SIST EN 60168:1997

SLOVENSKI STANDARD
01-november-1997
Tests on indoor and outdoor post insulators of ceramic material or glass for
systems with nominal voltages greater than 1000 V (IEC 168:1994)
Tests on indoor and outdoor post insulators of ceramic material or glass for systems with
nominal voltages greater than 1 kV
Prüfungen an Innenraum- und Freiluft-Stützisolatoren aus keramischem Werkstoff oder
Glas für Systeme mit Nennspannungen über 1 kV
Essais des supports isolants d'intérieur et d'extérieur, en matière céramique ou en verre,
destinés à des installations de tension nominale supérieure à 1 kV
Ta slovenski standard je istoveten z: EN 60168:1994
ICS:
29.080.10 Izolatorji Insulators
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

NORME CEI
INTERNATIONALE IEC
INTERNATIONAL
Quatrième édition
STANDARD
Fourth edition
1994-11
Essais des supports isolants d'intérieur et
d'extérieur, en matière céramique ou en verre,
destinés à des installations de tension nominale
supérieure à 1 000 V
Tests on indoor and outdoor post insulators
of ceramic material or glass for systems with
nominal voltages greater than 1 000 V
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– 3 –
168©IEC:1994
CONTENTS
Page
FOREWORD 7
INTRODUCTION 9
Section 1: General
Clause
11 1.1 Scope and object
1.2 Normative references
1.3 Definitions
Section 2: Insulators
2.1 Insulator designs and insulating materials
2.2 Values which characterize a post insulator 19
2.3 Identification of insulators
Section 3: Classification of the tests, sampling rules and procedures
3.1 Classification of the tests
3.2 Quality assurance
3.3 General requirements for type tests
27 3.4 General requirements for sample tests
Section 4: Test procedures for electrical tests
General requirements for high-voltage tests 29
4.1
4.2 Standard atmospheric conditions and correction factors for electrical tests
4.3 Artificial rain parameters for wet tests
4.4 Mounting arrangements for electrical tests
4.5 Dry lightning-impulse withstand voltage test – Type test
37 4.6 Dry or wet switching-impulse withstand voltage tests – Type test
4.7 Dry power-frequency withstand voltage test – Type test
(applicable only to post insulators for indoor use)
4.8 Wet power-frequency withstand voltage test – Type test
(applicable only to post insulators for outdoor use)
4.9 Puncture test – Sample test
4.10 Routine electrical test
168 ©IEC:1994 — 5
Page
Clause
Section 5: Test procedures for mechanical and other tests
45 Verification of the dimensions — Type and sample test
5.1
5.2 Mechanical failing load test — Type and sample test
53 5.3 Test for deflection under load — Special type test
5.4 Temperature cycle test — Sample test
Routine thermal shock test (applicable only to toughened glass insulating parts)
5.5
Porosity test — Sample test (applicable only to ceramic post insulators)
5.6
5.7 Galvanizing test — Sample test
5.8 Routine visual inspection
5.9 Routine mechanical test
Section 6: Tests applicable to post insulators
6.1 Type tests 69
6.2 Sample tests 69
Routine tests 6.3
71 6.4 Summary of tests on post insulators
Figures
Annexes
Methods of testing for tolerances of parallelism, eccentricity, angular deviations,
A
camber and shed angle of post insulators 79
85 Methods of routine testing of unassembled insulator units
B
C Bibliography 91
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168 ©IEC:1994
INTERNATIONAL ELECTROTECHNICAL COMMISSION
TESTS ON INDOOR AND OUTDOOR POST INSULATORS
OF CERAMIC MATERIAL OR GLASS FOR SYSTEMS
WITH NOMINAL VOLTAGES GREATER THAN 1 000 V
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization
comprising all national electrotechnical committees (IEC National Committees). The object of the IEC is to
promote international cooperation on all questions concerning standardization in the electrical and
electronic fields. To this end and in addition to other activities, the IEC publishes International Standards.
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. The 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 the IEC on technical matters, prepared by technical committees on
which all the National Committees having a special interest therein are represented, express, as nearly as
possible, an international consensus of opinion on the subjects dealt with.
3) They have the form of recommendations for international use published in the form of standards, technical
reports or guides and they are accepted by the National Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
International Standard IEC 168 has been prepared by sub-committee 36C, Insulators for
substations, of IEC technical committee 36: Insulators.
