IEC 61467:2008

IEC 61467
Edition 1.0 2008-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Insulators for overhead lines – Insulator strings and sets for lines with a nominal
voltage greater than 1 000 V – AC power arc tests

Isolateurs pour lignes aériennes – Chaînes d’isolateurs et chaînes d’isolateurs
équipées pour lignes de tension nominale supérieure à 1 000 V – Essais d’arc de
puissance en courant alternatif

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IEC 61467
Edition 1.0 2008-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Insulators for overhead lines – Insulator strings and sets for lines with a
nominal voltage greater than 1 000 V – AC power arc tests

Isolateurs pour lignes aériennes – Chaînes d’isolateurs et chaînes d’isolateurs
équipées pour lignes de tension nominale supérieure à 1 000 V – Essais d’arc
de puissance en courant alternatif

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
X
CODE PRIX
ICS 29.080.10; 29.240.20 ISBN 2-8318-9953-2
– 2 – 61467 © IEC:2008
CONTENTS
FOREWORD.4
1 Scope and object.6
2 Normative references .6
3 Terms and definitions .6
4 Symbols and abbreviations.7
5 Characteristics of the test current .8
6 Supply and return circuit conditions .9
7 Tests on insulator sets .11
7.1 General remarks.11
7.2 Test arrangement .11
7.3 Test current.11
7.4 Supply and return circuit conditions.11
7.5 Arc initiation .12
7.6 Ambient conditions .14
7.7 Test series and characteristics of the power arcs .14
8 Tests on short strings .14
8.1 General remark .14
8.2 Test arrangement .15
8.3 Test current.15
8.4 Supply and return circuit conditions.15
8.5 Arc initiation .15
8.6 Ambient conditions .15
8.7 Test series and characteristics of the power arcs .16
9 Test report.18
10 Evaluation of results .18
10.1 General remark .18
10.2 Visual examination .18
10.3 Porcelain or glass insulators.18
10.4 Composite insulators.19
10.5 Acceptance criteria.19
Annex A (normative) Examples of test arrangements and practical methods of tower
simulation (return circuit) .20
Annex B (normative) Determination of the r.m.s. value of the current.25
Annex C (informative) No-load voltage of the power source .27
Annex D (informative) Power arcs on insulator sets and their true simulation by
appropriate positioning of fusible wires .28
Annex E (informative) Wind velocity during power arc tests .30
Annex F (informative) Variation of the fault current magnitude and reasons for the
choice of the prescribed test parameters .31
Annex G (informative) Recommendations for the test report .33
Annex H (informative) Sample of a power arc test report .37
Bibliography.40

Figure 1 – Illustration of supply and return currents .10
Figure 2 – Arc initiation.13

61467 © IEC:2008 – 3 –
Figure 3 – Mounting arrangement for short strings .17
Figure A.1 – Test arrangement of vertical insulator set .21
Figure A.2 – Test arrangement of vertical insulator set using simplified tower steel
structure .22
Figure A.3 – Test arrangement of Vee insulator set located in the centre of the tower
(for the simplified tower steel structure and return circuit, see Figures A.1 and A.2).23
Figure A.4 – Test arrangement of horizontal insulator (for the simplified tower steel
structure and return circuit, see Figures A.1 and A.2) .24
Figure D.1 – 5 kA power arc test of a 145 kV string consisting of 7 cap and pin units.29
Figure F.1 – Distribution of arc current (I) and its supply circuit components (I , I )
S1 S2
along a 100 km long, 145 kV line connecting busbars of 28 kA short-circuit current .32

Table 1 – Supply and return conditions .9
Table 2 – Test series for insulator sets .14
Table 3 – Test series for short insulator strings.16
Table 4 – Test assessment criteria .19

– 4 – 61467 © IEC:2008
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INSULATORS FOR OVERHEAD LINES –
INSULATOR STRINGS AND SETS FOR LINES WITH
A NOMINAL VOLTAGE GREATER THAN 1 000 V –
AC POWER ARC TESTS
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
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2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
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6) All users should ensure that they have the latest edition of this publication.
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) 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.
International Standard IEC 61467 has been prepared by subcommittee 36B: Insulators for
overhead lines, of IEC technical committee 36: Insulators.
This first edition cancels and replaces IEC/TR 61467, which was published as a technical
report in 1997. It constitutes a technical revision and now has the status of an International
Standard.
The text of this standard is based on the following documents:
FDIS Report on voting
36B/277/FDIS 36B/280/RVD
Full information on the voting for the approval of this standard 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.

