Electrical insulating materials - Determination of the effects of ionizing radiation on insulating materials - Part 2: Procedures for irradiation and test

IEC 60544-2:2012 specifies the controls maintained over the exposure conditions during and after the irradiation of insulating materials with ionizing radiation prior to the determination of radiation-induced changes in physical or chemical properties. This standard specifies a number of potentially significant irradiation conditions as well as various parameters which can influence the radiation-induced reactions under these conditions. The objective of this standard is to emphasize the importance of selecting suitable specimens, exposure conditions and test methods for determining the effect of radiation on appropriately chosen properties. Since many materials are used either in air or in inert environments, standard exposure conditions are recommended for both of these situations. It should be noted that this standard does not consider measurements which are performed during the irradiation. This edition includes the following significant technical changes with respect to the previous edition:
- alignment with standards recently developed by SC 45A as well as with other parts in the IEC 60544 series.

Matériaux isolants électriques - Détermination des effets des rayonnements ionisants sur les matériaux isolants - Partie 2: Méthodes d'irradiation et d'essai

La CEI 60544-2:2012 spécifie d'abord les contrôles exercés sur les conditions d'exposition pendant et après l'irradiation de matériaux isolants par des rayonnements ionisants, avant de déterminer les changements de propriétés physiques ou chimiques induits par rayonnement. Cette norme discute certaines des principales conditions d'irradiation possibles d'une importance significative et spécifie les divers paramètres qui peuvent influer sur les réactions induites par rayonnement dans ces conditions. L'objectif de la présente norme est de démontrer l'importance du choix d'échantillons, de conditions d'exposition et de méthodes d'essai appropriés pour déterminer les effets des rayonnements sur des propriétés convenablement choisies. Comme un grand nombre de matériaux peuvent être utilisés soit dans l'air, soit dans des environnements inertes, des conditions normales d'exposition sont recommandées pour chacune de ces situations. Il convient de noter que cette norme ne prend pas en compte les mesures réalisées pendant l'irradiation. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
- alignement avec des normes récemment élaborées au sein du SC 45A, ainsi qu'avec d'autres parties de la série CEI 60544.

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Published
Publication Date
08-Jul-2012
Current Stage
PPUB - Publication issued
Start Date
09-Jul-2012
Completion Date
09-Jul-2012
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IEC 60544-2
Edition 3.0 2012-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE

Electrical insulating materials – Determination of the effects of ionizing radiation

on insulating materials –
Part 2: Procedures for irradiation and test
Matériaux isolants électriques – détermination des effets des rayonnements
Ionisants sur les matériaux isolants –
Partie 2: Méthodes d'irradiation et d'essai
IEC 60544-2:2012
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 60544-2
Edition 3.0 2012-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE

Electrical insulating materials – Determination of the effects of ionizing radiation

on insulating materials –
Part 2: Procedures for irradiation and test
Matériaux isolants électriques – détermination des effets des rayonnements
Ionisants sur les matériaux isolants –
Partie 2: Méthodes d'irradiation et d'essai
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX S
ICS 17.240; 29.035.01 ISBN 978-2-83220-223-4

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 – 60544-2 © IEC:2012
CONTENTS

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

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

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

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

3 Irradiation ......................................................................................................................... 9

3.1 Type of radiation and dosimetry .............................................................................. 9

3.2 Irradiation conditions ............................................................................................. 10

3.3 Sample preparation ............................................................................................... 10

3.4 Irradiation procedures ........................................................................................... 10

3.4.1 Irradiation dose-rate control ....................................................................... 10

3.4.2 Irradiation temperature control ................................................................... 10

3.4.3 Irradiation in air ......................................................................................... 11

3.4.4 Irradiation in a medium other than air ........................................................ 11

3.4.5 Irradiation in a vacuum .............................................................................. 11

3.4.6 Irradiation at high pressure ........................................................................ 12

3.4.7 Irradiation during mechanical stressing ...................................................... 12

3.4.8 Irradiation during electrical stressing ......................................................... 12

3.4.9 Combined irradiation procedures ............................................................... 12

3.5 Post-irradiation effects .......................................................................................... 12

3.6 Specified irradiation conditions .............................................................................. 12

4 Test ................................................................................................................................ 12

4.1 General ................................................................................................................. 12

4.2 Test procedures .................................................................................................... 13

4.3 Evaluation criteria ................................................................................................. 13

4.3.1 End-point criteria ....................................................................................... 13

4.3.2 Values of the absorbed dose ..................................................................... 14

4.4 Evaluation ............................................................................................................. 14

