IEC 60815

2024年2月3日发(作者：)

IEC TC36 – WG11 – 60815 Ed2 3rd -draft April 2001

IEC 60815: Guide for the selection and dimensioning of high-voltage

insulators for polluted conditions

Part 1 - : Definitions, information and general principles

Introduction from the Project Leader

What’s new ?

This draft takes into account the decisions taken at our Stockholm meeting.

It integrates the work submitted by RM on figure 2/Table 3.

It also integrates the work submitted by WV on definitions, figure 1, rapid

pollution, dust deposit gauges. Note that there is a suggested Figure 2b

showing the applicability of the approaches and the influence of simple profile

parameters.

I have left the schedule/content and orientation below so that we can keep

them in mind and update as necessary.

I have included both RS and WV ESDD/NSDD measurement procedures in

Annex B – we need to select the best from both.

Tasks, notes etc. arising from Renardières are outlined in yellow

Schedule

The following table shows the planned progress of the revision work. This schedule is based

on the availability of resources within Working Group 11 and an average of two meeting per

year. Since much of the content of the revision is based on the work of CIGRE TF 33.13.01,

the schedule also takes into account the project plans of this Task Force.

The dates are by no means fixed, since the progress of work on the successive parts of IEC

60815 will depend on the degree of acceptance of the first drafts of parts 1 and 2.

Part Expected availability

1st complete draft Part I (1CD) – Guide for the choice of insulators May 2001

under polluted conditions – Part 1: Definitions, information and

general principles

1st complete draft Part II (1CD) – Part 2: Porcelain and glass December 2001

insulators systems

1st complete draft Part III (1CD) ) – Part 3: Polymer insulators for April 2002

a.c. systems

1st complete draft Part IV (1CD) ) – Part 4: Porcelain and glass End 2002 ?

insulators systems

1st complete draft Part V (1CD) ) – Part 5: Polymer insulators for End 2003 ?

d.c. systems

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IEC TC36 – WG11 – 60815 Ed2 3rd -draft

Content and orientation

April 2001

In addition to the strategy and layout given by the task in 36/157/RVN, the orientation of the

work on the revision of IEC 60815 is also based largely on the following list of areas where

IEC 815 was perceived to be weak by CIGRE [1]:

•

•

•

•

•

•

•

•

•

•

Performance of polymeric insulators

Insulator orientation

Extension of applicability to voltages above 525

Design application

Insulators with semi-conducting glaze

Surge arrester housing performance, particularly with reference to polymeric materials

Longitudinal breaks in interrupter equipment

Radio interference, television interference, and audible noise of polluted insulators

Effect of altitude

Effect of heavy wetting

The revision of 60815 to take into account current experience, knowledge and practice related

to polluted insulators in general, and specifically to include polymer insulators and to cover

d.c. systems requires subdivision of the guide into the following five parts:

Part 1: Definitions, information and general principles

Part 2: Porcelain and glass insulators systems

Part 3: Polymer insulators systems

Part 4: Porcelain and glass insulators systems

Part 5: Polymer insulators systems

So far the work on parts 1 and 2 has concentrated on the elaboration of the requirements for

evaluation and measurement of site severity along with study of the relative applicability of

profile parameters to different insulators, materials and technologies.

In addition to the aforementioned aspects, the following major changes have been made or

are foreseen:

•

•

•

•

•

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;

Addition of the influence of non-soluble deposit density (NSDD) as a parameter of

severity;

Use of the results of natural and artificial pollution tests to help with dimensioning;

Recognition that creepage length is not always the sole determining parameter;

Recognition of the influence other geometry parameters (e.g. large or small diameters,

non-linearity …).

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IEC TC36 – WG11 – 60815 Ed2 3rd -draft April 2001

IEC 60815: Guide for the selection and dimensioning of high-voltage

insulators for polluted conditions

Part 1 - : Definitions, information and general principles

1. Scope and object

This guide 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 guide the insulators are divided into the following broad categories:

•

•

•

•

Ceramic insulators systems;

Polymeric insulators systems;

Ceramic insulators systems;

Polymeric insulators systems.

Ceramic insulators have an insulating part manufactured either of glass or porcelain, whereas

polymeric insulators have an insulating body consisting of one or more organic materials.

More precise definitions are given below.

This part of IEC 60815 gives general definitions and principles to arrive at an informed

judgement on the probable behaviour of a given insulator in certain pollution environments. It

also provides methods for the evaluation of pollution severity. The specific guidelines for each

of the types of insulator mentioned above are given in the further parts of IEC 60815, as

follows:

60815-2 - Ceramic insulators systems;

60815-3 - Polymeric insulators systems;

60815-4 - Ceramic insulators systems;

60815-5 - Polymeric insulators systems.

This structure is the same as that used in CIGRE 33.13 TF 01 documents [1, 2], which form a

useful complement to this guide for those wishing to study the performance of insulators

under pollution in greater depth.

This guide 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 aim of this guide is to give the user means to :

•

•

•

•

•

Characterise the type and severity of the pollution at a site;

Determine the nominal creepage distance for a "standard" insulator;

Determine the corrections to the creepage distance to take into account the specific

properties of the "candidate" insulators for the site, application and system type;

Determine the relative advantages and disadvantages of the possible solutions;

Asses the need and merits of "hybrid" solutions or palliative measures.

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IEC TC36 – WG11 – 60815 Ed2 3rd -draft April 2001

2. Normative references

The following normative documents contain provisions which, through reference in this text,

constitute provisions of this International Standard. At the time of publication, the editions

indicated were valid. All normative documents are subject to revision, and parties to

agreements based on this International Standard are encouraged to investigate the possibility

of applying the most recent editions of the normative documents indicated below. Members of

IEC and ISO maintain registers of currently valid International Standards.

IEC 60507

IEC 61245

List to be updated

3. Definitions

For the purpose of this publication, the following definitions apply.

3.1. Line Post Insulator

A rigid insulator consisting of one or more pieces of insulating material permanently

assembled with or without a metal base cap intended to be mounted rigidly on a supporting

structure by means of a central stud or one or more bolts.

3.2. Cap and Pin (Disc) Insulator

An insulator comprising an insulating part having the form of a disk or bell and fixing devices

consisting of an outside cap and an inside pin attached axially.

3.3. Long Rod Insulator

An insulator comprising an insulating part having a cylindrical shank provided with sheds, and

equipped at the ends with external or internal metal fittings.

