC 60156
Edition 3.0 2018-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Insulating liquids – Determination of the breakdown voltage at power
frequency – Test method
Isolants liquides – Détermination de la tension de claquage à fréquence
industrielle – Méthode d’essai
IEC 60156:2018-08(en-fr)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 60156
Edition 3.0 2018-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Insulating liquids – Determination of the breakdown voltage at power
frequency – Test method
Isolants liquides – Détermination de la tension de claquage à fréquence
industrielle – Méthode d’essai
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.040 ISBN 978-2-8322-5959-7

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

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 2 – IEC 60156:2018 © IEC 2018
CONTENTS

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

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

1 Scope ............................................................................................................................ 7

2 Normative references..................................................................................................... 7

3 Terms and definitions .................................................................................................... 7

4 Electrical apparatus ....................................................................................................... 7

4.1 General ................................................................................................................. 7

4.2 Voltage regulator ................................................................................................... 7

4.3 Step-up transformer .............................................................................................. 8

4.4 Switching system .................................................................................................. 8

4.5 Current-limiting resistors ....................................................................................... 8

4.6 Measuring system ................................................................................................. 8

5 Test assembly ............................................................................................................... 8

5.1 General ................................................................................................................. 8

5.2 Test cell ................................................................................................................ 9

5.3 Electrodes............................................................................................................. 9

5.4 Stirring device ..................................................................................................... 10

6 Preparation of electrodes ............................................................................................. 10

7 Test assembly preparation ........................................................................................... 10

8 Sampling ..................................................................................................................... 11

9 Test procedure ............................................................................................................ 11

9.1 Sample preparation ............................................................................................. 11

9.2 Filling of the cell .................................................................................................. 11

10 Application of the voltage ............................................................................................. 11

11 Report ......................................................................................................................... 12

12 Test data dispersion and reproducibility ....................................................................... 12

12.1 Test data dispersion ............................................................................................ 12

12.2 Reproducibility .................................................................................................... 13

Annex A (informative) Improved test method ...................................................................... 14

A.1 Test procedure for improved test method ............................................................. 14

A.2 Report ................................................................................................................ 15

Annex B (informative) Special test methods for low volume samples ................................... 16

B.1 Low volume sample test ...................................................................................... 16

Annex C (informative) Representative material for a performance test ................................. 18

Bibliography ....................................................................................................................... 19

Figure 1 – Examples of test cells with spherical electrodes 12,5 mm to 13,0 mm

diameter ............................................................................................................................... 9

Figure 2 – Examples of test cells with partially spherical electrodes with 25 mm radius

and diameter of 36 mm ......................................................................................................... 9

Figure 3 – Graphical representation of coefficient of variation versus mean breakdown

voltage ............................................................................................................................... 13

Figure A.1 – Example of a sequence of breakdown shots for determination of the

breakdown voltage .............................................................................................................. 15

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IEC 60156:2018 © IEC 2018 – 3 –

Figure B.1 – Example of low volume test cell, fixed electrode distance of 2 mm with

2 ml active volume under dielectric stress ........................................................................... 16

Figure B.2 – Example of low volume test cell, fixed electrode distance of 2,5 mm

(150 ml to 200 ml) ............................................................................................................... 17

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– 4 – IEC 60156:2018 © IEC 2018
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INSULATING LIQUIDS – DETERMINATION OF THE BREAKDOWN
VOLTAGE AT POWER FREQUENCY – TEST METHOD
FOREWORD

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

all national electrotechnical committees (IEC National Committees). The object of IEC is to promote

international co-operation on all questions concerning standardization in the electrical and electronic fields. To

this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,

Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC

Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested

in the subject dealt with may participate in this preparatory work. International, governmental and non-

governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely

with the International Organization for Standardization (ISO) in accordance with conditions determined by

agreement between the two organizations.

2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international

consensus of opinion on the relevant subjects since each technical committee has representation from all

interested IEC National Committees.