5 Report ............................................................................................................................ 15

5.1 General ................................................................................................................. 15

5.2 Material ................................................................................................................. 15

5.3 Irradiation .............................................................................................................. 15

5.4 Test ....................................................................................................................... 15

5.5 Results .................................................................................................................. 15

Annex A (informative) Examples of test reports .................................................................... 16

Bibliography .......................................................................................................................... 21

Figure A.1 – Change of mechanical properties as a function of absorbed dose for

magnetic coil insulation ......................................................................................................... 17

Figure A.2 – Breakdown voltage of insulating tape as a function of absorbed dose .............. 20

Table 1 – Critical properties and end-point criteria to be considered in evaluating the

classification of insulating materials in radiation environments .............................................. 14

Table A.1 – Example 1 – Magnetic coil insulation ................................................................. 16

Table A.2 – Example 2 – Cable insulation ............................................................................. 18

---------------------- Page: 4 ----------------------
60544-2 © IEC:2012 – 3 –

Table A.3 – Example 3 – Insulating tape ............................................................................... 19

---------------------- Page: 5 ----------------------
– 4 – 60544-2 © IEC:2012
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTRICAL INSULATING MATERIALS –
DETERMINATION OF THE EFFECTS OF IONIZING
RADIATION ON INSULATING MATERIALS –
Part 2: Procedures for irradiation and test
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

Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC

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

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transparently to the maximum extent possible in their national and regional publications. Any divergence

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

members of its technical committees and IEC National Committees for any personal injury, property damage or

other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and

expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC

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 60544-2 has been prepared by IEC technical committee 112:

Evaluation and qualification of electrical insulating materials and systems.

This third edition cancels and replaces the second edition, published in 1991, and constitutes

a technical revision.

This edition includes the following significant technical changes with respect to the previous

edition:

– alignment with standards recently developed by SC 45A as well as with other parts in the

IEC 60544 series.
---------------------- Page: 6 ----------------------
60544-2 © IEC:2012 – 5 –
The text of this standard is based on the following documents:
FDIS Report on voting
112/208/FDIS 112/216/RVD

Full information on the voting for the approval of this standard can be found in the report on

voting indicated in the above table.

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

A list of all parts of the IEC 60544 series can be found, under the general title Electrical

insulating materials – Determination of the effects of ionizing radiation on insulating materials,

on the IEC website.

Future standards in this series will carry the new general title as cited above. Titles of existing

standards in this series will be updated at the time of the next edition.

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

the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data

related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
---------------------- Page: 7 ----------------------
– 6 – 60544-2 © IEC:2012
INTRODUCTION

When selecting insulating materials for applications in radiation environments, the component

designers should have available reliable test data to compare candidate materials. To be

meaningful, the performance data should be obtained on each material by standardized

procedures, and the procedures should be designed to demonstrate the influence that

variations of the service conditions have on the significant properties. This point is of

particular concern where in normal service conditions low dose rates exist and where the

insulation materials have been selected from radiation endurance data obtained from tests

conducted at high dose rates.

Environmental conditions shall be well controlled and documented during the measurement of

radiation effects. Important environmental parameters include temperature, reactive medium

and mechanical and electrical stresses present during the irradiation. If air is present,

radiation-induced species can enter into reactions with oxygen that would not occur in its

absence. This is responsible for an observed influence of the absorbed dose rate for certain

types of polymers if irradiated in air. As a result, the resistance may be several orders of

magnitude lower than when the sample is irradiated under vacuum or in the presence of inert

gas. This is generally called the "dose-rate effect", which is described and reviewed in

references [1] to [14] .

NOTE For the user of this Part of IEC 60544 who wants to go into more detail, the cited references are listed in

the Bibliography. Where these are not publications in internationally available journals, addresses where the cited

scientific reports can be obtained are given at the end of the references.

The irradiation time can become relevant because of time-dependent complications caused by:

a) physical effects such as diffusion-limited oxidation [8], [10]; and

b) chemical phenomena such as rate-determining hydroperoxide breakdown reactions [10],

[14].

Typical diffusion-limited effects are commonly observed in radiation studies of polymers in air.