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IEC TC36 – WG11 – 60815 Ed2 3rd -draft April 2001

3.4. Station Post Insulator

A rigid insulator consisting of one or more pieces of insulating material permanently

assembled and equipped at the ends with external metal fittings intended to be mounted

rigidly on a supporting structure by means of one or more bolts.

3.5. Polymer Insulator

A polymer insulator is one made of at least two insulating parts, namely a shank and housing,

and equipped with metal fittings. Polymer insulators can consist either of individual sheds

mounted on the shank, with or without an intermediate sheath, or alternatively, of a housing

directly moulded or cast in one or several pieces on the shank. Polymer insulators can be of

the long rod, line post or station post type.

3.6. Insulator Shank (Ceramic Insulators)

The shank refers to the main body of the insulator and is designed to provide the required

mechanical characteristics.

3.7. Insulator Shank (Polymer Insulators)

The shank is the internal insulating part of a polymer insulator and is designed to provide the

required mechanical characteristics. It usually consists of continuous glass fibres which are

positioned in a resin-based matrix in such a manner as to achieve maximum tensile strength.

CE to combine

3.8. Sheds

The sheds are the projections from the shank of an insulator intended to increase the

creepage distance. Various typical types of shed and shed profiles are illustrated below.

Normal Shed Alternating Shed

Under ribbed Shed

Drawings of shed profiles to be updated, SN for ceramic posts/long rods/hollws, CL/KK for

cap & pin, RM/FS for composites.

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IEC TC36 – WG11 – 60815 Ed2 3rd -draft April 2001

Standard Disc Shed

Anti-Fog Disc Shed Aerodynamic Disc Shed

3.9. Ceramic Insulator Materials

Porcelain (usually glazed) and Glass (usually toughened).

3.10. Polymer Insulator Materials

Comprise resins, Silicone, EP or co-polymer rubbers

Check “EP”

3.11. Creepage Distance

The shortest distance, or the sum of the shortest distances, along the contours of the external

surfaces of the insulating parts of the insulator between those parts which normally have the

operating voltage between them.

3.12. Specific Creepage Distance

The overall creepage distance of an insulator divided by the highest operating voltage across

the insulator. It is generally expressed in mm/kV.

CE to check

3.13. Dry Arcing Distance

The shortest distance in air external to the insulator between those parts which normally have

the operating voltage between them.

3.14. Profile factors

TBA

3.15. Pollution severities

Site Severity - ?CL

Insulator Pollution – ESDD/NSDD/Surface conductivity ??? CL

4. Abbreviations

4.1. Shed Parameters

The important shed parameters are defined as follows:

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IEC TC36 – WG11 – 60815 Ed2 3rd -draft April 2001

P, P1, P2 = Shed Projection - The shed overhang

S = Shed Spacing - The vertical distance between two similar points of successive sheds.

C = Shed Clearance - the minimum distance between adjacent sheds of the same diameter,

measured by drawing a perpendicular from the lowest point of the outer rib of the upper shed

to the shed below of the same diameter.

S/P = Shed spacing-to-projection ratio -

4.2. Other abbreviations

M.S.C.D. : the Minimum Specific Creepage Distance

R.A.M. : Reliability, Availability, Maintainability.

ESDD : Equivalent Salt Deposit Density

NSDD : Non Soluble Deposit Density

TOV : Temporary Overvoltage

5.

5.1.

Pollution types and the flashover mechanism

Identification of types of pollution

There are two main forms of insulator pollution that can lead to flashover: pre-deposited and

instantaneous flashover occurs mainly at system voltage (Un to Um). BETTER TERMS

NEEDED CL/DAS

5.1.1. Pre-Deposit

Pre-deposit pollution is classified into two main categories, namely active pollution that forms

a conductive layer, and inert pollution that forms a binding layer for the conductive pollution.

These categories are described below.

5.1.1.1. Active pollution:

High solubility salts: NaCl, MgCl, NaSO4 etc.

Low solubility salts: Gypsum, fly ash etc.

Acids: SO2, SO3, NOx etc.

Active pollution is subdivided into conductive pollution (which is permanently

pollution with metallic conductive particles), high solubility salts (ie, salts that dissolve readily

into water), and low solubility salts (that need a large volume of water to dissolve). Active

pollution is measured in terms of an Equivalent Salt Deposit Density (ESDD) in mg/cm2

[3].

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IEC TC36 – WG11 – 60815 Ed2 3rd -draft

5.1.1.2. Inert pollution

April 2001

Hydrophilic pollution: Kaolin, clay, cement, etc.

Hydrophobic pollution: Silicone grease, oil, etc.

Inert pollution is classified as either hydrophilic (when it absorbs water) or hydrophobic (when

it repels water). Inert pollution is measured in terms of Non-soluble Deposit Density (NSDD)

in mg/cm2.

5.1.1.3. High NSDD

This is a low conductivity pollution that builds up in thick layers, e.g. cement dust and fly ash,

is termed as ‘high NSDD’.

5.1.1.4. Low NSDD

This is a high conductivity ‘thin’ pollution layer, e.g. marine salt and SO2, is termed as ‘low

NSDD’.

5.1.1.5. Sources of pre-deposit pollution

Possible sources of insulator pollutants and their effective distances of influence are given

below.

The sea (about 20 km from the coastline).

Factories emitting contaminants such as SO2 that can dissolve to form conductive layers

during acid rain conditions (up to 15 km).

Mining activities that produce dust-containing substances such as gypsum or Illmenite (up

to 15 km).

Agricultural activities such as crop spraying or ploughing (up to 2 km).

Bird droppings which are solidified or partially wet.

5.1.1.6. A brief description of the pollution flashover mechanism under pre-deposit

pollution

For ease of understanding the pre-deposit pollution flashover process, it is divided into six

phases described separately below. In nature these phases are not distinct but may tend to

merge.

The pollution flashover process of insulators is greatly affected by the insulator’s surface

properties. Two surface conditions are recognised: either hydrophilic or hydrophobic. A

hydrophilic surface is generally associated with glass and ceramic insulators whereas a

hydrophobic surface is generally associated with polymeric insulators, especially silicone

rubber. Under wetting conditions - such as rain, mist etc. - hydrophilic surfaces will wet out

completely so that an electrolyte film covers the insulator. In contrast, water beads into

distinct droplets on a hydrophobic surface under such wetting conditions.

The pollution flashover process is also significantly affected by the voltage waveform, a.c. or

d.c. It has been amply demonstrated experimentally that, for the same pollution severity, the

withstand voltage far exceeds the corresponding value conditions. Arc-propagation across the insulator surface can take several cycles and, therefore, the arc is

subject to an extinction and re-ignition process at around current zero.