61467 © IEC:2008 – 5 –
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 6 – 61467 © IEC:2008
INSULATORS FOR OVERHEAD LINES –
INSULATOR STRINGS AND SETS FOR LINES WITH
A NOMINAL VOLTAGE GREATER THAN 1 000 V –
AC POWER ARC TESTS
1 Scope and object
This International Standard applies to insulator strings and sets comprising string insulator
units of ceramic material, glass or composite material for use on a.c. overhead lines and
traction lines with a nominal voltage above 1 000 V and a frequency between 15 Hz and
100 Hz.
This standard also applies to insulator strings or sets of similar design used in substations.
This standard establishes a standard test procedure for power arc tests on insulator sets. It
also establishes a standard test procedure for power arc tests on short strings.
This standard does not apply to insulator sets mounted on non-metallic poles or towers.
This standard cannot be directly applied to line post insulators or sets, or to insulating
structures such as braced line-posts, since their mounting arrangement cannot be reproduced
by the standard arrangements as described herein. However, this standard can be used as a
basis for agreement for tests on such insulators and arrangements.
The object of this standard is
– to define the terms used,
– to prescribe a standard test procedure,
– to prescribe criteria to evaluate the results of the tests.
Power arc tests are not an obligatory element of line insulator specifications. The standard
test procedures and the evaluation criteria described in this standard are intended to provide
testing guidance when power arc tests are felt to be necessary. It is not the object of this
standard to introduce a general obligation to execute these tests.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60797, Residual strength of string insulator units of glass or ceramic material for
overhead lines after mechanical damage of the dielectric
IEC 60826, Design criteria of overhead transmission lines
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
NOTE Definitions of other terms used in this standard can be found in IEC 60050-471, IEC 60383-1 and
IEC 60383-2.
61467 © IEC:2008 – 7 –
3.1
test
one application of the specified test current for the specified duration to the insulator string or
set
3.2
test sequence
three successive tests on the same insulator string or set
3.3
test series
a group of test sequences used to characterize the power arc performance of an insulator
string or set
3.4
per cent initial asymmetry of current
deviation of the current from a symmetrical wave during the first cycle of a power arc
NOTE Per cent initial asymmetry is expressed as a function of the absolute peak value of the current of the first
cycle (I ) divided by the r.m.s. value of the current (I) as follows:
m
⎛ I ⎞
m
⎜ ⎟
−1 ×100
⎜ ⎟
I × 2
⎝ ⎠
3.5
supply circuit
electrical connection through which the current of a power arc flows to the line side of the test
object from the power source
3.6
return circuit
electrical connection through which the current of power arc flows from the earth side of the
test object to the power source
3.7
balanced circuit
supply or return circuit in which the current flow is in two diametrically opposed directions
3.8
unbalanced circuit
supply or return circuit in which the current flow is principally in one direction
3.9
short string (cap and pin units)
string of three to six insulator units having a minimum arcing distance of 400 mm
3.10
short string (long rod and composite units)
string of one or more insulator units having an arcing distance between 400 mm and
1 000 mm
4 Symbols and abbreviations
The following symbols and abbreviations are principally used in the tables and figures
hereafter.
Unless otherwise stated currents and voltages are expressed as r.m.s values.

