HD 588.1 S1:1991

SLOVENSKI STANDARD
01-januar-1998
High-voltage test techniques - Part 1: General definitions and test requirements
(IEC 60060-1:1989 + corrigendum March 1990)
High-voltage test techniques -- Part 1: General definitions and test requirements
Hochspannungs-Prüftechnik -- Teil 1: Allgemeine Festlegungen und Prüfbedingungen
Techniques des essais à haute tension -- Partie 1: Définitions et prescriptions générales
relatives aux essais
Ta slovenski standard je istoveten z: HD 588.1 S1:1991
ICS:
19.080 (OHNWULþQRLQHOHNWURQVNR Electrical and electronic
SUHVNXãDQMH testing
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

IEC 60060-1
Edition 2.0 1989-11
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
High-voltage test techniques –
Part 1: General definitions and test requirements

Techniques des essais à haute tension –
Partie 1: Définitions et prescriptions générales relatives aux essais

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
XB
CODE PRIX
ICS 19.080
IEC Publication 60-1
Publication 60-1 de la CEI
(Second edition - 1989)
(Deuxieme edition - 1989)
High-voltage test techniques
Techniques des essais A haute tension
Part 1 : General definitions
Premiere partie: Definitions et prescriptions
and test requirements
generales relatives aux essais
CORRIGENDUM
Page 112
Figure I
Remplacer la figure existante par la nouvelle figure suivante:
Replace the existing figure by the following new figure:
U (kV) peak
Figure 1 - Distance minimale D des objets sous tension ou A la terre A I'6lectrode
sous tension d'un objet en essai, pendant un essai en tension alternative
ou en tension de choc de manoeuvres positive avec tension maximale U
appliquke pendant I'essai.
Minimum clearance D of extraneous live or grounded objects to the
energized electrode of a test object, during an a.c. or positive switching
impulse test at the maximum voltage U applied during test.
Mars 1992 March 1992
60-1 0 IEC 1989
CONTENTS
Page
FOREWORD . 13
PREFACE . 13
Clause
Section 1: General . 15
1 Scope . 15
2 Object . 15
.........................................
Section 2: General Definitions 17
3 Impulses . 17
3.1 Lightning and switching impulses . 17
Characteristics related to disruptive discharge and test voltages . 17
4.1 Disruptive discharge . 17
4.2 Characteristics of the test voltage . 19
4.3 Disruptive discharge voltage of a test object . 19
4.4 Statistical characteristics of disruptive discharge voltages . 19
4.5 Withstand voltage of a test object . 21
4.6 Assured disruptive discharge voltage of a test object . 21
Classification of insulation in test objects . 21
5.1 External insulation . 21
5.2 Internal insulation . 23
5.3 Self-restoring insulation . 23
5.4 Non-Self-restoring insulation . 23
Section 3: General Requirements Relating to Test Procedures
and Test Objects . 25
6 General requirements for test procedures . 25
7 General arrangement of the test object . 25
8 Drytests . 27
9 Wet tests . : . 27
9.1 Standard wet test procedure . 27
9.2 Traditional procedures for wet tests with alternating voltages . 31