A complicating feature is the breakdown of the air between neighbouring points of the

insulator profile (e.g. between ribs or sheds) which reduces the flashover performance by

shorting out some of the insulator surface. In addition, drops or streams of water may

facilitate this reduction in performance.

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IEC TC36 – WG11 – 60815 Ed2 3rd -draft April 2001

The process is described below as encountered on hydrophilic surfaces, such as ceramic

materials.

Phase 1: The insulator becomes coated with a layer of pollution. If the pollution is non-conductive (high resistance) when dry, some wetting process (phase 2) is necessary

before flashover will occur.

Phase 2: The surface of the polluted insulator becomes wetted. The wetting of an

insulator can occur in the following ways: by moisture absorption, condensation and

precipitation. Heavy rain (precipitation) may wash away the electrolytic components of

part or the entire pollution layer without initiating other phases in the breakdown process,

or it may promote flashover by bridging the gaps between sheds. Moisture absorption

occurs during periods of high relative humidity (>75%RH) when the temperature of the

insulator and ambient air are the same [6,7]. Condensation occurs when the moisture in

the air condenses on a surface whose temperature is lower than the dew point [6]. This

condition usually occurs at sunrise or just before.

Phase 3: Once an energised insulator is covered with a conducting pollution layer,

surface leakage currents flow and their heating effect starts within a few power frequency

cycles to dry out parts of the pollution layer. This occurs where the current density is

where the insulator is at its narrowest. These result in the formation of what

are known as dry bands.

Phase 4: The pollution layer never dries uniformly, and in places the conducting path

becomes broken by dry bands which interrupt the flow of leakage current.

Phase 5: The line-to-earth voltage appearing across dry bands (which may be only a few

millimetres wide) causes air breakdown and the dry bands are bridged by arcs which are

electrically in series with the resistance of the undried and conductive portion of the

pollution layer. This causes a surge of leakage current each time the dry bands on an

insulator spark over.

Phase 6: If the resistance of the undried part of the pollution layer is low enough, the arcs

bridging the dry bands are sustained and will continue to extend along the insulator,

bridging more and more of its surface. This in turn decreases the resistance in series with

the arcs, increasing the current and permitting them to bridge even more of the insulator

surface. Ultimately, it is completely bridged and a line-to-earth fault (flashover) is

established.

One can summarise the whole process as an interaction between the insulator, pollutants,

wetting conditions, and applied voltage (and source impedance in laboratory conditions).

The likelihood of flashover increases with higher leakage current, and it is mainly the surface

layer resistance that determines the current magnitude. It can therefore be concluded that the

surface layer resistance is the underlying factor determining whether an insulator will flash

over or not, in terms of the above model.

Because pollution on the surface of a high-voltage insulator needs to become well wetted

before it can cause a flashover to occur, it may seem somewhat puzzling – upon a cursory

consideration – that pollution flashover can be a big problem in very dry areas such as

deserts. The explanation often lies with the “thermal lag” at sunrise between the temperature

of the surface of the insulator and the rapidly rising temperature of the ambient air. This

difference in temperature need only be a few degrees centigrade for substantial condensation

to take place, even at fairly low values of relative humidity [1]. The thermal capacity and

thermal conductivity of the insulating material control the rate at which its surface warms up. –

From DAS, needs editing

More information on pollution flashover processes and models is available in CIGRE 158.

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IEC TC36 – WG11 – 60815 Ed2 3rd -draft April 2001

5.1.2. Instantaneous pollution

5.1.2.1. Conductive Fog

‘Instantaneous pollution’ refers to a contamination of high conductivity which quickly deposits

on insulator surfaces, resulting in the condition where the insulator changes from an

acceptably clean, low conductive state to flashover in a short (< 1 hour) time and then returns

to a low conductive state when the event has passed.

For ease of understanding instantaneous pollution flashover the same process as described

in section 5.1.1.6 applies. However, the instantaneous pollution is normally deposited as a

highly conductive layer of liquid electrolyte, e.g. salt spray, salt fog or industrial acid fog, thus

phases 3 to 6 above may happen immediately. In nature these phases are not distinct but

they do merge. These only refer to hydrophilic surfaces. Areas most at risk are those

situated close chemical plants, or areas close to the coast with a known history of

temperature inversions.

5.1.2.2. Bird Streamer

A particular case of ‘instant’ pollution is bird streamer. This is a type of bird excrement,

which, on release, forms a continuous, highly (20-40 kΩ/m) conductive stream of such length

that the air gap is sufficiently reduced to cause flashover. In this case, the insulator geometry

and characteristics play little or no role [8].

5.2. A brief description of the pollution flashover mechanism on hydrophobic

surfaces

Due to the dynamic nature of a hydrophobic surface and the resulting complex interaction with

pollutants - both conducting and non-conducting - and wetting agents, there exists today no

generally adopted model of pollution flashover for hydrophobic insulator surfaces However, a

qualitative picture for the pollution flashover mechanism is emerging which involves such

elements as the migration of salt into water drops, water drop instability, formation of surface

liquid filaments and discharge development between filaments or drops when the electric field

is sufficiently high.

However, in service the hydrophobic materials are submitted to a dynamic process of pollution

deposition, wetting, localised discharges or high electric field which can combine to cause

parts or all of the surface to become temporarily more hydrophilic. Thus much of the physics

of the flashover process of hydrophilic surfaces also applies, albeit locally or for limited

periods of time, to nominally "hydrophobic" materials or surfaces.

6. Parameters and approaches for the insulator selection and dimensioning

The selection and dimensioning of outdoor insulators is an involved process; a large number

of parameters must be considered for a successful result to be obtained. For a given site or

project, the required inputs are in 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 1 below. These

parameters are further discussed in later chapters

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IEC TC36 – WG11 – 60815 Ed2 3rd -draft April 2001

Table 1 - Parameters for insulator selection and dimensioning

System requirements

Application

Withstand voltages

Reliability, availability,

maintainability. (R.A.M.)

Costs

Installation position,

clearance, …

Environmental Conditions

Pollution level and types

Rain, fog, dew, …

Wind

Temperature, humidity

Altitude

Lightning

Earthquakes

Vandalism

Type

Material

Profile

Creepage

Form factor (diameter)

Arcing distance

Insulator parameters

To select suitable insulators from the catalogues based on the system requirements and the

environmental conditions, three approaches (A, B, C, in figure 1 below) are recommended.

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.