– 8 – 61467 © IEC:2008
I Arc current
I Specified arc current
n
t Arc time
t Specified arc time
n
I Peak current value
m
I Currents in the return circuit
R1,2
I Currents in the supply circuit
S1,2
I Rated short-circuit current of the network system
sys
L Length of the insulator string
A
L Length of the insulator set
B
L Length of simulation of the return circuit
R
Length of simulation of the supply circuit
L
S
D Distance from the centre point of the tested insulator set to the surrounding framework
M Mechanical load on the tested insulator set
L
α Angle from the horizontal plane of a tension insulator set
SFL Specified minimum (electro-)mechanical failing load
SML Specified mechanical load
5 Characteristics of the test current
The tests shall be made with single-phase alternating current. Initial asymmetry (d.c.
component) shall not exceed 30 %.
NOTE This requirement is explained by the fact that the flashovers on a contaminated insulator set in service
generally occur in the vicinity of a voltage peak, consequently with a minimal direct current component.
For 50 Hz or 60 Hz systems, the frequency of the test circuit shall be from 45 Hz to 65 Hz. For
other system frequencies, the frequency of the test supply shall not in principle deviate from
the specified value by more than 10 %. By agreement with the user, tests may be performed
at a higher or lower frequency than the intended operating frequency. The frequencies may
vary within the above limits during each test.
The test circuit shall be adequate to supply the specified values of arc current (r.m.s) and arc
duration. Annex C gives information on no-load voltages suggested to achieve specified
current values. Unless agreed otherwise, the permissible tolerance of the arc current with
respect to the specified r.m.s. value of the current is ±10 %.
The actual arc current during the test shall be practically sinusoidal. The r.m.s. value of the
test current may be derived from the arithmetic mean of the peak values during the test
duration (see Annex B). If the measuring equipment permits, the r.m.s. value may be
calculated from the current function.
The test current shall be essentially constant over the arcing time. During the arcing time, the
following deviations from the specified value are permissible:
– the arc current crest values shall not deviate from the specified value (I 2 ) by more
n
than ±20 %;
– for arcing times greater than 0,2 s, the above tolerance may be exceeded during not more
than 20 % of the total arcing time.
In any case, the product of the actual arc current and duration I×t shall be within ±10 % of the
product of the specified arc current and duration I x t .
n n
61467 © IEC:2008 – 9 –
In cases where the movement of the arc root onto the tower or along the line conductor
occurs, these tolerances may be exceeded.
6 Supply and return circuit conditions
The supply and return circuits depend on the service conditions, notably on the location of the
insulator set along the line and on the tower geometry. The characteristic cases to be
simulated in tests are given in Table 1 and illustrated in Figure 1 for complete sets and in
Figure 3 for short strings.
Table 1 – Supply and return conditions

Balanced supply circuit Unbalanced supply circuit
A circuit B circuit
I = I /2 I = I /2
R1 n R1 n
I = I /2 I = I /2
R2 n R2 n
I = I /2 I = I
S1 n S1 n
Balanced return circuit
I = I /2 I = 0
S2 n S2
For example: For example:
Insulator set in the centre phase window Insulator set in the centre phase
of a tower in the middle of a line window of a tower at the extremity of a
line
C circuit D circuit
I = I   I = I
R1 n R1 n
I = 0   I = 0
R2 R2
I = I /2   I = I
S1 n S1 n
Unbalanced return circuit
I = I /2   I = 0
S2 n S2
For example: For example:
Insulator set on the lateral phase cross- Insulator set on the lateral phase
arm of a tower in the middle of a line cross-arm of a tower at the extremity of
a line
The permissible deviation of the currents I and I , I and I from their specified value
R1 R2 S1 S2
shall not exceed ±20 %. This may be verified by a circuit calibration test.

– 10 – 61467 © IEC:2008
I
R1
I
R2
I
Plasma mass flow
Power arc
I
Change-over point
I
S2
I
S1
IEC  1306/08
Figure 1 – Illustration of supply and return currents

