IEC 62231:2006

INTERNATIONAL IEC
STANDARD 62231
First edition
2006-02
Composite station post insulators
for substations with a.c. voltages
greater than 1 000 V up to 245 kV –
Definitions, test methods and
acceptance criteria
Reference number
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INTERNATIONAL IEC
STANDARD 62231
First edition
2006-02
Composite station post insulators
for substations with a.c. voltages
greater than 1 000 V up to 245 kV –
Definitions, test methods and
acceptance criteria
 IEC 2006  Copyright - all rights reserved
No part of this publication may be reproduced or utilized in any form or by any means, electronic or
mechanical, including photocopying and microfilm, without permission in writing from the publisher.
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Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch Web: www.iec.ch
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For price, see current catalogue

– 2 – 62231  IEC:2006(E)
CONTENTS
FOREWORD.4
INTRODUCTION.6

1 Scope and object.7
2 Normative references .7
3 Terms and definitions .8
4 Identification.11
5 Environmental conditions.11
6 Information on transport, storage and installation .12
7 Classification of tests .12
7.1 Design tests .12
7.2 Type tests .13
7.3 Sample tests .13
7.4 Routine tests .13
8 Design tests .14
8.1 General .14
8.2 Tests on interfaces and connections of end fittings.14
8.3 Assembled core load tests.15
8.4 Tests on shed and housing material .16
8.5 Tests on the core material .17
9 Type tests .17
9.1 Verification of dimensions .17
9.2 Electrical tests.17
9.3 Mechanical tests .19
10 Sample tests .20
10.1 General rules .20
10.2 Verification of dimensions (E1 + E2).21
10.3 Galvanizing test (E1 + E2).21
10.4 Verification of the specified mechanical loads (E1) .21
10.5 Re-testing procedure.22
11 Routine tests .22
11.1 Identification of the station post insulator .22
11.2 Visual examination .22
11.3 Tensile load test.22

Annex A (informative) Notes on the mechanical loads and tests .24
Annex B (informative) Determination of the equivalent bending moment caused by
combined cantilever and compression (tension) loads.26
Annex C (informative) Example of torsion load test arrangement .28
Annex D (normative) Tolerances of form and position .29
Annex E (informative) Notes on the compression and buckling test.32

Bibliography.33

62231  IEC:2006(E) – 3 –
Figure 1 – Thermal-mechanical pre-stressing test – Typical cycles .23
Figure B.1 – Combined loads applied to station post insulators.27
Figure D.1 – Parallelism, coaxiality and concentricity.29
Figure D.2 – Angular deviation of fixing holes: Example 1.30
Figure D.3 – Angular deviation of fixing holes: Example 2.30
Figure D.4 – Tolerances according to standard drawing practice.31

Table 1 – Tests to be carried out after design changes .12

– 4 – 62231  IEC:2006(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
___________
COMPOSITE STATION POST INSULATORS FOR SUBSTATIONS
WITH AC VOLTAGES GREATER THAN 1000 V UP TO 245 kV –
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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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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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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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 62231 has been prepared by subcommittee 36C: Insulators for
substations, of IEC technical committee 36: Insulators.
The text of this standard is based on the following documents:
FDIS Report on voting
36C/159/FDIS 36C/160/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.
This standard is to be read in conjunction with IEC 62217.

62231  IEC:2006(E) – 5 –
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.
A bilingual version of this publication may be issued at a later date.

