SIST-TP CLC/TR 62662:2011

SLOVENSKI STANDARD
SIST-TP CLC/TR 62662:2011
01-december-2011
Navodila za proizvodnjo, preskušanje in diagnosticiranje polimernih izolatorjev
glede na krhki prelom jedrnih materialov (IEC/TR 62662:2010)
Guidance for production, testing and diagnostics of polymer insulators with respect to
brittle fracture of core materials (IEC/TR 62662:2010)
Empfehlungen und Anleitungen für die Herstellung, Prüfung und Diagnose von
Polymerisolatoren hinsichtlich Sprödbruch des Kernwerkstoffes (IEC/TR 62662:2010)
Guide pour la production, les essais et diagnostiques des isolateurs polymériques en
rapport avec les ébréchures des matériaux du noyau (CEI/TR 62662:2010)
Ta slovenski standard je istoveten z: CLC/TR 62662:2011
ICS:
29.080.10 Izolatorji Insulators
SIST-TP CLC/TR 62662:2011 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST-TP CLC/TR 62662:2011

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SIST-TP CLC/TR 62662:2011

TECHNICAL REPORT
CLC/TR 62662

RAPPORT TECHNIQUE
October 2011
TECHNISCHER BERICHT

ICS 29.080.10


English version


Guidance for production, testing and diagnostics of polymer insulators
with respect to brittle fracture of core materials
(IEC/TR 62662:2010)


Guide pour la production, les essais et Empfehlungen und Anleitungen für die
diagnostiques des isolateurs polymériques Herstellung, Prüfung und Diagnose von
en rapport avec les ébréchures des Polymerisolatoren hinsichtlich Sprödbruch
matériaux du noyau des Kernwerkstoffes
(CEI/TR 62662:2010) (IEC/TR 62662:2010)







This Technical Report was approved by CENELEC on 2011-10-24.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus,
the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy,
Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia,
Spain, Sweden, Switzerland and the United Kingdom.





CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Management Centre: Avenue Marnix 17, B - 1000 Brussels


© 2011 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. CLC/TR 62662:2011 E

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SIST-TP CLC/TR 62662:2011
CLC/TR 62662:2011 - 2 -
Foreword
This document (CLC/TR 62662:2011) consists of the text of IEC/TR 62662:2010 prepared by IEC TC 36
"Insulators".

Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such patent
rights.

Endorsement notice
The text of the Technical Report IEC/TR 62662:2010 was approved by CENELEC as a Technical Report
without any modification.
In the official version, for Bibliography, the following note has to be added for the standard indicated:
IEC 60812:2006 NOTE  Harmonized as EN 60812:2006 (not modified).

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SIST-TP CLC/TR 62662:2011
- 3 - CLC/TR 62662:2011
Annex ZA
(normative)

Normative references to international publications
with their corresponding European publications

The following referenced documents are indispensable for the application 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.

NOTE  When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD
applies.

Publication Year Title EN/HD Year

IEC 61109 - Insulators for overhead lines - Composite EN 61109 -
suspension and tension insulators for a.c.
systems with a nominal voltage greater than
1 000 V - Definitions, test methods and
acceptance criteria


IEC/TR 62039 - Selection guide for polymeric materials for - -
outdoor use under HV stress

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SIST-TP CLC/TR 62662:2011

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SIST-TP CLC/TR 62662:2011

IEC/TR 62662
®
Edition 1.0 2010-08
TECHNICAL
REPORT

colour
inside
Guidance for production, testing and diagnostics of polymer insulators with
respect to brittle fracture of core materials


INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
Q
ICS 29.080.10 ISBN 978-2-88912-172-4
® Registered trademark of the International Electrotechnical Commission

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SIST-TP CLC/TR 62662:2011
– 2 – TR 62662 © IEC:2010(E)
CONTENTS
FOREWORD.3
INTRODUCTION.5
1 Scope.6
2 Normative references .6
3 Terms and definitions .6
4 Description of brittle fracture .7
5 Identification of brittle fracture .8
6 Failure mechanisms .8
6.1 Description of identified failure mechanisms.8
6.2 Mechanism M1 – Acid generated by electrical activity .8
6.3 Mechanism M2 – Acid ingress from environment .9
6.4 Mechanism M3 – Acid generated inside the core .10
7 Risk assessment .10
7.1 FMEA approach .10
7.2 Results.11
7.3 Discussions.13
8 Guidance for material selection and production .13
8.1 Rod materials and production process.13
8.1.1 Fibreglass .13
8.1.2 Resins .14
8.1.3 Rod production .14
8.2 Housing and sealing.14
9 Preventive methods.15
9.1 Sealing.15
9.2 Corona rings .15
9.3 Material selection .16
9.4 Housing quality .16
9.5 Handling, transportation and storage.16
Bibliography.17