61467 © IEC:2008 – 11 –
7 Tests on insulator sets
7.1 General remarks
The test procedure for insulator sets described in this standard consists of two possible series
of three power arc applications (sequences) at different current levels and of different
duration. This test procedure is intended to cover fault current conditions occurring at
representative points along a line. The test procedure is also intended to reproduce pollution-
induced power arc flashover, which creates the most severe conditions.
As the test procedure for insulator sets described in this standard is intended to simulate
conditions encountered in service, attention is drawn to the fact that it is not possible to
extrapolate the behaviour of an insulator set of a given length to that of an insulator set of
different length or equipped with fittings of different design or materials.
7.2 Test arrangement
The test arrangement shall duplicate the actual configuration of the complete insulator set and
as closely as possible that of the conductor and of the part of the tower nearest to the
insulator set. The actual protective fittings shall be used and their position with respect to the
insulator units, the clamps and the conductor shall be reproduced. The aim of the true
simulation of the actual configuration is to recreate the real electromagnetic field affecting the
arc movement.
The distances between the insulator set and the grounded structures simulating the tower
shall be the same as for the service configuration. In the case of some insulator sets (e.g.
extra high voltage, special configurations), the actual simulation of the tower may be limited
by the facilities of test laboratories. In the case of long insulator sets (L > 6 m), a distance D
B
of 6 m between tower and line conductors is sufficient.
The distance from the conductors to the ground plane shall be at least L /2 or 3 m for
B
L > 6 m.
B
The test arrangement shall include a conductor or conductor bundle having characteristics
similar to the one used in service. To create the real electrodynamic forces affecting the arc
movement, the conductor length on both sides of the insulator sets shall be at least equal to
the insulator set length but its minimum length shall be 2,5 m. In the case of long insulator
sets (L > 6 m), a conductor length L of 6 m is sufficient (see Annex A).
B S
Some appropriate test arrangements and tower simulations (return circuit) are shown in
Annex A.
In order to avoid poor electrical contacts and to ensure that the insulator set is correctly
positioned, a mechanical load shall be applied to the insulator set. In the case of vertical
insulator sets, this load can be applied by means of a suitable weight suspended from the
suspension clamp or conductor by means of an insulated link. The value of the load shall be
at least 5 kN on the complete insulator set. In the case of tension insulator sets, a higher
mechanical load may be necessary to reproduce the service angle of the insulator set (see
Figure A.4).
7.3 Test current
The characteristics of the test current shall be in accordance with Clause 5.
7.4 Supply and return circuit conditions
The supply and return circuits shall be chosen to represent the service conditions being
simulated (see Clause 6).
– 12 – 61467 © IEC:2008
7.5 Arc initiation
The arc shall be initiated by fusible wire of a low resistance material (e.g. silver, aluminium,
copper) with a maximum total cross-section of 1 mm . If more than one wire is used, they
shall be twisted together in parallel.
NOTE If there are problems in initiating the arc, a larger diameter fusible wire may be used. However it should be
noted that this can have an adverse effect on the test result due to reduced initial arc mobility and deposition of
metal on the insulator surface.
The aim of the specified arc initiation is to create conditions similar to that of a flashover
occurring on a contaminated insulator set. This kind of flashover can cause the arc to root on
intermediate points along the string. The description of the arcing phenomenon and the
detailed explanation of the positioning of fusible wires are given in Annex D.
The fusible wires shall be attached to the metal parts by a single point contact in the following
manner and as shown in Figure 2.
a) Cap and pin insulator sets
The first wire shall be attached to the cap of the earth side unit and to the pin of an
intermediate unit at an interval of three to five units. The following wire is placed in the
same manner, but on the opposite side of the string. This method shall be repeated up to
the end of the string. Figure 2a shows the positioning of the wires and the connection of
the wire to the limit point of the cap and the shed and to the pin. When there are practical
difficulties to attach the fusible wire to the pin (e.g. due to the shape of the insulators), it is
allowed to attach it to the cap of the next insulator.
In case of short insulator sets, having less than 6 units, one change-over point shall be
created on the string approximately in the middle.
b) Long rod and composite insulator sets
The wire shall be attached between the metal parts of the insulator and be wrapped
around the core in the middle of the insulator and continuing from there to the opposite
side. The different units shall have separate fuse wires according to Figure 2b.
In the case of longer insulator sets (e.g. unit insulator length >1,5 m) the wire shall be
attached between the metal parts of the insulator and be wrapped around the core and
continuing from there to the opposite side of the insulator at distances of 0,6 m to 0,8 m
according to Figure 2c.
In all cases (cap and pin, long rod, composite insulator sets, vertical-, Vee-, horizontal
insulator sets) the plane of the fuse wires shall have an angle of 45° to the conductors (see
Figures 2d and 2e).
The attachment point of the fusible wire shall be moved to an adjacent quadrant for each
successive test.
In case of multiple string insulator sets (Vee, double, etc.), the arcs in one test sequence shall
always be initiated on the same string. This string shall be chosen in such a manner that the
normal displacement of the arc due to electromagnetic forces is towards the other string(s) of
the insulator set.
61467 © IEC:2008 – 13 –
Wrapped or single
point contact
Fusible
wire
3 to 5
units
Single point
contact fixed for
3 to 5
example by
units Fusible
insulating tape
wire
or a cable tie
IEC  1308/08
3 to 5
units
IEC  1307/08
Figure 2b – Long rod
Figure 2a – Cap and pin insulators  insulators