60-1 0 IEC 1989 -5-
10 Artificial pollution tests . 31
10.1 Preparation of test object . 33
...........................................
10.2 Test procedures 33
10.3 Degree of pollution . 35
..........................................
11 Atmospheric conditions 37
11.1
Standard reference atmosphere . 37
11.2
Atmospheric correction factors . 37
11.3 Wet tests. tests under artificial pollution and combined tests . 39
11.4 Conflicting requirements for testing internal and external insulation . 41
.....................................
11.5 Measurement of humidity 41
Section 4: Tests with Direct Voltage . 43
12 Definitions for direct voltage tests . 43
12.1 Value of the test voltage . 43
12.2 Ripple . 43
Test voltage . 43
13.1 Requirements for the test voltage . 43
13.2 Generation of the test voltage . 43
.................................
13.3 Measurement of the test voltage 45
.................................
13.4 Measurement of the test current 47
14 Test procedures . 47
14.1 Withstand voltage tests . 47
14.2 Disruptive discharge voltage tests . 49
14.3
Assured disruptive discharge voltage tests . 49
Section 5: Tests with Alternating Voltage . 51
15 Definitions for alternating voltage tests . 51
15.1 Definitions for alternating voltage tests . 51
15.2 Peak value . 51
............................................
15.3 R.M.S. value 51
.................................................
16 Test Voltage 51
16.1 Requirements for the test voltage 51
................................
16.2 Generation of the test voltage . 53
16.3 Measurement of the test voltage . 55
17 Test procedures . 57
17.1 Withstand voltage tests . 57
17.2 Disruptive discharge voltage tests . 57
17.3 Assured disruptive discharge voltage tests 59
...........................
60-1 0 IEC 1989 -7-
...............................
Section 6: Tests with Lightning Impulse Voltage 61
18 Definitions for lightning impulse tests . 61
18.1 Definitions of general applicability . 61
.......................
18.2 Definitions applicable only to chopped impulses 63
........................................
18.3 Voltageltime curves 65
.................................................
19 Test Voltage 65
....................................
19.1 Standard lightning impulse 65
..............................................
19.2 Tolerances 65
...............................
19.3 Standard chopped lightning impulse 67
....................................
19.4 Special lightning impulses 67
..................................
19.5 Generation of the test voltage 67
19.6
Measurement of the test voltage and determination of impulse shape . 67
.................
19.7 Measurement of current during tests with impulse voltages 69
...............................................
20 Test Procedures 69
......................................
20.1 Withstand voltage tests 69
.........................
20.2 Procedures for assured discharge voltage tests 73
...................................
Section 7: Tests with Switching Impulses 75
21 Definitions for switching impulse tests . 75
.........................................
21.1 Switching impulse 75
21.2 Value . of the test voltage . 75
..........................................
21.3 Time to peak T, 75
.......................................
21.4 Time to half-value T2 75
21.5 Time above 90% T, . 75
...........................................
21.6 Time to zero To 75
........................................
2 1.7 Time to chopping T, 77
21.8 Linearly rising impulse . 77
.................................................
22 Test voltage 77
....................................
22.1 Standard switching impulse 77
22.2 Tolerances . 77
....................................
22.3 Special switching impulses 77
..................................
22.4 Generation of the test voltage 79
22.5 Measurement of test voltage and determination of impulse shape .
23 Test procedures . 79
.....................................
Section 8: Tests with Impulse Current
24 Definitions for impulse current tests . 81
24.1 Impulse current . 81
24.2 Value of the test current . 81
24.3 Front time T, . 81
24.4 Virtual origin 0, . 81
24.5 Time to half-value T2 . 81
24.6 Duration of peak of a rectangular impulse current T,
.................... 81
24.7 Total duration of a rectangular impulse current T. . 83

60-1 0 IEC 1989
25 Test current . 83
25.1 Standard impulse currents . 83
25.2 Tolerances . 83
25.3 Measurement of the test current . 85
25.4 Measurement of voltage during tests with impulse current . 85
Section 9: Combined and Composite Tests . 87
26 Combined voltage tests . 87
26.1 Value of the test voltage U . 87
............................................
26.2 Time delay At 87
26.3 Actual voltage shapes . 87
26.4 Arrangement of the test object . 89
26.5 Atmospheric correction factors . 89
27 Composite tests . 89
Appendix A: Statistical Treatment of Test Results . 91
A . 1 Classification of tests . 91
A.l.l Class 1: Multiple-level tests . 91
A.1.2 Class 2: Up-and-down tests . 91
A . 1.3 Class 3: Successive Discharge Tests . 91
A.2 Statistical Behaviour of Disruptive Discharge . 93
A.2.1 Confidence limits and statistical error
.............................. 93
A.3 Analysis of Test Results . 95
A.3.1 Treatment of Results from Class 1 Tests . 95
A.3.2 Treatment of Results from Class 2 Tests . 97
A.3.3 Treatment of Results from Class 3 Tests . 97
A.4 Application of likelihood methods . 99
A.4.1 The likelihood function . 99
A.4.2 Estim.ation of U,, and z . 101
Appendix B: Pollution Test Procedures . ; . 103
B.l Production of salt fog . 103
B.l.l Preparation of salt solution . 103
B.1.2 Details of spraying system . 103
B.2 Pre-deposition of pollution. coating and wetting procedure .
B.2.1 Preparation of coating material . 103
B.2.2 Main characteristics of the inert materials . 105
B.2.3 Solid coating and wetting procedure . 105
B.3 Measurement of the degree of pollution . 107
B.3.1 Surface conductivity of the insulating surface . 107

