IEC 61109:2008
(Main)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
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 61109:2008 applies to composite suspension/tension insulators consisting of a load-bearing cylindrical insulating solid core consisting of fibres - usually glass - in a resin-based matrix, a housing (outside the insulating core) made of polymeric material and end fittings permanently attached to the insulating core. The main technical changes with respect to the previous edition are
- removal of tests procedures now given in IEC 62217;
- inclusion of clauses on tolerances, environmental conditions, transport, storage and installation;
- general improvement of the description of tests and addition of a new Annex C on non-standard loads.
Isolateurs pour lignes aériennes - Isolateurs composites de suspension et d'ancrage destinés aux systèmes à courant alternatif de tension nominale supérieure à 1 000 V - Définitions, méthodes d'essai et critères d'acceptation
La CEI 61109:2008 s'applique aux isolateurs composites de suspension/d'ancrage constitués d'une charge portant un noyau isolant plein cylindrique réalisé en fibres - généralement de verre - en matrice à base de résine, d'un revêtement (à l'extérieur du noyau isolant) réalisé en matériau élastomère et des armatures d'extrémité fixées au noyau isolant. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
- suppression des procédures d'essai qui sont maintenant données dans la CEI 62217;
- ajout des articles sur les tolérances, les conditions environnementales, le transport, stockage et installation;
- amélioration générale des descriptifs d'essai et ajout d'un nouveau Annexe C sur les charges non-standards.
General Information
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Standards Content (Sample)
IEC 61109
Edition 2.0 2008-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
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
Isolateurs pour lignes aériennes – Isolateurs composites de suspension et
d’ancrage destinés aux systèmes à courant alternatif de tension nominale
supérieure à 1 000 V – Définitions, méthodes d'essai et critères d'acceptation
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IEC 61109
Edition 2.0 2008-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
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
Isolateurs pour lignes aériennes – Isolateurs composites de suspension et
d’ancrage destinés aux systèmes à courant alternatif de tension nominale
supérieure à 1 000 V – Définitions, méthodes d'essai et critères d'acceptation
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
U
CODE PRIX
ICS 29.080.10 ISBN 2-8318-9814-5
– 2 – 61109 ¤ IEC:2008
CONTENTS
FOREWORD.4
INTRODUCTION.6
1 Scope and object .7
2 Normative references.7
3 Terms, definitions and abbreviations .8
3.1 Terms and definitions .8
3.2 Abbreviations.10
4 Identification .10
5 Environmental conditions .10
6 Transport, storage and installation .10
7 Hybrid insulators.10
8 Tolerances .10
9 Classification of tests.11
9.1 Design tests .11
9.2 Type tests .11
9.3 Sample tests .11
9.4 Routine tests .11
10 Design tests .12
10.1 General .12
10.2 Test specimens for IEC 62217 .13
10.2.1 Tests on interfaces and connections of end fittings.13
10.2.2 Tracking and erosion test.13
10.2.3 Tests on core material .14
10.3 Product specific pre-stressing for IEC 62217.14
10.3.1 Sudden load release .14
10.3.2 Thermal-mechanical pre-stress .14
10.4 Assembled core load-time tests .14
10.4.1 Test specimens .14
10.4.2 Mechanical load test .15
11 Type tests.15
11.1 Electrical tests .15
11.2 Damage limit proof test and test of the tightness of the interface between end
fittings and insulator housing .16
11.2.1 Test specimens .16
11.2.2 Performance of the test.16
11.2.3 Evaluation of the test .17
12 Sample tests.17
12.1 General rules.17
12.2 Verification of dimensions (E1 + E2) .18
12.3 Verification of the end fittings (E2) .18
12.4 Verification of tightness of the interface between end fittings and insulator
housing (E2) and of the specified mechanical load, SML (E1).18
12.5 Galvanizing test (E2) .19
12.6 Re-testing procedure .19
13 Routine tests .19
13.1 Mechanical routine test.19
61109¤ IEC:2008 – 3 –
13.2 Visual examination .19
Annex A (informative) Principles of the damage limit, load coordination and testing for
composite suspension and tension insulators .21
Annex B (informative) Example of two possible devices for sudden release of load .25
Annex C (informative) Guidance on non-standard mechanical stresses and dynamic
mechanical loading of composite tension/suspension insulators.27
