IEC TS 60815-1:2025

IEC TS 60815-1 ®
Edition 2.0 2025-11
TECHNICAL
SPECIFICATION
Selection and dimensioning of high-voltage insulators intended for use in
polluted conditions -
Part 1: Definitions, information and general principles
ICS 29.080.10  ISBN 978-2-8327-0759-3

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CONTENTS
FOREWORD . 4
1 Scope . 7
2 Normative references . 7
3 Terms, definitions and abbreviated terms . 8
3.1 Terms and definitions. 8
3.2 Abbreviated terms . 11
4 Proposed approaches for the selection and dimensioning of an insulator . 12
4.1 Introductory remark . 12
4.2 Approach 1 . 12
4.3 Approach 2 . 12
4.4 Approach 3 . 12
4.5 Comparison of the three approaches . 12
5 Input parameters for the selection and dimensioning of insulators . 14
5.1 Introductory remark . 14
5.2 System requirements . 15
5.3 Environmental conditions . 16
5.3.1 Identification of types of pollution . 16
5.3.2 General types of environments . 17
5.3.3 Pollution severity parameters . 18
6 Determination of site pollution severity (SPS) class . 19
6.1 General . 19
6.2 Evaluation methods of the site pollution severity and their degree of
confidence . 19
6.3 SPS value and evaluation methods . 21
6.4 SPS class and determination methods . 22
6.4.1 SPS class . 22
6.4.2 Methods for determination of SPS class . 23
7 General guidance for insulation selection and dimensioning . 26
7.1 General description of the process . 26
7.2 General guidance on materials . 27
7.3 General guidance on shed profiles . 27
7.4 Considerations on creepage distance and insulator length . 30
7.5 Considerations for exceptional or specific applications or environments . 30
7.5.1 Hollow insulators . 30
7.5.2 Arid areas . 31
7.5.3 Proximity effects . 32
7.5.4 Orientation. 32
7.5.5 Maintenance and mitigative methods . 32
7.5.6 Cold energisation, wet switching of circuit breaker interrupter heads . 32
Annex A (informative) Flowchart representation of the design approaches . 33
Annex B (informative) Pollution flashover mechanisms . 36
B.1 Description of the pollution flashover mechanism under type A pollution . 36
B.2 Description of the pollution flashover mechanism under type B pollution . 37
B.2.1 Conductive fog . 37
B.2.2 Bird streamers . 37
B.3 The pollution flashover mechanism on hydrophobic surfaces . 37
Annex C (normative) Measurement of ESDD and NSDD . 39
C.1 Introductory remark . 39
C.2 Necessary equipment to measure pollution degree . 40
C.3 Pollution collection methods for ESDD and NSDD measurement . 40
C.3.1 General remark. 40
C.3.2 Procedure using a swab technique . 40
C.3.3 Procedure using washing technique (cap and pin insulators) . 41
C.4 Determination of ESDD and NSDD. 41
C.4.1 ESDD calculations . 41
C.4.2 NSDD calculations . 43
C.5 Chemical analysis of pollutants . 44
Annex D (normative) Evaluation of type B pollution severity . 45
D.1 Introductory remark . 45
D.2 Evaluation of SES for type B pollution by leakage current measurement . 45
D.2.1 Measurement of surface conductivity . 45
D.2.2 Measurement of surface leakage currents . 45
D.2.3 Calibration by a salt fog test . 45
D.3 Evaluation of SES for type B pollution by measurement of insulator flashover
stress . 46
D.4 How to estimate SPS for type B pollution . 46
Annex E (normative) Directional dust deposit gauge measurements . 47
E.1 Introductory remark . 47
E.2 Measurement procedure . 48
E.3 Correction for climatic influences . 49
Annex F (normative) Use of laboratory test methods . 50
Annex G (normative) Deterministic and statistical approaches for artificial pollution
test severity and acceptance criteria . 51
G.1 General remark . 51
G.2 Deterministic approach . 51
G.3 Statistical approach . 52
Annex H (informative) Example of a questionnaire to collect information on the
behaviour of insulators in polluted areas . 55
H.1 General information . 55
H.2 System data/requirements (see 5.2) . 55
H.3 Environmental and pollution conditions (see 5.3) . 55
H.4 Insulator parameters . 56
H.5 Details of incidents . 57
Annex I (informative) Form factor. 58
Annex J (informative) Correspondence between specific creepage distance and
USCD . 59
Bibliography . 60

Figure 1 – Type A site pollution severity – Relation between ESDD/NSDD and SPS
class for the reference cap and pin insulator for AC condition . 24
Figure 2 – Type A site pollution severity – Relation between ESDD/NSDD and SPS
class for the reference long rod insulator for AC condition . 24
Figure 3 – Type B site pollution severity – Relation between SES and SPS class for
reference cap and pin insulators for AC condition . 25
Figure 4 – Type B site pollution severity – Relation between SES and SPS class for
reference long rod insulator for AC condition . 25
Figure A.1 – Flowchart of Approach 1 . 33
Figure A.2 – Flowchart of Approach 2 . 34
Figure A.3 – Flowchart of Approach 3 . 35
