IEC TS 60815-4:2016

IEC TS 60815-4 ®
Edition 1.0 2016-10
TECHNICAL
SPECIFICATION
colour
inside
Selection and dimensioning of high-voltage insulators intended for use in
polluted conditions –
Part 4: Insulators for d.c. systems
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IEC TS 60815-4 ®
Edition 1.0 2016-10
TECHNICAL
SPECIFICATION
colour
inside
Selection and dimensioning of high-voltage insulators intended for use in

polluted conditions –
Part 4: Insulators for d.c. systems

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.080.10 ISBN 978-2-8322-3704-5

– 2 – IEC TS 60815-4:2016 © IEC 2016
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms, definitions and abbreviated terms . 8
3.1 Terms and definitions . 8
3.2 Abbreviated terms . 9
4 Principles . 9
4.1 General . 9
4.2 Overall design process . 10
5 Materials . 11
6 Site severity determination . 12
6.1 Input data . 12
6.2 d.c. pollution accumulation correction: K . 12
p
6.3 Chemical composition of the pollution layer (Type A pollution) . 13
6.4 Correcting for NSDD (Type A pollution) . 13
6.5 Correcting for CUR (Type A pollution, cap and pin insulators) . 14
6.6 Effect of diameter on the pollution accumulation K . 14
d
6.7 Correction for the number of similar insulators in parallel: K . 14
s
7 Determination of the reference d.c. site severity . 15
8 Determination of the reference d.c. USCD . 16
9 Correction of the RUSCD for each candidate insulator . 17
9.1 Correction for the effect of diameter on pollution withstand performance C . 17
d
9.2 Correction for altitude C . 18
a
9.3 Determination of the required USCD for each candidate . 18
10 Checking the profile parameters . 19
10.1 General . 19
10.2 Alternating sheds defined by shed overhang . 19
10.3 Spacing versus shed overhang . 20
10.4 Minimum distance between sheds . 20
10.5 Creepage distance versus clearance. 21
10.6 Shed angle . 22
10.7 Creepage factor . 22
11 Design verification . 23
11.1 General . 23
11.2 Operating experience . 23
11.3 Laboratory testing . 23
Annex A (informative) Hydrophobicity transfer materials . 24
A.1 Qualitative flashover behaviour . 24
Annex B (informative) Dependence of USCD on pollution severity . 26
B.1 Pollution type A . 26
B.2 Pollution Type B. 28
Bibliographic References . 29

Figure 1 – Overall design process for d.c. insulation – determination of d.c. Site
Pollution Severity . 10
Figure 2 – Overall design process for d.c. insulation – determination of the required
USCD for candidate insulating solutions . 11
dc
Figure 3 – RUSCD as a function of d.c. site pollution severity . 16
dc
Figure 4 – Correction for the effect of diameter on d.c. pollution withstand
performance . 18
Figure A.1 – Dependency of specific flashover voltage over conductivity of an
electrolyte (parameter: wettability of surface) . 24
Figure B.1 – d.c. overhead lines. Collected field experience on non HTM insulators
(uncoated glass and porcelain insulators) . 26
Figure B.2 – d.c. overhead lines. Collected field experience on HTM insulators
(composite line insulators) . 27
Figure B.3 – Composite insulators: Example of the influence of CF on USCD
(laboratory tests), see CIGRE Brochure [1] for more details . 28

Table 1 – Typical ranges of K according to climatic conditions . 13
p
– 4 – IEC TS 60815-4:2016 © IEC 2016
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SELECTION AND DIMENSIONING OF HIGH-VOLTAGE
INSULATORS INTENDED FOR USE IN POLLUTED CONDITIONS –