Their importance depends upon the interrelationship of the geometry of the polymer with the

oxygen permeation and consumption rates, both of which depend upon temperature [10]. This

means that the irradiation of thick samples in air may result in oxidation only near the air-

exposed surfaces of the sample, resulting in material property changes similar to those

obtained by irradiation in an oxygen-free environment. Therefore, when the material is to be

used in air for a long period of time at a low dose rate, depositing the same total dose at a

high dose rate in a short exposure period may not determine its durability. Previous

experiments or considerations of sample thickness combined with estimates of oxygen

permeation and consumption rates [8], [10] may eliminate such concerns. A technique that

may be useful for eliminating oxygen diffusion effects by increasing the surrounding oxygen

pressure is under investigation [8].

Radiation-induced reactions will be influenced by temperature. An increase in reaction rate

with temperature can result in a synergistic effect of radiation and heat. In the case of the

more commonly used thermal ageing prediction, the Arrhenius method is employed; this

makes use of an equation based on fundamental chemical kinetics. Despite considerable

ongoing investigations of radiation ageing methodologies, this field is much less developed [9].

General equations involving dose, time, Arrhenius activation energy, dose rate and

temperature are being tested for modelling of ageing experiments [10-12]. It should be noted

that sequential application of radiation and heat, as it is frequently practised, can give very

different results depending on the order in which they are performed, and that synergistic

effects may not be properly simulated [13], [14].

The electrical and mechanical properties required of insulating materials and the acceptable

amount of radiation-induced changes are so varied that it is not possible to establish

___________
References in square brackets refer to the bibliography.
---------------------- Page: 8 ----------------------
60544-2 © IEC:2012 – 7 –

acceptable properties within the framework of a recommendation. The same holds for the

irradiation conditions. Therefore, this standard recommends only a few properties and

irradiation conditions which previous experience has shown to be appropriate. The properties

recommended are those that are especially sensitive to radiation. For a specific application,

other properties may have to be selected.

Part 1 of IEC 60544 constitutes an introduction dealing very broadly with the problems

involved in evaluating radiation effects. It also provides a guide to dosimetry terminology,

several methods of determining the exposure and absorbed dose, and methods of calculating

the absorbed dose in any specific material from the dosimetry method applied. The present

part describes procedures for irradiation and test. Part 4 of IEC 60544 defines a classification

system to categorize the radiation endurance of insulating materials. It provides a set of

parameters characterizing the suitability for radiation service. It is a guide for the selection,

indexing and specification of insulating materials. The earlier Part 3 of IEC 60544 has been

incorporated into the present Part 2.
---------------------- Page: 9 ----------------------
– 8 – 60544-2 © IEC:2012
ELECTRICAL INSULATING MATERIALS –
DETERMINATION OF THE EFFECTS OF IONIZING
RADIATION ON INSULATING MATERIALS –
Part 2: Procedures for irradiation and test
1 Scope

This Part of IEC 60544 specifies the controls maintained over the exposure conditions during

and after the irradiation of insulating materials with ionizing radiation prior to the

determination of radiation-induced changes in physical or chemical properties.

This standard specifies a number of potentially significant irradiation conditions as well as

various parameters which can influence the radiation-induced reactions under these

conditions.

The objective of this standard is to emphasize the importance of selecting suitable specimens,

exposure conditions and test methods for determining the effect of radiation on appropriately

chosen properties. Since many materials are used either in air or in inert environments,

standard exposure conditions are recommended for both of these situations.

It should be noted that this standard does not consider measurements which are performed

during the irradiation.
2 Normative references

The following documents, in whole or in part, are normatively referenced in this document and

are indispensable for its application. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any
amendments) applies.

IEC 60093, Methods of test for volume resistivity and surface resistivity of solid electrical

insulating materials

IEC 60167, Methods of test for the determination of the insulation resistance of solid

insulating materials

IEC 60212, Standard conditions for use prior to and during the testing of solid electrical

insulating materials

IEC 60243-1, Electrical strength of insulating materials –Test methods – Part 1: Tests at

power frequencies

IEC 60544-1, Electrical insulating materials – Determination of the effects of ionizing radiation

– Part 1: Radiation interaction and dosimetry

IEC 60544-4, Electrical insulating materials – Determination of the effects of ionizing radiation

– Part 4: Classification system for service in radiation environments
– Determination of tensile stress-strain
ISO 37, Rubber, vulcanized or thermoplastic
properties
---------------------- Page: 10 ----------------------
60544-2 © IEC:2012 – 9 –

ISO 48, Rubber, vulcanized or thermoplastic – Determination of hardness (hardness between

10 IRHD and 100 IRHD)
ISO 178, Plastics – Determination of flexural properties
ISO 179 (all parts), Plastics – Determination of Charpy impact properties
ISO 527 (all parts), Plastics – Determination of tensile properties

ISO 815 (all parts), Rubber, vulcanized or thermoplastic – Determination of compression set

ISO 868, Plastics and ebonite – Determination of indentation hardness by means of a

durometer (Shore hardness)
3 Irradiation
3.1 Type of radiation and dosimetry
The following types of radiation are covered by the standard:
– X- and γ-rays;
– electrons;
– protons;
– neutrons;
– combined γ-rays and neutrons ("reactor" radiation).