Figure C.1 – Insulator strings for measuring ESDD and NSDD . 39
Figure C.2 – Wiping of pollutants on insulator surface. 41
Figure C.3 – Value of factor b . 42
Figure C.4 – Relation between σ and Sa . 43
Figure C.5 – Procedure for measuring NSDD . 44
Figure E.1 – Directional dust deposit gauges . 47
Figure G.1 – Illustration for design based on the deterministic approach . 52
Figure G.2 – Stress/strength concept for calculation of risk for pollution flashover . 52
Figure G.3 – Typical range for the correction factor K depending on the number of
r
insulators that are exposed to the same environment, C is the standard deviation of
ins
the flashover voltage from laboratory tests . 54
Figure I.1 – Form factor . 58

Table 1 – The three approaches to insulator selection and dimensioning . 13
Table 2 – Input parameters for insulator selection and dimensioning . 15
Table 3 – Description of typical pollution and wetting environments . 20
Table 4 – Directional dust deposit gauge pollution index in relation to site pollution
severity class . 26
Table 5 – Correction of site pollution severity class as a function of DDDG NSD levels . 26
Table 6 –Typical shed profiles and their main characteristics . 28
Table J.1 – Correspondence between specific creepage distance and unified specific
creepage distance . 59

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
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 this end and
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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) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in
respect thereof. As of the date of publication of this document, IEC had not received notice of (a) patent(s), which
may be required to implement this document. However, implementers are cautioned that this may not represent
the latest information, which may be obtained from the patent database available at https://patents.iec.ch. IEC
shall not be held responsible for identifying any or all such patent rights.
IEC TS 60815-1 has been prepared by IEC technical committee 36: Insulators. It is a Technical
Specification.
This second edition cancels and replaces the first edition of IEC TS 60815-1 published in 2008.
This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition :
a) In the Scope, it is clarified that this specification is applicable to AC and DC conditions while
it mainly refers to AC conditions. Detailed application indications refer to AC only. The
___________
IEC TS 60815-2 and IEC TS 60815-3 are being revised synchronously with this document. It is the intention of
the technical committee to revise IEC TS 60815-4 in the future, and these technical changes will also apply,
where applicable, to that document.
RUSCD is determined based on the SPS class of reference insulators, and this document
does not deal with the effects of ice and snow on polluted insulators;
b) Some terms and definitions are modified or introduced in this document, such as RUSCD,
creepage factor, average diameter, SPS value and SPS class, hydrophobicity transfer and
HTM, etc.;
c) Clause 5 is re-organized and revised regarding input parameters for the selection and
dimensioning of insulators, including system requirements and environmental conditions;
d) Clause 6 "Determination of site pollution severity (SPS) class" is re-organized and re-
written. A distinction was made between SPS value and SPS class. The measurement of
pollution that is made on the de-energized reference insulator is valid for AC only;
e) A new pollution class, extremely heavy class f, is added. It is applicable only to the special
situations of extremely heavy pollution when the RUSCD of class e cannot meet the
requirements. The RUSCD value for class f is not specified;
f) The parameters of reference insulators were defined;
g) The profiles of reference insulators for type B pollution, both cap-and-pin and long rod
insulators were added in this revision. The severity interval for pollution class definition was
differentiated for cap and pin insulators and long rod insulators for type B pollution, as
already foreseen for type A pollution;
h) The DDDG measurement method was also revised;
i) From RUSCD of reference insulator to USCD of candidate insulator, the correction factors
are introduced and revised, such as altitude correction, diameter correction, shed profile
correction and parallel insulator number correction;
j) Profile suitability on ceramic and glass insulators was simplified;
k) The general guidance on materials is revised. The concept of hydrophobicity transfer and
hydrophobicity transfer material (HTM) are introduced, recognising that a reduced creepage
distance may be used for HTM insulators;
l) In the laboratory artificial pollution test for solid layer, the relation between SDD and ESDD
is revised;
m) The statistical method is updated.