Figure 1 shows the data and decisions needed within each approach. PLEASE STUDY AND

COMMENT

In reality, the pollution performance of the insulator is determined by the complicated and

dynamic interactions among the environmental and the insulator parameters. Such

interactions are well represented on an operating line or substation and can be represented in

a test station. Such interactions can not be fully represented by laboratory tests, e.g. the tests

specified in IEC 60507 and IEC 61245. In approach C, such interaction can only be

represented in a limited degree by the correction factors. Approach C is simple and cheap for

the dimensioning process but the whole costs, including the R.A.M requirements have to be

considered when choosing among the three approaches. Whenever circumstances permit, the

approach A should be adopted.

Figure 2b shows domains of preferred applicability of these approaches as a function of

pollution severity and type.

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IEC TC36 – WG11 – 60815 Ed2 3rd -draft April 2001

APPROACH

A

•

APPROACH

B

APPROACH

C

Measure or estimate

site pollution severity.

• Use existing field or test

• Select candidate

• Measure or estimate site

insulators using profile

station experience to

pollution severity.

choose

and creepage guidance

• Use this data to choose

hereafter.

• and size insulation for

type and size of insulation

• Choose applicable

the same site, a nearby

based on profile and

laboratory test and test

site or a site with similar

creepage guidance

conditions.

criteria.

hereafter.

• Verify/adjust candidates

• System requirements.

• System requirements.

• System requirements

Input

• Environmental

• Environmental

• Environmental

Data

conditions.

conditions.

conditions.

• Insulator parameters.

• Insulator parameters.

• Insulator parameters.

• Performance history.

• Time and resources

• Time and resources

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?

YES NO

Use the same Use different

YES NO YES NO

insulation. insulation or

Measure Estimate Measure Estimate

different

size.

Decisions

• Is a different material,

• Type of pollution

type or profile to be used?

determines the laboratory

test

NO YES

Use the same Use different

• Site severity determines

insulation. insulation or

the test values

different

size.

• Use the type of pollution

• If necessary, use the

and climate to select

• Select candidates

profile and creepage

appropriate profiles using

• Test

guidance hereafter to

Selection

the guidance hereafter.

• Adjust selection/size

adapt the parameters of

Process

• Use the pollution level

the existing insulation to

according to the test

and profile factors to size

the new choice using

results if necessary.

the insulation using the

approach B or C.

guidance hereafter.

• A possibly over-designed

• A qualified selection

solution compared

with confidence of good

to A or B

• A selection with high

performance varying

• A selection with

Result

confidence of good

following the degree of

confidence of good

errors and/or shortcuts in

performance.

performance varying

the site severity

following the degree of

evaluation

errors and/or shortcuts in

the site severity evaluation

Figure 1 - The three approaches to insulator selection and dimensioning

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IEC TC36 – WG11 – 60815 Ed2 3rd -draft April 2001

6.1.1. Approach A

To obtain the operational experience of the existing line or substation, an example of a

questionnaire is given in Annex C. To utilise obtained information the flowchart below may be

followed.

6.1.2. Approach B

To utilise the existing test results or to specify new laboratory tests (methods and test

severity), the pollution level and type of the site should be obtained first. This subject is

presented in 6. The information obtained from existing lines or test stations can also be used.

For the laboratory test methods one can find them in corresponding IEC standards IEC 60507

(a.c.) and IEC 61245 (d.c.). Non-standard methods may be used, especially to represent

specific or special cases of pollution.

6.1.3. Approach C

To obtain the pollution level the method given in X should be followed. The required minimum

specific creepage distance and correction factors are given in chapter X.

7. Pollution Severity

CL & DAS find appropriate terms

7.1.1. Active pollution

Active pollution can itself be classified in two types :

•

•

conductive pollution : metallic deposits, bird droppings, acid rain, salt fog …

soluble pollution : wind-borne dry salt deposit from the sea, salt contained in desert sand,

gypsum coming from the ground or quarries, cement, fly ash, chemical pollution due to

industrial activity or use of fertilisers and treatments in agriculture ...

The global conductance of the pollution layer is the principal element in the severity level. In

the case of soluble salts, the global conductance depends on the amount of pollution in a

dissolved state and therefore on the amount of water spread on the insulator surface.

Two salt characteristics, the solubility and the time to dissolve, are important (see table 2).

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IEC TC36 – WG11 – 60815 Ed2 3rd -draft April 2001

For example, the more the pollution is soluble and fast dissolving, the less the pollution layer

needs water (rain, ) and time to form a highly conductive layer. On the other hand, this

type of pollution is generally easily leached or washed away by natural wetting events.

For a same severity level, the insulator withstand voltage will then depend on the salt

properties and on the wetting process characteristics.

In Figure 2 active pollution is characterised by means of the ESDD value. For soluble

pollution, these values are given for a completely dissolved state.

PARA by CE to cover risk under heavy wetting etc.

Table 2 - Classification of salts according to their solution properties

Fast dissolving salts

Slow dissolving salts

MgSO4, Na2SO4, CaSO4

Low solubility salts High solubility salts

MgCl2, NaCl, CaCl2, KCl

NaNO3, Ca(NO3)2, ZnCl2

7.1.2. Inert pollution

This type of pollution is not conductive but can indirectly influence the withstand voltage of an

insulator.

If the material constituting inert pollution is hydrophilic, as for example kaolin and tonoko used

in artificial pollution tests, water does stay in the shape of droplets but forms a film. In

addition, a thicker water film is retained on the insulator surface. During wetting periods, more

soluble salts are dissolved in a continuous film of solution and therefore the global

conductance is higher.

In addition, heavy or frequent deposits of non-soluble pollution onto hydrophobic materials

can mask the hydrophobic properties of the material. However, for many hydrophobic rubbers

the hydrophobic properties of the material transfer to the surface of the pollution layer thus

restoring the flashover performance.

In Figure 2 inert pollution is characterised at means of the NSDD value.

7.1.3. Evaluation of pollution severity

Need same for marine CE & WP

The application of this guide is directly related to the knowledge of the pollution severity of the

site where the insulators are to be installed.

The evaluation of the pollution severity can be made with a decreasing degree of confidence :

•

•

from measurements in situ.

from information on the behaviour of insulators from lines and substations already in

service on or close to the site (see Annex Y),

If not otherwise possible qualitatively from indications given in Table 3,

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IEC TC36 – WG11 – 60815 Ed2 3rd -draft April 2001

For measurements in situ, different methods are generally used. They are :

• either,

o ESDD and NSDD on the insulator surface of reference standard insulators (see annex

B) for “pre-deposit”;

or

o SES from on site current/surface conductance of reference standard insulators for

marine;

•

•

•

volume conductivity and sediment analysis for the pollutant collected by means of

directional gauges (see annex A);

total number of flashovers of insulators of various lengths;

leakage current of sample insulators.