Bibliography .29
Figure 1 − Thermal-mechanical test.20
Figure A.1 − Load-time strength and damage limit of a core assembled with fittings.22
Figure A.2 – Graphical representation of the relationship of the damage limit to the
mechanical characteristics and service loads of an insulator with a 16 mm diameter
core .23
Figure A.3 – Test loads .24
Figure B.1 − Example of possible device 1 for sudden release of load.25
Figure B.2 − Example of possible device 2 for sudden release of load.26
Table 1 – Tests to be carried out after design changes .12
Table 2 – Design tests .13
Table 3 – Mounting arrangements for electrical tests .16
Table 4 – Sample sizes .17
– 4 – 61109 ¤ IEC:2008
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
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
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
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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) 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 61109 has been prepared by subcommittee 36B: Insulators for
overhead lines, of IEC technical committee 36: Insulators.
This second edition cancels and replaces the first edition, published in 1992 and amendment 1,
published in 1995. This edition constitutes a technical revision.
The main technical changes with respect to the previous edition are listed below:
– removal of tests procedures now given in IEC 62217;
– inclusion of clauses on tolerances, environmental conditions, transport, storage and
installation;
– inclusion of hybrid insulators in the scope (see Clause 8);
– clarification and modification of the parameters determining the need to repeat design and
type tests;
61109¤ IEC:2008 – 5 –
– general improvement of the description of tests;
– modification of the specification of load application in bending tests to simplify testing;
– mechanical tests adapted to improved knowledge of failure mechanisms;
– additional requirements for visual examination;
– Annex A simplified and adapted to include the damage limit concept;
– addition of a new Annex C on non-standard loads.
The text of this standard is based on the following documents:
FDIS Report on voting
36B/274/FDIS 36B/276/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.
The committee has decided that the contents of this publication will remain unchanged until the
maintenance result 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.
– 6 – 61109 ¤ IEC:2008
INTRODUCTION
Composite insulators consist of an insulating core, bearing the mechanical load protected by a
polymeric housing, the load being transmitted to the core by end fittings. Despite these
common features, the materials used and the construction details employed by different
manufacturers may be quite different.
Some tests have been grouped together as "Design tests", to be performed only once on
insulators which satisfy the same design conditions. For all design tests of composite
suspension and tension insulators, the appropriate common clauses defined in IEC 62217 are
applied. As far as practical, the influence of time on the electrical and mechanical properties of
the components (core material, housing, interfaces etc.) and of the complete composite
insulators has been considered in specifying the design tests to ensure a satisfactory life-time
under normally known stress conditions of transmission lines. An explanation of the principles
of the damage limit, load coordination and testing is presented in Annex A.
It has not been considered useful to specify a power arc test as a mandatory test. The test
parameters are manifold and can have very different values depending on the configurations of
the network and the supports and on the design of arc-protection devices. The heating effect of
power arcs should be considered in the design of metal fittings. Critical damage to the metal
fittings resulting from the magnitude and duration of the short-circuit current can be avoided by
properly designed arc-protection devices. This standard, however, does not exclude the
possibility of a power arc test by agreement between the user and manufacturer.
gives details of a.c. power arc testing of insulator sets.
IEC 61467 [1]
Composite insulators are used in both a.c. and d.c. applications. In spite of this fact, a specific
tracking and erosion test procedure for d.c. applications as a design test has not yet been
defined and accepted. The 1 000 h a.c. tracking and erosion test of IEC 62217 is used to
establish a minimum requirement for the tracking resistance of the housing material.