The text of this Technical Specification is based on the following documents:
Draft Report on voting
36/614/DTS 36/634/RVDTS
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this Technical Specification is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
A list of all the parts in the future IEC TS 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.
NOTE The following print types are used in Table 2:
– non pollution related parameters: in italic type.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
– reconfirmed,
– withdrawn, or
– revised.
1 Scope
This part of IEC 60815, which is a technical specification, is applicable to the selection of
insulators, and the determination of their relevant dimensions, to be used in outdoor high-
voltage systems with respect to pollution. For the purposes of this technical specification series,
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 AC systems;
– IEC TS 60815-3 – Polymer insulators for AC systems;
– IEC TS 60815-4 – Insulators for DC systems.
This document provides general definitions, gives methods for the evaluation of site pollution
severity (SPS) and outlines the principles to arrive at an informed judgement on the probable
behaviour of a given insulator in certain pollution environments. The general principles
described are applicable to both AC and DC systems. However, the applicability part mainly
refers to AC. More information about DC can be found in IEC TS 60815-4.
This document is 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.
The objective of this technical specification series 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.
– characterise the type of pollution at a site and determine the site pollution severity (SPS)
value and the SPS class,
– determine the reference unified specific creepage distance (RUSCD) of "reference" insulator
based on the SPS class,
– select candidate insulators and determine corrections to apply to RUSCD to arrive at the
USCD of the "candidate" insulators by taking into account their specific properties (notably
their shed profiles), conditions of the site, the application and the type of system,
– evaluate the relative advantages and disadvantages of the possible solutions, using HTM or
non-HTM insulators,
– assess the need and merits of "hybrid" solutions or mitigative measures.

The IEC 60815 series does not deal with the effects of ice and snow on polluted insulators.
CIGRE documents [1], [2], [3], [4], [5], [6] and [7] form a useful complement to this technical
specification for those wishing to study in greater depth the performance of insulators under
pollution.
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.
IEC 60038, IEC standard voltages
___________
Numbers in square brackets refer to the Bibliography.
IEC 60050-471, International Electrotechnical Vocabulary (IEV) – Part 471: Insulators
IEC 60071-11, Insulation co-ordination – Part 11：Definitions, principles and rules for HVDC
system
IEC 60305:2021, Insulators for overhead lines with a nominal voltage above 1 000 V – Ceramic
or glass insulator units for AC systems – Characteristics of insulator units of the cap and pin
type
IEC 60433:2021, Insulators for overhead lines with a nominal voltage above 1 000 V – Ceramic
insulators for AC systems – Characteristics of insulator units of the long rod type
IEC 60507:2013, Artificial pollution tests on high-voltage ceramic and glass insulators to be
used on AC systems
IEC TS 61245, Artificial pollution tests on high-voltage ceramic and glass insulators to be used
on DC systems
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 and the
following apply.
ISO and IEC maintain terminological databases for use in standardisation at the following
addresses:
– ISO Online browsing platform: available at https://www.iso.org/obp
– IEC Electropedia: available at http://www.electropedia.org/
3.1.1
reference standard cap and pin insulator
U120B, U160BS or U160BL cap and pin insulator (according to IEC 60305:2021) normally used
in strings of 7 units to measure site pollution severity value
Note 1 to entry: For U120B, U160BS and U160BL cap and pin insulator, the nominal spacing is 146 mm, 146 mm
and 170 mm, the maximum nominal diameter of the insulating part is 255 mm, 280 mm and 280 mm, and the minimum
nominal creepage distance is 320 mm, 315 mm and 340 mm, respectively.
3.1.2
reference long rod insulator
L100 long rod insulator (according to IEC 60433:2021) 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
shed
projection from the trunk of an insulator intended to increase the creepage distance
Note 1 to entry: Some typical shed profiles are illustrated in 7.3.