7
Figure 1 – Typical brittle fracture .

Table 1 – Risk potential number (RPN) and standardized risk potential of brittle
fracture failure modes .11
Table 2 – Risk assessment of the identified brittle fracture failure modes.11

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SIST-TP CLC/TR 62662:2011
TR 62662 © IEC:2010(E) – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

GUIDANCE FOR PRODUCTION, TESTING
AND DIAGNOSTICS OF POLYMER INSULATORS
WITH RESPECT TO BRITTLE FRACTURE OF CORE MATERIALS


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
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
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.
The main task of IEC technical committees is to prepare International Standards. However, a
technical committee may propose the publication of a technical report when it has collected
data of a different kind from that which is normally published as an International Standard, for
example "state of the art".
IEC 62662, which is a technical report, has been prepared by IEC technical committee 36:
Insulators.
The text of this technical report is based on the following documents:
Enquiry draft Report on voting
36/294/DTR 36/297/RVC

Full information on the voting for the approval of this technical report can be found in the
report on voting indicated in the above table.

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SIST-TP CLC/TR 62662:2011
– 4 – TR 62662 © IEC:2010(E)
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
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.
A bilingual version of this publication may be issued at a later date.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.

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SIST-TP CLC/TR 62662:2011
TR 62662 © IEC:2010(E) – 5 –
INTRODUCTION
There is an urgent need within utilities and industry for material standards, which define the
physical properties of the polymers applied for outdoor insulation. As a first step, a state-of-
the-art report was issued by CIGRE which led to the publication of IEC 62039. This IEC
technical report presents – as a conclusion of the CIGRE-report – the important material
properties for polymeric materials used in outdoor insulation and, where applicable, lists the
standardized test methods including the minimum requirements. The acid (brittle fracture)
resistance of FRP core materials (see 3.7) was recognized as an important property for
suspension/tension composite insulators. This technical report presents more detailed
guidance on this subject taking into account different insulator designs and production
techniques. The risk of occurrence and the influencing parameters were evaluated by failure
mode effect analysis (FMEA). Brittle fracture is not the only failure mechanism for insulators
in service and is generally less frequently observed than other modes, such as failure due to
tracking and erosion. However, this subject is not yet covered by any IEC test procedures
specifically designed to detect or prevent brittle fracture.

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SIST-TP CLC/TR 62662:2011
– 6 – TR 62662 © IEC:2010(E)
GUIDANCE FOR PRODUCTION, TESTING
AND DIAGNOSTICS OF POLYMER INSULATORS
WITH RESPECT TO BRITTLE FRACTURE OF CORE MATERIALS



1 Scope
This technical report presents an analysis of the risk of influencing factors for brittle fracture
of composite insulators that are mostly loaded in the tensile mode (suspension and tension
insulators). Guidance is given to reduce the risk of in-service brittle fractures.
This phenomenon is limited to tension and suspension insulators. However, the general
information given concerning the importance of various parameters can be used as a
guideline for the design and production of any kind of composite insulator.
2 Normative references
The following referenced documents are indispensable for the application 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 61109, Insulators for overhead lines – Composite suspension and tension insulators for
a.c. systems with a nominal voltage greater than 1 000 V – Definitions, test methods and
acceptance criteria.
IEC/TR 62039, Selection guide for polymeric materials for outdoor use under HV stress
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
fibre reinforced plastic material
FRP
composite material consisting of reinforcing components e.g. glass or synthetic fibres that are
embedded in a polymer matrix e.g. epoxy or polyester. The FRP core is the integral load-
carrying part of a composite insulator
3.2
stress corrosion cracking
SCC
failure of material subjected to a constant tensile stress in a corrosive environment
3.3
brittle fracture
abnormal and sudden breakage of FRP core materials with well-defined characteristic fracture
patterns
NOTE Before brittle fracture, no apparent plastic deformation takes place. In the case of FRP core materials,
brittle fracture is caused by SCC.
3.4
failure mechanism
principal and fundamental process that leads to a characteristic failure, e.g. brittle fracture

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SIST-TP CLC/TR 62662:2011
TR 62662 © IEC:2010(E) – 7 –
NOTE A failure mechanism may have several modes of final failure.
3.5
failure mode
specific failure scenario or optional path of a failure mechanism
3.6
sealing system
technical arrangement to prevent the ingress of moisture, gases, etc., at a material transition
point exposed to the environment
3.7
failure mode effect analysis
FMEA
standardized risk assessment tool generally used for failure prevention
3.8
damage
degradation of a component leading to penetration by acid or moisture
4 Description of brittle fracture
Brittle fracture is the commonly used term for stress corrosion-induced failure of insulator core
rods manufactured from resin bonded glass fibre material (RBGF, commonly known as fibre
reinforced plastic FRP). This failure mechanism results in a complete mechanical separation
of the core (normally near the energized end fitting), and can occur at tensile loads well below
the rated mechanical strength of the insulators. In addition to a (minimum) tensile stress of
approximately 50 MPa, the brittle fracture mechanism requires the presence of acid from
either external or internal sources. The chemical process of stress corrosion is an ion
exchange mechanism whereby ions in the glass fibres are replaced by hydrogen ions from the
acid (see IEC/TR 62039).

