IEC TS 61245:2015

IEC TS 61245 ®
Edition 2.0 2015-03
TECHNICAL
SPECIFICATION
Artificial pollution tests on high-voltage ceramic and glass insulators to be used
on d.c. systems
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IEC TS 61245 ®
Edition 2.0 2015-03
TECHNICAL
SPECIFICATION
Artificial pollution tests on high-voltage ceramic and glass insulators to be used

on d.c. systems
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.080.10 ISBN 978-2-8322-2546-2

– 2 – IEC TS 61245:2015 © IEC 2015
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 8
2 Normative references. 8
3 Terms and definitions . 8
4 General test requirements . 11
4.1 General . 11
4.2 Test methods . 12
4.3 Arrangement of insulator for test . 12
4.3.1 Test configuration . 12
4.3.2 Insulator cleaning . 12
4.4 Requirements for the test circuit . 13
4.4.1 Test voltage . 13
4.4.2 Atmospheric corrections . 13
4.4.3 Characteristics of the measuring systems . 13
4.4.4 Identification of flashover . 13
5 Salt fog method . 14
5.1 General information . 14
5.2 Salt solution . 14
5.3 Spraying system . 16
5.4 Conditions before starting the test . 19
5.5 Preconditioning process . 19
5.6 Withstand test . 20
5.7 Acceptance criteria for the withstand test . 20
6 Solid layer method . 20
6.1 General information . 20
6.2 Main characteristics of inert materials . 21
6.3 Composition of the contaminating suspension . 21
6.4 Application of the pollution layer . 22
6.5 Determination of the degree of pollution of the test insulator . 23
6.6 Test procedure . 23
6.7 Withstand test and acceptance criteria . 24
Annex A (informative) Method for checking the uniformity of the layer . 25
Annex B (informative) Determination of the withstand characteristics of insulators . 27
B.1 General . 27
B.2 Determination of the maximum withstand degree of pollution at a given test
voltage . 27
B.3 Determination of the maximum withstand voltage at a given degree of
pollution . 27
B.4 Determination of the 50 % withstand voltage at a given degree of pollution . 28
Annex C (informative) Additional recommendations concerning the solid layer method
procedures . 29
C.1 General . 29
C.2 Contamination practice . 29
C.3 Drying of the pollution layer . 29
C.4 Checking the wetting action of the fog . 29

C.5 Checking fog uniformity for large or complex test objects . 30
C.6 Fog input to the test chamber . 30
C.7 Duration of the withstand test . 31
C.8 Evaluation of the reference salt deposit density (SDD) . 31
Annex D (informative) Information to check equipment for artificial pollution tests . 32
Annex E (informative) Supplementary information on artificial pollution tests on
insulators for voltage systems of ± 600 kV and above (solid layer method procedure B) . 34
E.1 General . 34
E.2 Test chamber . 34
E.3 Fog generator . 34
E.4 Wetting action and uniformity of fog density . 34
E.5 Test of very large insulators . 34
Annex F (informative) Further investigation . 35
Bibliography . 36

Figure 1 – Ripple amplitude and actual mean voltage, measured on a resistive load
absorbing 100 mA . 9
Figure 2 – Voltage drop and voltage overshoot and leakage current . 14
Figure 3 – Value of factor b versus solution temperature θ . 16
Figure 4 – Typical construction of fog spray nozzle . 18
Figure 5 – Test layout for inclined insulators . 19
Figure A.1 – Arrangement of the probe electrodes . 25
Figure A.2 – Circuit diagram of the meter . 26
Figure C.1 – Determination of layer conductance and evaluation of its rise time T = t
c 2
– t . 31
Table 1 – Salt-fog method: correspondence between the value of salinity and volume
conductivity of the solution at a temperature of 20 °C . 15
Table 2 – Main characteristics of the inert materials used in solid layer suspensions . 21
Table 3 – Kaolin (or Tonoko) composition: approximate correspondence between the
reference degrees of pollution on the insulator and the volume conductivity of the
suspension at a temperature of 20 °C . 22
Table D.1 – (Provisional) . 33