60-1 0 IEC 1989 . 11 .
B.3.2 Equivalent amount of sodium chloride per square centimetre of the insulating surface
(S.D.D. mglcm2) . 107
Appendix C: Calibration of a Non-Approved Measurement Device with a Rodmod Gap . 111
C.l General arrangement of a rodlrod gap .
C.2 Referencevalues . 111
...........................................
C.3 Calibration Procedure 111
......................................................
Figures 112
60-1 0 IEC 1989 - 13 -
INTERNATIONAL ELECTROTECHNICAL COMMISSION
HIGH VOLTAGE TEST TECHNIQUES
Part 1: General definitions and test requirements
FOREWORD
The formal decisions or agreements of the IEC on technical matters, prepared by Technical Committees on
1)
which all the National Committees having a special interest therein are represented, express, as nearly as
possible, an international consensus of opinion on the subjects examined.
They have the form of recommendations for international use and they are accepted by the National Committees
2)
in that sense.
In order to promote international unification, the IEC expresses the wish that all National Committees should
3)
adopt the text of the IEC recommendation for their national rules in so far as national conditions will permit.
Any divergence between the IEC recommendation and the corresponding national rules should. as far as
possible, be clearly indicated in the latter.
PREFACE
This standard has been prepared by IEC Technical Committee 42: High Voltage testing techniques .
The text of this standard is based upon the following documents:
Six Month's Rule Report on Voting
42(C0)40 42(C0)41
Full information on the voting for the approval of this standard can be found in the Voting Report indicated
in the above table.
60-1 0 IEC 1989
HIGH VOLTAGE TEST TECHNIQUES
PART 1:
GENERAL DEFINITIONS AND TEST REQUIREMENTS
Section 1: General
1 Scope
This standard is applicable to:
- dielectric tests with direct voltage;
- dielectric tests with alternating voltage;
- dielectric tests with impulse voltage;
- tests with impulse current;
- tests with combinations of the above.
This standard is applicable only to tests on equipment having its highest voltage for equipment U, above
1 kV.
This standard is not intended to be used for electromagnetic compatibility tests on electric or electronic
equipment.
2 Object
The object of this standard is:
- to define terms of both general and specific applicability;
- to present general requirements regarding test objects and test procedures;
- to describe methods for generation and measurement of test voltages and currents;
- to describe test procedures;
- to describe methods for the evaluation of test results and to indicate criteria for acceptance or
refusal.
Definitions and requirements concerning approved measuring devices and checking methods are given in
IEC Publication 60-3: High Voltage Test Techniques - Measuring Devices.
Alternative test procedures may be required to obtain reproducible and significant results. The choice of
a suitable test procedure should be made by the relevant Technical Committee.