Part 4: Insulators for d.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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2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
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6) All users should ensure that they have the latest edition of this publication.
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
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 60815-4, which is a technical specification, has been prepared by technical committee 36:
Insulators.
The text of this technical specification is based on the following documents:
DTS Report on voting
36/382/DTS 36/390/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 document has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 60815 series, published 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 document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
– 6 – IEC TS 60815-4:2016 © IEC 2016
INTRODUCTION
Work has been going on in CIGRE C4.303 and the IEC to produce d.c. pollution design guides
that represent the current state of the art. The CIGRE work has resulted in an HV d.c.
Pollution Application Guidelines brochure [1] and the IEC work in this final part of IEC 60815
– Selection and dimensioning of high-voltage insulators intended for use in polluted conditions
– Part 4: Insulators for d.c. systems.
The work represents a huge accumulation of pollution performance knowledge from various
sources (both published and unpublished) never before collated into a single opus.
Contrary to the parts of IEC 60815 dealing with a.c., this technical specification covers both
polymeric and glass and porcelain insulators for d.c. systems in a single publication. It also
covers hybrid insulators (the ceramic core is fully covered by a polymer).
NOTE The present document does not apply to insulators with coatings, due to the variety of coatings to be
considered. This  may be reconsidered at the next revision of this technical specification, after gaining more
knowledge and experience and a better definition of the coating characteristics and requirements.
The approach for d.c. insulator design and selection with respect to pollution given in this part
is different to that used for a.c. The key differences are:
• A simplified approach is presented which is intended for preliminary design. However,
since under d.c. pollution build-up and its effects can be more severe than under a.c., the
final design should be based as much as possible on a direct pollution severity measured
under d.c. for the site being studied. Equally direct evaluation of the insulators selected by
this process should be considered. (A statistical design approach is available in the
CIGRE guidelines for d.c. pollution [1]);
• Two approaches are considered to estimate pollution severity: one using prior d.c. site
severity experience, the other using site severity measurements on a.c. or unenergised
insulators;
• Correction of site severity for specific parameters that have an influence under d.c. (e.g.
pollution uniformity ratio, effect of diameter on pollution accumulation, NSDD) are
considered;
• Direct transfer from corrected site pollution severity to necessary USCD without any use of
discrete site severity classes (as made in IEC 60815 Parts 2 and 3);
• Recognition is made of the improved performance of Hydrophobicity Transfer Materials
(HTM) as a practical solution for many designs, notably at UHV, while taking into account
potential hydrophobicity loss;
• Importance of the influence of altitude;
• Distinct diameter correction for flashover performance.
Although there is some positive experience with validation by testing of traditional glass and
porcelain insulators, the full translation of such test results to service conditions is still under
consideration. Any such experience is mainly lacking for composite insulators, since an
agreed standardised testing procedure is not yet available. The problem is accentuated to
porcelain/glass as well composite technology by the continuing rise in system voltages where
over-design may result in unrealistic insulator lengths or heights. Hence for this first edition
the verification of a chosen insulator solution by testing is entirely subject to agreement.
For polymeric, notably HTM, the pollution withstand may not be the only necessary design
information. The design stress should be selected not only to avoid flashover, but also to
assure a limited ageing of the insulators in service. This item is however out of the scope of
the present specification.
Applications with controlled indoor environment are not included in the scope of this
document.
SELECTION AND DIMENSIONING OF HIGH-VOLTAGE
INSULATORS INTENDED FOR USE IN POLLUTED CONDITIONS –