IEC  2042/10
Figure 1 – Typical brittle fracture

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SIST-TP CLC/TR 62662:2011
– 8 – TR 62662 © IEC:2010(E)
5 Identification of brittle fracture
The macroscopic features associated with the brittle fracture of an FRP core rod have been
1
described by CIGRE [2] . A typical brittle fracture is shown in Figure 1. The fracture surfaces
typically have the following characteristics:
• a smooth, clean, planar surface perpendicular to the core axis, comprising a portion of the
rod cross-section. Multiple failure planes separated by axial delamination may be present;
• normal tensile fracture (fibrous) in the remaining rod cross-section.
In addition to these macroscopic features, confirmation of the brittle fracture mechanism is
possible through the identification of several distinctive features of the fracture surface of the
individual glass fibres using scanning electron microscopy [3].
• The mirror zone is a smooth region perpendicular to the fibre axis that includes the stress
corrosion initiation site for the individual fibre and may cover from <10% to >90% of the
fibre cross-section.
• The hackle zone is a rough region on the fibre fracture surface that failed mainly due to
mechanical stresses.
• The mist zone is a transition zone between the mirror and hackle zones and is
intermediate in roughness.
Chemical analysis techniques to show the change in the glass chemistry due to the ion
exchange mechanism may also be used as confirmation of the brittle fracture mechanism, see
[2], [4], [5], and [6].
6 Failure mechanisms
6.1 Description of identified failure mechanisms
For the time being, three failure mechanisms have been identified and are well described in
recent literature [7], [8], and [9]. The final physical-chemical mechanism is stress corrosion
cracking (SCC) which leads to “brittle fracture” of the FRP core. The initiation of SCC requires
the presence of acid in direct contact with the FRP core material for all mechanisms. The way
in which this acid appears on or inside the FRP core material can be differentiated into the
following three mechanisms.
NOTE Other mechanisms are currently under study, for example, crevice corrosion. The mechanisms are not yet
sufficiently investigated to be included in this technical report. However, all require the presence of water
(moisture).
6.2 Mechanism M1 – Acid generated by electrical activity
This mechanism is characterized by acid generation by internal and/or external electrical
discharges with the acid being finally the root cause for stress corrosion of the FRP core
material and the resulting brittle fracture of the FRP core.
Acid (nitrogenous acids) is generated by electrical discharges (corona) on the insulating
material (external), at the metal fittings (external) or by internal partial discharges within
internal voids. Electrical discharges in air generate radicals, ozone and nitrogen oxides which
form acids when combined with water (e.g. moisture from the air). Internal partial discharges
within voids of the FRP core material or at the interface between FRP core and housing may
lead to acid generation. In some cases moisture vapour transmission in a hot wet environment
followed by a cold cycle will cause condensation inside voids. The acid is then in direct
contact with the FRP core material. Moisture is required for all modes of this mechanism to
generate acid. Therefore the penetration path to the FRP core is a very critical criterion for
___________
1
 Figures in square brackets refer to the Bibliography.