In general, the radiation effects may be different for different types of radiation. However, in

many practical applications, it has been found that with analogous experimental conditions,

equal absorbed dose and equal linear energy transfer, the changes in properties will be only

slightly dependent on the type of radiation [15-17]. Thus, the preferred type of radiation

should be one for which the absorbed dose measurement is simple and precise, for example

Co γ-rays or fast electrons. For a comparison of the effect of reactor radiation with γ-rays or

fast electrons, specimens with the same chemical composition can be irradiated with these

various types of radiation and the radiation-induced changes can be compared.

Radiation-induced changes are related to the absorbed radiation energy, expressed by the

absorbed dose. Recommended methods of dosimetry are listed in IEC 60544-1. The

definitions of absorbed dose, absorbed dose rate and the units are also given in IEC 60544-1

and repeated here for convenience.

The absorbed dose, D, is the quotient of dε by dm, where dε is the mean energy imparted by

ionizing radiation to the matter in a volume element and dm is the mass of the matter in that

volume element.

The absorbed dose rate, D, is the increment of the absorbed dose dD in the time interval dt.

Units
The SI unit of absorbed dose is the gray (Gy);
---------------------- Page: 11 ----------------------
– 10 – 60544-2 © IEC:2012
1 Gy = 1 J/kg (= 10 rad).
Usual multiples for higher doses are the kilogray (kGy) or megagray (MGy).
The SI unit of absorbed dose rate is the gray per second;
1 Gy/s = 1 W/kg (=10 rad/s = 0,36 Mrad/h).
3.2 Irradiation conditions
The irradiation conditions which must be established are as follows:
– type and energy of the radiation;
– absorbed dose;
– absorbed dose rate;
– surrounding medium;
– temperature;
– mechanical, electrical and other stresses;
– sample thickness.

It is preferable to use γ-rays, X-rays or electrons for the irradiation (see 3.1). Their energy

should be so chosen that the homogeneity of the absorbed dose in the sample is within ±15 %.

3.3 Sample preparation

The test specimens shall be carefully prepared in accordance with the appropriate IEC and

ISO standards, because a variation in test results may be due to differences in the quality of

test specimens.

Because the effect of radiation can depend on the dimensions of the specimens, these shall

be uniform for all comparison studies. It is preferable to irradiate the test specimens in the

geometry needed for subsequent tests. If, however, the test specimens have to be cut from a

larger irradiated test piece, the position of the specimen in the test piece shall be reported.

Non-irradiated control specimens shall be produced in the same manner and subjected to the

same conditioning and post-irradiation treatment as the irradiated specimens.
3.4 Irradiation procedures
3.4.1 Irradiation dose-rate control

The exposure rate is usually non-uniform in the radiation field. In addition, it is reduced by the

energy absorption in the specimen itself. Therefore, the absorbed dose cannot be

homogeneous. Improvements in homogeneity may be achieved by filtering methods, by

irradiation of the specimens from several directions, by traversing the radiation field at a

constant rate or by scanning the specimen with the radiation beam. The homogeneity of the

absorbed dose rate should be improved rotating or moving the sample during the irradiation,

for example, by means of suitable equipments. It is expected that variations in dose rate

within ±15 % will not appreciably affect the results (see 3.2); variations outside this

recommended value shall be reported.
3.4.2 Irradiation temperature control

The specimens shall be conditioned at the irradiation temperature for 48 h, or until an

approximate equilibrium with the irradiation temperature is ensured.

The temperatures shall be chosen from the standardized series given in IEC 60212.

---------------------- Page: 12 ----------------------
60544-2 © IEC:2012 – 11 –

The temperature of the specimens during irradiation shall be determined by the use of a

supplementary specimen containing a temperature-measuring device, irradiated under the

same conditions as the other specimens. The measuring device and its position in the

specimen have to be carefully chosen so to avoid that the irradiation influences the

temperature measurements.

The temperature variations are a function of the actual temperature of the experiment. Larger

tolerances (e.g. ±5 K) are allowed at ambient temperatures up to approximately 40 °C,

smaller tolerances (e.g. ±2 K) are reaso
...

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