SIST EN 61325:1997

SLOVENSKI STANDARD
SIST EN 61325:1997
01-november-1997
Insulators for overhead lines with a nominal voltage above 1000 V - Ceramic or
glass insulator units for d.c. systems - Definitions, test methods and acceptance
criteria (IEC 1325:1995)
Insulators for overhead lines with a nominal voltage above 1 kV - Ceramic or glass
insulator units for d.c. systems - Definitions, test methods and acceptance criteria
Isolatoren für Freileitungen mit einer Nennspannung über 1 kV - Keramik- oder
Glasisolatoren für Gleichspannungssysteme - Begriffe, Prüfverfahren und
Annahmekriterien
Isolateurs pour lignes aériennes de tension nominale supérieure à 1 kV - Eléments
d'isolateurs en céramique ou en verre pour systèmes à courant continu - Définitions,
méthodes d'essai et critères d'acceptation
Ta slovenski standard je istoveten z: EN 61325:1995
ICS:
29.080.10 Izolatorji Insulators
29.240.20 Daljnovodi Power transmission and
distribution lines
SIST EN 61325:1997 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN 61325:1997

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SIST EN 61325:1997

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SIST EN 61325:1997

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SIST EN 61325:1997

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SIST EN 61325:1997

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SIST EN 61325:1997
NORME CEI
INTERNATIONALE IEC
1325
INTERNATIONAL
Première édition
STANDARD
First edition
1995-03
Isolateurs pour lignes aériennes
de tension nominale supérieure à 1 000 V —
Eléments d'isolateurs en céramique ou en verre
pour systèmes à courant continu —
Définitions, méthodes d'essai et critères
d'acceptation
Insulators for overhead lines with a nominal
voltage above 1 000 V —
Ceramic or glass insulator units
for d.c. systems —
Definitions, test methods and acceptance
criteria
© CEI 1995 Droits de reproduction réservés— Copyright — all rights reserved
Aucune partie de cette publication ne peut être reproduite ni No part of this publication may be reproduced or utilized in
utilisée sous quelque forme que ce soit et par aucun pro- any form or by any means, electronic or mechanical,
cédé, électronique ou mécanique, y compris la photocopie et including photocopying and microfilm, without permission
les microfilms, sans l'accord écrit de l'éditeur. in writing from the publisher.
Bureau Central de la Commission Electrotechnique Internationale 3, rue de Varembé Genève, Suisse
Commission Electrotechnique Internationale CODE PRIX
International Electrotechnical Commission PRICE CODE
E MewayHapoaHan 3neKrporexHH4ectsafa HOMHCCHI
catalogue en vigueur
Pour prix, voir •
For price, see current catalogue

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SIST EN 61325:1997
1325 © IEC:1995 – 3 –
CONTENTS
Page
FOREWORD 9
SECTION 1: GENERAL
Clause
11
1 Scope
13
2 Normative references
15
3 Definitions
SECTION 2: INSULATORS
23
4 Insulator classes and type
23
5 Insulating materials
23 6 Specified characteristics and features of a d.c. insulator unit
25
7 Identification of insulators
SECTION 3: CLASSIFICATION OF TESTS, SAMPLING RULES AND PROCEDURES
27
8 Classification of tests.
27 8.1 Type tests
27
8.2 Sample tests
27
8.3 Routine tests
9 Quality assurance 29
29 10 Procedures for type and sample tests
29
10.1 Insulator selection for type tests
29 10.2 Sampling rules and procedures for sample tests
31 10.3 Re-test procedure for the sample tests
SECTION 4: TEST PROCEDURES FOR ELECTRICAL TESTS
33
11 General requirements for high-voltage tests.
33
12 Standard atmospheric conditions and correction factors for electrical tests
33 12.1 Standard reference atmosphere
33 12.2 Correction factors for atmospheric conditions
35 13 Mounting arrangements for electrical tests
35
14 Lightning impulse voltage tests
35
14.1 Test procedure
37 14.2 Acceptance criteria
37
15 Dry d.c. voltage tests
37
15.1 Test procedure
37
15.2 Acceptance criteria
37
16 SF6 puncture withstand test
37
16.1 Test method
16.2 Acceptance criteria 39
17 Impulse overvoltage puncture withstand test 39