- 17 -
60-1 0 IEC 1989
Section 2: General Definitions
3 Impulses
An impulse is an intentionally applied aperiodic transient voltage or current which usually rises rapidly
to a peak value and then falls more slowly to zero.
For special purposes, impulses having approximately linearly rising fronts or transients of oscillating or
approximately rectangular form are used.
The term "impulse" is to be distinguished from the term "surge" which refers to transients occurring in
electrical equipment or networks in service.
3.1 Lightning and switching impulses
A distinction is made between lightning and switching impulses on the basis of duration of the front.
Impulses with front duration up to 20 p are defined as lightning impulses and those with longer fronts
are defined as switching impulses.
Generally, switching impulses are also characterized by total durations considerably longer than those of
lightning impulses.
4 Characteristics related to disruptive discharge and test voltages
4.1 Disruptivedischarge
In this standard, the term "disruptive discharge" (sometimes referred to as "electrical breakdown") relates
to phenomena associated with the failure of insulation under electrical stress, in which the discharge
completely bridges the insulation under test, reducing the voltage between the electrodes practically to
zero. It applies to electrical breakdown in solid, liquid and gaseous dielectrics and combinations of these.
Non-sustained disruptive discharge in which the test object is momentarily bridged by a spark or arc may
occur. During these events the voltage across the test object is momentarily reduced to zero or to a very
small value. Depending on the characteristics of the test circuit and the test object, a recovery of dielectric
strength may occur and may even permit the test voltage to reach a higher value. Such an event should
be interpreted as a disruptive discharge unless otherwise specified by the relevant Technical Committee.
Non-disruptive discharges such as those between intermediate electrodes or conductors may also occur
without reduction of the test voltage to zero. Such an event should not be interpreted as a disruptive
discharge unless so specified by the relevant Technical Committee.
Some non-disruptive discharges are termed "partial discharges" and are dealt with in IEC Publication 270:
Partial Discharge Measurements.
The term "sparkover" is used when a disruptive discharge occurs in a gaseous or liquid medium.

60-1 0 IEC 1989
The term "flashover" is used when a disruptive discharge occurs over the surface of a dielecmc in a
gaseous or liquid medium.
The term "puncture" is used when a disruptive discharge occurs through a solid dielectric.
A disruptive discharge in a solid dielecmc produces permanent loss of dielecmc strength; in a liquid or
gaseous dielectric the loss may be only temporary.
4.2 Characteristics of the test voltage
The characteristics of a test voltage are those characteristics specified in this standard for designating the
different types of voltage excursion that define the test voltage.
4.2.1
Prospective characteristics of a test voltage
The prospective characteristics of a test voltage causing disruptive discharge are the characteristics which
would have been obtained if no disruptive discharge had occurred. When a prospective characteristic is
used, this shall always be stated.
4.2.2 Actual characteristics of a test voltage
The actual characteristics of a test voltage are those which occur during the test at the terminals of the
test object.
4.2.3 Value of the test voltage
The value of the test voltage is defined in the relevant Clauses of the present standard.
4.3 Disruptive discharge voltage of a test object
The disruptive discharge voltage of a test object is the value of the test voltage causing disruptive
discharge, as specified, for the various tests, in the relevant Clauses of the present standard.
4.4 Statistical characteristics of disruptive discharge voltages
Disruptive discharge voltages are subject to random variations and, usually, a number of observations must
be made in order to obtain a statistically significant value of the voltage. The test procedures, described
in the present standard, are generally based on statistical considerations. Information on the statistical
evaluation of test results is given in Appendix A.
4.4.1 Disruptive discharge probability p of a test object
The disruptive discharge probability p of a test object is the probability that one application of a certain
prospective voltage value of a given shape will cause disruptive discharge in the test object. The parameter
p may be expressed as a percentage or a fraction.

60-1 0 IEC 1989
4.4.2 Withstand probability q of a test object
The withstand probability q of a test object is the probability that one application of a certain prospective
voltage value of a given shape does not cause a disruptive discharge on the test object. If the disruptive
discharge probability is p, the withstand probability q is (1 -p).
4.4.3 50% disruptive discharge voltage U,, of a test object
The 50% disruptive discharge voltage is the prospective voltage value which has a 50% probability of
producing a disruptive discharge on the test object.
4.4.4 p% disruptive discharge voltage Up of a test object
The p% disruptive discharge voltage of a test object is the prospective voltage value which has p%
probability of producing a disruptive discharge on the test object.
4.4.5 Conventional deviation z of the disruptive discharge voltage of a test object
The conventional deviation z of the disruptive discharge voltage of a test object is the difference between
its 50% and 16% disruptive discharge voltages. It is often expressed in per unit or percentage value,
referred to the 50% disruptive discharge voltage.
NOTE - If the disruptive-discharge probability function (see Appendix A) is close to a Gaussian function, 2
is correspondingly close to its standard deviation.
4.5 Withstand voltage of a rest object
The withstand voltage of a test object is a specified prospective voltage value which characterizes the
insulation of the object with regard to a withstand test.
Unless otherwise specified, withstand voltages are referred to standard reference atmospheric conditions
(see Clause 11.1).
4.6 Assured disruptive discharge voltage of a test object
The assured disruptive discharge voltage of a test object is a specified prospective voltage value which
characterizes its performance with regard to a disruptive discharge test.
5 Classification of insulation in test objects
Insulation systems of apparatus and high voltage structures must basically be classified into self-restoring
and non-self-restoring insulation and may consist of external and/or internal insulation.
5.1 External insulation
External insulation is the air insulation and the exposed surfaces of solid insulation of the equipment,
which are subject both to dielectric stresses and to the effects of aunospheric and other external conditions
such as pollution, humidity and vermin.