The mechanism of brittle fracture has been investigated by CIGRE B2.03 and conclusions are
published in [2, 3]. Brittle fracture is a result of stress corrosion induced by internal or external
acid attack on the resin bonded glass fibre core. CIGRE D1.14 has developed a test procedure
for core materials based on time-load tests on assembled cores exposed to acid, along with
chemical analysis methods to verify the resistance against acid attack [4]. In parallel IEC
TC36WG 12 is studying preventive and predictive measures.
Composite suspension/tension insulators are not normally intended for torsion or other non-
tensile loads. Guidance on non-standard loads is given in Annex C.
Wherever possible, IEC Guide 111 [5] has been followed for the drafting of this standard.
___________
Figures in square brackets refer to the bibliography.
International Council on Large High Voltage Electric Systems: Working Group B2.03.
61109¤ IEC:2008 – 7 –
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
1 Scope and object
This International Standard applies to composite suspension/tension insulators consisting of a
load-bearing cylindrical insulating solid core consisting of fibres – usually glass – in a resin-
based matrix, a housing (outside the insulating core) made of polymeric material and end
fittings permanently attached to the insulating core.
Composite insulators covered by this standard are intended for use as suspension/tension line
insulators, but it should be noted that these insulators can occasionally be subjected to
compression or bending, for example when used as phase-spacers.
This standard can be applied in part to hybrid composite insulators where the core is made of a
homogeneous material (porcelain, resin), see Clause 8.
The object of this standard is to
– define the terms used,
– prescribe test methods,
– prescribe acceptance criteria.
This standard does not include requirements dealing with the choice of insulators for specific
operating conditions.
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 60383-1, Insulators for overhead lines with a nominal voltage above 1 000 V – Part 1:
Ceramic or glass insulator units for a.c. systems – Definitions, test methods and acceptance
criteria
IEC 60383-2, Insulators for overhead lines with a nominal voltage above 1 000 V – Part 2:
Insulator strings and insulator sets for a.c. systems – Definitions, test methods and
acceptance criteria.
IEC 61466-1, Composite string insulator units for overhead lines with a nominal voltage
greater than 1 000 V – Part 1: Standard strength classes and end fittings
IEC 62217:2005, Polymeric insulators for indoor and outdoor use with a nominal voltage
> 1 000 V – General definitions, test methods and acceptance criteria
ISO 3452 (all parts), Non-destructive testing – Penetrant testing
– 8 – 61109 ¤ IEC:2008
3 Terms, definitions and abbreviations
For the purposes of this document, the following terms, definitions and abbreviations apply.
NOTE Certain terms from IEC 62217 are reproduced here for ease of reference. Additional definitions applicable
to insulators can be found in IEC 60050-471 [6].
3.1 Terms and definitions
3.1.1
polymeric insulator
insulator whose insulating body consists of at least one organic based material
NOTE Polymeric insulators are also known as non-ceramic insulators.
NOTE 2 Coupling devices may be attached to the ends of the insulating body.
[IEV 471-01-13]
3.1.2
composite insulator
insulator made of at least two insulating parts, namely a core and a housing equipped with
metal fittings
NOTE Composite insulators, for example, can consist either of individual sheds mounted on the core, with or
without an intermediate sheath, or alternatively, of a housing directly moulded or cast in one or several pieces on to
the core.
[IEV 471-01-02]
3.1.3
core of a composite insulator
internal insulating part of a composite insulator which is designed to ensure the mechanical
characteristics
NOTE The core usually consists of either fibres (e.g. glass) which are positioned in a resin-based matrix or a
homogeneous insulating material (e.g. porcelain or resin).
[IEV 471-01-03, modified]
3.1.4
insulator trunk
central insulating part of an insulator from which the sheds project
NOTE Also known as shank on smaller insulators.
