IEC TS 60815-1:2008

IEC/TS 60815-1
Edition 1.0 2008-10
TECHNICAL
SPECIFICATION
Selection and dimensioning of high-voltage insulators intended for use in
polluted conditions –
Part 1: Definitions, information and general principles

IEC/TS 60815-1:2008(E)
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IEC/TS 60815-1
Edition 1.0 2008-10
TECHNICAL
SPECIFICATION
Selection and dimensioning of high-voltage insulators intended for use in
polluted conditions –
Part 1: Definitions, information and general principles

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
XA
ICS 29.080.10 ISBN 978-2-88910-301-0
– 2 – TS 60815-1 © IEC:2008(E)
CONTENTS
FOREWORD.4
1 Scope and object.6
2 Normative references .7
3 Terms, definitions and abbreviations .7
3.1 Terms and definitions .7
3.2 Abbreviations .9
4 Proposed approaches for the selection and dimensioning of an insulator.9
4.1 Approach 1.10
4.2 Approach 2.10
4.3 Approach 3.10
5 Input parameters for the selection and dimensioning of insulators .12
6 System requirements.12
7 Environmental conditions.13
7.1 Identification of types of pollution .13
7.1.1 Type A pollution .13
7.1.2 Type B pollution .14
7.2 General types of environments .14
7.3 Pollution severity.15
8 Evaluation of site pollution severity (SPS) .15
8.1 Site pollution severity .15
8.2 Site pollution severity evaluation methods .16
8.3 Site pollution severity (SPS) classes .17
9 Insulation selection and dimensioning .20
9.1 General description of the process .20
9.2 General guidance on materials .21
9.3 General guidance on profiles.21
9.4 Considerations on creepage distance and insulator length .23
9.5 Considerations for exceptional or specific applications or environments .23
9.5.1 Hollow insulators .23
9.5.2 Arid areas.24
9.5.3 Proximity effects.24
9.5.4 Orientation .24
9.5.5 Maintenance and palliative methods .25
Annex A (informative) Flowchart representation of the design approaches.26
Annex B (informative) Pollution flashover mechanisms .29
Annex C (normative) Measurement of ESDD and NSDD .32
Annex D (normative) Evaluation of type B pollution severity.38
Annex E (normative) Directional dust deposit gauge measurements .40
Annex F (normative) Use of laboratory test methods.44
Annex G (normative) Deterministic and statistical approaches for artificial pollution

test severity and acceptance criteria .45
Annex H (informative) Example of a questionnaire to collect information on the
behaviour of insulators in polluted areas.48
Annex I (informative) Form factor.51
Annex J (informative) Correspondence between specific creepage distance and USCD.52

TS 60815-1 © IEC:2008(E) – 3 –
Bibliography.53

Figure 1 – Type A site pollution severity – Relation between ESDD/NSDD and SPS for
the reference cap and pin insulator .18
Figure 2 – Type A site pollution severity – Relation between ESDD/NSDD and SPS for
the reference long rod insulator .18
Figure 3 – Type B site pollution severity – Relation between SES and SPS for
reference insulators or a monitor .19
Figure C.1 – Insulator strings for measuring ESDD and NSDD.32
Figure C.2 – Wiping of pollutants on insulator surface.34
Figure C.3 – Value of b .35
Figure C.4 – Relation betweenσ and Sa .36
Figure C.5 – Procedure for measuring NSDD.37
Figure E.1 – Directional dust deposit gauges .40
Figure G.1 – Illustration for design based on the deterministic approach.46
Figure G.2 – Stress/strength concept for calculation of risk for pollution flashover .46
Figure H.1 – Form factor.51

Table 1 – The three approaches to insulator selection and dimensioning .11
Table 2 – Input parameters for insulator selection and dimensioning.12
Table 3 – Directional dust deposit gauge pollution index in relation to SPS class.19
Table 4 – Correction of site pollution severity class as a function of DDDG NSD levels.19
Table 5 – Examples of typical environments .20
Table 6 – Typical profiles and their main characteristics .22
Table D.1 – Directional dust deposit gauge pollution index in relation to site pollution
severity class.42
Table D.2 – Correction of site pollution severity class as a function of DDDG NSD
levels.42
Table J.1 – Correspondence between specific creepage distance and unified specific
creepage distance .52

