IEC TS 60815-3:2008

IEC/TS 60815-3
Edition 1.0 2008-10
TECHNICAL
SPECIFICATION
Selection and dimensioning of high-voltage insulators intended for use in
polluted conditions –
Part 3: Polymer insulators for a.c. systems

IEC/TS 60815-3:2008(E)
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IEC/TS 60815-3
Edition 1.0 2008-10
TECHNICAL
SPECIFICATION
Selection and dimensioning of high-voltage insulators intended for use in
polluted conditions –
Part 3: Polymer insulators for a.c. systems

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
R
ICS 29.080.10 ISBN 978-2-88910-303-4
– 2 – TS 60815-3 © IEC:2008(E)
CONTENTS
FOREWORD.3
1 Scope and object.5
2 Normative references .5
3 Terms, definitions and abbreviations .6
3.1 Terms and definitions .6
3.2 Abbreviations .6
4 Principles .6
5 Materials .7
5.1 General information on common polymer housing materials .7
5.2 Issues specific to polymer housing materials under pollution .7
5.2.1 Reduction of creepage distance.7
5.2.2 Extreme pollution.8
6 Site severity determination .9
7 Determination of the reference USCD.9
8 General recommendations for polymer profiles .10
9 Checking of profile parameters .11
9.1 General remark .11
9.2 Alternating sheds and shed overhang.12
9.3 Spacing versus shed overhang.12
9.4 Minimum distance between sheds .13
9.5 Creepage distance versus clearance .13
9.6 Shed angle.14
9.7 Creepage factor .14
10 Correction of RUSCD .14
10.1 Correction for altitude K .14
a
10.2 Correction for insulator diameter K .15
ad
11 Determination of the final minimum creepage distance .15
12 Confirmation by testing.15
Annex A (informative) Background information on pollution induced degradation of
polymers.17
Bibliography.20

Figure 1 – RUSCD as a function of SPS class .9
Figure 2 – Typical “open” profiles.10
Figure 3 – Typical steep polymeric profile .10
Figure 4 – Typical shallow under-ribs on open profile .10
Figure 5 – Typical deep under-rib profile.11
Figure 6 – Typical “alternating” profiles .11
Figure 7 – K versus average diameter and illustration of parameters.15
ad
Figure A.1 – Operating areas as a function of pollution severity and USCD (for a fixed
insulating length) .19

TS 60815-3 © IEC:2008(E) – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SELECTION AND DIMENSIONING OF HIGH-VOLTAGE INSULATORS
INTENDED FOR USE IN POLLUTED CONDITIONS –

Part 3: Polymer insulators for a.c. systems

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
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agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
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between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
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5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
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6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
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Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
The main task of IEC technical committees is to prepare International Standards. In
exceptional circumstances, a technical committee may propose the publication of a technical
specification when
• the required support cannot be obtained for the publication of an International Standard,
despite repeated efforts, or
• The subject is still under technical development or where, for any other reason, there is
the future but no immediate possibility of an agreement on an International Standard.
Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
IEC/TS 60815-3, which is a technical specification, has been prepared by technical
committee 36: Insulators.
– 4 – TS 60815-3 © IEC:2008(E)
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
36/266/DTS 36/272A/RVC
Full information on the voting for the approval of this technical specification can be found in
the report on voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all the parts in the future IEC 60815 series, under the general title Selection and
dimensioning of high-voltage insulators intended for use in polluted conditions, can be found
on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• transformed into an International standard,
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

TS 60815-3 © IEC:2008(E) – 5 –
SELECTION AND DIMENSIONING OF HIGH-VOLTAGE INSULATORS
INTENDED FOR USE IN POLLUTED CONDITIONS –

Part 3: Polymer insulators for a.c. systems

1 Scope and object
IEC/TS 60815-3, which is a technical specification, is applicable to the selection of polymer
insulators for a.c. systems, and the determination of their relevant dimensions, to be used in
high voltage systems with respect to pollution.
This part of IEC/TS 60815 gives specific guidelines and principles to arrive at an informed
judgement on the probable behaviour of a given insulator in certain pollution environments.