This fourth edition cancels and replaces the third edition published in 1988 and constitutes
a technical revision.
The text of this standard is based on the following documents:
DIS Report on voting
36C(CO)60
36C(CO)58
Full information on the voting for the approval of this standard can be found in the repo rt
on voting indicated in the above table.
Annexes A, B and C are for information only.

168©IEC:1994 -9-
INTRODUCTION
The main purpose in preparing this edition has been to align the text and presentation as
far as practicable with the fourth edition of IEC 383-1 and IEC 383-2.
Concepts of electrical and mechanical equivalence of post insulators have been
introduced, and the clauses dealing with mechanical testing have been redrafted to clarify
the test requirements.
168 ©IEC:1994 - 11 -
TESTS ON INDOOR AND OUTDOOR POST INSULATORS
OF CERAMIC MATERIAL OR GLASS FOR SYSTEMS
WITH NOMINAL VOLTAGES GREATER THAN 1 000 V
Section 1: General
1.1 Scope and object
This International Standard IEC 168 is applicable to post insulators and post insulator
units of ceramic material or glass, for indoor and outdoor use in electrical installations or
equipment, operating on alternating current with a nominal voltage greater than 1 000 V
and a frequency not greater than 100 Hz.
This standard may be regarded as a provisional standard for post insulators for use on
d.c. systems. IEC 438 gives general guidance for those insulators.
This standard does not apply to composite insulators, or to those indoor post insulators in
organic materiel which are covered by another IEC standard [1]*.
The object of this standard is to define:
- the terms used;
- the electrical and mechanical characteristics of post insulators;
the conditions under which the specified values of these characteristics are verified;
-
the methods of test;
-
the acceptance criteria.
Numerical values of characteristics of post insulators are specified in IEC 273.
This standard does not include requirements dealing with the choice of post insulators for
specific operating conditions.
NOTES
1 A guide for the choice of insulators under polluted conditions is available, see [2].
This standard does not include radio interference tests or artificial pollution tests. These subjects and
relevant test methods are dealt with in other IEC publications, see [3], [4] and [5].
3 When this standard is applied to hollow post insulators, other IEC publications should also be taken
into account, see [6] and [7].
The figures in square brackets refer to annex C (Bibliography).

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168 ©IEC:1994
1.2 Normative references
The following normative documents contain provisions which, through reference in this
text, constitute provisions of this International Standard. At the time of publication, the
editions indicated were valid. All normative documents are subject to revision, and pa rties
to agreements based on this International Standard are encouraged to investigate the
possibility of applying the most recent edition of the normative documents listed below.
Members of IEC and ISO maintain registers of currently valid normative documents.
International Electrotechnical Vocabulary (lEV) - Chapter 471:
IEC 50(471): 1984,
Insulators
High-voltage test techniques - Part 1: General definitions and test
IEC 60-1: 1989,
requirements
Insulation co-ordination - Part 1: Definitions, principles and rules
IEC 71-1: 1993,
Insulation co-ordination - Part 2: Application guide
IEC 71-2: 1976,
Insulation co-ordination - Part 3: Phase-to-phase insulation co-ordination.
IEC 71-3: 1982,
Principles, rules and application guide
IEC 273: 1990, Characteristics of indoor and outdoor post insulators for systems with
nominal voltages greater than 1 000 V
Tests and dimensions for high-voltage d.c. insulators
IEC 438: 1973,
Metallic coatings - Protection against corrosion by hot dip galvanizing -
ISO 1459: 1973,
Guiding principles
Metallic coatings - Hot dip galvanized coatings on ferrous metals -
ISO 1460: 1992,
Gravimetric determination of the mass per unit area
Metallic coatings - Hot dip galvanized coatings on fabricated ferrous
ISO 1461: 1973,
products - Requirements
ISO 1463: 1982, Metal and oxide coatings - Measurement of coating thickness -
Microscopical method
Metallic and other non-organic coatings - Definitions and conventions
ISO 2064: 1980,
concerning the measurement of thickness
Non-magnetic coatings on magnetic substrates - Measurement of coating
ISO 2178: 1982,
thickness - Magnetic method
1.3 Definitions
For the purposes of this standard, the following definitions apply.