– 4 – IEC TS 61245:2015 © IEC 2015
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ARTIFICIAL POLLUTION TESTS ON HIGH-VOLTAGE CERAMIC
AND GLASS INSULATORS TO BE USED ON D.C. SYSTEMS

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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8) Attention is drawn to the normative references cited in this publication. Use of the referenced publications is
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9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
The main task of IEC technical committees is to prepare International Standards. In
exceptional circumstances, a technical committee may propose the publication of a technical
specification when
• the required support cannot be obtained for the publication of an International Standard,
despite repeated efforts, or
• the subject is still under technical development or where, for any other reason, there is the
future but no immediate possibility of an agreement on an International Standard.
Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
IEC TS 61245, which is a technical specification, has been prepared by IEC technical
committee 36: Insulators.
This second edition cancels and replaces the first edition published in 1993. This edition
constitutes a technical revision.

This edition includes the following significant technical changes with respect to the previous
edition:
a) Corrections and the addition of explanatory material;
b) The addition of Clause 4.4.2 on atmospheric correction;
c) The change of upper limit of volume conductivity of tap water for insulator cleaning to
0,1 S/m;
d) The extension to UHV voltages; and
e) The addition of Annex B "Determination of the withstand characteristics of insulators" and
Annex E "Supplementary information on artificial pollution tests on insulators for voltage
systems of  600 kV and above (solid layer method procedure B)
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
36/352/DTS 36/359/RVC
Full information on the voting for the approval of this technical specification can be found in
the report on voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC website under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• transformed into an International standard,
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.
The contents of the corrigendum of August 2018 have been included in this copy.

– 6 – IEC TS 61245:2015 © IEC 2015
INTRODUCTION
The electrical strength of d.c. insulation under pollution conditions determines, in many cases,
the dimensions and the design of the insulation.
The d.c. test procedures as specified in this technical specification follow closely the ones
established for a.c. by IEC 60507. This does not exclude the possibility that at a later time
other d.c. test procedures will be defined.
The main differences between this technical specification and IEC 60507 are:
– test circuit requirements include ripple factor, voltage drop and voltage overshoot. No
requirements are made for the minimum short circuit current or ratio between short circuit
and leakage currents;
– different criteria for the identification of flashover are given;
– for the salt fog test, a pre-conditioning process with d.c. voltage may be used by
agreement;
– the wetting rate, rather than the steam injection rate, is prescribed; the measurement of
the layer conductance is used to check the wetting action of the fog;
– as regards the solid layer methods, only the test procedure type "B" is considered due to
the high scatter of the results obtained with tests carried out according to the type "A"
procedure.
The tests are deemed to be not a suitable measure to prove the insulation performance of
polymeric or special types of insulators (e.g. insulators with semiconducting glaze or covered
with any organic insulating material) under polluted conditions. The test procedures given in
this standard do not take account of the different properties of insulators such as surface
hydrophobicity and hydrophobicity transfer through the pollution layer etc. These questions
are under consideration by CIGRE SC D1.
For the test methods described in this technical specification, it is recommended that the
voltage for the withstand voltage tests be specified as the highest value of operating voltage
which occurs under normal operating conditions. Other test voltages may be agreed upon. If
not otherwise specified and agreed between the parties, voltage of the negative polarity will
be applied.
Only those test methods in which the voltage is held constant during the whole test are
considered suitable for standardization. Variants in which the voltage is raised continuously to
flashover are not included in this technical specification.
The leakage current may be used for interpretation of the test results, and therefore it is
recommended that this current be continuously measured during the artificial pollution tests.
To achieve repeatable results, the artificial layer for d.c. pollution tests should be as uniform
as possible, since non-uniformity can influence d.c. withstand and flashover voltages.
The amount of non-soluble material on the insulator surface may affect the test results.
Although this matter is under consideration and no requirements can be given, the definition
of non-soluble deposit density has been introduced into this technical specification for
reference.
The type and quantity of non-soluble material, the steam rate and the preconditioning
procedure with salt fog (either by a.c. or d.c. voltage) may affect the test results.