60-1 0 IEC 1989
5.2 Internal insulation
Internal insulation comprises the internal solid, liquid or gaseous elements of the insulation of equipment,
which are protected from the effects of atmospheric and other external conditions such as pollution,
humidity and vermin.
5.3 Self-restoring insulation
Self-restoring insulation is the insulation which completely recovers its insulating properties after a
disruptive discharge caused by the application of a test voltage.
5.4 Non-self-restorin insulation
Non-self-restoring insulation is insulation which loses its insulating properties, or does not recover them
completely, after a disruptive discharge caused by the application of a test voltage.
NOTE - In high voltage apparatus, parts of both self-restoring and non-self-restoring insulation are always
operating in combination and some parts may be degraded by repeated or continued voltage applications. The
behaviour of the insulation in this respect shall be taken into account by the relevant Technical Committee when
specifying the test procedures to be applied.

Section 3: General Requirements Relating to Test Procedures
and Test Objects
6 General requirements for test procedures
The test procedures applicable to particular types of test objects, for example, the polarity to be used, the
preferred order if both polarities are to be used, the number of applications and the interval between
applications shall be specified by the relevant Technical Committee, having regard to such factors as:
- the required accuracy of test results;
- the random nature of the observed phenomenon and any polarity dependence of the measured
characteristics;
- the possibility of progressive deterioration with repeated voltage applications.
7 General arrangement of the test object
At the time of a test, the test object shall be complete in all essential details, and it should have been
processed in the normal manner for similar equipment.
The disruptive discharge characteristics of an object may he affected by its general arrangement (for
example, by its clearance from other live or grounded structures, its height above ground level and the
arrangement of its high voltage lead). The general arrangement should be specified by the relevant
Technical Committee.
A clearance to extraneous structures not less than 1.5 times the length of the shortest possible discharge
path on the test object usually makes such proximity effects negligible. In wet or pollution tests, or
wherever the voltage distribution along the test object and the electric field around its energized electrode
are sufficiently independent of external influences, smaller clearances may be acceptable, provided that
discharges do not occur to extraneous structures.
In the case of a.c. or positive switching impulse tests above 750 kV (peak) the influence of an extraneous
structure may be considered as negligible if its distance from the energized electrode is also not less than
the height of this electrode above the ground plane. A practical lower limit to this clearance is given in
figure 1, as a function of the highest test voltage.
A withstand test may be acceptable when successfully performed with shorter distances to earthed objects.

