Tests on indoor and outdoor post insulators of ceramic material or glass for systems with nominal voltages greater than 1 kV

Applies to post insulators and post insulator units of ceramic material or glass for indoor and outdoor service 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. Notes: -May also be regarded as a provisional standard for insulators for use on d.c. systems, see IEC 60438. -When considering hollow insulators, see HD 329. -Tests on indoor post insulators of organic material will be covered by a future publication: Tests on indoor post insulators of organic material for systems with nominal voltages greater than 1 000 V up to but not including 300 kV. -For artificial pollution and radio-interference tests, see EN 60437 and 60507. -For numerical values for insulator characteristics and for selection of insulators for specific operating conditions, see EN 60273.

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

S'applique aux supports isolants et éléments de supports isolants d'intérieur et d'extérieur, en matière céramique ou en verre, destinés à l'équipement d'installations ou d'appareils électriques fonctionnant en courant alternatif à une tension nominale supérieure à 1 000 V et à une fréquence au plus égale à 100 Hz. Notes: 1. Cette norme peut aussi être considérée comme s'appliquant provisoirement aux supports isolants destinés aux réseaux fonctionnant en courant continu, voir CEI 60438. Lorsqu'il s'agit d'isolateurs creux, voir HD 329. Les essais des supports isolants d'intérieur en matière organique feront l'objet d'une future publication: Essais des supports isolants d'intérieur en matière organique destinés à des installations de tension nominale supérieure à 1 000 V jusqu'à 300 kV non compris. 4. Pour les essais de pollution artificielle et de perturbations radioélectriques, voir EN 60437 et 60507. 5. Pour les valeurs numériques de caractéristiques d'isolateur et pour la sélection d'un isolateur en fonction du service qu'il doit assurer, voir EN 60273.

Tests on indoor and outdoor post insulators of ceramic material or glass for systems with nominal voltages greater than 1000 V (IEC 168:1994)

General Information

Status
Withdrawn
Publication Date
28-Feb-1995
Withdrawal Date
30-Nov-1995
Drafting Committee
Parallel Committee
Current Stage
6060 - Document made available - Publishing
Start Date
21-Dec-1994
Completion Date
21-Dec-1994

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SLOVENSKI STANDARD
SIST EN 60168:1997
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
SIST EN 60168:1997 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN 60168:1997
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SIST EN 60168:1997
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SIST EN 60168:1997
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SIST EN 60168:1997
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SIST EN 60168:1997
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SIST EN 60168:1997
NORME CEI
INTERNATIONALE IEC
168
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
réservés— Copyright — all rights reserved
© CEI 1994 Droits de reproduction
No part of this publication may be reproduced or utilized in
Aucune partie de cette publication ne peut être reproduite ni

utilisée sous quelque forme que ce soit et par aucun pro- any form or by any means, electronic or mechanical,

including photocopying and microfilm, without permission
cédé, électronique ou mécanique, y compris la photocopie et
in writing from the publisher.
les microfilms. sans l'accord écrit de l'éditeur.

Bureau Central de la Commission Electrotechnique Internationale 3, rue de Varembé Genève, Suisse

CODE PRIX
Commission Electrotechnique Internationale
International Electrotechnical Commission
PRICE CODE
MeecoyHapoAHaa 3nenrporexHn4ecean HoMNCCNa
IEC
Pour prix, voir catalogue en vigueur •
For price, see current catalogue
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SIST EN 60168:1997
– 3 –
168©IEC:1994
CONTENTS
Page
FOREWORD 7
INTRODUCTION 9
Section 1: General
Clause
11 1.1 Scope and object
13
1.2 Normative references
13
1.3 Definitions
Section 2: Insulators
17
2.1 Insulator designs and insulating materials
2.2 Values which characterize a post insulator 19
21
2.3 Identification of insulators
Section 3: Classification of the tests, sampling rules and procedures
21
3.1 Classification of the tests
23
3.2 Quality assurance
23
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
31
4.2 Standard atmospheric conditions and correction factors for electrical tests
31
4.3 Artificial rain parameters for wet tests
33
4.4 Mounting arrangements for electrical tests
37
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
41
(applicable only to post insulators for indoor use)
4.8 Wet power-frequency withstand voltage test – Type test
41
(applicable only to post insulators for outdoor use)
43
4.9 Puncture test – Sample test
43
4.10 Routine electrical test
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SIST EN 60168:1997
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
49
5.2 Mechanical failing load test — Type and sample test
53 5.3 Test for deflection under load — Special type test
55
5.4 Temperature cycle test — Sample test
57
Routine thermal shock test (applicable only to toughened glass insulating parts)
5.5
57
Porosity test — Sample test (applicable only to ceramic post insulators)
5.6
57
5.7 Galvanizing test — Sample test
61
5.8 Routine visual inspection
65
5.9 Routine mechanical test
Section 6: Tests applicable to post insulators
6.1 Type tests 69
6.2 Sample tests 69
71
Routine tests 6.3
71 6.4 Summary of tests on post insulators
76
Figures
Annexes

Methods of testing for tolerances of parallelism, eccentricity, angular deviations,

camber and shed angle of post insulators 79
85 Methods of routine testing of unassembled insulator units
C Bibliography 91
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SIST EN 60168:1997
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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.
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SIST EN 60168:1997
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.
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SIST EN 60168:1997
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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SIST EN 60168:1997
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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).
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SIST EN 60168:1997
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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SIST EN 60168:1997
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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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SIST EN 60168:1997
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168©IEC:1994

cavity core cylindrical post insulators, with external metal fittings, having an internal

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

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-

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

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,

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);*

the specified wet switching-impulse withstand voltage (for outdoor insulators only);*

* 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.
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SIST EN 60168:1997
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168©IEC:1994

the specified dry power-frequency withstand voltage (for indoor insulators only);

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.

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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SIST EN 60168:1997
- 23 - 168 ©IEC:1994

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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SIST EN 60168:1997
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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 %;
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.
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SIST EN 60168:1997
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 %.
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 th
...

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