The contents of this technical specification are based on CIGRE 33.13 TF 01 documents [1],
[2] , which form a useful complement to this technical specification for those wishing to study
in greater depth the performance of insulators under pollution.
This technical specification does not deal with the effects of snow or ice on polluted
insulators. Although this subject is dealt with by CIGRE [3], current knowledge is very limited
and practice is too diverse.
The object of this technical specification is to give the user means to
• determine the reference unified specific creepage distance (USCD) from site pollution
severity (SPS) class,
• choose appropriate profiles,
• apply correction factors for altitude, insulator shape, size and position, etc. to the
reference USCD.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60050-471, International Electrotechnical Vocabulary – Part 471: Insulators
IEC/TS 60815-1, Selection and dimensioning of high-voltage insulators for polluted conditions
– Part 1: Definitions, information and general principles
IEC/TR 62039, Selection guide for polymeric materials for outdoor use under HV stress
IEC/TS 62073, Guidance on the measurement of wettability of insulator surfaces
___________
Figures in square brackets refer to the bibliography.

– 6 – TS 60815-3 © IEC:2008(E)
3 Terms, definitions and abbreviations
3.1 Terms and definitions
For the purposes of this document, the following terms, definitions and abbreviations apply.
The definitions given below are those which either do not appear in IEC 60050-471 or differ
from those given in IEC 60050-471.
3.1.1
unified specific creepage distance
USCD
creepage distance of an insulator divided by the r.m.s. value of the highest operating voltage
across the insulator
NOTE 1 This definition differs from that of specific creepage distance where the line-to-line value of the highest
voltage for the equipment is used (for a.c. systems usually U /√3). For line-to-earth insulation, this definition will
m
result in a value that is √3 times that given by the definition of specific creepage distance in IEC/TR 60815 (1986).
NOTE 2 For ‘U ’ see IEV 604-03-01 [3].
m
NOTE 3 It is generally expressed in mm/kV and usually expressed as a minimum.
3.1.2
reference unified specific creepage distance
RUSCD
initial value of unified specific creepage distance for a pollution site before correction for size,
profile, mounting position, etc. according to this technical specification and generally
expressed in mm/kV
3.2 Abbreviations
CF creepage factor
ESDD equivalent salt deposit density
HTM hydrophobicity transfer material
NSDD non-soluble deposit density
SDD salt deposit density
SES site equivalent salinity
SOR safe operating regions
SPS site pollution severity
USCD unified specific creepage distance
RUSCD reference unified specific creepage distance
4 Principles
The overall process of insulation selection and dimensioning can be summarized as follows:
Firstly, using IEC/TS 60815-1:
• determine the appropriate approach 1, 2 or 3 as a function of available knowledge, time
and resources;
• collect the necessary input data, notably system voltage, insulation application type (line,
post, bushing, etc.);
• collect the necessary environmental data, notably site pollution severity and class.
At this stage a preliminary choice of possible candidate insulators suitable for the applications
and environment may be made.
TS 60815-3 © IEC:2008(E) – 7 –
Then, using this technical specification:
• refine choice of possible candidate polymer insulators suitable for the environment;
• determine the reference USCD for the insulator types and materials, either using the
indications in the this technical specification, or from service or test station experience in
the case of approach 1 (Clause 7);
• choose suitable profiles for the type of environment (Clause 8);
• verify that the profile satisfies certain parameters, with correction or action according to
the degree of deviation (Clause 9);
• modify, where necessary (approaches 2 and 3), of the reference USCD by factors
depending on the size, profile, orientation, etc. of the candidate insulator (Clauses 10 and
11);
• verify that the resulting candidate insulators satisfy the other system and line
requirements such as those given in Table 2 of IEC/TS 60815-1 (e.g. imposed geometry,
dimensions, economics);
• verify the dimensioning, if required in the case of approach 2, by laboratory tests (see
Clause 12).
NOTE Without sufficient time and resources (i.e. using approach 3), the determination of the necessary USCD will
have less accuracy.
5 Materials
5.1 General information on common polymer housing materials
The present practice is to use housings manufactured from several base polymers, for
instance silicone rubbers based on dimethyl siloxane, cross linked polyolefins such as EPDM
rubber, or semi-crystalline ethylene copolymers such as EVA, or rigid highly cross-linked
epoxy resins based on cycloaliphatic components.
None of these polymers will give satisfactory performance in an outdoor environment without
a sophisticated additive package to modify their behaviour. Typically, such additives include
anti-tracking agents, UV screens and stabilizers, antioxidants, ionic scavengers, etc. Within
each material type the base material, the additives and even their processing can have a
significant influence on material performance.
Some polymer insulators can collect more pollutants compared to ceramic and glass
insulators due to their surface characteristics.
Polymer materials which exhibit hydrophobicity and the capability to transfer hydrophobicity to
the layer of pollution are referred to in this technical specification as hydrophobicity transfer
materials (HTM); materials which do not exhibit hydrophobicity transfer are referred to as non-
HTM. Hydrophobicity may be lost in certain conditions (see 5.2), either temporarily or in some
cases permanently. IEC/TS 62073 gives guidance on the measurement of wettability of
insulator surfaces.
5.2 Issues specific to polymer housing materials under pollution
5.2.1 Reduction of creepage distance
Polymeric insulators present certain advantages over ceramic and glass insulators due to
their form and materials. These advantages include a generally improved pollution withstand
behaviour when compared to similar ceramic or glass insulators of equal creepage distance;
this improvement is even more enhanced by use of HTM. In principle and purely from a
pollution withstand or flashover point of view, it can thus be concluded that a reduced
creepage distance may be used for such insulators. However, compared to traditional
insulating materials, polymer materials are more susceptible to degradation by the
environment, electric fields and arc activity which may, in certain conditions, reduce insulator