3.1.4
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
Note 1 to entry: The surface of cement or of any other non-insulating jointing material is not considered as forming
part of the creepage distance.
Note 2 to entry: 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.
[SOURCE: IEC 60050-471:2007, 471-01-04, modified – "the surface on an insulator between
two conductive parts" replaced by "the insulating parts of the insulator between those parts",
"e.g. semi-conductive glaze" added to Note 2 to entry.]
3.1.5
unified specific creepage distance
USCD
creepage distance of an insulator divided by the base voltage
Note 1 to entry: 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 AC systems usually U ). For line-to-earth insulation, this definition of
m
unified specific creepage distance will result in a value that is √3 times that given by the definition of specific creepage
distance in IEC TR 60815:1986 [8].
Note 2 to entry: The base voltage for AC is the RMS value of the highest operating voltage across the insulator.
Note 3 to entry: The base voltage for DC is defined in IEC 60071-11.
Note 4 to entry: For 'U ' see IEC 60050-614:2016, 614-03-01 [9].
m
Note 5 to entry: It is generally expressed in mm/kV and usually expressed as a minimum.
Note 6 to entry: The total creepage distance used to calculate the USCD is the sum of the nominal, not minimum,
creepage distance of each unit of an insulator string. The nominal creepage distance is referred to IEC 60383-1 [10].
3.1.6
reference unified specific creepage distance
RUSCD
unified specific creepage distance which applies to a reference insulator for a specific pollution
site in mm/kV
Note 1 to entry: It is the starting value to evaluate the USCD of the candidate insulators. USCD can be obtained
after applying the necessary corrections to RUSCD, e.g., for size, profile, mounting position, number of insulators in
parallel and if necessary, required system reliability (acceptable risk of flashover).
3.1.7
average diameter
average diameter D as defined by the equation
a
l
D()x dx
∫
D =
a
l
where D(x) is the value of the diameter at creepage distance x, measured from one electrode
and l is the total creepage distance of the insulator
Note 1 to entry: Simplified equations are reported in IEC TS 60815-2, IEC TS 60815-3 and IEC TS 60815-4.
3.1.8
insulator profile parameters
set of geometrical parameters that have an influence on pollution performance
3.1.9
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/cm
3.1.10
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/cm
3.1.11
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
3.1.12
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/m
3.1.13
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
3.1.14
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 g
3.1.15
site pollution severity value
SPS value
maximum value of either ESDD/NSDD, SES or DDGI-S/DDGI-N, recorded over an appropriate
period of time
3.1.16
site pollution severity class
SPS class
classification of pollution severity at a site, from very light to very heavy (including extremely
heavy), as a function of the SPS value
3.1.17
hydrophobicity
surface of a solid insulating material characterized by its capacity to repel water or aqueous
electrolyte solutions
Note 1 to entry: Hydrophobicity of a polymeric insulating material is, in general, a volume property by means of the
chemical composition of a material at its surface.
Note 2 to entry: Nonetheless, hydrophobicity is strongly affected by surface effects such as:
- surface structure (i. e. roughness);
- chemical interaction between water and the solid surface (adsorption, absorption, swelling of the solid material
in contact with water);
- an accumulated pollution layer.
Note 3 to entry: Furthermore, the conditions during an evaluation of hydrophobicity (temperature, pressure,
humidity), and the method for cleaning or electrostatic charges can affect the measured degree of hydrophobicity.
[SOURCE: IEC TR 62039:2021 [11], 3.1, modified (deleting of "climatic" in Note 3 to entry)]
3.1.18
hydrophobicity transfer
phenomenon of a transfer of hydrophobicity from the bulk of the housing material to the pollution
layer on its surface
3.1.19
hydrophobicity transfer material
HTM
polymeric material which exhibits hydrophobicity and the capability to transfer hydrophobicity
to the layer of pollution, which is a combined dynamic behaviour of retention and transfer of
hydrophobicity specific to different insulator materials
Note 1 to entry: Materials which are not HTM are called non-HTM.
[SOURCE: IEC TS 60815-4:2016, 3.1.4. modified – text after "pollution" added, Note to entry
deleted and Note to entry on non-HTM added.]