[IEV 471-01-11]
3.1.5
housing
external insulating part of a composite insulator providing the necessary creepage distance and
protecting core from the environment
NOTE An intermediate sheath made of insulating material may be part of the housing.
[IEV 471-01-09]
61109¤ IEC:2008 – 9 –
3.1.6
shed of an insulator
insulating part, projecting from the insulator trunk, intended to increase the creepage distance.
NOTE The shed can be with or without ribs
[IEV 471-01-15]
3.1.7
interfaces
surface between the different materials
NOTE Various interfaces occur in most composite insulators, e.g.
– between housing and fixing devices,
– between various parts of the housing, e.g. between sheds, or between sheath and sheds,
– between core and housing
[Definition 3.10 of IEC 62217]
3.1.8
end fitting
integral component or formed part of an insulator intended to connect it to a supporting
structure, or to a conductor, or to an item of equipment, or to another insulator
NOTE Where the end fitting is metallic, the term “metal fitting” is normally used.
[IEV 471-01-06]
3.1.9
connection zone
zone where the mechanical load is transmitted between the insulating body and the end fitting
[Definition 3.12 of IEC 62217]
3.1.10
coupling
part of the end fitting which transmits the load to the accessories external to the insulator
[Definition 3.13 of IEC 62217, modified]
3.1.11
specified mechanical load
SML
load, specified by the manufacturer, which is used for mechanical tests in this standard
3.1.12
routine test load
RTL
load applied to all assembled composite insulators during a routine mechanical test
3.1.13
failing load
maximum load that is reached when the insulator is tested under the prescribed conditions
– 10 – 61109 ¤ IEC:2008
3.2 Abbreviations
The following abbreviations are used in this standard:
E1, E2 Sample sets for sample tests
M Average 1 min failing load of the core assembled with fittings
AV
RTL Routine test load
SML Specified mechanical load
4 Identification
In addition to the requirements of IEC 62217, each insulator shall be marked with the SML.
It is recommended that each insulator be marked or labelled by the manufacturer to show that
it has passed the routine mechanical test.
5 Environmental conditions
The normal environmental conditions to which insulators are submitted in service are defined in
IEC 62217.
6 Transport, storage and installation
In addition to the requirements of IEC 62217, information on handling of composite insulators
can be found in CIGRE Technical Brochure 184 [7]. During installation, or when used in non-
standard configurations, composite suspension insulators may be submitted to high torsion,
compression or bending loads for which they are not designed. Annex C gives guidance on
catering for such loads.
7 Hybrid insulators
As stated in Clause 1, this standard can be applied in part to hybrid composite insulators where
the core is made of a homogeneous material (porcelain, resin). In general, the load-time
mechanical tests and tests for core material are not applicable to porcelain cores. For such
insulators, the purchaser and the manufacturer shall agree on the selection of tests to be used
from this standard and from IEC 60383-1.
8 Tolerances
Unless otherwise agreed, a tolerance of
± (0,04 × d + 1,5) mm when d ≤ 300 mm,
± (0,025 × d + 6 ) mm when d > 300 mm with a maximum tolerance of ± 50 mm,
shall be allowed on all dimensions for which specific tolerances are not requested or given on
the insulator drawing (d being the dimension in millimetres).
The measurement of creepage distances shall be related to the design dimensions and
tolerances as determined from the insulator drawing, even if this dimension is greater than the
value originally specified. When a minimum creepage is specified, the negative tolerance is
also limited by this value.
61109¤ IEC:2008 – 11 –
In the case of insulators with creepage distance exceeding 3 m, it is allowed to measure a
short section around 1 m long of the insulator and to extrapolate.
9 Classification of tests
9.1 Design tests
These tests are intended to verify the suitability of the design, materials and method of
manufacture (technology). A composite suspension insulator design is defined by the following
elements:
– materials of the core, housing and their manufacturing method;
– material of the end fittings, their design and method of attachment (excluding the coupling);
– layer thickness of the housing over the core (including a sheath where used);
– diameter of the core.