– 6 – 62231  IEC:2006(E)
INTRODUCTION
Composite station post insulators consist of a cylindrical solid insulating core made of resin
impregnated fibres, bearing the mechanical load, protected by an elastomer 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 for
insulators of the same design. The design tests are performed in order to eliminate insulator
designs, materials and manufacturing technologies not suitable for high-voltage applications.
The influence of time on the electrical and mechanical properties of the complete composite
station post insulator and its components (core material, housing material, interfaces, etc.)
has been considered in specifying the design tests in order to ensure a satisfactory lifetime
under normal service conditions.
The approach for mechanical testing under bending loads used in this Standard is based on
IEC 61952. This approach uses the concept of a damage limit that is the maximum stress that
can be developed in the insulator before damage begins to occur. Work is underway to
validate the acoustic emission technique to determine the inception of damage.
In some cases, station post insulators can be subjected to a combination of loads. In order to
give some guidance, Annex B explains how to calculate the equivalent bending moment in the
insulators resulting from the combination of bending, tensile and compression loads.
Pollution tests, as specified in IEC 60507 and IEC 61245, are not included in this document,
their applicability to composite station post insulators having not been proven. Such pollution
tests performed on composite insulators do not correlate with experience obtained from
service. Specific pollution tests for composite insulators are under consideration.
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 the manu-
facturer. IEC 61467 gives details of a.c. power arc testing of insulator sets.
Impulse (mechanical) loads in substation are typically caused by short-circuits. Post
insulators are affected by forces due to the interaction of the currents circulating in
conductors/busbars supported by insulators.
The impulse load or peak load may be evaluated using guidance found in the IEC 60865
series.
Work is in progress in CIGRE ESCC (Effects of Short-Circuit Currents) task force to review
impulse loads caused by short-circuit currents in substations. The aim of this work is to
introduce a new concept: the ESL factor (Equivalent Static Load factor) which is frequency
dependent. The actual peak load may be replaced, in a first approximation, by the peak load
times the ESL factor. This new value may be used as the MDCL in this document for the
determination of the cantilever strength.
Radio interference and corona tests are not specified in this standard since the radio
interference and corona performances are not characteristics of the insulator alone.
Composite hollow core station post insulators are currently not dealt with in this standard.
IEC 61462 gives details of tests on hollow core composite insulators, many of which can be
applied to such station post insulators.

62231  IEC:2006(E) – 7 –
COMPOSITE STATION POST INSULATORS FOR SUBSTATIONS
WITH AC VOLTAGES GREATER THAN 1 000 V UP TO 245 kV –
DEFINITIONS, TEST METHODS AND ACCEPTANCE CRITERIA

1 Scope and object
This International Standard applies to composite station post insulators consisting of a load
bearing cylindrical insulating solid core made of resin impregnated fibres, a housing (outside
the insulating solid core) made of elastomer material (e.g. silicone or ethylene-propylene) and
end fittings attached to the insulating core. Composite station post insulators covered by this
standard are subjected to cantilever, torsion, tension and compression loads. They are
intended for substations with a.c. voltages greater than 1 000 V up to 245 kV.
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 60050-471, International Electrotechnical Vocabulary (IEV) – Chapter 471: Insulators
IEC 60060-1, High-voltage test techniques – Part 1: General definitions and test requirements
IEC 60168:1994, Tests on indoor and outdoor post insulators of ceramic material or glass for
systems with nominal voltages greater than 1 000 V
IEC 62217: , Polymeric insulators for indoor and outdoor use with a nominal voltage greater
than 1000 V – General definitions, test methods and acceptance criteria
ISO 1101, Technical drawings – Geometrical tolerancing – Tolerancing of form, orientation,
location and run-out – Generalities, definitions, symbols, indications on drawings
ISO 3452, Non-destructive testing – Penetrant inspection – General principles

