IEC 61952:2008
(Main)Insulators for overhead lines - Composite line post 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 line post insulators for A.C. systems with a nominal voltage greater than 1 000 V - Definitions, test methods and acceptance criteria
IEC 61952:2008 applies to composite line post insulators consisting of a load-bearing, cylindrical, insulating solid core made up of fibres - usually glass - in a resin-based matrix, a housing (outside the insulating core) made of elastomer material (e.g. silicone or ethylene-propylene) and end fittings permanently attached to the insulating core. The object of this standard is to
- define the terms used,
- prescribe test methods,
- prescribe acceptance or failure criteria.
This standard does not include requirements dealing with the choice of insulators for specific operating conditions. This edition includes the following significant technical changes with respect to the previous edition:
- removal of tests procedures now given in IEC 62217;
- inclusion of clauses on tolerances, environmental conditions, transport, storage and installation;
- changes in the parameters determining the need to repeat design and type tests; and
- modification of the specification of load application in bending tests to simplify testing.
Isolateurs pour lignes aériennes - Isolateurs composites rigides à socle pour systèmes à courant alternatif de tension nominale supérieure à 1 000 V - Définitions, méthodes d'essai et critères d'acceptation
La CEI 61952:2008 est applicable aux isolateurs composites rigides à socle constitués d'un noyau isolant cylindrique supportant la charge, composé de fibres - habituellement en verre - dans une matrice à base de résine, d'un revêtement (extérieur au noyau isolant) en matériau élastomère (par exemple silicone ou éthylène-propylène) et d'armatures d'extrémité reliées de façon permanente au noyau isolant. La présente norme a pour objet:
- de définir les termes employés,
- de fixer les méthodes d'essai,
- de fixer les critères d'acceptation ou de rejet d'une fourniture.
Cette norme n'inclut pas d'exigences relatives au choix des isolateurs pour des conditions de service spécifiques. 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 d'articles concernant les tolérances, les conditions environnementales, le transport, le stockage et l'installation;
- modification des paramètres déterminant la nécessité de répéter les essais de conception et de type et modification des exigences d'application des charges dans les essais de flexion pour faciliter les essais.
General Information
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Standards Content (Sample)
IEC 61952
Edition 2.0 2008-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Insulators for overhead lines – Composite line post 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 rigides à socle pour
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 61952
Edition 2.0 2008-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Insulators for overhead lines – Composite line post 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 rigides à socle pour
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; 29.240.20 ISBN 2-8318-9784-X
– 2 – 61952 © IEC:2008
CONTENTS
FOREWORD.4
INTRODUCTION.6
1 Scope.8
2 Normative references .8
3 Terms and definitions .8
4 Abbreviations .10
5 Identification.10
6 Environmental conditions.11
7 Transport, storage and installation.11
8 Tolerances .11
9 Classification of tests .11
9.1 Design tests .11
9.2 Type tests .12
9.3 Sample tests .12
9.4 Routine tests .12
10 Design tests .13
10.1 General .13
10.2 Test specimens for IEC 62217.14
10.2.1 Tests on interfaces and connections of end fittings.14
10.2.2 Tracking and erosion test .14
10.2.3 Tests on core material .15
10.3 Product specific pre-stressing for IEC 62217 tests on interfaces and
connections of end fittings.15
10.3.1 Thermal-mechanical pre-stressing .15
10.4 Assembled core load tests.15
10.4.1 Test for the verification of the maximum design cantilever load
(MDCL).15
10.4.2 Tensile load test .16
11 Type tests .16
11.1 Electrical tests.17
11.1.1 Vertical mounting arrangement .17
11.1.2 Horizontal mounting arrangement .17
11.2 Mechanical tests .18
11.2.1 Cantilever failing load test .18
12 Sample tests .19
12.1 General rules .19
12.2 Verification of dimensions (E1 + E2).19
12.3 Galvanizing test (E1 + E2).19
12.4 Verification of the SCL (E1) .19
12.4.1 Test procedure .19
12.4.2 Acceptance criteria.20
12.5 Re-testing procedure.20
13 Routine tests .20
13.1 Tensile load test.20
13.2 Visual examination .20
61952 © IEC:2008 – 3 –
Annex A (informative) Notes on the mechanical loads and tests .22
Annex B (informative) Determination of the equivalent bending moment caused by
combined loads.24
Bibliography.27
Figure 1 – Thermal-mechanical pre-stressing test – Typical cycles .21
Figure B.1 – Combined loads applied to unbraced insulators .25
Figure B.2 – Combined loads applied to braced insulators .26
Table 1 – Tests to be carried out after design changes .13
Table 2 – Design tests .14
Table 3 – Mounting arrangements for electrical tests .17
Table 4 – Sample sizes according to lot size.19
– 4 – 61952 © IEC:2008
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INSULATORS FOR OVERHEAD LINES –
COMPOSITE LINE POST 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
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
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between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
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5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
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6) All users should ensure that they have the latest edition of this publication.