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SIST-TP CLC/TR 62662:2011
TR 62662 © IEC:2010(E) – 9 –
this mechanism. Moisture penetration may be possible if the sealing system is defective or
insufficient. Other paths for moisture penetration to the FRP core may be housing damage or
housing porosity. The moisture penetration can occur in the form of molecular diffusion due to
the moisture permeability of the housing. Acids generated by electrical discharges are in
general strong inorganic acids. The main chemical structures are HNO and HNO . Polymeric
2 3
compounds show in general a high resistance to HNO and are often resistant to other acids.
3
The same applies to the sealing systems at the end fitting (triple) point realized with such
material compounds. Two main grades of FRP core materials exist:
• acid resistant core materials that pass the chemical resistance test in accordance with
IEC 62039;
• non-acid resistant core materials that do not pass the chemical resistance test.
Acid resistant rods can resist acid for a much longer time period than non-resistant materials
(see Clause 8).
The critical design features of composite insulators regarding this mechanism are:
• chemical (acid) resistance of the FRP core material;
• quality of the FRP core material regarding internal voids that may lead to internal partial
discharges;
• quality of the macroscopic interface between housing and FRP core material regarding
voids that may lead to internal partial discharges;
• long-term tightness of the sealing system;
• corona protection and field grading to reduce the appearance of acid-producing corona or
partial discharges;
• resistance of the housing and sealing system regarding transportation and handling
damage.
6.3 Mechanism M2 – Acid ingress from environment
This mechanism is characterized by acid ingress from the environment (e.g. pollution) with the
acid being finally the root cause for SCC of the FRP core material and the resulting brittle
fracture of the FRP core.
Acid or its anhydrides are present in the environment of the insulator installation. To obtain an
acidic solution moisture is also necessary. Therefore the penetration path to the core is also a
very critical criterion for this mechanism. Acid penetration may be possible if the sealing
system is defective or insufficient. Other paths for acid penetration to the FRP core may be
housing damages or housing porosity. Acids in the environment may be weak to strong acids
depending on the kind of pollution. Inorganic polymeric compounds show in general a high
resistance against such acids. Silicone or EPDM housing materials are sufficiently resistant to
most acids but also may exhibit porosity. The same applies to the sealing systems realised
with such material compounds. Two grades of FRP core materials exist:
• acid resistant core materials that pass the chemical resistance test in accordance with
IEC 62039;
• non-acid resistant core materials that do not pass the chemical resistance test.
Acid resistant rods can resist acid for a much longer time period than non-resistant materials
(see Clause 8).
The critical design features of composite insulators regarding this mechanism are:
• chemical (acid) resistance of the FRP core material;
• long-term tightness of the sealing system;

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SIST-TP CLC/TR 62662:2011
– 10 – TR 62662 © IEC:2010(E)
• porosity or penetration resistance of the housing;
• resistance of the housing and sealing system regarding transportation and handling
damage.
6.4 Mechanism M3 – Acid generated inside the core
This mechanism is characterized by acid present or generated inside the FRP core material
(excess of hardener or trapped humidity) with the acid being finally the root cause for SCC of
the FRP core material and the resulting brittle fracture of the FRP core [4] and [5].
Acids generated by excess of hardener are in general weak organic acids. Acids generated by
partial discharges and trapped humidity may be inorganic or organic acids. Both processes
require moisture. Therefore the penetration path of moisture to the core is also a very critical
criterion also for this mechanism. Moisture penetration may be possible if the sealing system
is defective or insufficient. Other paths for moisture penetration to the FRP core may be
housing damages and housing porosity. The moisture penetration can occur in the form of
molecular diffusion due to the moisture permeability of the housing. Two main grades of FRP
core materials exist:
• acid resistant core materials that pass the chemical resistance test in accordance with
IEC 62039;
• non-acid resistant core materials that do not pass the chemical resistance test.
Acid resistant rods can resist acid for a much longer time period than non-resistant materials.
The critical design features of composite insulators regarding this mechanism are:
• chemical (acid) resistance of the FRP core material;
• quality of the matrix system used for the core material in regard to the content of
excessive anhydride hardener;
• long-term tightness of the sealing system;
• quality of the macroscopic interface between housing and FRP core material regarding
voids that may lead to internal partial discharges;
• quality of the FRP core material regarding internal voids that may lead to internal partial
discharges;
• porosity or penetration resistance of the housing;
• resistance of the housing and sealing system regarding transportation and handling
damage.
7 Risk assessment
7.1 FMEA approach
The risks associated with brittle fracture of polymer suspension insulators were evaluated
using FMEA (similar to the method given in IEC 60812 [1]). The Ishikawa procedure was used
to identify the principle mechanisms of failure. It was then repeated for each mechanism to
identify the modes that could initiate the mechanism.
FMEA was then used to take into account the risk of appearance (probability) of the different
modes for each failure mechanism and included factors for the severity of the mode and for
ease of avoidance and identification of the failure or damage. These were combined to create
a Risk Potential Number (RPN) which is scaled from 1 to 1000 according to the risk severity.
The relation is:
RPN = P (probability of occurrence) × S (severity) × D (difficulty of avoidance or detection)

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SIST-TP CLC/TR 62662:2011
TR 62662 © IEC:2010(E) – 11 –
7.2 Results
A risk assessment performed by means of the FMEA method leads to the following risk
potentials for the individual modes of the respective failure mechanisms. Table 1 shows the
definition of the risk potential and Table 2 the results of the risk assessment.
Table 1 – Risk potential number (RPN)
and standardized risk potential of brittle fracture failure modes
RPN Risk potential
750 – 1 000 Very high
500 – 750 High
300 – 500 Medium – High
150 – 300 Medium
100 – 150 Low – Medium
75 – 100 Low
<75 Very low

Table 2 – Risk assessment of the identified brittle fracture failure modes
Risk potential Mechanism Mode Root cause and d
...