When changes in the design occur, re-qualification shall be carried out in accordance with
Table 1.
When a composite suspension insulator is submitted to the design tests, it becomes a parent
insulator for a given design and the results shall be considered valid for that design only. This
tested parent insulator defines a particular design of insulators which have all the following
characteristics:
a) same materials for the core and housing and same manufacturing method;
b) same material of the fittings, the same connection zone design, and the same housing-to-
fitting interface geometry;
c) same or greater minimum layer thickness of the housing over the core (including a sheath
where used);
d) same or smaller stress under mechanical loads;
e) same or greater diameter of the core;
f) equivalent housing profile parameters, see Note (a) in Table 1.
9.2 Type tests
The type tests are intended to verify the main characteristics of a composite insulator, which
depend mainly on its shape and size. They also confirm the mechanical characteristics of the
assembled core (see Clause A.4). They are made on insulators whose class has satisfied the
design tests, more details are given in Clause 11.
9.3 Sample tests
The sample tests are for the purpose of verifying other characteristics of composite insulators,
including those which depend on the quality of manufacture and on the materials used. They
are made on insulators taken at random from lots offered for acceptance.
9.4 Routine tests
The aim of these tests is to eliminate composite insulators with manufacturing defects. They
are made on every composite insulator offered for acceptance.
– 12 – 61109 ¤ IEC:2008
Table 1 – Tests to be carried out after design changes
IF the change in insulator design concerns: THEN the following tests shall be repeated:
Design tests Type tests
62217 62217
62217 61109 Tests on housing Tests on the 61109
material core material
c)
1 Housing materials
X X X X X X
a)
2 Housing profile X X X
3 Core material X X X X X
b)
4 Core diameter
X X X X X
Core and end-fitting manufacturing
5 X X X X X
process
Core and end-fitting assembly
X X X
process
c) c)
7 Housing manufacturing process X X X X X X X
c) c)
8 Housing assembly process
X X X X
9 End fitting material X X X
10 End fitting connection zone design X X X
Core/housing/end fitting interface
c) c)
11 X X
X X
design
12 Coupling type X
a)
Variations of the profile within following tolerances do not constitute a change:
- overhang : ± 10 %
- diameter : +15 %, -0 %
- thickness at base and tip : ± 15 %
- spacing : ± 15 %
- shed inclinations : ± 3°
- shed repetition : identical
b)
Variations of the core diameter within ± 15 % do not constitute a change.
c)
Not necessary if it can be demonstrated that the change has no influence on the assembled core strength.
10 Design tests
10.1 General
These tests consist of the tests prescribed in IEC 62217 as listed in Table 2 below and a
specific assembled core load-time test. The design tests are performed only once and the
results are recorded in a test report. Each part can be performed independently on new test
specimens, where appropriate. The composite insulator of a particular design shall be qualified
only when all insulators or test specimens pass the design tests.
Interfaces and
connections of end
fittings
Assembled core load–
time tests
Hardness test
Accelerated weathering
test
Tracking and erosion
test
Flammability test
Dye penetration test
Water diffusion test
Electrical type tests
Mechanical type tests
61109¤ IEC:2008 – 13 –
Table 2 – Design tests
Tests on interfaces and connections of end fittings
Pre-stressing – Sudden load release pre-stressing
Thermal-mechanical pre-stressing
(see 10.2.1 and 10.3 below)
Water immersion pre-stressing
Verification tests
Visual examination
Steep-front impulse voltage test
Dry power-frequency voltage test
Tests on shed and housing material
Hardness test
Accelerated weathering test
Tracking and erosion test – see 10.2.2 below for specimens
Flammability test
Tests on the core material – see 10.2.3 below for specimens
Dye penetration test
Water diffusion test
Assembled core load-time test
Determination of the average failing load of the core of the assembled insulator
Control of the slope of the strength-time curve of the insulator
10.2 Test specimens for IEC 62217
10.2.1 Tests on interfaces and connections of end fittings
Three insulators assembled on the production line shall be tested. The insulation length (metal
to metal spacing) shall be not less than 800 mm. Both end fittings shall be the same as on
standard production insulators. The end fittings shall be assembled so that the insulating part
from the fitting to the closest shed shall be identical to that of the production line insulator. If
spacers, joining rings or other features are used in the insulator design (notably for longer
insulators), the sample shall include any such devices in a typical position.