3) IEC Publications have the form of recommendations for international use and are accepted by IEC National

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Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any

misinterpretation by any end user.

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between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in

the latter.

5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity

assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any

services carried out by independent certification bodies.

6) All users should ensure that they have the latest edition of this publication.

7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and

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Publications.

8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is

indispensable for the correct application of this publication.

9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of

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

International Standard IEC 60156 has been prepared by IEC technical committee TC 10:

Fluids for electrotechnical applications.

This third edition cancels and replaces the second edition published in 1995. This edition

constitutes a technical revision and, mainly, confirms the content of the previous edition even

if some advances are included. The test method has not been changed for practical reason

due to the very large number of instrumentation disseminated around the world, although the

use of stirring is now recommended.
The text of this International Standard is based on the following documents:
FDIS Report on voting
10/1061/FDIS 10/1065/RVD

Full information on the voting for the approval of this International Standard can be found in

the report on voting indicated in the above table.
---------------------- Page: 6 ----------------------
IEC 60156:2018 © IEC 2018 – 5 –

This document has been drafted in accordance with the ISO/IEC Directives, Part 2.

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

stability date indicated on the IEC website under "http://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.
---------------------- Page: 7 ----------------------
– 6 – IEC 60156:2018 © IEC 2018
INTRODUCTION

As normally applied, breakdown voltage of insulating liquids is not a basic material property

but an empirical test procedure intended to indicate the presence of contaminants such as

water and solid suspended matter and the advisability of carrying out a drying and filtration

treatment.

The AC breakdown voltage value of insulating liquids strongly depends on the particular set of

conditions used in its measurement. Therefore, standardized testing procedures and

equipment are essential for the unambiguous interpretation of test results.

The method described in this document applies to either acceptance tests on new deliveries

of insulating liquids, or testing of treated liquids prior to or during filling into electrical

equipment, or to the monitoring and maintenance of oil-filled apparatus in service. It specifies

rigorous sample-handling procedures and temperature control that should be adhered to when

certified results are required. For routine tests, especially in the field, less stringent

procedures may be practicable and it is the responsibility of the user to determine their effect

on the results.

Annex A (informative) describes, for comparison, an alternative test method which could be

introduced in the future. Annex B (informative) describes special test methods, using cells

which may include low volume samples. Annex C (informative) describes a reference material

for a performance test and check according to IEC 60060-3[1] .
—————————
Numbers in square brackets refer to the Bibliography.
---------------------- Page: 8 ----------------------
IEC 60156:2018 © IEC 2018 – 7 –
INSULATING LIQUIDS – DETERMINATION OF THE BREAKDOWN
VOLTAGE AT POWER FREQUENCY – TEST METHOD
1 Scope

This document specifies the method for determining the dielectric breakdown voltage of

insulating liquids at power frequency. The test procedure is performed in a specified

apparatus, where the oil sample is subjected to an increasing AC electrical field until

breakdown occurs. The method applies to all types of insulating liquids of nominal viscosity

up to 350 mm /s at 40 °C. It is appropriate both for acceptance testing on unused liquids at

the time of their delivery and for establishing the condition of samples taken in monitoring and

maintenance of equipment.
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 60475, Method of sampling insulating liquids
3 Terms and definitions
No terms and definitions are listed in this document.

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
4 Electrical apparatus
4.1 General
The electrical apparatus consists of the following units:
1) voltage regulator,
2) step-up transformer,
3) switching system,
4) current-limiting resistors,
5) measuring device.
Two or more of these units may be integrated in any equipment system.
4.2 Voltage regulator

The test voltage shall be increased with an automatic control of the required uniform voltage

rate of rise. The device should not introduce harmonics disturbances (< 3%) and the AC

source should be free from harmonics.
---------------------- Page: 9 ----------------------
– 8 – IEC 60156:2018 © IEC 2018
4.3 Step-up transformer

The test voltage is obtained by using a step-up or resonant transformer supplied from an AC

source using 48 Hz to 62 Hz (sinusoidal waveform). The voltage source value is constantly

increased. The controls of the variable low-voltage source shall be capable of varying the test

voltage smoothly, uniformly and without overshoots or transients. Incremental increases

(produced, for example, by a variable auto-transformer or an amplifier) shall not exceed 2 %

of the expected breakdown voltage.