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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 61952 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 2002. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
– removal of tests procedures now given in IEC 62217,
– inclusion of clauses on tolerances, environmental conditions, transport, storage and
installation,
– changes in the parameters determining the need to repeat design and type tests,
– clarification of the mounting arrangements for electrical type tests,
– modification of the specification of load application in bending tests to simplify testing,
61952 © IEC:2008 – 5 –
– additional requirements for the visual examination,
– removal of the annex explaining the concept of classes for design tests.
The text of this standard is based on the following documents:
FDIS Report on voting
36B/273/FDIS 36B/275/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 – 61952 © IEC:2008
INTRODUCTION
Composite line post insulators consist of a cylindrical solid insulating core, bearing the
mechanical load, protected by a polymeric housing, the loads being transmitted to the core by
metal fittings. Despite these common features, the materials used and the construction details
employed by different manufacturers may be different.
Some tests have been grouped together as "design tests", to be performed only once on
insulators which satisfy the same design conditions. All the design tests defined in IEC 62217
are applied for composite line post insulators; additional specific mechanical tests are given in
this standard. 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.
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 approach for mechanical testing under bending loads used in this standard is based on
the work of CIGRE [1] . This approach uses the concept of a damage limit which is the
maximum stress which can be developed in the insulator before damage begins to occur.
Annex A gives some notes on the mechanical loads and tests used in this standard.
Line post insulators are often used in braced structures whose geometry varies from line to
line. A combined loading test to reproduce the complex loading cases in such structures is
outside the scope of this standard and it would be very difficult to specify a general test which
covers the majority of geometry and loading cases. In order to give some guidance, Annex B
explains how to calculate the moment in the insulators resulting from combined loads. This
moment can then be equated to an equivalent bending load or stress for design purposes.
Further information is available from CIGRE [2].
Compression load tests are not specified in this standard. The mechanical loads expected
from service stress acting on line post insulators are mostly combined loads. These loads will
cause some deflection on the insulator. Compression loads applied on pre-deflected
insulators will lead to results largely dependent on the pre-deflection. Therefore a pure
compression test has little meaning since the deflection prior to the cantilever load test cannot
be specified.
Pollution tests, as specified in IEC 60507 [3], are not included in this standard, their
applicability to composite line post insulators not having been proven. Such pollution tests
performed on insulators made of non-ceramic materials do not correlate with experience
obtained from service. Specific pollution tests for non-ceramic insulators are under
consideration.
———————
Figures in square brackets refer to the bibliography.
61952 © IEC:2008 – 7 –
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. IEC 61467 [4] gives details of a.c. power arc testing of
insulator sets.
Radio interference and corona tests are not specified in this standard since the RIV and
corona performance are not characteristics of the insulator alone.
Composite hollow core line post insulators are currently not dealt with in this standard.
IEC 61462 [5] gives details of tests on hollow core composite insulators, many of which can
be applied to such line post insulators.
Torsion loads are not dealt with in this standard since they are usually negligible in the
configuration in which line post insulators are generally used. Specific applications where high
torsion loads can occur are outside the scope of this standard.
The application of this standard to hybrid line post insulators (e.g. those having a core made
of a material other than resin impregnated fibres) has not been fully studied. For example, in
general the load-time mechanical tests and tests for core material are not applicable to
porcelain cores. It is therefore recommended that this standard be considered as a provisional
standard for hybrid line post insulators, using an agreed selection of tests from this standard
and from IEC 60383-1.
Wherever possible, IEC Guide 111 [6] has been followed for the drafting of this standard.
– 8 – 61952 © IEC:2008
INSULATORS FOR OVERHEAD LINES –
COMPOSITE LINE POST INSULATORS FOR A.C.
SYSTEMS WITH A NOMINAL VOLTAGE
GREATER THAN 1 000 V –
DEFINITIONS, TEST METHODS AND ACCEPTANCE CRITERIA
1 Scope
This International Standard applies to composite line post 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 line post insulators covered by this standard are subjected to cantilever, tensile
and compressive loads, when supporting the line conductors. They are intended for use on
a.c. overhead lines with a rated voltage greater than 1 000 V and a frequency not greater than
100 Hz.
The object of this standard is
– to define the terms used,
– to prescribe test methods,
– to prescribe acceptance or failure 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 62217, Polymeric insulators for indoor and outdoor use with a nominal voltage above
1 000 V – General definitions, test methods and acceptance criteria
ISO 3452, Non-destructive testing – Penetrant inspection – General principles
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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) [7]).