The definitions given below are those which either do not appear in IEC 50(471), or differ
from those given in IEC 50(471).

168 ©I EC:1994 - 15 -
term "insulator" is used in this standard to refer to the object being
1.3.1 insulator: The
tested. Unless otherwise specified, this refers to an assembled post insulator, complete
with metal fittings. In this standard, the term "post insulator" shall be taken to mean post
insulator, or post insulator unit, as required by the text.
NOTES
The term "approximately cylindrical shape" covers a unit of circular cross-section, which may vary in
diameter.
For indoor installations subject to excessive condensation, outdoor post insulators, or special indoor
post insulators may be used.
1.3.2 lot: A group of insulators offered for acceptance from the same manufacturer, of
the same design and manufactured under similar conditions of production. One or more
lots may be offered together for acceptance; the lot(s) offered may consist of the whole, or
part, of the quantity ordered.
lightning-impulse voltage which the
1.3.3 d ry lightning-impulse withstand voltage: The
under the prescribed conditions of test.
post insulator withstands d ry ,
The value of the lightning-impulse
1.3.4 50 % dry lightning impulse flashover voltage:
voltage which, under the prescribed conditions of test, has a 50 % probability of producing
flashover on the post insulator, dry.
NOTE — The term "flashover" used in this standard includes flashover across the insulator surface as well
as disruptive discharges by sparkover through air adjacent to the insulator. Disruptive discharges should
only occur occasionally elsewhere (for instance, to other structures or to earth), in which event they should
not be taken into account for the purpose of this standard.
switching-impulse voltage
or wet switching-impulse withstand voltage: The
1.3.5 d ry
which the post insulator withstands, dry or wet respectively, under the prescribed
conditions of test.
The value of the switching-
50 % dry or wet switching-impulse flashover voltage:
1.3.6
impulse voltage which, under the prescribed conditions of test, has a 50 % probability of
producing flashover on the post insulator, dry or wet respectively.
voltage
1.3.7 dry or wet power-frequency withstand voltage: The power-frequency
which the post insulator withstands dry or wet respectively, under the prescribed
conditions of test.
The arithmetic mean value of the
1.3.8 dry or wet power-frequency flashover voltage:
measured voltages which cause flashover on the post insulator, dry or wet respectively,
under the prescribed conditions of test.
The voltage which causes puncture of a post insulator under the
1.3.9 puncture voltage:
prescribed conditions of test.
The maximum load reached when a post insulator is
1.3.10 mechanical failing load:
tested under the prescribed conditions of test.

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168 © I EC:1994
1.3.11 creepage distance: The shortest distance, or the sum of the shortest distances,
along the contours of the external surfaces of the ceramic or glass insulating parts of the
rts which normally have the operating voltage between
post insulator between those pa
them.
NOTES
1 The surface of cement, or other non-insulating jointing material, is not considered as forming part of
the creepage distance.
If a high-resistance coating is applied to parts of the surface of an insulator, such parts are considered
to be effective insulating surfaces, and the distance over them is included in the creepage distance.
6 Q, but may be as low as
3 The surface resistivity of such high-resistance coatings is usually about 10
104 n.
4 If high-resistance coatings are applied to the whole surface of the post insulator (the so-called stabil-
ized insulator), the questions of surface resistivity and creepage distance should be subject to agreement
between the purchaser and the manufacturer.
5 The creepage distance according to this definition is specified as minimum nominal creepage distance
in IEC 273.
specified characteristic: A specified characteristic is:
1.3.12
- either the numeric value of a voltage, of a mechanical load, or any other charac-
teristic specified in an IEC standard,
- or the numeric value of any such characteristic agreed between the purchaser and
the manufacturer.
Specified withstand and flashover voltages are referred to standard atmospheric
conditions (see 4.2.1).
The maximum difference in the height of a post
1.3.13 parallelism of the end faces:
insulator measured across the surfaces of the metal fittings at each end.
NOTE – The difference in height is usually related to a circle of 250 mm diameter.
The displacement, perpendicular to the axis of the post insulator,
1.3.14 eccentricity:
between the centres of the pitch circles of the fixing holes in the top and bottom metal
fittings.
The rotational displacement, expressed as
angular deviation of the fixing holes:
1.3.15
an angle, between corresponding fixing holes in the metal fittings at the top and bottom of
a post insulator.