– 8 – 62231  IEC:2006(E)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
composite station post insulator
post insulator consisting of a solid load bearing cylindrical insulating core, a housing and end
fittings attached to the insulating core
3.2
core (of an insulator)
central insulating part of an insulator which provides the mechanical characteristics
NOTE The housing and sheds are not part of the core.
[IEV 471-01-03]
3.3
housing
external insulating part of composite insulator providing necessary creepage distance and
protecting core from environment
NOTE An intermediate sheath made of insulating material may be part of the housing.
[IEV 471-01-09]
3.4
housing profile
shape and dimensions of the housing of the composite station post insulator which include the
following:
– shed overhang(s)
– shed thickness at the base and at the tip
– shed spacing
– shed repetition
– shed inclination(s)
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
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]
3.7
creepage distance
shortest distance or the sum of the shortest distances along the surface on an insulator
between two conductive parts which normally have the operating voltage between them
NOTE 1 The surface of cement or of any other non-insulating jointing material is not considered as forming part of
the creepage distance.
62231  IEC:2006(E) – 9 –
NOTE 2 If a high resistance coating is applied to parts of the insulating part of an insulator, such parts are
considered to be effective insulating surfaces and the distance over them is included in the creepage distance.
[IEV 471-01-04]
3.8
arcing distance
shortest distance in air external to the insulator between the metallic parts which normally
have the operating voltage between them
[IEV 471-01-01]
NOTE The term “dry arcing distance” is also used.
3.9
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.
[IEC 62217]
3.10
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]
3.11
connection zone
zone where the mechanical load is transmitted between the insulating body and the end fitting
[IEC 62217]
3.12
coupling
part of the fixing device which transmits load to the hardware external to the insulator
[IEC 62217]
3.13
tracking
process which forms irreversible degradation by formation of conductive paths (tracks)
starting and developing on the surface of an insulating material
NOTE These paths are conductive even under dry conditions.
[IEC 62217]
3.14
erosion
irreversible and non-conducting degradation of the surface of the insulator that occurs by loss
of material which can be uniform, localized or tree-shaped
NOTE Light surface traces, commonly tree-shaped, can occur on composite insulators as on ceramic insulators,
after partial flashover. These traces are not considered to be objectionable as long as they are non-conductive.
When they are conductive they are classified as tracking.
[IEC 62217]
– 10 – 62231  IEC:2006(E)
3.15
delamination (of the core)
loss of bonding between fibres and matrix
3.16
crack
any internal fracture or surface fissure of depth greater than 0,1 mm
[IEC 62217]
3.17
specified cantilever load
SCL
cantilever load which can be withstood by the insulator when tested under the prescribed
conditions
3.18
maximum design cantilever load
MDCL
cantilever load level above which damage to the insulator begins to occur and that should not
be exceeded in service
3.19
specified torsion load
SToL
torsion load level which can be withstood by the insulator when tested under the prescribed
conditions
3.20
maximum design torsion load
MDToL
torsion load level above which damage to the insulator begins to occur and that should not be
exceeded in service
3.21
specified tension load
STL
tension load which can be withstood by the insulator when tested under the prescribed
conditions
3.22
maximum design tension load
MDTL
tension load level above which damage to the insulator begins to occur and that should not be
exceeded in service
3.23
specified compression load
SCoL
compression load which can be withstood by the insulator when tested under the prescribed
conditions
3.24
buckling load
compression load that induces buckling of the insulator core

62231  IEC:2006(E) – 11 –
3.25
maximum design compression load
MDCoL
load level above which damage to the insulator begins to occur and that should not be
exceeded in service
3.26
failing load (of a composite station post insulator)
maximum load that is reached when tested under the prescribed conditions
NOTE Damage to the core is likely to occur at loads lower than the insulator failing load.
3.27
overall length
distance from flange face to flange face of the end fitting
3.28
puncture (of an insulator)
permanent loss of dielectric strength due to a disruptive discharge passing through the solid
insulating material of an insulator
[IEV 471-01-14]
3.29
residual deflection
the difference between the initial deflection, if any, of the tip of the insulator measured prior to
cantilever load application and the final deflection measured after load release
NOTE The residual deflection may depend on the duration of application of the load and on the time duration
between the load release and the measurement of the deflection.
3.30
residual angular displacement
the difference between the initial angular displacement, if any, of one of the insulator end
fitting with respect to the other insulator end fitting measured prior to the application of the
torsion load and the final angular displacement measured after torsion load release
NOTE The residual angular displacement may depend on the duration of application of the torsion load and on
the time duration between the torsion load release and the measurement of the displacement.
4 Identification
The manufacturer's drawing shall show the relevant dimensions and values necessary for
identifying and testing the insulator in accordance with this standard. The drawing shall also
show applicable manufacturing tolerances. In addition, the relevant IEC designation, when
available, shall figure on the drawing.
Each insulator shall be marked with the name or trademark of the manufacturer and the year
of manufacture. In addition, each insulator shall be marked with at least the Maximum Design
Cantilever Load (MDCL) (example: MDCL: 4 kN) or, when available, with the relevant IEC
designation. These markings shall be legible and indelible.
NOTE At present there is no IEC standard giving designations of composite station post insulators.
5 Environmental conditions
See description in IEC 62217.
– 12 – 62231  IEC:2006(E)
6 Information on transport, storage and installation
See description in IEC 62217.
7 Classification of tests
The tests are divided into four groups as follows:
7.1 Design tests
These tests are intended to verify the suitability of the design, materials and manufacturing
technology (see Annex A for notes on the concept of damage limit).
A composite station post insulator design is defined by
– materials of the core, housing and manufacturing method;
– material of the end fittings, their design and method of attachment;
– 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 done according to Table 1.
Table 1 – Tests to be carried out after design changes
IF the insulator design changes the. THEN the following design tests shall be repeated:

8.2 8.3 8.4 8.4 8.4 8.4 8.5 8.5

1 Housing materials
X X X X X
1)
2 Housing profile
X
3 Core material X X   X X
4 Core diameter
X X   X X
5 Manufacturing process
X X X X X X X
6 End fitting material
X X
7a End fitting connection zone design X X
7b End fitting coupling design
X
7c Core-housing-end fitting interface design
X
8 End fitting method of attachment to core
X X
1)
The following variation of the housing profile within following tolerances do not constitute a change:
Overhang:  ±10 % Spacing:   ±10 %
Diameter: +15 %, –0 % Mean inclination: ±3 °
Thickness at base and tip: ±15 % Shed repetition:  identical

Interfaces and
connections of
end fittings
Assembled
core load tests
Hardness test
Accelerated
weathering
Tracking and
erosion test
Flammability
test
Dye penetra-
tion test
Water diffusion
test
62231  IEC:2006(E) – 13 –
When a composite station 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;
b) same material of the fittings, the same design, and the same method of attachment;
c) same or greater minimum layer thickness of the housing over the core (including a sheath
where used) within a tolerance of ±15 %;
d) same or smaller stress under mechanical loads;
e) same or greater cross-diameter of the core;
f) same housing profile parameters, see the table footnote in Table 1.
7.2 Type tests
These tests are intended to verify the main characteristics of a composite station post
insulator, which depend mainly on its shape and size. Type tests shall be applied to
composite insulators belonging to an already qualified design. The type tests shall be
repeated only when the type of the composite insulator is changed.
Electrically, an insulator type is defined by the
– arcing distance,
– creepage distance,
– housing profile.
The electrical type tests shall be performed only once on insulators satisfying the above
design criteria for one type and shall be performed with arcing and field grading devices, if
they are an integral part of the insulator type.
The electrical type tests shall be repeated only when one or more of the above characteristics
is changed.
Mechanically, an insulator type is defined by the
– length (only for the compression and buckling withstand load test),
– core diameter and material,
– design and method of attachment of the end fittings.
The mechanical type tests shall be performed only once on insulators satisfying the above
criteria for each type.
The mechanical type tests shall be repeated only when one or more of the above character-
istics is changed.
7.3 Sample tests
These tests are intended to verify the characteristics of composite station post insulators,
which depend on the quality of manufacture and materials used. They shall be made on
insulators taken at random from lots offered for acceptance.
7.4 Routine tests
These tests are intended to eliminate composite station post insulators with manufacturing
defects. They shall be made on every composite station post insulator to be supplied.