61952 © IEC:2008 – 9 –
3.1
composite line post insulator
insulator consisting of a load-bearing cylindrical insulating solid core, a housing and end
fittings attached to the insulating core. It is intended to be subjected to cantilever, tensile and
compressive loads
3.2
core of a composite insulator
the internal insulating part of a composite insulator which is designed to ensure the
mechanical characteristics. 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]
3.3
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]
3.4
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]
3.5
shed of an insulator
insulating part, projecting from the insulator trunk, intended to increase the creepage
distance. The shed can be with or without ribs
[IEV 471-01-15]
3.6
interfaces
surface between the different materials. 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
[IEC 62217, definition 3.10 ]
3.7
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, modified]
– 10 – 61952 © IEC:2008
3.8
connection zone
zone where the mechanical load is transmitted between the insulating body and the end fitting
[IEC 62217, definition 3.12]
3.9
coupling
part of the end fitting which transmits the load to the accessories external to the insulator
[IEC 62217, definition 3.13 modified]
3.10
delamination of the core
irreversible loss of bonding within fibre laminates perceivable by the naked eye
3.11
failing load
maximum load that is reached when the insulator is tested under the prescribed conditions
3.12
specified cantilever load
SCL
cantilever load which can be withstood by the insulator at the line end fitting when tested
under the prescribed conditions. This value is specified by the manufacturer
3.13
maximum design cantilever load
MDCL
load level above which damage to the core begins to occur and which is the ultimate limit for
service loads. This value and direction of the load are specified by the manufacturer
3.14
specified tensile load
STL
tensile load which can be withstood by the insulator when tested under the prescribed
conditions. This value is specified by the manufacturer
4 Abbreviations
The following abbreviations are used in this standard:
E1, E2 Sample sets for sample tests
MDCL Maximum design cantilever load
SCL Specified cantilever load
STL Specified tensile load
5 Identification
In addition to the requirements of IEC 62217, each insulator shall be marked with the MDCL
or with the relevant IEC designation.
It is recommended that each insulator be marked or labelled by the manufacturer to show that
it has passed the routine mechanical test.
NOTE At present, there is no IEC standard giving designations of composite line post insulators.
61952 © IEC:2008 – 11 –
6 Environmental conditions
The normal environmental conditions to which line post insulators are submitted in service are
defined in IEC 62217.
7 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 [8]. During installation composite insulators
may be submitted to torsion loads for which they are not designed. In the absence of specific
guidance from the manufacturer, torsion loads leading to stress in the core above 15 MPa
shall be avoided.
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.
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 line post 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 line post 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;
– 12 – 61952 © IEC:2008
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;
a)
f) equivalent housing profile parameters, see footnote in Table 1.
9.2 Type tests
These tests are intended to verify the main characteristics of a composite line post insulator
which depend mainly on its shape and size. Type tests shall be applied to composite
insulators, the class of which has passed the design tests. They shall be repeated only when
the type or material of the composite insulator is changed (see 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
These tests are intended to eliminate composite line post insulators with manufacturing
defects. They shall be made on every composite line post insulator offered for acceptance.
61952 © IEC:2008 – 13 –
Table 1 – Tests to be carried out after design changes
IF the change in insulator design concerns:. THEN the following design tests shall be repeated:
Design tests Type tests
IEC 62217
IEC 62217
IEC IEC Tests on
Tests on housing IEC 61952
62217 61952 the core
material
material
b)
1 Housing materials X X X X X X
a)
X
2 Housing profile X X
X
3 Core material X X X X
X
4 Core diameter X X X X
Core and end-fitting manufacturing X
5 X X X X
process
X
6 Core and end-fitting assembly process X X
b)
b)
X
7 Housing manufacturing process X X X X X X
b)
b)
X
8 Housing assembly process X X X
X
9 End fitting material X X
X
10 End fitting connection zone design X X
b)
X
X
11 Base end fitting coupling design
b) b)
X
X X X
12 Core/housing/end fitting interface design
a)
Variations of the profile within following tolerances do not constitute a change:
Overhang: ± 10 %
+15
Diameter: %
Thickness at base and tip: ± 15 %
Spacing: ± 15 %
Mean shed inclination: ± 3°
Shed repetition: Identical
b)
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 line post insulator of a particular design will be
qualified only when all insulators or test specimens pass the design tests.
Interfaces and
connections of end
fittings
Assembled core load
tests
Hardness test
Accelerated weathering
test
Tracking and erosion
test
Flammability test
Dye penetration test
Water diffusion test
Electrical type tests
Mechanical type tests
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Table 2 – Design tests
Tests on interfaces and connections of end fittings
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 tests
Verification of the maximum design cantilever load (MDCL)
Tensile load test
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 at least 15 times the core diameter. 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 samples for this test shall include any such devices
in a typical position.