The standard results are intended as results obtained in laboratories close to sea level
(altitude ≤ 1 000 m). Test results obtained at higher altitude or in test chambers with non-
standard air densities are to be corrected for air density.

– 8 – IEC TS 61245:2015 © IEC 2015
ARTIFICIAL POLLUTION TESTS ON HIGH-VOLTAGE CERAMIC
AND GLASS INSULATORS TO BE USED ON D.C. SYSTEMS

1 Scope
This technical specification is applicable for the determination of the d.c. withstand
characteristics of ceramic and glass insulators to be used outdoors and exposed to polluted

atmospheres, on d.c. systems with the highest voltage of the system greater than ± 1 000 V.
These tests are not applicable to polymeric insulators, to greased insulators or to special
types of insulators (e.g. insulators with semiconducting glaze or covered with any organic
insulating material).
The object of this technical specification is to prescribe procedures for artificial pollution tests
applicable to insulators for overhead lines, substations and traction lines and to bushings.
It may also be applied to hollow insulators with suitable precautions to avoid internal
flashover. In applying these procedures to apparatus incorporating hollow insulators, the
relevant technical committees should consider their effect on any internal equipment and the
special precautions which may be necessary.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC TS 60815-1, Selection and dimensioning of high-voltage insulators intended for use in
polluted conditions – Part 1: Definitions, information and general principles
IEC 60060-1, High-voltage test techniques – Part 1: General definitions and test requirements
IEC 60060-2, High-voltage test techniques – Part 2: Measuring systems
3 Terms and definitions
For the purpose of this technical specification, the following terms and definitions apply.
3.1
individual test
one single process consisting in applying to the object a specified test voltage, for a specified
time or until flashover occurs, at a specified degree of pollution
3.2
actual mean voltage
U
a
mean value of the voltage at a given instant over a time interval ending at the instant
considered and having a duration equal to that of one cycle of the alternating voltage
supplying the rectifier
Note 1 to entry: When it is not possible to determine the cycle of the supply voltage, the time interval is 20 ms.