– 14 – 62231  IEC:2006(E)
8 Design tests
8.1 General
The design tests shall be performed only once and the results shall be recorded in a test
report. Each test can be performed independently on new test specimens where appropriate.
The composite station post insulator of a particular design shall be deemed qualified only
when the insulators or test specimens pass all the design tests.
8.2 Tests on interfaces and connections of end fittings
See IEC 62217.
8.2.1 Test specimens
See IEC 62217.
8.2.2 Reference voltage and temperature for verification tests
See IEC 62217.
8.2.3 Reference dry power frequency test
See IEC 62217.
8.2.4 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 repeated
twice. Each temperature cycle has two temperature levels with a duration of at least 8 h, one
at +50 °C ± 5 K, the other at –35 °C ± 5 K. 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 perpendicularly to the insulator's axis as near as possible to the
normal load application point, either directly at the normal conductor position or at a hardware
attachment point. 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. 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.
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.
8.2.5 Water immersion pre-stressing
See IEC 62217.
8.2.6 Verification tests
See IEC 62217.
62231  IEC:2006(E) – 15 –
8.3 Assembled core load tests
Extreme service temperatures may affect the mechanical behaviour of composite insulators.
A general rule to define “extreme high or low” insulator temperatures is not available at this
time; for this reason the supplier should always specify service temperature limitations.
NOTE Whenever the insulators are subjected to very high or low temperatures for long periods of time, it is
advisable that customer and supplier agree on a mechanical test at higher or lower temperatures than that
mentioned in this standard.
8.3.1 Test for the verification of the maximum design cantilever load (MDCL)
8.3.1.1 Test procedure
Three insulators made on the production line using the standard end fittings shall be selected.
The overall length of the insulators shall be at least 8 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.
The base end-fitting has to be fixed rigidly. The insulators shall be gradually loaded to
1,1 times the MDCL rating at a temperature of 20 °C ± 10 K and held for 96 h. The load shall
be applied to the insulators at the conductor position, perpendicular to the direction of the
conductor, and perpendicular to the core of the insulators.
At 24 h, 48 h, 72 h and 96 h, the deflection of the insulators at the point of application of the
load shall be recorded, as additional information.
After removal of the load, the steps below shall be followed:
– visually inspect the base end fitting for cracks or permanent deformation,
– check that threads of the end fitting are re-usable,
– if required, measure the residual deflection.
Cut each insulator 90° to the axis of the core and about 50 mm from the base of the end fitting,
then cut the base end fitting part of the insulator 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 delaminations,
– perform a dye penetration test according to ISO 3452 to the cut surfaces to reveal cracks.
8.3.1.2 Acceptance criteria
Observation of any cracks, permanent deformation or delaminations shall constitute failure of
the test.
8.3.2 Test for the verification of the maximum design torsion load (MDToL)
8.3.2.1 Test procedure
Three insulators made on the production line using the standard end fittings shall be selected.
The overall length of the insulators shall be at least 8 times the diameter of the core, unless
the manufacturer does not have facilities to make such a length. In this case, the length of
insulators shall be as near as possible to the prescribed length range.

– 16 – 62231  IEC:2006(E)
The torsion load shall be applied to the insulators perpendicularly with the axis of the core of
the insulator. No bending moment should be applied. The insulators shall be gradually loaded
to 1,1 times the MDToL rating at a temperature of 20 °C ± 10 K and held for 30 min. The
angular displacement shall be measured at 30 min as additional information. An acceptable
value of the angular displacement shall be agreed between manufacturer and user.
NOTE In a torsion test, the angular displacement is proportional to the length of the core between the end fittings.
An example of a test arrangement can be found in Annex C.
After removal of the load, the steps below shall be followed:
– if required, measure the residual angular displacement,
– visually inspect the end fittings for cracks or permanent deformation,
– check that threads of the end fitting are re-usable,
– cut each insulator 90° to the axis of the core at about 50 mm from the end fittings, and in
the middle part of this cut section,
– polish the cut surfaces by means of fine abrasive cloth (grain size 180),
– visually inspect the cut surfaces for cracks and delaminations,
– perform a dye penetration test according to ISO 3452 to the cut surfaces to reveal cracks
or delaminations.
8.3.2.2 Acceptance criteria
Observation of any cracks, permanent deformation or delaminations shall constitute failure of
the test.
8.3.3 Verification of the specified tension load (STL)
8.3.3.1 Test procedure
Three insulators made on the production line using the standard end fittings shall be selected.
The overall length of the insulators shall be at least 8 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.
The tensile load shall be applied to the insulators in line with the axis of the core of the
insulator at a temperature of 20 °C ± 10 K. The load shall be increased rapidly but smoothly
from zero to approximately 75 % of the specified tensile load and shall then be gradually
increased in a time between 30 s and 90 s until the specified tensile load is reached. If 100 %
of the STL is reached in less than 90 s, the load (100 % of STL) shall be maintained for the
remainder of the 90 s.
8.3.3.2 Acceptance criteria
The test shall be regarded as passed if there is no evidence of
– pullout or slip of the core from the end fitting, or
– breakage of the end fitting.
8.4 Tests on shed and housing material
See IEC 62217.
62231  IEC:2006(E) – 17 –
8.5 Tests on the core material
See IEC 62217.
These tests can be carried out on specimens either with or without housing material.
9 Type tests
Insulators made on the production line using the standard end fittings shall be selected.
9.1 Verification of dimensions
Unless otherwise agreed, a tolerance of
± (0,04 x d + 1,5) mm when d < 300 mm, or
± (0,025 x d + 6,0) 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 (d being
the dimensions in millimetres).
The measurement of creepage distance shall be related to the design dimensions and
tolerances as determined from the insulator drawing, even though this dimension may be
greater than the value originally specified by the purchaser. When the creepage distance is
specified as a minimum value, the negative tolerance is zero.
Tolerances of parallelism, eccentricity, angular deviation are given in Annex D.
9.2 Electrical tests
Tests in accordance with 9.2.1 and 9.2.2 shall be performed with the insulator in the position
in which it will be used in service (vertical or horizontal). If field-grading devices are used in
service they shall be used in the tests.
Interpolation of electrical test results may be used for insulators of intermediate length as long
as 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.
9.2.1 Dry lightning impulse voltage test
The post insulator shall be tested under the conditions prescribed in 4.1, 4.2 and 4.4.1 of
IEC 60168. The impulse generator shall be adjusted to produce a 1,2/50 impulse (see
IEC 60060-1).
Impulses of both positive and negative polarity shall be used. However, when it is evident
which polarity will give the lower flashover voltage, it shall be sufficient to test with that
polarity.
Two test procedures are in common use for the lightning impulse test:
– the withstand voltage procedure with 15 impulses;
– the 50 % flashover voltage procedure.
NOTE The 50 % flashover voltage procedure gives more information.
The test procedure selected shall be agreed between the purchaser and the manufacturer.