Section 2: Insulators
2.1 Insulator designs and insulating materials
2.1.1 Insulator designs
Post insulators and post insulator units are divided into different design categories
according to their construction. The design categories covered by the tests in this
standard are:
1) solid-core cylindrical post insulators with external metal fittings, having solid
insulating material throughout the height of each post insulator unit, i.e. a puncture-
proof insulator (see figure 1);

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168©IEC:1994
cavity core cylindrical post insulators, with external metal fittings, having an internal
2)
ceramic barrier produced and fired integrally in each post insulator unit (see figure 2);
cylindrical post insulators with internal metal fittings in which the length of the
3)
shortest puncture path through solid insulating material is at least equal to half the
external arcing distance between the metal fittings, i.e. a puncture-proof insulator
(see figure 3);
cylindrical post insulators with internal metal fittings in which the length of the short-
4)
est puncture path through solid insulator material is less than half the external arcing
distance between the metal fittings (see figure 4);
pedestal post insulators, in which each post insulator unit comprises metal fittings
5)
with one or more insulating components, where the thickness of the solid insulating
material is small compared with the external dimensions (see figure 5);
cylindrical post insulators, in which each post insulator unit comprises metal fittings,
6)
and multiplicity of insulating components where the thickness of the solid insulating
material of each component is small compared with the external dimensions, and also
where the whole assembly is characterized as puncture-proof (see figure 6).
NOTE – The term "cylindrical insulators" is intended to cover insulators of the truncated conical form also.
The type, sample, and routine tests applicable to post insulators in each of the above
categories are detailed in section 6 and summarized in tables 3, 4, and 5.
2.1.2 Insulating materials
The insulating materials of post insulators covered by this standard are:
ceramic material, porcelain;
annealed glass, being glass in which the mechanical stresses have been relaxed by
–
thermal treatment;
toughened glass, being glass in which controlled mechanical stresses have been
–
induced by thermal treatment.
NOTES
Further information on the definition and classification of ceramic and glass insulating materials can be
found in other IEC publications, see [8] and [9].
The term "ceramic material" is used in this standard to refer to porcelain materials and, contrary to
North American practice, does not include glass.
2.2 Values which characterize a post insulator
A post insulator is characterized by the following values, where applicable:
a) the specified dry lightning-impulse withstand voltage;
the specified dry switching-impulse withstand voltage (for indoor insulators only);*
b)
the specified wet switching-impulse withstand voltage (for outdoor insulators only);*
c)
* Switching-impulse withstand voltage should be specified only for post insulators for use on a.c. systems,
with highest voltage of equipment equal to or above 300 kV.

–21 –
168©IEC:1994
the specified dry power-frequency withstand voltage (for indoor insulators only);
d)
e) the specified wet power-frequency withstand voltage (for outdoor insulators only);
f) the specified minimum puncture voltage (for insulators in design categories 4)
and 5) only, see 2.1.1);
g) the specified mechanical failing load(s);
the specified significant dimensions, including the creepage distance.
h)
NOTE – Experience has shown that with many existing systems from 300 kV to 420 kV highest voltage of
equipment, the switching-impulse withstand voltage has not been a critical factor in the design of post
insulators. Therefore, for post insulators used to extend such existing systems, switching-impulse tests
should only be carried out by agreement between the purchaser and the manufacturer.
The following characteristics may also be agreed between the purchaser and the manu-
facturer:
– deflection under bending load;
–
radio interference characteristics, see [3];
- artificial pollution withstand characteristics, see [4].
The applicability of the characteristics as a function of the highest voltage for equipment
shall be determined by reference to IEC 71.
2.3 Identification of insulators
Each post insulator shall be marked with the name or trade mark of the manufacturer, the
year of manufacture, and the post insulator reference mark. These markings shall be
legible and indelible.
The designations included in IEC 273 may also be used, where no ambiguity can result.
Section 3: Classification of the tests,
sampling rules and procedures
3.1 Classification of the tests
The tests are divided into three groups, as follows:
3.1.1 Type tests
The type tests are intended to verify the main characteristics of an insulator, which depend
mainly on its design. They are usually carried out on one insulator, and once only for a
new design or manufacturing process, and then subsequently repeated only when the de-
sign, material or manufacturing process is changed; when the change only affects certain
characteristics, only the test(s) relevant to those characteristics need to be repeated.