60-1 0 IEC 1989
8 Dry tests
The test object shall be dry and clean. If not otherwise specified by the relevant Technical Committee, the
test should be made at ambient temperature and the procedure for voltage application shall be as specified
in the relevant Clauses of this standard.
9 Wet tests
The preferred wet test procedure, described in 9.1, is intended to simulate the effect of natural rain on
external insulation and is a revision of earlier test methods. It is recommended for tests with all types of
test voltages and on all types of apparatus, but either of the alternative test methods given below are
permitted if specified by the relevant Technical Committee.
Two earlier test methods, not intended to simulate natural rain, are described in 9.2. They have been in
use for many years for tests with alternating voltages on apparatus having U, up to 420 kV and many test
data obtained by these methods exist.
For a.c. apparatus of large dimensions, such as those having U, higher than 800 kV, no appropriate wet
test procedure is available at present.
The relevant Technical Committee shall specify the arrangement of the test object during the test proce-
dure.
9.1 Standard wet test procedure
The test object shall be sprayed with water of prescribed resistivity and temperature (see table 1) falling
on it as droplets (avoiding fog and mist) and directed so that the vertical and horizontal components of
the spray intensity are approximately equal. These intensities are measured with a divided collecting vessel
having openings of 100 cm2 to 750 cm2, one. horizontal and one vertical, the vertical opening facing the
spray.
The position of the test object relative to the vertical and horizontal rain components shall be specified
by the relevant Technical Committee.
In general, the reproducibility of wet test results is less than that for other high voltage discharge or
withstand tests. To minimize the dispersion the following precautions shall be taken:
- The collecting vessel shall be placed close to the test object, but avoiding the collection of drops
or splashes from it. During the measuring period, it should be moved slowly over a sufficient
area to average but not completely mask the effect of non-uniformities of the spray from
individual nozzles. This measuring zone shall have a width equal to that of the test object and
a maximum height of 1 m.
- For test objects between 1 m and 3 m in height, the individual measurements shall be made at
the top, centre and bottom of the test object. Each measuring zone shall cover only one third of
the height of the test object.

60-1 0 IEC 1989 - 29 -
- For test objects exceeding 3 m in height, the number of measuring zones shall be increased to
cover the full height of the test object without overlapping.
- The above procedures shall be suitably adapted for test objects having large horizontal dimen-
sions.
- The spread of results may be reduced if the test object is cleaned with a surface-active detergent
which has to be removed before the beginning of wetting.
- The spread of results may also be affected by local anomalous (high or low) precipitation rates.
It is recommended to detect these by localized measurements and to improve the uniformity of
the spray, if necessary.
The spray apparatus shall be adjusted to produce, within the specified tolerances, precipitation conditions
at the test object given in table 1.
Any type and arrangement of nozzles meeting the requirements given in table 1 may be used. Examples
of several nozzles which have been found satisfactory in practice are shown in figures 2a, 2b and 2c,
together with typical performance data for each type. Greater spray distances may be obtained if the
nozzles are directed upward at an angle of about 15'-25' to the horizontal. Note that if the water pressure
is increased above the recommended limits, the water jets may break up prematurely and cause an
unsatisfactory spray at the test object.
Table 1 - Precipitation conditions for standard procedure
Average precipitation rate of all measurements
- vertical component mmlmin 1.0 to 2.0
- horizontal component mmlmin 1,O to 2,O
Limits for any individual measurement
and for each component mm/min kO.5 hm average
Temperature of water 'C Ambient temperature + 15
Resistivity of water Rm 100k 15
The water temperature and resistivity shall be measured on a sample collected immediately before the
water reaches the test object. They may also be measured at other locations (e.g., in a storage reservoir)
provided that a check ensures that no significant change occurs by the time the water reaches the test
object.
The test object shall be pre-wetted initially for at least 15 min under the above specified conditions and
these conditions shall remain within the specified tolerances throughout the test which should be performed
without interrupting the wetting. The pre-wetting time shall not include the time needed for adjusting the
spray. It is also possible to perform an initial pre-wetting by unconditioned mains water for 15 min,
followed without interruption of the spray by a second pre-wetting for at least 2 min before the test begins,