If the manufacturer only has facilities to produce insulators shorter than 15 times the core
diameter, 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.
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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 tests on interfaces and connections
of end fittings
The pre-stressing shall be carried out on the three specimens as indicated below.
10.3.1 Thermal-mechanical pre-stressing
The three specimens shall be submitted to a mechanical load in two opposite directions and
to temperature cycles as described in Figure 1. The 24 h temperature cycle shall be
performed twice. Each 24 h temperature 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 load applied to the specimens shall correspond to the MDCL.
The load shall be applied to the insulator at the conductor position. The initial direction shall
be appropriate for the end fittings, and approximately perpendicular to the axis of the insulator
at the point of application
When the load is not applied at the normal application point, it shall be corrected to produce
the same bending moment at the base of the insulator as the one exerted by the MDCL.
The direction of the cantilever load applied to the specimens shall be reversed once,
generally at the cooling passage through ambient temperature as described in Figure 1.
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 the load direction reversal and 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.
10.4 Assembled core load tests
10.4.1 Test for the verification of the maximum design cantilever load (MDCL)
10.4.1.1 Test specimens
Three insulators made on the production line using standard end fittings shall be selected.
The overall length of the insulators shall be between 15 and 18 times the diameter of the
core, unless the manufacturer does not have facilities to make such a length. In this case, the
length of insulator shall be as near as possible to the prescribed length range.
If not already routine tested, the insulators shall be examined visually and their conformity
with the drawing shall be checked. They shall then be subjected to the tensile load routine
test according to 13.1.
10.4.1.2 Test procedure
The insulator shall be gradually loaded to 1,1 times the MDCL at a temperature of (20 ± 10) °C.
This load shall be maintained for 96 h. The load shall be applied to the insulator at the
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conductor position, in the direction appropriate for the end fittings, and initially perpendicular
to the core of the insulator.
After removal of the load, the following steps shall be taken:
– visually inspect the base end fitting for cracks or permanent deformation;
– check that threads of the end fitting are re-usable.
Cut each insulator at 90º to the axis of the core and about 50 mm from the base end fitting,
and then cut the base end fitting longitudinally into two halves in the plane of the previously
applied cantilever load. The cut surfaces shall be smoothed by means of fine abrasive cloth
(grain size 180).
– Visually inspect the cut halves for cracks and delamination.
– Perform a dye penetration test according to ISO 3452 to the cut surfaces to reveal cracks.
10.4.1.3 Acceptance criteria
Failure under the applied load, cracks or permanent deformation in the base end fitting,
unusable threads, or the presence of cracks or delamination in the rod on any sample shall
constitute failure.
10.4.2 Tensile load test
10.4.2.1 Test procedure
Three insulators made on the production line using the standard end fittings shall be selected.
If not already routine tested, the insulators shall be examined visually and their conformity
with the drawing shall be checked. They shall then be subjected to the tensile load routine
test according to 13.1.
The tensile load shall be applied in line with the axis of the core of the insulator, at or near the
intended service attachment point. The load shall be increased rapidly but smoothly from zero
to approximately 75 % of the STL and shall then be gradually increased in a time between
30 s and 90 s until the STL is reached. If the STL is reached in less than 90 s, the load shall
be maintained for the remainder of the 90 s.
10.4.2.2 Acceptance criteria
The test shall be regarded as passed if there is no evidence of:
– pull-out of the core from the end fitting,
– breakage of the end fitting.
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.
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An insulator type is mechanically defined by the
– SCL,
– core material,
– core diameter,
– method of attachment of the end fittings,
– coupling zone of the base end fitting.
The mechanical type tests shall be performed only once on insulators satisfying the above
criteria for each type.
Furthermore, Table 1 indicates additional insulator design characteristics that, when changed,
require a repeat of the mechanical type tests.
If not already routine tested, the insulators shall be examined visually and their conformity
with the drawing shall be checked using the tolerances given in Clause 8. They shall then be
subjected to the mechanical routine test according to 13.1.
11.1 Electrical tests
The electrical tests in Table 3 shall be performed according to 11.1.1 or 11.1.2 (for insulators
without line accessories) or according to IEC 60383-2 (for insulators with line accessories) 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.
The electrical tests shall be performed with the insulator either vertical or horizontal, in the
position nearest that in which it will be used in service.
Table 3 – Mounting arrangements for electrical tests
Test Mounting arrangement
Standard mounting arrangement of a line post insulator
Dry lightning impulse withstand voltage test (11.1.1 or 11.1.2) or insulator set (IEC 60383-2) when
switching impulse tests are not required
Standard mounting arrangement of a line post insulator
Wet power – frequency test (11.1.1 or 11.1.2)
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