Moreover, it is not necessary to perform all the electrical and mechanical type tests on a
new design of insulator if a valid test certificate is available for a post insulator of equi-
valent design. The meaning of electrically equivalent design is given in 3.3.3 and of
mechanically equivalent design in 3.3.4.

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The results of type tests are certified either by test certificates accepted by the purchaser
or by test certificates confirmed by a qualified organization. For mechanical tests, the
certificates shall be valid for 10 years from the date of issue. There is no time limit for the
validity of certificates for electrical type tests.
Type tests shall be carried out only on insulators from a lot which meets the requirements
of all the relevant sample and routine tests not included in the type tests.
3.1.2 Sample tests
The sample tests are carried out to verify the characteristics of an insulator, which can
vary with the manufacturing process and the quality of the component materials of the
insulator. Sample tests are used as acceptance tests on a sample of post insulators, taken
at random from a lot which has met the requirements of the relevant routine tests.
3.1.3 Routine tests
The routine tests are intended to eliminate defective units and are carried out during the
manufacturing process. Routine tests are carried out on every insulator.
NOTE – When, in certain cases, the type, sample and routine tests are carried out as a whole on a new
design of insulator, they are referred to as "prototype tests".
3.2 Quality assurance
A quality assurance programme, taking into account the requirements of this standard, can
be used, after agreement between the purchaser and the manufacturer, to verify the
quality of the insulators during the manufacturing process.
NOTES
Detailed information on the use of quality assurance is given in ISO standards, see [10], [11], [12], [13]
and [14].
ISO 9002 is recommended as a guide for a quality system for insulators.
Certain well-established national standards for quality assurance programmes are also available.
3.3 General requirements for type tests
Insulator selection for type tests
3.3.1
Normally, only one post insulator shall be subjected to each test. It shall be taken from a
lot of insulators which meets the requirements of all the relevant sample and routine tests.
Insulators which have been submitted to type tests which may affect their mechanical
and/or electrical characteristics shall not be used in service.
Verification of the dimensions
3.3.2
The relevant dimensions of the post insulator used for type tests shall be verified, before
other tests are commenced, in accordance with clause 5.1.

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168 ©I EC:1994
NOTE – By agreement between the purchaser and the manufacturer, an insulator, having dimensional
variations outside the tolerances specified on the drawing or in the standard, may be used provided it is
agreed that these discrepancies will not affect the performance under test. This also applies to the use for
type tests of an insulator having larger areas of glaze defects than are permitted by clause 5.8.
3.3.3 Electrical type tests
The electrical type tests, as indicated in table 3 (clause 6.4), shall be carried out on one
post insulator, and once only.
The results obtained during the electrical type tests on a post insulator of "electrically
equivalent design" shall be extended to all post insulators represented by it. These are
insulators made with the same materials, and by the same manufacturing process, and
having the following characteristics when compared with the post insulator of electrically
equivalent design:
a) the arcing distance is the same or greater;
b) the nominal core diameter is the same or smaller;
c) the number and approximate position of metal fittings is the same;
d) the nominal shed spacing is the same within ±5 %;
e) the nominal shed projection is the same within ±10 %;
f)
the shed profile is the same.
NOTES
1 A post insulator of "electrically equivalent design" will normally be an outdoor cylindrical post insulator.
Other designs of post insulator, particularly pedestal post insulators, are unlikely to be of "electrically
equivalent design".
2 The effect of the shape and size of metal fittings on the electrical equivalence of a design may need to
be taken into consideration.
3 The flashover and withstand voltages of insulators under service conditions may differ from the
flashover and withstand voltages under standard testing conditions. This effect has been recognized with
lightning impulse testing, especially for very high voltages of equipment, but the effect of ambient con-
ditions and the arrangement of post insulators and associated metalwork is much greater with switching
impulses, due to the differences in electric field distribution between the standard test arrangement and the
mounting arrangement in service. The verification of the specified switching impulse withstand voltage
therefore may be required with a mounting arrangement which closely represents the service conditions.
The details of the mounting arrangement should then be agreed between the purchaser and the manufac-
turer.
4 The concept of "electrical equivalence of design" primarily applies in respect of the tests included in
this standard. The effect of different nominal creepage distances on post insulators of "electrically equi-
valent design" may need to be considered in relation to pollution performance.