Part 4: Insulators for d.c. systems

1 Scope
This part of IEC 60815, which is a Technical Specification, is applicable as first approach for
the determination of the required d.c. Unified Specific Creepage Distance for insulators with
respect to pollution. To avoid excessive over or under design, existing operation experience
should be compared and eventually additional appropriate tests may be performed by
agreement between supplier and customer.
It is applicable to:
• Glass and porcelain insulators;
• Composite and hybrid insulators with an HTM or non-HTM housing.
This part of IEC 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 structure and approach of this part of IEC 60815 are similar to those explained in Part 1,
but adapted for the specific issues encountered with polluted HV d.c. insulation.
The aim of this Technical Specification is to give the user simplified means to:
• Identify issues specific to d.c. applications that can affect the choice and design process;
• Determine the equivalent d.c. Site Pollution Severity (SPS) from measurements, correcting
for electrostatic effects, diameter, pollution distribution and composition;
• Determine the reference USCD for different candidate insulating solutions, taking into
account materials, dimensions and risk factors;
• Evaluate the suitability of different insulator profiles;
• Discuss the appropriate methods to verify the performance of the selected insulators, if
required;
This simplified process is intended to be used when comparable operational experience from
existing d.c. system is incomplete or not available.
The simplified design approach might result in a solution that exceeds the physical constraints
of the project. More refined approaches for such cases, e.g. using a statistical approach, are
given in the CIGRE d.c. guidelines [1]. In extreme cases, e.g. for exceptionally severe site
conditions, alternative solutions such as changing the line route, relocation of converter
stations or using an indoor d.c. yard may need to be considered.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements 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.
– 8 – IEC TS 60815-4:2016 © IEC 2016
IEC TS 61245, Artificial pollution tests on high-voltage ceramic and glass insulators to be
used on d.c. systems
IEC TS 60815-1:2008, Selection and dimensioning of high-voltage insulators intended for use
in polluted conditions – Part 1: Definitions, information and general principles
IEC TS 60815-2, Selection and dimensioning of high-voltage insulators intended for use in
polluted conditions – Part 2: Ceramic and glass insulators for a.c. systems
IEC TS 60815-3, Selection and dimensioning of high-voltage insulators intended for use in
polluted conditions – Part 3: Polymer insulators for a.c. systems
IEC TS 62073, Guidance on the measurement of hydrophobicity of insulator surfaces
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60050-471:2007
and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1.1
Unified Specific Creepage Distance
USCD
creepage distance of an insulator divided by the maximum operating voltage across the
insulator. It is generally expressed in mm/kV
Note 1 to entry: For d.c. the maximum operating voltage is the d.c. system voltage as defined in IEC 60071-5.
3.1.2
Reference d.c. Unified Specific Creepage Distance
RUSCDdc
value of Unified Specific Creepage Distance for a d.c. system at a pollution site determined
from ESDD and NSDD values corrected for NSDD, CUR, etc. according to this document
Note 1 to entry: This is generally expressed in mm/kV.
3.1.3
Contamination Uniformity Ratio
CUR
ratio of the pollution deposit density on the lower surface of insulators to that of the upper
surface
Note 1 to entry: Referred to as Pollution Uniformity Ratio (PUR) in some countries.
Note 2 to entry: This is referred to as Contamination Uniformity Ratio in some countries.
3.1.4
Hydrophobicity Transfer Material
HTM
polymer materials which exhibit hydrophobicity and the capability to transfer hydrophobicity to
the layer of pollution
Note 1 to entry: Further information on HTM is given in Annex A.
3.2 Abbreviated terms
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
SPS Site Pollution Severity
USCD Unified Specific Creepage Distance
RUSCD Reference Unified Specific Creepage Distance
CUR Pollution (Contamination) Uniformity Ratio
RUSCDdc Reference d.c. Unified Specific Creepage Distance
4 Principles
4.1 General
The overall process of insulation selection and dimensioning can be summarised as follows:
• Determination of the appropriate approach (deterministic, statistical etc.) as a function of
available knowledge, time and resources as recommended in IEC TS 60815-1. The
following steps concern the simplified, deterministic approach as described in IEC TS
60815-1; if the statistical approach is chosen, please refer to IEC TS 60815-1 for full
details.
Therefore, using IEC TS 60815-1:
• collection of the necessary input data, notably system voltage, insulation application type
(line, post, bushing, etc.);
• collection of the necessary environmental data, notably site pollution severity.
At this stage, a preliminary choice of possible candidate insulators suitable for the
applications and environment may be made.
Then, using this document for:
• determination of the d.c. site severity by application of correction factors;
• determination of the reference d.c. USCD (RUSCD);
• correction of the RUSCD for each candidate insulator;
• checking the profile parameters;
• verification.
It is to be noted that in the following the USCD and the correction factors are based on a
median behaviour derived from widely spread results (see [1] ). Despite this, when the
process is benchmarked against service experience the results are consistent enough to give
useful orientation to identify a range of preliminary solutions (see [1]).
___________
Numbers in square brackets refer to the bibliography.

– 10 – IEC TS 60815-4:2016 © IEC 2016
4.2 Overall design process
The overall design process is shown in the flowcharts in Figures 1 and 2. From these
flowcharts it can be seen that the creepage distance is only selected after multiple steps to
correct site pollution measurements for the factors which can influence d.c. performance and
which often have a more pronounced effect under d.c. than for a.c. The design process is
complicated by several factors:
• d.c. energised insulators exhibit a greatly different pollution accumulation behaviour
compared to a.c. and un-energised insulators due to electrostatic effects, this
accumulation is affected by wind, particle size etc.;
• composition of the pollution (low solubility or slow-dissolving salts);
• effect of the amount of non-soluble deposit;
• CUR “Contamination Uniformity Ratio”;
• effect of diameter on pollution accumulation;
• non-uniformity of the pollution layer along or around the insulator;
• effect of diameter on pollution performance;
• effect of insulator material on pollution performance.
These points are described in more detail in Figures 1 and 2.
Measurements from d.c. test site/ Measurements from a.c. installations
station or existing nearby or similar or on non-energised insulators as per
installations – See 6.1 IEC 60815-1 – See 6.1
Correct for d.c. pollution accumulation
ESDD
dc
a
(Correct for electrostatic attraction,
NSDD
a
taking into account climatic data:
CUR
a
wind, rain) – See 6.2
Pollution composition
a
Should be measured
ESDD
dc
b
NSDD
b
CUR
a
Pollution composition
b
Preferably measured or
else use default values
Correct for chemical composition of the
pollution layer (type of salt) – See 6.3
Correct for NSDD to a reference value of
0,1 mg/cm – See 6.4
d.c. site severity
Continued into Figure 2
IEC
Figure 1 – Overall design process for d.c. insulation –
determination of d.c. Site Pollution Severity

d.c. site severity
a
For each candidate insulating solution This process is followed separately
a
(Candidates 1.n) for each of the identified candidates
Check profile parameters
– See 10
Correct for the non-uniformity of the
pollution layer (CUR) – See 6.5
Correct severity for effect of diameter
on pollution accumulation – See 6.6
Statistical data correction Number of events
– See 6.7 Number of insulators
Reference d.c.
severity – See 7
Preliminary estimation of the
Reference USCD for the candidate
dc
type and
...