The centre-point of the secondary winding of the transformer should be connected to earth.

4.4 Switching system

The circuit shall be opened automatically if a sustained arc between the electrodes occurs

and the voltage between the electrodes collapses to a voltage less than 500 V. The primary

circuit of the step-up transformer shall be fitted with a circuit-breaker operated by the current

sensing device, resulting from the breakdown of the sample and shall break the voltage within

10 ms.

The sensitivity of the current or voltage sensing element depends on the energy-limiting

device employed and only approximate guidance can be given.

A cut-off time of < 100 µs, as given in the previous edition of this document, is needed to

perform multiple breakdowns on silicone liquids.
4.5 Current-limiting resistors

To protect the equipment and to avoid excessive decomposition at the instant of breakdown of

liquids such as silicone or ester liquids, a resistance limiting the breakdown current shall be

inserted in series with the test cell.

The short-circuit current of the transformer and associated circuits shall be within the range of

10 mA to 25 mA for all voltages higher than 15 kV. This may be achieved by a combination of

resistors in either or both the primary and secondary circuits of the high-voltage transformer.

4.6 Measuring system

For the purposes of this document, the magnitude of the test voltage is defined as its peak

value divided by 2 .

The output voltage of the step-up transformer may be measured by means of a measuring

system consisting of a voltage divider or a measuring winding of the step-up transformer

coupled with a peak-voltmeter. The measuring system shall be calibrated up to the upper

scale voltage to be measured. A method of calibration which has been found satisfactory is

the use of a transfer standard. This is an auxiliary measuring device which is connected in

place of the test cell between the high-voltage terminals to which it presents an impedance

similar to the one of the sample liquid. The auxiliary device is separately calibrated against a

primary standard [2],[3].
5 Test assembly
5.1 General

The breakdown voltage test is performed following the method described herewith as a

routine test.
---------------------- Page: 10 ----------------------
IEC 60156:2018 © IEC 2018 – 9 –
5.2 Test cell
The volume of the cell shall be between 350 ml and 600 ml.

The cell shall be made from electrically insulating materials, that are not hygroscopic. The cell

shall be transparent and chemically inert, resistant to the insulating liquid and to the cleaning

agent that shall be used. A glass cell is the preferred option.

The cell shall be provided with a cover and shall be designed to permit easy removal of the

electrodes for cleaning and maintenance. To improve homogenization of the test liquid, a

rounded bottom shape of the cell is recommended. Containers and covers shall be cleaned by

washing with a suitable solvent or clean insulating liquid to remove residues of an earlier

sample. After cleaning, containers shall be immediately capped and kept closed until used

again. Electrodes shall be stored in clean insulating liquids.

NOTE It is preferable, in the case of esters, to use similar liquid to store the electrodes.

Examples of suitable cell designs are given in Figures 1 and 2.
Dimensions in millimetres
2,5
IEC

NOTE The stirring device can be mounted on the top (right side figure) or on the bottom (left side figure). The

stirring device position and Vernier shifter are reported only as reference.
Figure 1 – Examples of test cells with spherical electrodes
12,5 mm to 13,0 mm diameter
Dimensions in millimetres
R25
2,5
IEC

NOTE The stirring device can be mounted on the top (right side figure) or on the bottom (left side figure). The

stirring device position and Vernier shifter are reported only as reference.
Figure 2 – Examples of test cells with partially spherical electrodes
with 25 mm radius and diameter of 36 mm
5.3 Electrodes