The first three methods do not require expensive equipment and can be easily performed. The

volume conductivity method gives no direct information by itself on the frequency and on the

severity of the contamination events on a natural site. The ESDD/NSDD method characterises

the pollution severity of the site. Information on wetting shall be separately obtained.

The accuracy of all these methods depends upon the frequency of measurement and the

duration of the study.

For other pollution environments, such as for sites close to industries where pollution deposit

is regular, weekly or monthly measurements could be sufficient.

The method based on total flashovers needs expensive test facilities. Reliable information can

be obtained only for insulators having a length close to the actual length and flashing over at

a voltage near the operating voltage.

The last two methods which need a power source and special recording equipment have the

advantage that the effects of pollution are continuously monitored. These techniques have

been developed for assessing the pollution rate and the results, when related to test data, are

used to indicate that the pollution is still at a level known to be safe for operational service or

whether washing or re-greasing is required.

In any case where measurements are carried out on standard profile insulators it can be very

useful to include insulators with other profiles and orientations in order to determine the

influence of self-cleaning and deposit mechanism for the site under study. This information

can then be used to refine the choice of an appropriate profile.

Pollution events are often seasonal and related to the climate, therefore the measurement

period has to last at least one year. Longer periods may be necessary to take exceptional

pollution events into account or to identify trends. Equally it may be necessary to measure

over at least three years for arid areas.

7.2. Pollution severity levels

For the purposes of standardisation, five levels of pollution characterising the site severity are

qualitatively defined, from very light pollution to very heavy pollution.

Table 3 gives, for each level of pollution, an approximate description of some typical

corresponding environments. The list of environments is not exhaustive and the descriptions

should preferably not be used alone to determine the severity level of a site.

Figure 2 gives ranges of ESDD/NSDD values for standard cap and pin insulators. These

values are deduced from field measurements, experience and pollution tests. The values are

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IEC TC36 – WG11 – 60815 Ed2 3rd -draft April 2001

the maximum values that can be found from regular measurements taken over a minimum one

year period.

Some insulator characteristics, for example profile, have an important influence on the

pollution quantity deposed on insulators themselves. Therefore, these typical values are only

available for standard glass or ceramic cap and pin insulators.

!

Figure 2 - Relation between ESDD/NSDD and site severity for standard profile cap and pin

insulators.

Figure promised by Germany

Figure 2a - Relation between ESDD/NSDD and site severity for standard profile long rod

insulators.

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IEC TC36 – WG11 – 60815 Ed2 3rd -draft April 2001

Table 3 - Examples of typical environments

Site

severity

Very Light

Examples of typical environments

> 50 km

I from the sea, a desert, or open dry land

> 10 km from man-made pollution sources

II

Within a shorter distance than mentioned above of pollution sources, but:

• prevailing wind not directly from these pollution sources

• and/or with regular monthly rain washing

Light

10-50 km

I from the sea, a desert, or open dry land

5-10 km from man-made pollution sources

II

Within a shorter distance than mentioned above of pollution sources, but:

• prevailing wind not directly from these pollution sources

• and/or with regular monthly rain washing

Medium

3-10 km

III from the sea, a desert, or open dry land

1-5 km from man-made pollution sources

II

Within a shorter distance than mentioned above of pollution sources, but:

• prevailing wind not directly from these pollution sources

• and/or with regular monthly rain washing

Further away from pollution sources than mentioned above (distance in the range specified for

“Light” areas) but:

• dense fog (or drizzle) often occurs after a long (several weeks or months) dry pollution

accumulation season

• and/or the present heavy rain with high conductivity

• and/or there is a high NSDD level, between 5 and 10 times the ESDD

Heavy

Within 3 km

IV of the sea, a desert, or open dry land

Within 1 km of man-made pollution sources

II

With a longer distance from pollution sources than mentioned above (distance in the range specified

for “Medium” areas) but:

• dense fog (or drizzle) often occurs after a long (several weeks or months) dry pollution

accumulation season

• and/or the present heavy rain with high conductivity

• and/or there is a high NSDD level, between 5 and 10 times the ESDD

Very

heavy

Within the same distance of pollution sources as specified for “Heavy” areas and:

• directly subjected to sea-spray or dense saline fog

• or directly subjected to contaminants with high conductivity, or cement type dust with high density,

and with frequent wetting by fog or drizzle

Desert areas with fast accumulation of sand and salt, and

regular condensation

Light to

heavy

Within 3 km

IV of the sea,

Within 1 km of man-made pollution sources

II

Associated with the possibility of heavy sea-fog and/or industrial particulate fog.

"

#

$

&

'

(

)

!

I. during a storm, the ESDD level at such a distance from the sea may reach a much higher level.

II. the presence of a major city will have an influence over a longer distance, i.e. the distance specified for sea,

desert and dry land.

III. depending on the topography of the coastal area and the wind intensity

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IEC TC36 – WG11 – 60815 Ed2 3rd -draft

April 2001

Increasing

useful

effect

of

open

profiles

Approach A

and/or B with

solid layer

method

Increasing need

for profile

promoting

natural washing

Approach A

and/or C

Approach A

and/or B with

salt fog method

!Increasing useful effect of hydrophobicity

Figure 2b – Trends in applicability of approaches and profiles.

8. System requirements

Besides the information on the environmental conditions, system requirements have also to

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. )

It is well known from service experiences and from laboratory test results, that

insulation requires a much higher value of specific creepage distance compared

insulation for the same site conditions. This effect is dealt with in detail in parts 2 to 5.

• Maximum operating voltage across the insulation

Usually -system is characterised by the voltage Um, which is the s.

phase-to-phase voltage for which an equipment is designed in respect of its insulation. Um

is the maximum value of the highest voltage of the system for which the equipment may be

used (IEC 60071-1, 1976, Clause 4).

Line-to-earth insulation is stressed with the line-to-earth voltage Ul-e = Um/√3.

Phase-to-phase insulation is stressed with the phase-to-phase voltage Uph-ph = Um [IEC

60071-1, Clause 7.5].

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IEC TC36 – WG11 – 60815 Ed2 3rd -draft April 2001

In the case of -system usually the maximum system voltage is equal to the maximum

line-to-earth voltage stressing the line-to-earth insulation.

The maximum operating voltage across an insulator requires a minimum arcing. In

contrast insulation co-ordination may require also a maximum arcing distance [IEC 60071-1, Clause xx].