– 4 – TS 60815-1 © IEC:2008(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SELECTION AND DIMENSIONING OF HIGH-VOLTAGE INSULATORS
INTENDED FOR USE IN POLLUTED CONDITIONS –

Part 1: Definitions, information and general principles

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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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/TS 60815-1, which is a technical specification, has been prepared by IEC technical
committee 36: Insulators.
TS 60815-1 © IEC:2008(E) – 5 –
This first edition of IEC/TS 60815-1 cancels and replaces IEC/TR 60815, which was issued as
a technical report in 1986. It constitutes a technical revision and now has the status of a
technical specification.
The following major changes have been made with respect to IEC/TR 60815:
• Encouragement of the use of site pollution severity measurements, preferably over at least
a year, in order to classify a site instead of the previous qualitative assessment (see
below).
• Recognition that “solid” pollution on insulators has two components, one soluble quantified
by ESDD, the other insoluble quantified by NSDD.
• Recognition that in some cases measurement of layer conductivity should be used for SPS
determination.
• Use of the results of natural and artificial pollution tests to help with dimensioning and to
gain more experience in order to promote future studies to establish a correlation between
site and laboratory severities.
• Recognition that creepage length is not always the sole determining parameter.
• Recognition of the influence other geometry parameters and of the varying importance of
parameters according to the size, type and material of insulators.
• Recognition of the varying importance of parameters according to the type of pollution.
• The adoption of correction factors to attempt to take into account the influence of the
above pollution and insulator parameters.
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
36/264/DTS 36/270/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.

– 6 – TS 60815-1 © IEC:2008(E)
SELECTION AND DIMENSIONING OF HIGH-VOLTAGE INSULATORS
INTENDED FOR USE IN POLLUTED CONDITIONS –

Part 1: Definitions, information and general principles

1 Scope and object
IEC/TS 60815-1, which is a technical specification, is applicable to the selection of insulators,
and the determination of their relevant dimensions, to be used in high-voltage systems with
respect to pollution. For the purposes of this technical specification, the insulators are divided
into the following broad categories, each dealt with in a specific part as follows:
− IEC/TS 60815-2 – Ceramic and glass insulators for a.c. systems;
− IEC/TS 60815-3 – Polymeric insulators for a.c. systems;
− IEC/TS 60815-4 – equivalent to 60815-2 for d.c. systems ;
− IEC/TS 60815-5 – equivalent to 60815-3 for d.c. systems .
This part of IEC 60815 gives general definitions, methods for the evaluation of pollution site
severity (SPS) and outlines the principles to arrive at an informed judgement on the probable
behaviour of a given insulator in certain pollution environments.
This technical specification is generally applicable to all types of external insulation, including
insulation forming part of other apparatus. The term “insulator” is used hereafter to refer to
any type of insulator.
CIGRE C4 documents [1], [2], [3] , 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, ice or altitude on polluted
insulators. Although this subject is dealt with by CIGRE [1], [4], current knowledge is very
limited and practice is too diverse.
The object of this technical specification is to
• understand and identify parameters of the system, application, equipment and site
influencing the pollution behaviour of insulators,
• understand and choose the appropriate approach to the design and selection of the
insulator solution, based on available data, time and resources,
• characterize the type of pollution at a site and determine the site pollution severity (SPS),
• determine the reference unified specific creepage distance (USCD) from the SPS,
• determine the corrections to the “reference” USCD to take into account the specific
properties (notably insulator profile) of the "candidate" insulators for the site, application
and system type,
• determine the relative advantages and disadvantages of the possible solutions,
• assess the need and merits of "hybrid" solutions or palliative measures,
• if required, determine the appropriate test methods and parameters to verify the
performance of the selected insulators.
___________
At the time of writing these projects have yet to be initiated.
References in square brackets refer to the bibliography.