The electrodes shall be made either of brass, bronze or austenitic stainless steel. They shall

be polished and, in shape, either spherical (12,5 mm to 13,0 mm diameter) as shown in

Figure 1 or in partially spherical shape (25 mm ± 0,25 mm radius) as shown in Figure 2. The

axis of the electrode system shall be horizontal and shall be at least 40 mm below the surface

ø36
---------------------- Page: 11 ----------------------
– 10 – IEC 60156:2018 © IEC 2018

of the test liquid. Any part of the cell or stirrer shall not influence the electric field between the

electrodes. The gap between the electrodes shall be 2,50 mm ± 0,05 mm.

The electrodes shall be examined frequently for pitting or other damage and shall be

maintained or replaced as soon as such damage is observed.

NOTE The electrodes can be replaced or refurbished typically after 5 000 single breakdowns. The surface of the

electrodes can be polished with a maximum grain diameter of 10 µm. The limit of the arithmetical mean deviation of

the roughness profile of the electrodes can be Ra ≤ 0,5 µm, according to ISO 4287[4].

5.4 Stirring device

The use of an automatic stirring device is recommended, to be used at all times throughout

the test.

The stirrer shall be mounted in the test cell in order to maximize the homogenization of the

liquid. It shall be designed so that it is easily cleaned. Stirring shall be achieved by means of

a two-bladed or appropriate stirrer of effective diameter 25 mm to 35 mm, axial depth 5 mm to

10 mm, rotating at a speed of 200 r/min to 300 r/min. The stirrer shall not produce air bubbles.

It shall be fully immersed in the liquid sample. Examples of stirring systems mounted in test

cells are reported in Figures 1 and 2.

NOTE 1 To avoid bubbles between the electrodes the stirrer can rotate preferably in such a direction that bubbles

can be removed [5].

NOTE 2 The stirring device can be mounted on the top or on the bottom. In Figures 1 and 2, the stirring device

position is reported only as reference.
NOTE 3 A magnetic stirring device can be also used.
6 Preparation of electrodes

New electrodes shall be cleaned and fulfil the requirements of 5.3. Preparation of the

electrodes shall be according to the following procedure:

– clean all surfaces with a suitable volatile solvent and allow the solvent to evaporate;

– polish with fine abrasive powder (for example, jeweller’s rouge) or abrasive paper or cloth,

for example crocus cloth (see 5.3);

– after polishing, clean with petroleum spirit (reagent quality: boiling range of about 40 °C to

80 °C) followed by acetone (reagent quality);

– assemble the electrodes in the cell, fill with a clean, unused insulating liquid of the type to

be tested;
– before the first breakdown test, raise the voltage until breakdown 24 times.
This procedure shall be repeated after each cleaning or change of electrodes.
7 Test assembly preparation

It is recommended that a separate test cell assembly be reserved for different insulating liquid

types.

Test assemblies shall be stored in a dry place, covered and filled with dry insulating liquid of

the type in regular use in the cell.

On change of the type of liquid under test, remove all residues of the previous liquid with an

appropriate solvent, rinse the assembly with a clean, dry liquid of the same type as the one to

be tested, drain and refill.
---------------------- Page: 12 ----------------------
IEC 60156:2018 © IEC 2018 – 11 –
8 Sampling
Sampling shall be carried out in accordance with IEC 60475.

NOTE Breakdown voltage is extremely sensitive to the slightest contamination of the sample by water and

particulate matter. Special precautions can be implemented to avoid contamination of the sample and the need for

trained personnel and experienced supervision. Unless otherwise required, the sample is taken where the liquid is

likely to be most contaminated, usually at the lowest point of the container holding it.

The test is carried out, unless otherwise specified, on the sample as received without drying

or degassing.
9 Test procedure
9.1 Sample preparation

Immediately before filling the test cell, the sample container is gently agitated and turned over

several times in such a way as to ensu
...

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