3.3
test voltage
U
t
actual mean voltage at the beginning of an individual test
3.4
ripple
periodic deviation from the arithmetic mean value of the test voltage
3.5
ripple amplitude
U
r
half the difference between maximum and minimum values
3.6
ripple factor
ratio of the ripple amplitude to the actual mean voltage
See: U /U in Figure 1
r a
U = M/2
r
U /U (Ripple factor)
r a
Time
IEC
Figure 1 – Ripple amplitude and actual mean voltage, measured on
a resistive load absorbing 100 mA
3.7
voltage drop
∆u
t
difference between the test voltage and the actual mean voltage
See: Figure 2
3.8
relative voltage drop
ratio of the voltage drop ∆u to the test voltage (U ) usually expressed as a percentage
t t
U
a
(Actual mean voltage at a load
current of 100 mA)
M
(Ripple
amplitude
– 10 – IEC TS 61245:2015 © IEC 2015
3.9
voltage overshoot
difference between the actual mean voltage and the test voltage
See: Figure 2
3.10
relative voltage overshoot
ratio of the voltage overshoot to the test voltage U , usually expressed as a percentage
t
3.11
leakage current
current measured in series with the insulator surface at its earth end during a pollution test
3.12
short circuit current
current delivered by the complete testing circuit, when the test object is energized at the test
voltage and then short- circuited
3.13
salinity
S
a
concentration of the solution of salt in tap water, expressed by the amount of salt divided by
the volume of solution
Note 1 to entry: This is generally expressed in kg/m .
3.14
pollution layer
conducting electrolytic layer on the insulator surface, composed of salt plus non-soluble
materials
3.15
layer conductance
G
L
ratio current/voltage measured as specified in Annex C.3
3.16
salt deposit density
SDD
amount of salt in the deposit on a given surface of the insulator (metal parts and assembling
materials are not to be included in this surface), divided by the area of this surface
Note 1 to entry: See 6.5.
Note 2 to entry: This is generally expressed in mg/cm .
3.17
non-soluble deposit density
NSDD
amount of non-soluble material in the deposit on a given surface of the insulator (metal parts
and assembling materials are not to be included in this surface), divided by the area of this
surface
Note 1 to entry: This is generally expressed in mg/cm .
3.18
degree of pollution
value of the quantity (salinity, salt deposit density) which characterizes the artificial pollution
applied to the test insulator
3.19
reference salinity
value of the salinity used to characterize an individual test
3.20
reference salt deposit density
value of the salt deposit density used to characterize an individual test
Note 1 to entry: This is defined as the average of the salt deposit density values measured on a few insulators (or
on parts of them), which are chosen for this purpose from among the contaminated ones prior to their submission
to any test.
3.21
specified withstand degree of pollution
reference degree of pollution at which an insulator shall withstand the specified test voltage in
at least three individual tests out of four, under the conditions described in the relevant
Subclauses 5.6 or 6.7
3.22
maximum withstand degree of pollution
highest degree of pollution at which an insulator has withstood at least three individual tests
out of four at the specified test voltage, under the conditions described in Clause B.1
3.23
maximum withstand voltage
highest test voltage at which an insulator has withstood at least three individual withstand
tests out of four at the specified degree of pollution, under the conditions described in Clause
B.2
3.24
50 % withstand voltage
test voltage at which an insulator has 50 % probability to withstand one individual test
Note 1 to entry: See Clause B.3.
4 General test requirements
4.1 General
Pollution tests can be carried out for two main objectives:
– to obtain information about the pollution performance of insulators e.g. for comparison of
different insulator types/profile;
– to check the performance in a configuration as close as possible to the in-service
conditions.
To reach the first objective, tests on relatively short insulator sets (e.g. arcing distance
≥ 1,5 m – if representative of the full set in terms of radial geometry and profile) may be
sufficient.
Tests to reach the second objective may be agreed between the manufacturer and the user
whenever optimisation of the design is necessary and/or whenever it is expected that the
mounting condition or the inner active parts in apparatus can affect the performance. Such
tests shall be made simulating the relevant service conditions as closely as possible. In
particular tests in other positions from the vertical (inclined, horizontal) duplicating actual
service conditions may be agreed between the supplier and the user.
Tests at higher system voltages (of ± 600 kV and above) may present particular requirements
as reported in Annex E.
– 12 – IEC TS 61245:2015 © IEC 2015
4.2 Test methods
The two following pollution test methods are recommended for standard tests:
– the salt fog method (Clause 5) in which the insulator is subjected to a defined ambient
pollution;
– the solid layer method (Clause 6) in which a fairly uniform layer of a defined solid pollution
is deposited on the insulator surface.
In these test methods the voltage is held constant for a period of at least several minutes.
Variants in which the voltage is raised continuously to flashover are not standardized but may
be used for special purposes.
NOTE In testing of full scale insulators for system voltages of higher than ± 600 kV experiences with salt-fog
method are not available yet. The application of solid layer method is therefore preferred. More information on the
solid layer method for such insulators are given in Annex E.
4.3 Arrangement of insulator for test
4.3.1 Test configuration
The vertical position is in general suggested for comparison of different insulator types. Tests
in other positions (inclined, horizontal) reproducing actual service conditions may be carried
out when agreed between the manufacturer and the purchaser. When there are special
reasons not to test insulators in the vertical position (e.g. wall bushings and circuit-breaker
longitudinal insulation), only the service position shall be considered.
The minimum clearances between any part of the insulator and any earthed object other than
the structure which supports the insulator and the columns of the nozzles, when used, shall
be not less than 0,5 m per 100 kV of the test voltage and, in any case, not less than 1,5 m.
The configuration of the supporting structure and the energized metal parts, at least within
the minimum clearance from the insulator, shall reproduce those expected in service.
As regards their influence on the test results, the available experience indicates that:
– external components, e.g. fittings, do not significantly affect the results;
– the internal components may affect the withstand value namely with low pollution severity.
4.3.2 Insulator cleaning
The insulator shall be carefully cleaned so that all traces of dirt and grease are removed. After
cleaning, the insulating parts of the insulator shall not be touched by unprotected hand.
The surface of the insulator is deemed to be sufficiently clean and free from any grease if
large continuous wet areas are observed after rinsing.
In the case of the solid-layer method, before the first contamination, scrubbing with a slurry of
water and inert material such as kaolin shall be done, after which the insulator shall be
thoroughly rinsed with tap water. A detergent may be added to the slurry.
Before every subsequent contamination, the insulator shall again be thoroughly washed with
tap water only. Hand wiping might be necessary, if either the SDD-levels or the test results
become inconsistent.
In the case of the salt-fog method, water, preferably heated to about 50 °C, with the addition
of trisodium phosphate or other detergent, shall be used, after which the insulator shall be
thoroughly rinsed with tap water. Before this final treatment, scrubbing as for the solid-layer
method may be done if necessary.