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SIST EN 61325:1997
1325 © I EC:1995 - 5 -
Page
Clause
18 Ion migration test 39
39 18.1 Reference conditions used to calculate the expected charge
18.2 Test validity 39
41
18.3 Test procedure
45
18.4 Acceptance criteria
45
19 Electrical body resistance test
45
19.1 Test procedure
45
19.2 Acceptance criteria
45
20 Thermal runaway test
45
20.1 Duration
45
20.2 Procedure
47
20.3 Acceptance criteria
47
21 Routine electrical test
SECTION 5: TEST PROCEDURES FOR MECHANICAL AND OTHER TESTS
49
22 Verification of the dimensions
23 Electromechanical failing load test 49
23.1 Test procedure 49
51
23.2 Acceptance criteria
53
icient for type tests 23.3 Coeff
53
icients for sample tests 23.4 Coeff
53
24 Mechanical failing load test
53
24.1 Test procedure
53
24.2 Acceptance criteria
55 25 Thermal-mechanical performance test
55
25.1 Test procedure
55
25.2 Acceptance criteria
55
26 Residual mechanical strength test
55
26.1 Previous tests
55
26.2 Preparation of the test pieces.
57
26.3 Test procedure
57
26.4 Test results
57 26.5 Acceptance criteria for the type test
57
26.6 Acceptance criteria for the sample test
57 26.7 Comparison between type and sample test results
59 27 Verification of the axial, radial and angular displacements
59
27.1 Test procedure
59 27.2 Acceptance criteria for cap and pin insulators
59
27.3 Acceptance criteria for long rod insulators
61
28 Verification of the locking system
61
28.1 Conformity of the locking device
61 28.2 Verification of locking
61
28.3 Position of the locking device
63
28.4 Procedure for the operation test
63
28.5 Acceptance criteria for the operation test

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SIST EN 61325:1997
— 7 —
1325 ©IEC:1995
Page
Clause
63
29 Temperature cycle test
63
29.1 Test procedure for string insulator units composed of ceramic material
65
29.2 Special test procedure for insulators with thick sections or very large insulators
65 29.3 Complementary specifications
67
29.4 Acceptance criteria
67
30 Thermal shock test
67
30.1 Test procedure
67 30.2 Acceptance criteria
67
31 Porosity test
67
31.1 Test procedure
67
31.2 Acceptance criteria
67
32 Galvanizing test
69
32.1 Test procedures
32.2 Acceptance criteria 69
71 33 Routine visual inspection
33.1 Insulators with ceramic insulating parts 71
73 33.2 Insulators with glass insulating parts
73
34 Routine mechanical test
75
35 Zinc sleeve test
75 35.1 General requirements concerning the zinc sleeve
75
35.2 Type test procedure
75 35.3 Sample test procedure
75
36 Zinc collar test
75 36.1 General requirements for zinc collar
77 36.2 Type and sample test procedure
SECTION 6: TESTS ON STRING INSULATOR UNITS
79
37 General
Tables 80
85
Figures
Annexes
A — Method of comparison of the results of the electromechanical or mechanical failing load type
89 and sample tests
91
B — Bibliography

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SIST EN 61325:1997
1325 ©IEC:1995 – 9 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
INSULATORS FOR OVERHEAD LINES
WITH A NOMINAL VOLTAGE ABOVE 1 000 V -
Ceramic or glass insulator units for d.c. systems -
Definitions, test methods and acceptance criteria
FOREWORD
1) The IEC (International Electrotechnical Commission) is a world-wide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of the lEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, 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.
The formal decisions or agreements of the IEC on technical matters, prepared by technical committees on which
2)
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
er.
indicated in the latt
International Standard IEC 1325 has been prepared by sub-committee 36B: Insulators for
overhead lines, of IEC technical committee 36: Insulators.
The text of this standard is based on the following documents:
DIS Report on voting
36B(CO)112 36B/135/RVD
Full information on the voting for approval of this standard can be found in the report on voting
indicated in the above table.
Annexes A and B are for information only.

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SIST EN 61325:1997
1325 @ IEC:1995 - 11 -
INSULATORS FOR OVERHEAD LINES
WITH A NOMINAL VOLTAGE ABOVE 1 000 V —
Ceramic or glass insulator units for d.c. systems —
Definitions, test methods and acceptance criteria
Section 1: General
1 Scope
This International Standard is applicable to string insulator units of ceramic material or glass
for use on d.c. overhead power lines with a nominal voltage greater than 1 000 V.
It is not applicable to composite insulators.
The application of this standard to insulators for use in other situations under d.c. voltage
will be left to the relevant technical committees.
This standard specifies:
- the characteristics of insulators;
- the conditions under which the specified values of these characteristics shall be
verified;
- acceptance criteria.
It specifies basic characteristic tests in a manner similar to that of IEC 383-1. Certain
additional tests have been found to be necessary to ensure satisfactory long-term
performance of d.c. insulators. At present, these additional tests concern only cap and pin
insulators.
In view of the lack of significant performance data regarding long rod insulators on d.c.
lines, it is not possible at present to define or validate special d.c.-oriented tests for such
insulators.
This standard does not include requirements, or special tests, dealing with the choice of
insulators for specific operating conditions (e.g. ageing arising from specific operating
conditions).
NOTES
1 This standard does not include radio interference tests, artificial pollution tests or tests on insulator
sets. These subjects and some relevant test methods are dealt with in the following IEC Publications:
IEC 383-2, IEC 437 and IEC 1245.
2 Many of the requirements and tests in this standard are relevant to insulators for use on d.c. traction
lines, but other tests may be required. Reference can be made to IEC 383-1.