3.3.4 Mechanical failing load type tests
The type test for mechanical strength shall be carried out on one post insulator, and once
only. Normally, this test will be a mechanical failing load test carried out in bending. When
additional information is required, then by agreement between the purchaser and the
manufacturer, one or more of the following tests may also be carried out as a type test:
- tensile test;
- torsion test;
-
compression test.
168 ©I EC:1994 - 27 -
The results obtained during the mechanical failing load type tests on a post insulator of
mechanically equivalent design shall be extended to all post insulators represented by it.
These are insulators made in the same factory, with the same materials, and by the same
manufacturing process, and having the following characteristics, when compared with the
post insulator of mechanically equivalent design:
a) the nominal core diameter is the same;
b) the design of the connection between the insulating component and the metal
fittings is the same;
c) the shape and size of the parts of the metal fittings which connect to the insulating
components are the same;
the nominal height does not differ by more than ±20 %.
d)
NOTES
1 Since all the factors (materials, manufacturing process, and dimensions) which influence the mech-
anical strength of post insulators should be the same for mechanical equivalence, the values of the
o the tensile strength, and the torsional strength will then be the same as
bending moment strength (P x h),
those for the post insulator of mechanically equivalent design, by which they are represented. Lower, but
not greater, values of one or more of these mechanical strength characteristics, when compared with the
post insulator of "mechanically equivalent design", may be agreed between the purchaser and the manu-
facturer.
2 When applying the concept of mechanical equivalence of design, the effect of differences in height on
the compression strength of the post insulator may need to be considered.
3 A post insulator of "mechanically equivalent design" may have different fixing arrangements, e.g. as
table IVA of IEC 273.
4 In establishing mechanical equivalence of design, the effect of a significant difference in nominal
external diameter, due to a change of shed overhang and of shed spacing may need to be considered.
3.4 General requirements for sample tests
3.4.1
Sampling rules and procedures for sample tests
The number of post insulators selected for test shall be in accordance with table 1. The
purchaser has the right to make the selection from a lot which meets the requirements of
the routine tests.
Table 1 - Number of samples for sample tests
Number of insulators
Number of
in the lot
samples
(n
n)
n
5 100 By agreement
1)
100< n 5 500 1 %
1)
500 < n
1 , 5 n
4 +
1 000
If the percentage or calculation does not give a
1)
whole number, then the next whole number above
shall be chosen.
Insulators which have been submitted to sample tests which may affect their mechanical
and/or electrical characteristics shall not be used in service.

168 ©IEC:1994 - 29 -
3.4.2 Retest procedure for sample tests
If only one post insulator or metal fitting fails to comply with any of the sample tests, a new
sample, equal to twice the quantity originally submitted to that test, shall be subjected to
retesting. The retesting shall comprise the test in which failure occurred, preceded by
those tests which may be considered as having influenced the results of the original test.
If two or more post insulators or metal fittings, fail to comply with any of the sample tests,
or if any failure occurs during the retesting, the complete lot is considered as not
complying with this standard, and shall be withdrawn by the manufacturer.
Provided the cause of the failure can be clearly identified, the manufacturer may sort the
lot to eliminate all the insulators with that defect. The sorted lot, or part thereof, may then
be re-submitted for testing.
The number then selected shall be three times the first quantity chosen for the tests. The
retesting shall comprise the test in which failure occurred, preceded by those tests which
may be considered as having influenced the results of the original test. If any insulator
fails during this retesting, the complete lot is considered as not complying with this
standard.
NOTE – Where failure in the galvanizing test is due to a mechanical load in a previous test in excess of
the routine test load, the retest may be carried out, either on unassembled metal fittings, or on other post
insulators in the lot.
If, during the sample testing, one or more post insulators fail to comply with the tolerances
as specified in clause 5.1, or on the relevant drawing, then, by agreement between the
purchaser and the manufacturer, the retesting procedure may be replaced by a routine
test of tolerances.
An agreement may also be reached to use post insulator units or post insulators which are
outside the specified tolerances. In such cases, the manufacturer shall either mark the
magnitude and position of the deviations which are outside the specified tolerances on
each post insulator unit, or, when possible, assemble the units into a complete post
insulator. The units, and the measured deviations, if any, from the specified tolerances on
the complete post, shall then be marked so that the purchaser can make an identical
reassembly of the post after delivery.