When the volume conductivity of tap water is higher than 0,1 S/m, demineralized water shall
be used.
NOTE If necessary, the metal parts and the assembling materials can be painted with a salt-water resistant paint
to ensure that no corrosion products wash down on to the insulating surface during a test.
4.4 Requirements for the test circuit
4.4.1 Test voltage
Throughout the test, the insulator shall be continuously energized at the specified test voltage
and polarity.
The ripple factor of the test voltage demonstrated in a suitable way shall be ≤ 3 % for a
current of 100 mA with a resistive load (Figure 1).
The relative voltage drop (Figure 2) occurring during individual tests resulting in withstand
shall not exceed 10 %.
The relative voltage overshoot (Figure 2), usually due to load- release caused by extinction of
electrical discharges on the insulator surface, shall not exceed 10 %.
If a flashover occurs during the time when a relative voltage overshoot is between 5 %
and 10 %, the test is not valid.
The voltage measurement shall be carried out by voltage divider according to IEC 60060-2
suitable to measure continuous voltage and transients with required accuracy.
4.4.2 Atmospheric corrections
No humidity correction factor shall be applied. Test voltages shall be corrected for air density
according to IEC 60060-1. The coefficient m is however still under investigation.
NOTE 1 The temperature in test chamber for relative air density calculation is temperature measured at the height
of the test object before the test.
NOTE 2 The coefficient m depends on many factors such as pollution severity and insulator characteristics. For
the time being provisionally reference can be made to value m = 0,35 [1] .
NOTE 3 Atmospheric correction factors for polluted insulators are presently under consideration by CIGRE
SC D1.
4.4.3 Characteristics of the measuring systems
The systems used for measuring voltage and leakage current shall have an upper limiting
frequency of at least 1 kHz.
4.4.4 Identification of flashover
The complete bridging of the insulator under test by the short-circuit arc in the case of
apparent flashover shall be demonstrated. One of the following criteria is sufficient:
– the voltage recording clearly indicates a breakdown to arc-voltage;
– the current measurements indicate the short-circuit of the complete circuit by an arc;
– the peak value of the current of the test circuit, measured in the microsecond range with a
shunt resistor of suitable response, is higher than 0,5 U /R ;
t s
___________
Numbers in square brackets refer to the bibliography.