using water with all the correct precipitation conditions, which should be measured immediately before
starting the test.
Unless otherwise specified by the relevant Technical Committee, the test procedure for wet tests shall be
the same as that specified for the corresponding dry tests. The test duration for an a.c. test shall be 60 s.
if not otherwise specified. In general, for alternating and direct voltage wet withstand tests, it is recom-
mended that one flashover should be permitted provided that in a repeat test no further flashover occurs.
9.2 Traditional procedures for wet tests with alternating voltages
For alternating voltage tests, two other procedures are also in use, details of which are given in table 2.
They differ from the standard procedure, 9.1, primarily in that the precipitation rates are higher and that
the minimum pre-wetting time is only 1 m.
Only the vertical component of the spray is specified; determination of the horizontal component is
replaced by a visual estimate of the spray angle which should be approximately 45' at the test object.
Table 2 - Precipitation conditions for traditional procedures with alternating voltages
Characteristics
Empean Practice
practice in U.S.A.
Average precipitation rate of all measurements:
- vertical component m-in 3 f 0,3 5 f 0.5
Limits for any individual measurement mdmin 3 f 0.75 5f 125
Water temperature 'C Ambient temperature f15
Water resistivity Rm 100f 10 178 + 27
Type of nozzle as shown in figures
2a2b 2~ figure 2d
Duration of wet withstand test s 60 10
10 Artificial pollution tests
. .
Artificial pollution tests are intended to provide information on the behaviour of external insulation under
conditions representative of pollution in service, although they do not necessarily simulate any particular
service conditions.
60-1 0 IEC 1989 - 33 -
The following specifications give some general guidance on artificial pollution testing. It is left to the
relevant Technical Committee to introduce variations or to give more specific requirements for particular
classes of apparatus. Such specific information is given in one instance by IEC 507.
The effects of washing of insulators in service by natural rain is not taken into consideration in any of the
specified procedures.
10.1 Preparalion of test object
Before testing for the first time, the metal parts of the test object, and any cement joints, may be painted
with salt-water-resistant paint to ensure that corrosion products will not contaminate the insulating surfaces
during a test.
The test object should then be carefully cleaned by washing with tap water to which uisodium phosphate
(Na,PO,) has been added and rinsed with clean tap water. It shall not subsequently be touched by hand.
Usually the insulating surfaces can be considered sufficiently clean and free of grease or other contarni-
nating material if large continuous wet areas are observed during wetting.
It is left to he relevant Technical Committee to decide whether the test object should be tested in a vertical,
horizontal or an inclined position.
10.2 Test procedures
Artificial pollution tests involve application of the pollution and the simultaneous or subsequent applica-
tion of voltage. Generally, only methods in which the test voltage is held constant for at least several
minutes are recommended. Other methods in which the voltage is raised gradually to flashover are not
proposed for standardization but may be used for special purposes.
The pollution test may be made either to determine the maximum degree of pollution of the test object
which allows a given test voltage to be withstood, or to determine the withstand voltage for a specified
degree of pollution. For the purpose of comparing the results of several tests, or the performance of several
test objects, the former procedure is preferable. Whichever test procedure is adopted, the number of
measurements should be sufficient to obtain consistent average values, taking into account the statistical
nature of the phenomenon. The number of tests required shall be specified by the relevant Technical
Committee.
The pollution tests fall into two categories, the salt-fog method and the pre-deposited pollution method.
a) The salt-fog method
The test object is placed in a special chamber which can be filled by a salt fog. The method for producing
the fog is described in Appendix B1. The ambient temperature in the chamber at the start of the test shall
not be less than S'C, nor greater than 30'C and the test object and the salt water shall be in thermal
equilibrium with the ambient temperature.
The test object is thoroughly wetted with clean tap water. The salt-fog system, supplied by water of the
prescribed salinity, is started when the test object is still wet and, simultaneously, the voltage is applied
to the test object, raised rapidly to the specified value and kept constant during the specified time, usually