– 8 – TS 60815-3 © IEC:2008(E)
pollution performance or lifetime. Annex A gives more information on this effect, including the
following points:
– Reduced creepage distance may, in certain site conditions, result in increased discharge
activity and negate any advantage in pollution performance if hydrophobicity is totally lost,
and may lead in some cases to flashover or degradation.
– Conversely, risk of material changes or degradation due to localized arc activity may be
increased when creepage distance per unit length is excessive.
Other points of importance are as follows:
– Use of grading rings is generally necessary at high voltages, the exact voltage level at
which they become necessary depends on design and materials.
– More pollution may accumulate on some polymer surfaces, and may reduce their pollution
performance advantage over comparable glass and porcelain insulators.
– Some polymers can be subject to fungal growths which affect hydrophobicity.
– HTM polymeric insulators generally show less influence of diameter and air density on
their pollution performance; this influence may increase if the surface becomes
hydrophilic.
Therefore, in many cases, it could be advisable to accept improved pollution performance and
avoid degradation or flashover problems by using the same creepage distance as
recommended for porcelain and glass insulators.
Nevertheless, the use of reduced creepage distance can be envisaged in certain
circumstances or conditions. These circumstances cannot be precisely defined since they
depend on a large number of factors; however, some general examples of conditions (or
combinations thereof) in which the use of reduced creepage distance can be adopted are
given below. It is important that, whenever possible, the decision to use reduced creepage be
discussed and agreed by all interested parties.
Examples include:
– Proof by line trial, test station or historic data with the same design, materials and electric
stress.
– The pollution is predominately type A, with no risk of extreme events (wetting or pollution
deposition).
– There is no frequent or daily cyclic wetting or other environmental
...