• Overvoltages

Lightning and switching overvoltages need not be considered due to their short duration.

Temporary overvoltages (TOV) may occur due to a sudden load release of generators and

lines or line-to-earth faults. The duration of the TOV depends on the structure of the

system and can last for less than 2 seconds to half a hour or even more in the case of a

grounded neutral system. See IEC 60071-2 for more information on the definition of TOV

and CIGRE 158 for information their influence.

Depending on the duration of the TOV and its probability of occurrence the TOV may have

to be considered.

• Reliability, availability, maintainability (RAM)

Some customers may request performance guarantees for the outdoor insulation, i. e. the

numbers of pollution flashovers allowed per station or per 100 km line length in a given

time period. These requirements may also include a maximum outage time after a

flashover.

Besides the insulator dimensioning according to the site conditions, these demands could

become a controlling factor for the choice of insulator parameters.

• Clearances, imposed geometry, dimensions

There could be several cases, or a combination thereof, where special solutions for

insulation dimensioning are required.

Examples are:

•

•

•

•

compact lines;

unusual position of an insulator;

unusual design of towers and substations;

requirement for a low visual impact.

9. Insulator Characteristics

(All to be completed at the next WG meeting)

9.1. Materials

9.1.1. Glass

9.1.2. Porcelain

9.1.3. Porcelain with Semi-conducting Glaze

9.1.4. Polymers

9.1.5. Hybrids

Hybrid insulators as known today, consist of a shank of porcelain and a polymer housing.

They are not common in service.

9.1.6. Hydrophobic Coatings

Ceramic insulators can be coated with a polymer layer thereby creating a hydrophobic

surface.

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IEC TC36 – WG11 – 60815 Ed2 3rd -draft

9.2. Design

9.2.1. Line Insulators

9.2.2. Post Insulators

9.2.3. Hollow insulators

9.2.4. Profile Design

9.2.4.1. Purpose

April 2001

The principal purpose of insulator surface profile is to extend the distance for a leakage

current travelling on the polluted surface. In order to avoid local flashover which can damage

the insulator or lead to total flashover, there are different important factors.

10. Creepage Distance and Form Factor

(All to be completed at the next WG meeting)

Factor

m distance c between sheds.

er(s)

s/p between spacing and shed overhang

ld/d between creepage distance and clearance

ating sheds

ation of sheds

ge factor

e factor

ation

-linearity (overall length)

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IEC TC36 – WG11 – 60815 Ed2 3rd -draft April 2001

11. Insulation selection and dimensioning

This clause will describe the general principles of how to use parts 2 to 5 for insulator

selection and dimensioning, i.e.

determination of minimum creepage distance for candidate insulators,

correction for profile, design and material,

specific considerations for a given type/design/material,

Renard58 ,

considerations for exceptional or specific environments or applications.

R. Martin contribution

DAS – needs editing

In Tunisia, flashover problems with ceramic insulators still occur in some areas in spite of

them having a specific creepage path of 52 mm/kV system [2]. Soil analysis has shown

that local desert sand in this country contains calcium and sodium salts, which are blown

on to the insulator’s surface to produce a pollution severity of ESDD as great as 0.65

mg/cm squared. A semiconducting glaze provides a continuous flow of current – of about

1 mA – which helps to keep it dry in such conditions. As yet, I know of no publication that

provides a definitive conclusion on the pollution flashover performance of polymeric

insulators in such arid environments.

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IEC TC36 – WG11 – 60815 Ed2 3rd -draft April 2001

Annex A : Directional Dust Deposit Gauge Measurements

A.1 Introduction

Four dust gauges, each gauge set to one of the four cardinal points of the compass, are used

to collect the pollution particles carried in the atmosphere. The pollution is collected in the

four plastic containers attached to the bottom of the gauges. At monthly intervals these

containers are removed and the contents collected is mixed with 500 ml of distilled water.

The conductivity of this solution is measured and the pollution index is defined as the mean of

the conductivities of the four gauges expressed in µS/cm and normalised to a 30-day interval.

The advantage of this technique is its simplicity and the fact that it can be used at an

unenergised site without insulators or facilities other than those required for the mounting of

the gauges.

Figure A1: Directional Dust Deposit Gauges (Note: the rain gauge is an optional extra, used if the

monthly rainfall at that site needs to be measured.)

The nominal dimensions are a 40mm wide slot with 20mm radii at each end. The distance

between the centres of the radii is 351mm. (The overall slot length thus being 391mm). The

tube is at 500mm long with 75mm outside diameter. Distance from the top of the tube to the

top of the slot is 30mm. The tubes should be mounted with the bottom of the slot

approximately 3 metres from the ground. This just keeps the gauge out of reach of casual

tampering but the jars can be easily and safely changed.

Its major disadvantage is that actual insulators are not used and therefore it is not possible to

assess the self-cleaning properties of insulators and the effect of the shed profile on the

deposition process on the insulator surface. In areas of high rainfall, a higher index can be

tolerated, whereas in areas of low rainfall but with a high occurrence of fog, the actual

severity is higher than that indicated by the gauges.

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IEC TC36 – WG11 – 60815 Ed2 3rd -draft April 2001

A.2 Test equipment

•

•

•

•

•

•

•

•

•

•

•

Clip board, pencil and paper: To record raw data results.

Portable ladder: 2.5 metre ladder to reach dust containers.

Spray Bottle: To spray residual pollutants from each dust gauge cylinders into container,

using distilled water.

Measuring Cylinder: To measure 500 ml distilled water to be poured into each container.

Distilled water: Average 3 litres of water per set of containers. Volume conductivity

should not exceed 5µS/cm.

Portable conductivity meter: Values are given in µS/cm and are usually compensated to

20°C. If meter (e.g. Greisinger GLM 020) is not compensated to 20°C, specify

conductivity and temperature readings in report.

Temperature probe: Used to measure temperature of dust gauge solution if conductivity

meter is not compensated to 20°C.

Tap water: Used to clean vertical slots and containers after measurements have been

taken.

Paper towels: Used if additional cleaning is necessary.

Thick, black waterproof marker pen: Used to mark location and date of testing on

containers.

Extra set of containers: If containers are taken back to the laboratory, a replacement set

is needed, otherwise the current set is cleaned and replaced onto the dust gauge

cylinders after measurements have been taken.

A.3 Test procedure

• The gauge slots to which the containers are connected must be sprayed with a little

distilled water so that any residual pollutants in each dust gauge cylinder rinses into its

container. This prevents any deposit build up from previous months washing into the

container when rain occurs.