– 18 – 62231  IEC:2006(E)
9.2.1.1 Withstand voltage test using the withstand voltage procedure
The withstand voltage test shall be performed at the specified voltage corrected for the
atmospheric conditions at the time of test (see 4.2.2 of IEC 60168). Fifteen impulses shall be
applied to the post insulator.
The acceptance criteria are as follows:
– the station post insulator passes the test if the number of flashovers does not exceed two
for each series of 15 impulses.
The station post insulator shall not be damaged by these tests but slight marks on the surface
of the housing shall be permitted.
9.2.1.2 Voltage test using the 50 % flashover voltage procedure
The lightning impulse withstand voltage shall be calculated from the 50 % lightning impulse
flashover voltage, determined by the up-and-down method described in IEC 60060-1.
The 50 % lightning impulse voltage shall be corrected in accordance with 4.2.2 of IEC 60168.
The acceptance criteria are as follows:
the station post insulator passes the test if the 50 % lightning impulse flashover voltage is not
less than (1/(1 – 1,3 σ )) = 1,040 times the specified lightning impulse withstand voltage,
where σ is the standard deviation (assumed equal to 3 %).
The station post insulator shall not be damaged by these tests, but slight marks on the
surface of the housing shall be permitted.
9.2.2 Wet power frequency withstand voltage test
9.2.2.1 Test procedure
The test circuit shall be in accordance with IEC 60060-1.
The station post insulator shall be tested under the conditions prescribed in 4.1, 4.2, 4.3 and
4.4.1 of IEC 60168.
The test voltage to be applied to the station post insulator shall be the specified wet power
frequency withstand voltage corrected for the atmospheric conditions at the time of test (see
4.2.2 of IEC 60168). The test voltage shall be maintained at this value for 1 min. As additional
information, the voltage can be raised until the flashover occurs.
9.2.2.2 Acceptance criteria
The station post insulator passes the test if no flashover or puncture occurs during the test.
NOTE If flashover occurs on the insulator tested, then a second test on the same unit may be performed, after
verifying the rain conditions.
9.2.2.3 Wet power frequency flashover voltage
To provide information, when agreed between the purchaser and the manufacturer, the wet
flashover voltage of the station post insulator may be determined by increasing the voltage
gradually, from about 75 % of the wet power-frequency withstand voltage with a rate of rise of
about 2 % of this voltage per second. The wet flashover voltage is the arithmetic mean of five
consecutive readings, and the value, after correction to standard atmospheric conditions (see
4.2.2 of IEC 60168), shall be recorded.

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