TS 60815-1 © IEC:2008(E) – 7 –
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 60038, IEC standard voltages
IEC 60050-471, International Electrotechnical Vocabulary – Part 471:Insulators
IEC 60305, Insulators for overhead lines with a nominal voltage above 1 000 V – Ceramic or
glass insulator units for a.c. systems – Characteristics of insulator units of the cap and pin
type
IEC 60433, Insulators for overhead lines with a nominal voltage above 1 000 V – Ceramic
insulators for a.c. systems – Characteristics of insulator units of the long rod type
IEC 60507:1991, Artificial pollution tests on high-voltage insulators to be used on a.c.
systems
IEC/TR 61245, Artificial pollution tests on high-voltage insulators to be used on d.c. systems
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
reference cap and pin insulator
U120B or U160B cap and pin insulator (according to IEC 60305) normally used in strings of 7
to 9 units to measure site pollution severity
3.1.2
reference long rod insulator
L100 long rod insulator (according to IEC 60433) with plain sheds without ribs used to
measure site pollution severity having a top angle of the shed between 14° and 24° and a
bottom angle between 8° and 16° and at least 14 sheds
3.1.3
insulator trunk
central insulating part of an insulator from which the sheds project
NOTE Also known as shank on smaller diameter insulators.
3.1.4
shed
projection from the trunk of an insulator intended to increase the creepage distance
NOTE Some typical shed profiles are illustrated in 9.3.
3.1.5
creepage distance
shortest distance, or the sum of the shortest distances, along the insulating parts of the
insulator between those parts which normally have the operating voltage between them

– 8 – TS 60815-1 © IEC:2008(E)
NOTE 1 The surface of cement or of any other non-insulating jointing material is not considered as forming part of
the creepage distance.
NOTE 2 If a high resistance coating, e.g. semi-conductive glaze, 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.
[IEV 471-01-04, modified]
3.1.6
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 [5].
m
NOTE 3 It is generally expressed in mm/kV and usually expressed as a minimum.
3.1.7
insulator profile parameters
set of geometrical parameters that have an influence on pollution performance
3.1.8
salt deposit density
SDD
amount of sodium chloride (NaCl) in an artificial deposit on a given surface of the insulator
(metal parts and assembling materials are not included in this surface) divided by the area of
this surface, generally expressed in mg/cm²
3.1.9
equivalent salt deposit density
ESDD
amount of sodium chloride (NaCl) that, when dissolved in demineralized water, gives the
same volume conductivity as that of the natural deposit removed from a given surface of the
insulator divided by the area of this surface, generally expressed in mg/cm²
3.1.10
non soluble deposit density
NSDD
amount of non-soluble residue removed from a given surface of the insulator divided by the
area of this surface, generally expressed in mg/cm
3.1.11
site equivalent salinity
SES
salinity of a salt fog test according to IEC 60507 that would give comparable peak values of
leakage current on the same insulator as produced at the same voltage by natural pollution at
a site, generally expressed in kg/m³
3.1.12
dust deposit gauge index – soluble
DDGI-S
volume conductivity, generally expressed in μS/cm, of the pollutants collected by a dust
deposit gauge over a given period of time when dissolved in a given quantity of demineralized
water
TS 60815-1 © IEC:2008(E) – 9 –
3.1.13
dust deposit gauge index – non-soluble
DDGI-N
mass of non-soluble residue collected by a dust deposit gauge over a given period of time,
generally expressed in mg
3.1.14
site pollution severity
SPS
maximum value of either ESDD/NSDD, SES or DDGIS/DDGIN, recorded over an appropriate
period of time
3.1.15
site pollution severity class
classification of pollution severity at a site, from very light to very heavy, as a function of the
SPS.
3.2 Abbreviations
DDDG directional dust deposit gauge
DDGI-S dust deposit gauge index – soluble
DDGI-N dust deposit gauge index – non-soluble
D dry months (for DDDG)
m
ESDD equivalent salt deposit density
F fog days (for DDDG)
d
F form factor
f
NSD non soluble deposit
NSDD non soluble deposit density
PI pollution index (for DDDG)
SDD salt deposit density
SES site equivalent salinity
SPS site pollution severity
TOV temporary overvoltage
USCD unified specific creepage distance
4 Proposed approaches for the selection and dimensioning of an insulator
4.1 Introductory remark
To select suitable insulators from catalogues based on system requirements and
environmental conditions, three approaches (1, 2 and 3, in Table 1 below) are recommended.
These approaches are also shown in flowchart form in Annex A.