– 14 – IEC TS 61245:2015 © IEC 2015
– photographic or video recordings with sufficient resolution clearly show the complete
short-circuit arc.
(A)
Voltage overshoot
∆U (voltage drop)
t
One cycle of the supply a.c. voltage
Leakage current
Time
IEC
Figure 2 – Voltage drop and voltage overshoot and leakage current
5 Salt fog method
5.1 General information
The salt fog test procedure simulates type B pollution (see IEC TS 60815-1) where a liquid
conductive layer covers the insulator surface. In practice, this layer does not contain any
significant insoluble material.
The degree of pollution in a test is defined by the salinity of the salt fog expressed in kg of
salt (NaCl) per m of water.
The test consists of two parts – preconditioning process (the aim of which is cleaning of the
tested insulator surface) and withstand test. The detailed description of both procedures is in
5.5 and 5.6.
The salt fog test is currently not recommended for tests of insulator configurations at system
voltages of higher than ± 600 kV. Further investigations are necessary to extend the
applicability of this method also to higher system voltages.
5.2 Salt solution
The salt solution shall be made of sodium chloride (NaCl) of commercial purity and tap water.
Tap water with high hardness, e.g. with a content of equivalent CaCO greater than 350 g/m ,
can cause limestone deposits on the insulator surface. In this case deionized water shall be
used for preparation of the salt solution.
U
t
(Test voltage)
U
a
(Actual mean voltage)
NOTE Hardness of tap water is measured in terms of content of equivalent CaCO in accordance with the
Condensed Chemical Dictionary, revised by Gessner G. Hawley: Encyclopaedia of Chemistry; Van Nostrand
Reinhold Company New York (USA), 1971.
The salinity to be used shall be one of the values: 2,5; 3,5; 5; 7; 10; 14; 20; 28; 40; 56; 80;
112; 160; 224 kg/m .
The maximum permissible tolerance in salinity is ± 5 % of the specified value. It is
recommended that the salinity be determined either by measuring the conductivity or by
measuring the density with a correction for temperature. Table 1 gives the correspondence
between the value of salinity, volume conductivity and density of the solution at a temperature
of 20 °C.
When the solution temperature is not at 20 °C, conductivity and density values shall be
corrected according to formulas (1) or (2).
Care shall be taken that the temperature of the salt solution is between 5 °C and 30 °C, since
no experiment is available to validate tests performed outside this range of solution
temperature.
Table 1 – Salt-fog method: correspondence between the value
of salinity and volume conductivity of the solution
at a temperature of 20 °C
Salinity Volume conductivity
Sa σ20
kg/m S/m
2,5 0,43
3,5 0,60
5 0,83
7 1,15
10 1,6
14 2,2
20 3,0
28 4,1
40 5,6
56 7,6
80 10
112 13
160 17
224 20
The conductivity correction shall be made using formula (1):
σ = σ [1 – b (θ – 20)] (1)
20 θ
where:
θ is the solution temperature (°C)
σ is the volume conductivity at a solution temperature of θ °C (S/m)
θ
σ is the volume conductivity at a solution temperature of 20 °C (S/m)
b is the factor depending on solution temperature θ, as obtained by the following
equation, and as shown in Figure 3:

– 16 – IEC TS 61245:2015 © IEC 2015
-8 3 -5 2 -4 -2
b = –3,200  10   1,032  10  – 8,272  10   3,544  10

Figure 3 – Value of factor b versus solution temperature 
The density correction shall be made using formula (2):
–6
20 =  [1  (200  1,3 Sa) ( – 20)  10 ] (2)
where:
 is the solution temperature (°C)
 is the density at a solution temperature of °C (kg/m )
20 is the density at a solution temperature of 20 °C (kg/m )
)
Sa is the salinity (kg/m
This correction formula is only valid for salinities over 20 kg/m .
5.3 Spraying system
The fog is produced in the test chamber by means of a specified number of fog spray nozzles
which atomize the solution by a stream of compressed air from the air nozzle blowing at right
angles to the solution nozzle. The nozzles consist of corrosion resistant tubes, the internal
diameter of the air nozzles being 1,2 mm  0,02 mm and the internal diameter of the solution
nozzles being 2,0 mm  0,02 mm. Both nozzles shall have an outside diameter of
3,0 mm  0,05 mm and the ends of the nozzles shall be square-cut and polished.
The end of the solution nozzle shall lie on the axis of the air nozzle to within 0,05 mm. The
distance between the end of the air nozzle and the central line of the solution nozzle shall be
3 mm  0,05 mm. The axes of the two nozzles shall lie in the same plane to within 0,05 mm.
Figure 4 shows a typical construction of the fog spray nozzle.
The fog spray nozzles shall be in two columns parallel to and on opposite sides of the
insulator which shall have its axis in the same plane as the columns, i.e. a vertical insulator
shall be tested with vertical columns and a horizontal insulator with horizontal columns. In the