1 h, or until flashover occurs. This procedure is repeated several times. Before each procedure the test
object is thoroughly washed with clean tap water to remove any trace of salt.
For the salt-fog method, the minimum distance between any part of the test object and any earthed object
other than the jets and the structure which supports the insulator shall be not less than 0,5 m per 100 kV
of the test voltage and, in any case, not less than 2 m.
If the test is intended to determine the maximum degree of salinity for a specified withstand voltage, the
whole procedure must be repeated using various salinities.
Pre-conditioning of the test object by a number of flashovers during the application of pollution is required
before the real test begins. This pre-conditioning should be followed by a washing.
b) The pre-deposited pollution method
The test object is coated with a reasonably uniform layer of a conductive suspension and shall be permitted
to dry. The ambient temperature in the test chamber at the start of the test should not be less than 5'C nor
greater than 30'C and the test object should be in thermal equilibrium with the ambient. The wetting shall
be accomplished by means of a steam fog generator which provides a uniform fog distribution over the
whole length and around the test object. The temperature of the fog in the vicinity of the test object shall
not exceed 40'C. To obtain the necessary wetting within a reasonable time, enough steam fog shall be
introduced inside the test chamber. The steam generation rate shall be specified by the relevant Technical
Committee.
In one procedure- the voltage is applied before the test object is wetted by the fog and continues until
flashover or for about twice the time for the insulator to achieve its maximum conductivity. In another
procedure, the test voltage is applied only when the conductivity has reached its maximum value, which
should occur between 20 and 40 min from the start of fogging. The voltage shall be kept constant during
the specified 15-min test time or until flashover occurs.
Examples of suitable coating and wetting procedures and of the measurement of the surface resistivity are
given in Appendix B.
The procedure above may be repeated several times; before each test. the test object shall be washed,
re-coated and allowed to dry.
When the test is intended to determine the maximum degree of pollution for a specified withstand voltage,
the coating, wetting and test procedures must be repeated using various suspension resistivities.
The minimum distance between any part of the test object and any earthed object other than the structure
which supports the test object shall be not less than 0,5 m per 100 kV of the test voltage.
10.3 Degree of pollution
The degree of pollution of a test object is specified by the salinity (g/L) of the salt fog, by the surface
conductivity (pS) or by the amount of salt (NaC1) per square centimetre of the insulating surface (gm/cm2).
This latter is normally referred to as the Salt Deposit Density (S.D.D.). Information about these methods
is given in Appendix B.
60-1 0 IEC 1989
11 Atmospheric conditions
1 1.1 Standard reference atmosphere
The standard reference atmosphere is:
temperature to = 20'C
pressure bo = 101,3 kPa (1013 mbar)
absolute humidity h, = 11 g/m3
NOTE - A pressure of 101.3 kPa corresponds to the height of 760 mm in a mercury barometer at O'C. If the
barometer height is H rnm of mercury. the atmospheric pressure in kilopascals is approximately:
Correction for temperature with respect to the height of the mercury column is considered to be negligible.
11.2 Atmospheric correction factors
The disruptive discharge of external insulation depends upon the atmospheric conditions. Usually, the
in either air density or
disruptive discharge voltage for a given path in air is increased by an increase
humidity. However, when the relative humidity exceeds about 80%, the disruptive discharge voltage
becomes irregular, especially when the disruptive discharge occurs over an insulating surface.
By applying correction factors, a disruptive discharge voltage measured in given test conditions (temper-
ature 1, pressure b, humidity h) may be converted to the value which would have been obtained under the
standard reference atmospheric conditions (to, 6,. b). Conversely, a test voltage specified for given
reference conditions can be converted into the equivalent value under the test conditions.
The disruptive discharge voltage is proportional to the atmospheric correction factor Kt, that results from
the product of two correction factors:
- the air density correction factor k, (see 11.2.1);
- the humidity correction factor k, (see 11.2.2).
Kt = klk,
If not otherwise specified by the relevant Technical Committee, the voltage U to be applied during a test
on external insulation is determined by multiplying the specified test voltage Uo by K,:
Similarly, measured disruptive discharge voltages U are corrected to Uo corresponding to standard refer-
ence atmosphere by dividing by K,:

60-1 0 IEC 1989 - 39 -
The test report shall always contain the actual atmospheric conditions during the test and the correction
factors applied.
11.2.1 Air density correction factor k,
The air density correction factor k, depends on the relative air density 6 and can be generally expressed
as:
where m is an exponent given in 11.2.3.
When the temperatures t and to are expressed in degrees Celsius and the atmospheric pressures b and bo
are expressed in the same units (kilopascals or millibars), the relative air density is:
11.2.2 Humidity correction factor k,
The humidity correction factor may be expressed as:
where w is an exponent given in 11.2.3 and k is a parameter that depends on the type of test voltage and
that, for practical purposes, may Ire approximately obtained as a function of the ratio of absolute humidity,
h, to the relative air density, 6, using the curves of figure 3. For values of h / 6 in excess of 15 g/m3
humidity corrections are still under consi
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