NOTE If the manufacturer only has facilities to produce insulators shorter than 800 mm, the design tests may be
performed on insulators of those lengths available to him, but the results are only valid for up to the lengths tested.
10.2.2 Tracking and erosion test
If spacers, joining rings or other features are used in the insulator design (notably for longer
insulators), the samples for this test shall include any such devices in a typical position.
IEC 62217 specifies that the creepage distance of the sample shall be between 500 mm and
800 mm. If the inclusion of spacers or joints, as mentioned above, requires a longer creepage
distance, the design tests may be performed on insulators of lengths as close to 800 mm as
possible. If the manufacturer only has facilities to produce insulators with creepage shorter
than 500 mm, the design tests may be performed on insulators of those lengths he has
available, but the results are only valid for up to the tested lengths.
– 14 – 61109 ¤ IEC:2008
10.2.3 Tests on core material
The specimens shall be as specified in IEC 62217. However, if the housing material is not
bonded to the core, then it shall be removed and the remaining core thoroughly cleaned to
remove any traces of sealing material before cutting and testing.
10.3 Product specific pre-stressing for IEC 62217
The tests shall be carried out on the three specimens in the sequence as indicated below.
10.3.1 Sudden load release
With the insulator at –20 °C to –25 °C, every test specimen is subjected to five sudden load
releases from a tensile load amounting to 30 % of the SML.
NOTE 1 Annex B describes two examples of possible devices for sudden load release.
NOTE 2 In certain cases, a lower temperature may be selected by agreement.
10.3.2 Thermal-mechanical pre-stress
Before commencing the test, the specimens shall be loaded at the ambient temperature by at
least 5 % of the SML for 1 min, during which the length of the specimens shall be measured to
an accuracy of 0,5 mm. This length shall be considered to be the reference length.
The specimens are then submitted to temperature cycles under a continuous mechanical load
as described in Figure 1, the 24 h temperature cycle being perfomed four times. Each 24 h
cycle has two temperature levels with a duration of at least 8 h, one at (+50 ± 5) °C, the other
at (–35 ± 5) °C. The cold period shall be at a temperature at least 85 K below the value actually
applied in the hot period. The pre-stressing can be conducted in air or any other suitable
medium.
The applied mechanical load shall be equal to the RTL (at least 50 % of the SML) of the
specimen. The specimen shall be loaded at ambient temperature before beginning the first
thermal cycle.
NOTE The temperatures and loads in this pre-stressing are not intended to represent service conditions, they are
designed to produce specific reproducible stresses in the interfaces on the insulator.
The cycles may be interrupted for maintenance of the test equipment for a total duration of 2 h.
The starting point after any interruption shall be the beginning of the interrupted cycle.
After the test, the length shall again be measured in a similar manner at the same load and at
the original specimen temperature (this is done in order to provide some additional information
about the relative movement of the metal fittings).
10.4 Assembled core load-time tests
10.4.1 Test specimens
Six insulators made on the production line shall be tested. The insulation length (metal to metal
spacing) shall be not less than 800 mm. Both end fittings shall be identical in all aspects to
those used on production line insulators, except that they may be modified beyond the end of
the connection zone in order to avoid failure of the couplings.
61109¤ IEC:2008 – 15 –
The six insulators shall be examined visually and a check made that their dimensions conform
with the drawing.