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SIST EN 61325:1997
1325 © IEC:1995 - 13 -
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 parties to
agreements based on this International Standard are encouraged to investigate the possibility
of applying the most recent edition of the normative documents indicated below. Members of
maintain registers of currently valid International Standards.
IEC and ISO
IEC 50(471): 1984, International Electrotechnical Vocabulary (IEV) - Chapter 471: Insulators
High-voltage test techniques - General definitions and test requirements
IEC 60-1: 1989,
IEC 120: 1984, Dimensions of ball and socket couplings of string insulator units
Characteristics of string insulator units of the cap and pin type
IEC 305: 1978,
Locking devices for ball and socket couplings of string insulator units -
IEC 372: 1984,
Dimensions and tests
Insulators for overhead lines with a nominal voltage above 1 000 V - Part 1:
IEC 383-1: 1993,
Ceramic or glass insulator units for a.c. systems - Definitions, test methods and acceptance
criteria
IEC 433: 1980, Characteristics of string insulator units of the long rod type
Dimensions of clevis and tongue couplings of string insulator units
IEC 471: 1977,
Residual strength of string insulator units of glass or ceramic material for
IEC 797: 1984,
overhead lines after mechanical damage to the dielectric
Insulators of ceramic material or glass for overhead lines with a nominal
IEC 1211: 1994,
voltage greater than 1 000 V - Puncture testing
Artificial pollution tests on high-voltage insulators to be used on d.c. systems
IEC 1245: 1993,
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 products
ISO 1461: 1973,
- Requirements
Metallic and oxide coatings - Measurement of coating thickness -
1463: 1982,
ISO
Microscopical method

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SIST EN 61325:1997
1325 ©IEC:1995 - 15 -
ISO 2064: 1980, Metallic and other non-organic coatings - Definitions and conventions
concerning the measurement of thickness
2178: 1982,
ISO Non-magnetic coatings on magnetic substrates - Measurement of coating
thickness - Magnetic method
3 Definitions
For the purpose of this International Standard the following definitions apply.
The term "insulator" is used in this standard to refer to the object being tested.
The definitions given below are those which either do not appear in IEC 50(471) or differ
from those given in IEC 50(471).
3.1 Insulator string
One or more connected string insulator units intended to give flexible support to overhead
line conductors and stressed mainly in tension.
3.2 Lot
A group of insulators offered for acceptance from the same manufacturer, of the same
design and manufactured under presumed 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.
3.3 Flashover
A disruptive discharge external to the insulator, connecting those parts which normally have
the operating voltage between them.
NOTE — The term "flashover" used in this standard includes a flashover across the insulator surface as well
as disruptive discharge by sparkover through air adjacent to the insulator.
3.4 Dry lightning impulse withstand voltage
The lightning impulse voltage which the insulator withstands dry, under the prescribed
conditions of test.
3.5 50 % dry lightning impulse flashover voltage
The value of the lightning impulse voltage which, under the prescribed conditions of test,
has a 50 % probability of producing flashover on the insulator, dry. Represented by
U50.
3.6 Dry d.c. withstand voltage
The d.c. voltage which the insulator withstands dry, under the prescribed conditions of test.
3.7 Electromechanical failing load
The maximum load reached when a string insulator unit is tested under the prescribed
conditions of test.