– 10 – TS 60815-1 © IEC:2008(E)
Table 1 shows the data and decisions needed within each approach. The applicability of each
approach depends on available data, time and economics involved in the project. The degree
of confidence that the correct type and size of insulator has been selected varies also
according to the decisions taken during the process. It is intended that if “shortcuts” have
been taken in the selection process, then the resulting solution will represent over-design
rather than one with a high failure risk in service.
In reality, the pollution performance of the insulator is determined by complicated and
dynamic interactions between the environment and the insulator. Annex B gives a brief
summary of the pollution flashover mechanism.
4.2 Approach 1
In Approach 1, such interactions are well represented on an operating line, or substation, and
can also be represented in a test station.
4.3 Approach 2
In Approach 2, these interactions cannot be fully represented by laboratory tests, e.g. the
tests specified in IEC 60507 and IEC/TR 61245.
4.4 Approach 3
In Approach 3, such interactions can only be represented and catered for to a limited degree
by the correction factors. Approach 3 can be rapid and economical for the selection and
dimensioning process but may lead to under-estimation of the SPS or to a less economical
solution due to over-design. The overall costs, including imposed performance requirements,
have to be considered when choosing from the three approaches. Whenever circumstances
permit, Approaches 1 or 2 should be adopted.
The time-scales involved in the three approaches are as follows:
• For service experience (Approach 1), a period of satisfactory operation of five to ten years
can be considered as acceptable. This period may be longer or shorter according to the
frequency and severity of climatic and pollution events.
• For test station experience (Approach 1), a period of investigation of two to five years can
be considered as typical. This period may be longer or shorter according to the test
protocol and severity.
• For measurement of site severity (Approaches 2 and 3), a period of at least one year is
necessary (see 8.2).
• For estimation of site severity (Approaches 2 and 3), it is necessary to carry out research
into the climate and the environment and to identify and analyse all possible pollution
sources. Hence, estimation is not necessarily an immediate process and may require
several weeks or months.
• For laboratory testing (Approach 2), the necessary time is a matter of weeks or months
depending on the type and scale of tests.

TS 60815-1 © IEC:2008(E) – 11 –
Table 1 – The three approaches to insulator selection and dimensioning
APPROACH 1
APPROACH 2 APPROACH 3
(Use past experience)
(Measure and test) (Measure and design)
• Measure or estimate site
pollution severity
• Measure or estimate site
• Select candidate
• Use existing field or test pollution severity
insulators using profile
station experience for the • Use these data to choose
and creepage guidance
Method
same site, a nearby site type and size of insulation
hereafter
or a site with similar
based on profile and
• Choose applicable
conditions creepage guidance
laboratory test and test
hereafter
criteria
• Verify/adjust candidates
• System requirements • System requirements • System requirement
• Environmental conditions • Environmental conditions • Environmental conditions
Input
• Insulator parameters • Insulator parameters • Insulator parameters
data
• Performance history • Time and resources • Time and resources
available available
• Does the existing
insulation satisfy the
• Is there time to measure • Is there time to measure
project requirements and
site pollution severity? site pollution severity?
is it intended to use the
same insulation design ?
YES NO
Use the same Use different
YES NO
Decisions
insulation insulation
Measure Estimate
design design,
materials or
YES NO
size. Use Measure Estimate
• Type of pollution
experience to
determines the laboratory
pre-select the
test method to be used
new solution
• Site severity determines
or size
the test values
• Use the type of pollution
• If necessary, use the • Select candidates and climate to select
profile and creepage • Test if pollution appropriate profiles using
guidance hereafter to performance data is not the guidance hereafter
Selection
adapt the parameters of available for candidates
• Use the pollution level and
process
the existing insulation to • If necessary, adjust correction factors for profile
the new choice using
selection/size according design and material to size
Approach 2 or 3
to the test results the insulation using the
guidance hereafter
• A possibly over or under-
• A selection with an dimensioned solution
compared with approaches
accuracy varying
according to the degree of 1 or 2
errors and/or shortcuts in
• A selection with an
• A selection with a good
Accuracy
the site severity accuracy varying according
accuracy
evaluation and with the to the degree of errors
assumptions and/or
and/or shortcuts in the site
limitations of the chosen severity evaluation and the
laboratory test applicability of the selected
correction factors
The following clauses give more information on system requirements, environment and site
pollution severity determination.
An example of a questionnaire that can be used in Approach 1 to obtain operational
Annex H.
experience from an existing line or substation is given in
Guidelines for using laboratory tests in Approach 2 are described in general terms in Annex F.
Both deterministic and statistical design methods are available to design and select