3.1.20
arcing distance
shortest distance in the air external to the insulator between the metallic parts which normally
have the operating voltage between them
3.2 Abbreviated terms
DDDG directional dust deposit gauge
DDGI-S dust deposit gauge index – soluble
DDGI-N dust deposit gauge index – non-soluble
D number of dry months (for DDDG)
m
ESDD equivalent salt deposit density
F number of fog days (for DDDG)
d
F form factor
f
HTM hydrophobicity transfer material
NSD non soluble deposit
NSDD non soluble deposit density
PI pollution index (for DDDG)
RUSCD reference unified specific creepage distance
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 (Approaches 1, 2 and 3 in Table 1) are recommended. These
approaches are also shown in flowchart form in Annex A.
Table 1 shows the data and decisions needed within each approach. The applicability of each
approach depends on available data and time 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 under different pollution types and different hydrophobicity
states of the insulator.
4.2 Approach 1
In Approach 1, such interactions mentioned above are well represented on an operating line or
substation, and can also be represented in a test station.
NOTE If questionable, SPS evaluation might be necessary to establish a similarity between the new and existing
project (via SPS measurements or other methods), especially Type B instantaneous pollution events, as it can be
very localised.
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 TS 61245. Different test methods can be selected according to
the test conditions and project requirements. In the artificial pollution test, proper selection of
artificial pollution level, SDD, NSDD and salinity is very important.
4.4 Approach 3
In Approach 3, such interactions can only be represented and catered to a limited degree by
use of correction factors. Approach 3 can be rapid and economical for the selection and
dimensioning process but might lead to under-estimation of the SPS or to a less economical
solution due to over-design.
4.5 Comparison of the three approaches
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.
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)
- Use existing field or test - Measure site pollution - Measure or estimate site
station experience for severity pollution severity
the same site, a nearby
- Select candidate - Use these data to choose
site or a site with similar
insulators using profile type and size of insulation
conditions
and creepage guidance based on profile and
Method
hereafter creepage guidance
hereafter
- Choose applicable
laboratory test and test
criteria
- System requirements - System requirements - System requirement

- Environmental - Environmental conditions - Environmental conditions
conditions
Input data
- Insulator parameters - Insulator parameters
- Insulator parameters
- Time and resources - Time and resources
- Performance history available available
- Does the existing - Is there time to measure - Is there time to measure
insulation satisfy the site pollution severity? site pollution severity?
project requirements and
is it intended to use the
same insulation design ?
YES NO YES NO YES NO
Use the same Use different Measure and Estimate Measure and Estimate
insulation insulation evaluate SPS evaluate SPS
Decisions
design design, value and value and
materials or determine determine SPS
size. Use SPS class class
experience to
pre-select the
- Type of pollution
new solution
determines the
or size
laboratory test method to
be used
- Site pollution severity
determines the test
values
- If necessary, use the - Select candidates - Use the type of pollution
profile and creepage and climate to select
- Test if pollution
guidance hereafter to appropriate profiles using
performance data is not
adapt the parameters of the guidance hereafter
available for candidates
the existing insulation to
Selection
- Use the pollution level and
the new choice using
- If necessary, adjust
process
correction factors for
Approach 2 or 3
selection/size according
profile design and material
to the test results
to size the insulation
using the guidance
hereafter
A selection with an accuracy Accuracy varying according to
depending on the degree of the degree of errors and/or
errors and/or shortcuts shortcuts in the site pollution
adopted in the site pollution severity evaluation and the
A selection with a good
Accuracy
severity evaluation and on applicability of the selected
accuracy
the assumptions and/or correction factors
limitations of the chosen
laboratory test
– 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 pollution severity (Approaches 2 and 3), a period of two to three
years is normally considered as sufficient for balanced pollution accumulation. This period
may be longer or shorter according to the variations of weather conditions (rain, fog or
dryness) and pollution events. Pollution events are often seasonal and related to the specific
environmental conditions (frequency of pollution events and speed of pollution
accumulation, frequency of wetting and washing events). Longer periods for measurements
can be necessary to consider the specifics of local environment, especially for arid areas
with long period of pollution accumulation.
– For estimation of site pollution severity (Approaches 2 and 3), it is necessary to carry out
research into the climate and pollution environment. Hence, the estimation is not an
immediate process and can 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.
Clause 6 and Clause 7 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 experience
from an existing line or substation is given in Annex H.
...