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SIST EN 61325:1997
1325 ©IEC:1995 - 17 -
3.8 Mechanical failing load
The maximum load reached when a string insulator unit or a rigid insulator is tested under
the prescribed conditions of test.
3.9 Residual mechanical strength
The maximum mechanical load which can be reached when an insulator unit, which has had
its insulating part mechanically damaged in the prescribed manner, is tested under the
prescribed conditions.
3.10 SF6 puncture withstand voltage
under the prescribed
The d.c. voltage which a string insulator unit withstands in SF 6
conditions of test.
3.11 Ion migration
The migration of ions in the dielectric of an insulator under d.c. voltage, which may or may
not lead to a change in the electrical or mechanical characteristics of the insulator.
3.12 Expected charge
Q50
years under the reference
The total charge expected to flow through an insulator during 50
depends on the electrical resistance
ambient conditions and applied voltage. Q 50
characteristic of the insulator dielectric.
3.13 Electrical body resistance
The d.c. resistance of an insulator unit measured in the zone between the cap and the pin.
3.14 Thermal runaway
The phenomenon which occurs when the internal heat generated within a solid with a
negative resistance/temperature coefficient is greater than the heat dissipated externally.
3.15 Zinc sleeve
A piece of zinc metal fused to an insulator pin shank to protect it from electrolytic corrosion
by acting as a sacrificial electrode.
3.16 Zinc collar
A piece of zinc metal fused to the base of an insulator cap to protect it from electrolytic
corrosion by acting as a sacrificial electrode.
3.17
Impulse overvoltage puncture withstand voltage
The peak value of the impulse voltage which the insulator withstands without puncture under
the prescribed conditions of test.

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SIST EN 61325:1997
1325 © IEC:1995 - 19 -
3.18 Creepage distance
The shortest distance or the sum of the shortest distances along the ceramic or glass
insulating parts of the insulator between those parts which normally have the operating
voltage between them.
NOTE The surface of cement or other non-insulating jointing material is not considered as forming part of
the creepage distance. If 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.
3.19 Displacements
3.19.1 Axial or radial displacement
The maximum positional variation of a definite point of the considered insulator during one
complete revolution about the insulator axis.
3.19.2 Angular displacement
The angular deviation about the insulator axis between corresponding planes of the two
coupling pieces.
3.20 Short standard string
standard string is used to verify characteristics of a unit which are significant only
A short
for an insulator string. It consists of:
- for cap and pin units: an insulator string of a least five insulator units and not more
than 1,5 min length;
- for long rod insulator units: an insulator string between 1 m and 2 m in length for long
rod insulator units intended to be assembled in a string. For long rod insulator units less
than 1 m long intended to be used singly as a string, the unit itself is considered as a
short standard string.
3.21 Mechanically equivalent design
A mechanically equivalent insulator design is a type made in the same factory, with the
same materials and by the same process, and having the same strength class, the same
coupling size and the same design of connection between insulating components and metal
parts, and has in addition the following characteristics:
-
for long rod insulators:
• nominal core diameter is the same;
• nominal shed spacing is the same or larger;
• nominal shed projection is the same or smaller;
• nominal creepage distance is the same or smaller;
• nominal arcing distance is the same or smaller;
- for cap and pin insulators:
• nominal diameter is the same or smaller;
• nominal creepage distance is the same or smaller.

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SIST EN 61325:1997
1325 © IEC:1995 - 21 -
3.22 Specified characteristics
A specified characteristic is:
- either the numeric value of a voltage or of a mechanical load or any other character-
istic 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 clause 12).

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SIST EN 61325:1997
1325 © IEC:1995 - 23 -
Section 2: Insulators
4 Insulator classes and type
Overhead line string insulator units are divided into two classes according to their design.
Class A is an insulator or insulator unit in which the length of the shortest puncture path
through solid insulating material is at least equal to half the arcing distance. An example of
a class A insulator is a long rod insulator with external fittings.
Class B is an insulator or insulator unit in which the length of the shortest puncture path
through solid insulating material is less than half the arcing distance. An example of a class
B insulator is a cap and pin insulator.
5 Insulating materials
The insulating materials of d.c. overhead line insulators covered by this standard are:
- ceramic material, porcelain;
- toughened glass, being glass in which controlled mechanical stresses have been
induced by thermal treatment.
NOTES
1 Further information on the definition and classification of ceramic and glass insulating materials can be
found in IEC 672-1 and IEC 672-3.
2 The term "ceramic material" is used in this standard to refer to porcelain materials and, contrary to
North American practice, does not include glass.
6 Specified characteristics and features of a d.c. insulator unit
It shall be noted that specific insulating materials and design are necessary for d.c.
applications since special features are required for satisfactory insulator performance.
Hence specific tests, excluding artificial pollution tests, are included in this standard to
verify the material and design characteristics. Artificial pollution testing of d.c. insulators is
covered in IEC 1245.
Corrosion problems due to unidirectional current flow in contaminated conditions make the
use of a zinc sleeve mandatory on the pin of cap and pin insulators (see clause 35). For
some applications enhanced corrosion protection of the cap may be used (see clause 36).
An insulator unit for use on d.c. lines is characterized by the following values:
- all insulators:
a) the specified significant dimensions, including the creepage distance;
the specified dry lightning impulse withstand voltage determined on a short
b)
standard string;