NOTE If the manufacturer only has facilities to produce insulators shorter than 800 mm, the design tests may be
performed on insulators of those lengths he has available, but the results are only valid for up to the tested lengths.
10.4.2 Mechanical load test
This test is performed in two parts at ambient temperature.
10.4.2.1 Determination of the average failing load of the core of the assembled
insulator M
AV
Three of the specimens shall be subjected to a tensile load. The tensile load shall be increased
rapidly but smoothly from zero to approximately 75 % of the expected mechanical failing load
and shall then be gradually increased in a time between 30 s and 90 s until breakage of the
core or complete pull-out occurs. The average of the three failing loads M shall be
AV
calculated.
10.4.2.2 Verification of the 96 h withstand load
Three specimens shall be subjected to a tensile load. The tensile load shall be increased
rapidly but smoothly from zero up to 60 % of M , as calculated in 10.4.2.1 and then
AV
maintained at this value for 96 h without failure (breakage or complete pull-out). If for any
reason the load application is interrupted, then the test shall be restarted on a new specimen.
11 Type tests
An insulator type is electrically defined by the arcing distance, creepage distance, shed
inclination, shed diameter and shed spacing.
The electrical type tests shall be performed only once on insulators satisfying the conditions
above and shall be performed with arcing or field control devices (which are generally
necessary on composite insulators at transmission voltages) if they are an integral part of the
insulator type.
Furthermore, Table 1 outlines the insulator design characteristics that, when changed, also
require a repeat of the electrical type tests.
An insulator type is mechanically defined principally by a maximum SML for the given core
diameter, method of attachment and coupling design.
The mechanical type tests shall be performed only once on insulators satisfying the criteria for
each type.
Furthermore, Table 1 indicates additional insulator design characteristics that, when changed,
require a repeat of the mechanical type tests.
11.1 Electrical tests
The electrical tests in Table 3 shall be performed according to IEC 60383-2 to confirm the
specified values. Interpolation of electrical test results may be used for insulators of
intermediate length, provided that the factor between the arcing distances of the insulators
whose results form the end points of the interpolation range is less than or equal to 1,5.
Extrapolation is not allowed.
– 16 – 61109 ¤ IEC:2008
Table 3 – Mounting arrangements for electrical tests
Test Mounting arrangement
Standard mounting arrangement of an insulator string or
Dry lightning impulse withstand voltage test insulator set when switching impulse tests are not
required
Standard mounting arrangement of an insulator string or
Wet power-frequency test insulator set when switching impulse tests are not
required
Wet switching impulse withstand voltage test for Standard mounting arrangement of an insulator string or
insulator set when switching impulse tests are required
insulators intended for systems with U ≥ 300 kV
m
11.2 Damage limit proof test and test of the tightness of the interface between end
fittings and insulator housing
11.2.1 Test specimens
Four insulators taken from the production line shall be tested. In the case of long insulators,
specimens may be manufactured, assembled on the production line, with an insulation length
(metal to metal spacing) not less than 800 mm. Both end fittings shall be the same as on
standard production insulators. The fittings shall be assembled such that the insulating part
from the fitting to the closest shed is identical to that of the production line insulator. The
insulators shall be examined visually and checked to see that the dimensions conform with the
drawing; they shall then be subjected to the mechanical routine test according to 13.1.
NOTE If the manufacturer only has facilities to produce insulators shorter than 800 mm, the design tests may be
performed on insulators of those lengths available to him, but the results are only valid for up to the lengths tested.
11.2.2 Performance of the test
a) The four specimens are subjected to a tensile load applied between the couplings at
ambient temperature. The tensile load shall be increased rapidly but smoothly from zero up
to 70 % of the SML and then maintained at this value for 96 h.
b) Both ends of one of the four specimens shall, at the end of the 96 h test, be subjected to
crack indication by dye penetration, in accordance with ISO 3452, on the housing in the
zone embracing the complete length of the interface between the housing and metal f
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