Section 4: Test procedures for electrical tests
This section gives the test procedures and requirements for electrical testing of post
insulators. The application of these tests is given in section 6.
NOTE – Reference should be made to IEC 60-1 for complete details of the test procedures.
4.1 General requirements for high-voltage tests
a) The lightning- and switching-impulse voltage and power-frequency voltage test
procedures shall be in accordance with IEC 60-1.
b) Lightning- and switching-impulse voltages shall be expressed by their prospective
peak values, and power-frequency voltages shall be expressed as peak values divided
by' 2.
168 ©IEC:1994 - 31 -
c) When the natural atmospheric conditions at the time of the test differ from the
standard values (see 4.2.1), it is necessary to apply correction factors in accordance
with 4.2.2.
The insulators shall be clean and dry before starting high-voltage tests.
d)
Special precautions shall be taken to avoid condensation on the surface of the
e)
insulator, especially when the relative humidity is high. For example, the insulator shall
be maintained at the ambient temperature of the test location for sufficient time for ther-
mal equilibrium to be reached before the test starts.
Except by agreement between the purchaser and the manufacturer, dry tests shall not
be made if the relative humidity exceeds 85 %.
f) The time intervals between consecutive applications of the voltage shall be
sufficient to avoid effects from the previous application of voltage in flashover or with-
stand tests.
4.2 Standard atmospheric conditions and correction factors for electrical tests
4.2.1 Standard reference atmosphere
The standard reference atmospheric conditions shall be in accordance with IEC 60-1.
4.2.2 Correction factors for atmospheric conditions
The correction factors shall be determined in accordance with IEC 60-1. If the atmospheric
conditions at the time of test differ from the standard reference atmosphere, then the
(k 1 ) and humidity (k2) shall be calculated, and the product
correction factors for air density
determined. The test voltages shall then be corrected as follows:
K = k1 x k2
withstand voltages (lightning impulse, switching impulse and power frequency):
-
applied test voltage = K x specified withstand voltage;
- flashover voltages (lightning impulse, switching impulse and power frequency):
measured flashover voltage
recorded flashover voltage -
K
NOTE – For wet power-frequency voltage tests, and for wet switching-impulse voltage tests, no correction
for humidity should be applied, i.e. k2 = 1 and K= k1.
for wet tests
4.3 Artificial rain parameters
The standard wet test procedure described in IEC 60-1 shall be used. The characteristics
of the artificial rain shall be in accordance with the requirements of IEC 60-1.
NOTE – When tests are made on insulators in the horizontal or inclined positions, an agreement should
be reached between the purchaser and the manufacturer regarding the direction of rainfall.

168 ©IEC:1994 - 33 -
4.4 Mounting arrangements for electrical tests
The mounting arrangements for electrical tests on post insulators depend on whether
switching-impulse tests are required (see clause 2.2), and on whether service conditions
are to be reproduced. All the electrical tests on a post insulator shall be carried out using
the applicable mounting arrangement detailed in one of the following subclauses.
4.4.1 Standard mounting arrangement of a post insulator for use in systems with
highest voltage of equipment below 300 kV
The post insulator shall be mounted vertically upright on a horizontal metal suppo rt
consisting of a U-channel section with the flanges pointing downwards. The earthed metal
support shall have a width about equal to the diameter of the mounting face of the post
insulator under test and a length at least equal to twice the height of the post insulator,
and shall be placed at least 1 m above ground for post insulators not higher than 1,80 m.
For higher post insulators, the distance above ground shall be at least 2,50 m.
A cylindrical conductor, maintained in the horizontal plane, and perpendicular to the
earthed suppo rt, shall be attached to the top insulator. The length of the conductor shall
be at least equal to 1,5 times the height of the post insulator, and it shall extend at least
1 m on each side of the post insulator axis. The diameter of the conductor shall be approxi-
mately 1,5 % of the height of the post insulator, with a minimum of 25 mm.
The test voltage shall be applied between the conductor and the earthed suppo rt, the high-
voltage connection being made at one end of the conductor.
During the test, no object other than those described in this clause shall be nearer to the
top of the post insulator than 1 m or 1,5 times the height of the post insulator, whichever is
the greater.