Remove the four containers from the slots facing the four dominant wind directions, noting

the date of instalment on the data result sheet

Pour 500 ml of distilled water into each container and swirl contents to ensure that the

soluble deposits are totally dissolved.

Measure the conductivity of the distilled water as well as its temperature, if meter is not

compensated to 20°C

Measure the volume conductivity of the solution in the containers with the hand-held

probe and record results.

Record the number of days since the previous test measurement. The time interval

should not be less than 20 days nor more than 40 days

Wash and clean vertical slots and containers after measurements have been taken, with

tap water and install clean containers to dust gauges. Write the date on the containers

with black waterproof marker pen.

•

•

•

•

•

•

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IEC TC36 – WG11 – 60815 Ed2 3rd -draft April 2001

Annex B : Measurement of ESDD and NSDD

B.1 Introduction

When anti-pollution design of the insulator is made, it is indispensable to determine pollution

degree. The pollution degree is generally determined by measuring equivalent salt deposit

density (ESDD) on the insulators which are removed from the existing transmission lines

and/or field testing stations. In addition to ESDD, non-soluble material deposit density (NSDD)

should be measured, especially in case that much dust or sand is estimated to accumulate on

the insulator surface in such an area as desert or industrial factories. This Appendix describes

how to measure ESDD and NSDD, and how to make chemical analysis of the pollutants.

The equivalent salt deposit density (ESDD) is the equivalent deposit of NaCl in mg/cm² of the

surface area of an insulator, which will have an electrical conductivity equal to that of the

actual deposit dissolved in the same amount of water.

The general technique for measurements of ESDD involves dissolving the surface deposits in

a known quantity of water with a low conductivity, measuring the temperature of the solution

and calculating the ESDD from the measured conductivity, the volume of water and the

insulator surface area.

One of the important advantages of this technique is that it can be carried out on actual

insulators, and the self-cleaning properties and shed profile performance can be assessed.

For site pollution severity measurement purposes we standardise the measurements by using

a string of 7 glass cap and pin insulators (U120BS). The unenergized insulator string is

located at a height as close as possible to that of the line or busbar insulators. Each disc of

the insulator string is monitored at a defined every month, every three months,

each year, after two years, etc.

Dummy disk 7

Analysed every two years

Analysed every year

Analysed every six months

Analysed every three months

Analysed every month

Dummy disk 1

Figure B1: ESDD string

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IEC TC36 – WG11 – 60815 Ed2 3rd -draft April 2001

B.2 Measuring ESDD (Vosloo)

Test equipment

• Measuring Cylinder: To measure distilled water used for each insulator.

• Distilled water: Two litres of water per insulator. Volume conductivity should not exceed

5µS/cm. Take extra 2 litres along in case of spillage, etc.

• Portable conductivity meter: Values are given in µS/cm and are usually compensated to

20°C. If meter (e.g. Greisinger GLM 020) is not compensated to 20°C, specify

conductivity and temperature readings in report.

• Temperature probe: Used to measure temperature of salt solution if conductivity meter is

not compensated to 20°C.

• Washing bowl: The bowl should be large enough to hold an insulator. Preferably made

of perspex or plastic.

• Surgical gloves: To ensure that no additional contaminants are added when washing

insulator with hands. If not available, ensure that hands are thoroughly cleaned.

• Tin foil or Plastic wrap: Used to cover cap and pin of insulator prior to washing.

• Tap water: Used to clean bowl and wash gloves after measurements have been taken.

• Paper towels: Used to dry or clean bowl if necessary.

• Thick, black waterproof marker pen: Used to mark location, date of testing and insulator

details on containers.

• Set of containers: Two containers per insulator. Wash water should be poured into the

containers (top and bottom surfaces separately) and then measured.

Test procedure

• The unenergized string consists of seven discs as shown in the figure. The two end discs

are excluded from the test - only 2, 3, 4, 5 and 6 are tested.

• The glass surfaces of the discs should not be touched to avoid any loss of pollution.

• Cover the cap and pin respectively with tin foil without covering the glass surface.

• Ensure that the bowl, which the discs are to be washed in, is clean. Clean rubber gloves

(scientific) or thoroughly washed hands are a prerequisite to perform these tests.

• Measure down one litre of distilled water (1 - 5µS/cm) and pour into bowl.

• Place the test insulator on its foil-covered cap in the water and wash the top surface with

gentle hand strokes without any wash water wetting the bottom surface (ribbed profile).

• After top surface has been washed, gently shake off any remaining water on the tin foil,

remove insulator from bowl and pour water into a container. Take care that all deposits

are removed from bowl.

• Rinse bowl before the commencement of next test.

• Measure down one litre of distilled water (1 - 2µS/cm) and pour into bowl.

• Place the same insulator as mentioned above on its cap in the bowl and gently wash

pollution off the bottom surface (ribbed profile) with your hands.

• Pour water in second container taking care again that no deposits remain in the bowl.

• Swirl water content in containers to ensure that salts are totally dissolved prior to

measuring.

• Use the hand-held conductivity probe to measure the volume conductivity (µ/cm).

• Disc 2 is tested monthly, disc 3 every three months, disc 4 every six months, disc 5 at the

end of each year and disc 6 at the end of two years. Disc 1 and 7 are dummy discs used

to ensure that the aerodynamic profile is maintained over discs 2 and 6.

NON SOLUBLE DEPOSIT DENSITY (NSDD)

This is basically a continuation of the ESDD tests whereby the non-soluble deposits (from the

measured ESDD solution) are filtered and weighed using standard filter paper. The dry filter

paper is weighed before and after the solution has been filtered through it in order to

determine the weight of the non-soluble residue left behind (NSDD)

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IEC TC36 – WG11 – 60815 Ed2 3rd -draft

April 2001

B.3 Necessary equipment to measure pollution degree (Suzuki)

The following equipment is necessary for measurement of both ESDD and NSDD.

•

•

•

•

•

•

•

•

•

•

Conductivity meter

Beaker/bottle

Measuring cylinder

Absorbent cotton/brush/sponge

Filter paper

Funnel

Desiccator

Balance

Distilled water/demineralized water

Gloves

Typical examples of measuring tools are shown in Table 1.

Portable tools such as a small bottle instead of a beaker are recommendable for in-situ

measurement in the field.