case of an inclined insulator (see Figure 5) the plane containing the insulator and the columns
shall intersect the horizontal plane in a line at right angles to the insulator axis; in this case,
the axis of the solution nozzles is vertical. The distance between the solution nozzles and the
insulator axis shall be 3 m  0,05 m.
The fog spray nozzles shall be spaced at 0,6 m intervals, each air nozzle pointing at right
angles to the column axis towards its counterpart on the other column and within an angle of
1° to the plane of the fog spray nozzles. This alignment can be checked for fog spray nozzles
on vertical columns by lowering the solution nozzles, and passing water through the air
nozzles and directing it towards the opposing nozzles. Then the solution nozzles are raised to
the operating position. The mid-point of the insulator shall preferably be in line with the mid-
points of the columns of fog spray nozzles. Both columns shall extend beyond the insulator at
both ends by at least 0,6 m.
The minimum number N of fog spray nozzles per column shall be, for a length H in metres of
the insulator:
H
N  3
0,6
The air nozzles shall be supplied with filtered, oil-free air at a relative pressure of
(7,0  0,35)  10 Pa.
The flow of solution to each solution nozzle shall be (0,5  0,05) dm³/min for the period of the
test and the tolerance on the total flow to all sprays shall be 5 % of the nominal value.
13,2 0,05
A
(See note 3)
3 0,05
Compressed
air nozzle
Salt water
nozzle
Block
Mounting holes
(See note 5)
Tapped holes for
locking screws
Both nozzles to have
62 38
a close sliding
fit within block
(See note 4)
A
Section A-A showing nozzles in position
IEC
All dimensions in millimeters (except thread)

14,2 0,05
– 18 – IEC TS 61245:2015 © IEC 2015
Drill and tap ¼ NPT
Drill and tap ¼ NPT
28 10,2 14,2
Drill ∅1,2 thru Drill ∅2 thru
60° inclusive angle
60° inclusive angle
Compressed air nozzle Salt water nozzle

IEC
NOTES: HARDWARE REQUIREMENTS:
NOTE 1 Machine all over ± 0,1 mm unless stated 2 off stainless steel fittings with hose barb (Swagelok No.:
otherwise. SS-4-HC-1-4)
NOTE 2 Concentricity of nozzles within 0,1 mm. 2 off stainless steel set screws (as required).
NOTE 3 Outer face of both nozzles to be square and Rubber hose as required with retaining clamps.
polished.
NOTE 4 Finishing of nozzles in the block with a sized Corrosion-resistant mounting hardware (as required).
milling cutter is suggested to achieve the best fit.
NOTE 5 Remove all sharp edges except as Note 3. MATERIAL REQUIREMENTS:
NOTE 6 Mounting holes should be drilled through to allow Salt water nozzle – stainless steel Type 303
unit to be positioned from either side. Compressed air nozzle – stainless steel Type 303
NOTE 7 Unit should initially be assembled with nozzle Block – nonabsorbent plastic*
shoulders flush with inboard surfaces of block as shown
above. If required, small adjustments in the positioning of *POM (polyoxymethylene) is recommended for ease of
the nozzles can be made to optimize spray properties. machining and dimensional stability

Figure 4 – Typical construction of fog spr
...