– 12 – TS 60815-1 © IEC:2008(E)
appropriate insulator solutions based on SPS and laboratory test results; a short description
of these two methods is given in Annex G.
For Approach 3, required minimum unified specific creepage distance and correction factors
are given in the relevant parts of this publication.
5 Input parameters for the selection and dimensioning of insulators
The selection and dimensioning of outdoor insulators is an involved process; a large number
of parameters have to be considered for a successful result to be obtained. For a given site or
project, the required inputs are considered under three categories: system requirements,
environmental conditions of the site and insulator parameters from manufacturer's catalogues.
Each of these three categories contains a number of parameters as indicated in Table 2
below. These parameters are further discussed in later clauses.
Table 2 – Input parameters for insulator selection and dimensioning
System requirements Environmental conditions Insulator parameters
Type of system: Pollution types and levels: Overall length:
a
Maximum operating voltage Rain, fog, dew, snow and ice Type
across the insulation
Insulation co-ordination Wind, storms Material
parameters
Temperature, humidity Profile
Imposed performance Altitude Creepage distance
requirements
Clearances, imposed geometry, Lightning, earthquakes Diameters
dimensions
Vandalism, animals Arcing distance
Live line working and Biological growths Mechanical and electrical design
maintenance practice
a
Non pollution related parameters are given in italics and are not dealt with in this technical
specification; however, they may influence or limit the choice of the type of insulator to be used.
6 System requirements
System requirements shall be taken into account for the selection and dimensioning of
outdoor insulation. The following points may strongly influence insulator dimensioning and
therefore need to be considered.
• Type of system (a.c. or d.c.)
It is well known from service and from laboratory test results that, for the same pollution
conditions, some d.c. insulation may require a somewhat higher value of unified specific
creepage distance compared to a.c. insulation. This effect will be dealt with in detail in
future parts of IEC 60815 dealing with d.c. systems.
• Maximum operating voltage across the insulation
Usually an a.c. system is characterized by the highest voltage for equipment U (see
m
IEC 60038).
Phase-to-earth insulation is stressed with the phase-to-earth voltage U = U /√3.
ph-e m
Phase-to-phase insulation is stressed with the phase-to-phase voltage U = U .
ph-ph m
In the case of a d.c. system, usually the maximum system voltage is equal to the
maximum line-to-earth voltage. In the case of mixed voltage waveforms, the r.m.s. value
of the voltage may need to be used.
• Overvoltages
The effects of transient overvoltages need not be considered due to their short duration.

TS 60815-1 © IEC:2008(E) – 13 –
Temporary overvoltages (TOV) may occur due to a sudden load release of generators and
lines or line-to-earth faults and cannot always be ignored.
NOTE The duration of the TOV depends on the structure of the system and can last for up to 30 min or even
longer in the case of an isolated neutral system. Depending on the duration of the TOV and its probability of
occurrence, the combined effect of TOV and insulator pollution may have to be considered. CIGRE 158 [1] gives
information on this subject and on other risks such as cold switch-on.
• Imposed performance requirements
Longitudinal insulation used for synchronization can be stressed up to a value of 2,5 times
the phase-to-earth voltage.
Some customers may require performance levels for outdoor insulation with regard to
availability, maintainability and reliability. This may be specified, for example, as the
maximum number of pollution flashovers allowed per station, or per 100 km line length,
over a given time. Such requirements may also include a maximum outage time after a
flashover.
In addition to the insulator dimensioning according to the site conditions, imposed
requirements could become the controlling factor for the insulator parameters.
• Clearances, imposed geometry and dimensions
There could be several cases, or a combination thereof, where special solutions for
insulation types and dimensions are required.
Examples include:
– compact lines and substations;
– unusual position of an insulator;
– unusual design of towers and substations;
– insulated conductors;
– lines or substations with a low visual impact.
7 Environmental conditions
7.1 Identification of types of pollution
There are two main basic types of insulator pollution that can lead to flashover:
Type A: where solid pollution with a non-soluble component is deposited onto the insulator
surface. This deposit becomes conductive when wetted. This type of pollution can be best
characterized by ESDD/NSDD and DDGIS/DDGIN measurements. The ESDD of a solid
pollution layer may also be evaluated by surface conductivity under controlled wetting
conditions.
Type B: where liquid electrolytes are deposited on the insulator with very little or no non-
soluble components. This type of pollution can be best characterized by conductance or
leakage current measurements.
Combinations of the two types can arise.
Annex A gives a short description of the pollution flashover mechanisms for type A and type B
pollution.
7.1.1 Type A pollution
Type A pollution is most often associated with inland, desert or industrially polluted areas (see
7.2). Type A pollution can also arise in coastal areas in cases where a dry salt layer builds up
and then rapidly becomes wetted by dew, mist, fog or drizzle.