Table 1 Typical examples of measuring tools

Tools

Conductivity meter

Item

Measuring range

Accuracy of conductivity

Resolution of temperature

Balance

Measuring range

Resolution

±2%

0.1°

0g - 60g

0,001g

Specifications

1×10-4S/m - 2 S/m

B.4 Measuring ESDD (Suzuki)

B.4.1 Measuring procedure

For simple description, absorbent cotton, a beaker and distilled water are mentioned in the

following procedures. In practice, other tools such as a brush or a sponge, demineralized

water and a bottle can be used instead of absorbent cotton, distilled water and a beaker,

respectively.

a) A beaker, a measuring cylinder, etc. shall be washed well enough to remove electrolyte

prior to the measurement. Gloved hands also shall be washed clean.

b) Distilled water of 100-300 cm3 or more shall be put into a beaker and absorbent cotton

shall be immersed into water. The conductivity of water with the immersed cotton shall be

less than 0.001 S/m.

c) The pollutants shall be wiped off separately from the top and the bottom surfaces of a cap

and pin type insulator with the squeezed cotton. In the case of a long-rod or a post

insulator, pollutants shall usually be collected from a part of the shed as shown in Fig.1.

d) The cotton with pollutants shall be put back into the beaker as shown in Fig. 1. The

pollutants shall be dissolved into the water by shaking and squeezing the cotton in the

water.

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IEC TC36 – WG11 – 60815 Ed2 3rd -draft April 2001

e) Wiping shall be repeated until no further pollutants remain on the insulator surface. If

pollutants remain even after several wipings, pollutants shall be removed by a spatula,

and be put into the water containing pollutants.

f) Attention shall be taken not to lose the water. That is, the quantity shall not be changed

very much before and after collecting pollutants.

g) The conductivity of the water containing the pollutants shall be measured with a

conductivity meter; at the same time the temperature of the water shall be measured. The

measurements are made after enough stirring of the water. A short stirring time, e.g., a

few minutes, is required for the high solubility pollutants. The low solubility pollutants

generally require alonger stirring time, e.g., 30-40 minutes.

NOTES: -

1) Careful attention should be paid to the specimen insulators, not touching the insulator surface until

measurement starts.

2) For a close ESDD measurement in the range of 0.001 mg/cm2, it is recommended to use very low conductivity

water, e.g., less than a few 10-4

S/m. Normal distilled/demineralized water less than 0.001 S/m also can be used for

this purpose by subtracting the equivalent salt amount of the water itself from the measured equivalent salt amount

of the water containing pollutants.

3) Quantity of the distilled/demineralized water depends on kind and amount of pollutants. Large quantity of water

is recommended for measurements of very heavy pollution or low solubility pollutants. In practice, 2-10 litres of

water per m2 of the cleaned surface can be used. In order to avoid underestimating the amount of pollutants, the

quantity of the water would be so increased to have the conductivity less than around 0.2 S/m. If very high

conductivity is measured, there might be some doubt of remaining pollutants not dissolved due to small amount of

water.

4) Stirring time before conductivity measurement depends on kind of pollutants. For low solubility pollutants,

conductivity is measured at some interval with time up to about 30-40 minutes and is determined when the

measured values level off. To dissolve pollutants quickly, special methods such as boiling method and ultrasonic

method can also be used.

Fig. A1 Wiping of pollutants on insulator surface

B.4.2 Calculation of ESDD

The conductivity and the temperature of the water containing the pollutants shall be

measured.

The conductivity correction shall be made using the formula (1). This calculation is based on

Clause 16.2 and Clause 7 of IEC Standard 60507.

σ20 = σθ[1- b (θ-20)] ----------------------------------------------(1)

where:

θis the solution temperature (°C).

σθ is the volume conductivity at temperature of θ°C (S/m).

σ20 is the volume conductivity at temperature of 20°C (S/m).

b is the factor depending on the temperature θ, as obtained by the formula (2), and as

shown in Fig. 2.

b = -3.200×10-8 θ3 + 1.032×10-5 θ2 -8.272×10-4 θ+ 3.544×10-2 --(2)

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IEC TC36 – WG11 – 60815 Ed2 3rd -draft April 2001

b

(Factor

depending

on

temperature

θ)0,0350,030,0250,020,

Fig.A2 – Value of b

θ (solution temperature), °C

The ESDD on the insulator surface shall be calculated by the formulas (3) and (4). This

calculation is based on Clause 16.2 of IEC Standard 60507. Relation between σ20 and Sa

(Salinity, kg/m3) is shown in Fig.3.

Sa = (5.7σ20)1.03-----------------------------------------------------------(3)

ESDD = Sa × V / A----------------------------------------------------------(4)

where:

σ20 is the volume conductivity at temperature of 20°C (S/m).

ESDD is Equivalent salt deposit density (mg/cm2).

V is the volume of distilled water (cm3).

A is the area of the insulator surface for collecting pollutants (cm2).

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IEC TC36 – WG11 – 60815 Ed2 3rd -draft April 2001

10,1Sa,

kg/m30,010,0010,0010,01σ20, S/m0,1

Fig.A3 Relation betweenσ20 and Sa

B.5 Measuring NSDD

The water containing pollutants after measuring ESDD shall be filtered out by funnel and filter

paper.

The filter paper containing pollutants shall be dried, and then be weighed together with

residuum of pollutants as shown in Fig.4.

The NSDD shall be calculated by the formula (5).

NSDD =1000(Wf-Wi)/A------------------------------------------------------(5)

where:

NSDD is non-soluble material deposit density (mg/cm2).

Wf is the weight of the filter paper containing pollutants under dry condition (g).

Wi is the initial weight of the filter paper under dry condition (g).

A is the area of the insulator surface for collecting pollutants (cm2).

Fig. A4 - Procedure of measuring NSDD

Note: A quantitative chemical analysis can be made on pollutant solution and residuum after the measurement to

identify chemical components of the pollutants. The analysis results can be useful for close examination of

pollution conditions.

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IEC TC36 – WG11 – 60815 Ed2 3rd -draft April 2001

Annex C - Informative References

1

2

3

CIGRE Taskforce 33.13.01 - Polluted insulators: A review of current knowledge, CIGRE

brochure N° 158-2000

CIGRE Taskforce 33.13.01 - Polluted insulators: Application guidelines, CIGRE brochure

N° ???-2000

CIGRE Taskforce 33.13.07 - Influence of snow and ice…Electra April 2000

Annex D - Example of a questionnaire to collect information on the

behaviour of insulators in polluted areas

The existing questionnaire of IEC 60815 will be included here, possibly with some minor

revision/modification.

Annex E - Site severity measurement protocol

The relevant part of CIGRE 33.13 TF03 site severity measurement protocol (33-93_TF04-03_5IWD) will be inserted here, this will include recommendations for meteorological data.

____________

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