The post insulator shall be complete with those parts which are considered necessarily
associated with the post insulator, and are specified as such by the manufacturer.
4.4.2 Standard mounting arrangement of a post insulator for use in systems with
highest voltage of equipment equal to or above 300 kV.
rtical earthed metal suppo rt .
The post insulator shall be mounted vertically upright on a ve
The upper part of the metal suppo rt preferably shall have a square mounting surface, with
the width of each side between one and two times the diameter of the metal fitting at the
base of the post insulator under test. Round or rectangular mounting surfaces may also be
used, provided that their dimensions are within those prescribed for the square mounting
surface. The shape of the suppo rt below the mounting surface shall not influence the test
result and to ensure that this is so (applicable to switching-impulse voltage tests in parti-
cular), no part of the suppo rt above 50 % of its height shall extend beyond the ve rtical
projection of the mounting surface.
The mounting surface of the metal support of outdoor post insulators shall be placed at a
height
H above the ground, in accordance with table 2.

168 © IEC:1994 - 35 -
Table 2 - Mounting height of outdoor post insulators
Height (H) above ground
Overall height
(h)
of the mounting surface
of post insulator
of the metal support
mm
mm
h 5 2500 2 500
2500< h<_ 3200 3 000
3 200 < h <_ 4 200 4 000
5 000
4 200 < h
A horizontal cylindrical conductor shall be attached to the top of the post insulator. The
length of the conductor, on each side of the post insulator axis, shall be at least equal
to 0,75 times the height of the post insulator, and preferably at least equal to the height of
the post insulator for switching-impulse voltage tests. The diameter of the conductor shall
be between 1,5 % and 2 % of the height of the post insulator. To avoid sparkover from the
two ends of the conductor, each end shall be protected by means of a suitable device
(for instance, by means of a metal ring).
The test voltage shall be applied between the conductor and the earthed support, the high-
voltage connection being made at one end of the conductor.
During the test, no object other than those described in this clause shall be nearer to the
top of the post insulator than 1,5 times the height of the post insulator.
The post insulator shall be complete with those parts which are considered necessarily
associated with the post insulator, and are specified as such by the manufacturer.
NOTES
1 The height H of the earthed metal support is chosen to give the optimum test configuration for compari-
son of the switching-impulse withstand behaviour of different post insulator designs.
2 The results of these tests are not necessarily valid for the design of sub-station equipment, since post
insulators are often mounted on supports of lower heights. In these cases, tests in accordance with 4.4.3
may be necessary.
4.4.3 Mounting arrangements when service conditions are to be represented
When so agreed, tests may be made under conditions representing service conditions as
closely as possible. The extent to which service conditions are simulated shall be agreed
between the purchaser and the manufacturer, taking into account all the factors which may
influence the post insulator performance.
NOTE – Under these non-standard conditions, the characteristics may differ from the values measured
using the standard method of mounting. The difference may be considerable when dealing with post insu-
lators with height greater than 1,80 m, especially in switching-impulse tests, or with reduced heights above
ground (e.g. indoor post insulators).

- 37 -
168 ©IEC:1994
4.5 Dry lightning-impulse withstand voltage test - Type test
The post insulator shall be tested under the conditions prescribed in clauses 4.1, 4.2 and 4.4.
The impulse generator shall be adjusted to produce a 1,2/50 impulse (see IEC 60-1).
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 withstand 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.
4.5.1 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). Fifteen impulses shall be applied to
the post insulator.
4.5.1.1 Acceptance criteria
The post insulator passes the test if the number of flashovers does not exceed two.
rface of
The post insulator shall not be damaged by these tests, but slight marks on the su
the insulating parts, or chipping of the cement or other material used for assembly, shall
be permitted.
Withstand voltage test using the 50 % flashover voltage procedure
4.5.2
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 60-1.
The 50 % lightning impulse voltage shall be corrected in accordance with 4.2.2.
4.5.2.1 Acceptance criteria
The post insulator passes the test if the 50 % lightning-impulse flashover voltage is not
1,040 times the specified lightning-impulse withstand voltage,
less than (1/(1-1,3 6)) =
where 6 is the standard deviation (assumed equal to 3 %).
rface of
The post insulator shall not be damaged by these tests, but slight marks on the su
the insulat
...