– 14 – TS 60815-1 © IEC:2008(E)
Type A pollution has two main components, namely soluble pollution that forms a conductive
layer when wetted, and non-soluble pollution that forms a binding layer for soluble pollution.
These are described below.
• Soluble pollution:
Soluble pollution is subdivided into high solubility salts (e.g. salts that dissolve readily into
water), and low solubility salts (e.g. salts that hardly dissolve). Soluble pollution is
measured in terms of an equivalent salt deposit density (ESDD) in mg/cm .
• Non-soluble pollution
Examples of non-soluble pollution are dust, sand, clay, oils, etc. Non-soluble pollution is
measured in terms of non-soluble deposit density (NSDD) in mg/cm .
NOTE The influence of the solubility of salts on the pollution withstand voltage is not taken into account in this
technical specification and is currently under consideration. Similarly, the influence of the type of non-soluble
pollution is not taken into account. Furthermore, the non-soluble component may contain conductive pollution ( e.g.
pollution with metallic conductive particles).
Reference [1] gives more information on the influence of types of pollutant materials.
7.1.2 Type B pollution
Type B pollution is most often associated with coastal areas where salt water or conductive
fog is deposited onto the insulator surface. Other sources of type B pollutions are, for
example, crop spraying, chemical mists and acid rain.
7.2 General types of environments
For the purposes of this technical specification, environments are described by the following
five types. These types describe the typical pollution characteristics for a region. Examples of
the type of pollution (A or B according to 7.1) are shown in the text. In practice, most polluted
environments comprise more than one of these types, for example coastal regions with sandy
beaches; in such cases it is important to determine which pollution type (A or B) is dominant.
• “Desert” type environments
These are areas which are characterized by sandy soils with extended periods of dry
conditions. These areas can be extensive. The pollution layer in these areas normally
comprises salts that dissolve slowly in combination with a high NSDD level (type A). The
insulators are polluted mainly by wind borne pollution. Natural cleaning can occur under the
infrequent periods of rain or by “sand blasting” during strong wind conditions. Infrequent rain,
combined with the slow dissolving salts in this type of pollution, causes natural cleaning to be
less effective. Critical wetting, which poses a risk for insulator flashover, can occur relatively
frequently in the form of dew on the insulators.
• “Coastal” type environments
These areas are typically in the direct vicinity of the coast, but in some cases, depending on
topography, they can be as far as 50 km inland. Pollution is deposited onto the insulators
mainly by spray, wind and fog. The pollution build-up is generally rapid, especially during
spray or conductive fog conditions (type B). A build-up of pollution over a longer term can also
occur through a deposit of wind-borne particles, where the pollution layer on the insulators
consists of quick dissolving salts with a degree of inert component (type A) which depends on
the local ground characteristics. Natural cleaning of the insulators is typically effective as the
active pollution consists mainly of fast dissolving salts
• “Industrial” type environments
These are areas located in close proximity to an industrial pollution source, and may affect
only a few installations. The pollution layer may constitute conductive particulate pollution,
such as coal, metallic deposits; or dissolved gasses, such as NOx, SOx (type B); or pollution
that dissolves slowly, such as cement, gypsum (type A). The pollution layer may have a
medium to high inert component (medium to high NSDD) (type A). The effectiveness of

TS 60815-1 © IEC:2008(E) – 15 –
natural cleaning in industrial areas can vary greatly depending on the type of pollution
present. The pollution is often heavy particles which settle on horizontal surfaces.
• “Agricultural” type environments
These are areas which are situated in the vicinity of agricultural activity. Typically this will be
areas subjected to ploughing (type A) or crop spraying (type B). The pollution layer on the
insulators consist mostly of fast or slow dissolving salts such as chemicals, bird droppings or
salts present in the soil. The pollution layer will normally have a medium to high inert
component (medium to high NSDD). Natural cleaning of the insulators can be quite effective
depending on the type of salt deposited. The pollution is often heavy particles which settle on
horizontal surfaces, but it may also be wind borne pollution.
• “Inland” type environments
These are areas with a low level of pollution without any clearly identifiable sources of
pollution.
7.3 Pollution severity
Pollution severity measurements at a site (e.g. by gauges, dummy insulators, current monitors
etc) are generally expressed in terms of
– ESDD and NSDD for type A pollution,
– site equiva
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