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SIST EN 61325:1997
1325 © IEC:1995 - 25 -
c) the specified positive dry d.c. withstand voltage value of a single unit;
the specified electromechanical or mechanical failing load;
d)
- class B insulators only:
the specified positive d.c. puncture withstand voltage in SF6;
e)
f) the specified impulse overvoltage puncture withstand voltage;
g) the electrical body resistance.
In addition the insulator unit shall be capable of passing the following special tests
described in this standard:
h) ion migration*;
i) thermal runaway*;
j) test on the zinc sleeve of the pin (class B insulators only).
7 Identification of insulators
Each insulator shall be marked, either on the insulating component or on a metal part, with
the name or trade mark of the manufacturer and the year of manufacture. In addition, each
string insulator unit shall be marked with the specified electromechanical or mechanical
failing load whichever is applicable. These markings shall be legible and indelible.
The designations included in IEC 305 and 433 may be used.
At present, this test has been validated for cap and pin insulators only.

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SIST EN 61325:1997
1325 © IEC:1995 - 27 -
Section 3: Classification of tests,
sampling rules and procedures
8 Classification of tests
The tests are divided into three groups as follows:
8.1 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 a small number of insulators and only
once for a new design or manufacturing process of insulator and then subsequently
repeated only when the design or manufacturing process is changed; when the change
affects only certain characteristics, only the test(s) relevant to these characteristics need to
be repeated. It is not necessary to carry out the mechanical and thermal-mechanical type
tests on a new design of insulator if a valid test certificate is available on an insulator of
mechanically equivalent design and same manufacturing process. The meaning of
mechanically equivalent design is defined in 3.21. The concept of electrically equivalent
insulator designs is not applicable to high-voltage d.c. insulators.
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 type test
certificate shall be valid for ten years from the date of issue. Within the above limits, the
mechanical type test certificates remain valid while there is no significant disparity between
the results of the type tests and subsequent corresponding sample tests. A method for
comparing type and sample test results is given in annex A.
There is no time limit for the validity of type test 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.
8.2 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 insulators taken at random from
a lot which has met the requirements of the relevant routine tests.
NOTE – The acceptance coefficients and sample sizes used in this standard for the statistical evaluation of
results by variables have been chosen to reproduce as closely as possible the operating characteristic (OC)
curves of the method by attributes used in former editions of IEC 383 for current lot sizes. For other lot
sizes, the OC curves will be different. Further information on the statistical evaluation of test results and
calculation of OC curves can be found in ISO 2859-1, ISO 2859-2 and ISO 3951. IEC 591 gives methods for
statistical evaluation of test results on insulator units.
8.3 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.

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SIST EN 61325:1997
1325 © IEC:1995 - 29 -
NOTES
1 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".
2 Only routine tests applicable to complete insulators are considered in this standard. The choice of
routine tests carried out on unassembled insulators is left to the manufacturer as they are most often
carried out during the manufacturing process.
9 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.
NOTE — Detailed information on the use of quality assurance is given in the following ISO standards:
ISO 9000, ISO 9001, ISO 9002, ISO 9003 and ISO 9004.
ISO 9002 is a recommendable guideline for a quality system for insulators. Certain well-
' established National Standards for quality assurance programmes are also available.
10 Procedures for type and sample tests
10.1 Insulator selection for type tests
The quantity of insulators to be tested for each test, as indicated in tables 1 and 2 in section
6, shall be taken from a lot of insulators which meets the requirements of all the relevant
sample and routine tests.
NOTE — This selection is normally carried out by the manufacturer.
10.2 Sampling rules and procedures for sample tests
For the sample tests, three samples are used, E1, E2 and E3. The sizes of these samples
are into a number of lots comprising between 2 000 and 10 000 insulators. The results of
the tests shall be indicated in the table below. When more than 10 000 insulators are
concerned they shall be divided evaluated separately for each lot.
The insulators shall be selected at random from the lot. The purchaser has the right to make
the selection.
The samples shall be subjected to the applicable sample tests shown in tables 1 and 2 in
section 6. In the case of failure of the sample to satisfy a test, the relevant re-test procedure
(see 10.3) shall be applied.
Insulators which have been submitted to sample tests which may affect their mechanical and/or
electrical characteristics shall not be used in service.
Lot size Sample size
El E2 E3
(N)
I
Sub ect to agreement
N5300
3 4
300 8 4 8
2000 12 6 12
5000
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SIST EN 61325:1997
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10.3 Re-test procedure for the sample tests
When specified in the acceptance criteria, the following re-test procedure applies:
If only one insulator
...