I
S2
I I
R1 R2
0,6 m to 0,8 m
45°
I
Fusible S1
0,6 m to 0,8 m
wire
Planes seen from direction S in Figures A.1 and A.3
IEC  1310/08
Figure 2d – Planes of the fusible wires,
vertical and V strings
0,6 m to 0,8 m
I I
R1 R2
45°
0,6 m to 0,8 m
Planes seen from direction S in Figure A.4
IEC  1309/08
IEC  1311/08
Figure 2c – Longer sets Figure 2e – Planes of the fusible wires, horizontal strings

Figure 2 – Arc initiation
– 14 – 61467 © IEC:2008
7.6 Ambient conditions
The wind velocity and all other ambient conditions (atmospheric pressure, rain, humidity and
temperature) shall be recorded in all cases.
As the wind has an influence on the arc movement, the tests may be carried out in a test
chamber or, when performed outdoors, shall be carried out in calm weather whenever
possible. To enable efficient comparison of lower current power arc tests (<10 kA), a
maximum wind speed of 5 m/s is allowed.
Annex E gives an explanation of the importance of wind on power arc tests.
Other atmospheric conditions are considered to have no significant influence on the results.
7.7 Test series and characteristics of the power arcs
In accordance with Table 1 and Figure 1, the X or Y test series from Table 2 shall be chosen
depending on the type of the tower. To choose the test series Y is reasonable only if the
return circuit is always unbalanced, for example when the tower does not have a centre phase
window. For practical purposes, in applications where different tower geometries exist and
would normally require both X and Y test series, the X series shall be chosen in preference,
this being more stringent. In all cases, if the test series X is performed, then series Y is not
necessary.
Table 2 – Test series for insulator sets
Test Test circuit Short-circuit current Number and duration of tests
series (see Table 1) (test sequence)
A = 0,2 I Two of t = 0,2 s and one of t = 1 s
I
n sys n n
X
Two of t = 0,2 s and one of t = 1 s
A I = 0,5 I
n n
n sys
B Two of t = 0,2 s and one of t = 0,5 s
I = I
n n
n sys
C I = 0,2 I Two of t = 0,2 s and one of t = 1 s
n sys n n
Y C Two of t = 0,2 s and one of t = 1 s
I = 0,5 I
n n
n sys
D I = I Two of t = 0,2 s and one of t = 0,5 s
n sys n n
The minimum interval between two successive tests shall be 20 min. The replacement of
damaged units or of the whole insulator set is allowed after every 3 tests performed at the
same current.
The number of tests and their duration are chosen to represent the conditions arising on the
majority of systems. If different values are required to represent specific network
characteristics, they shall be subject to prior agreement.
Annex F gives an explanation of the above prescribed values.
8 Tests on short strings
8.1 General remark
The test procedure for short strings is included in this standard as a means to evaluate the
behaviour of insulator materials, design and construction under the thermal stresses
encountered during a power arc. This test cannot be used to determine or predict the
behaviour of a complete insulator set.

61467 © IEC:2008 – 15 –
8.2 Test arrangement
The test arrangement for short strings is shown in Figure 3. The short string is hung vertically
by an insulated conductor (wire, tube or rod) below an insulating plate intended to avoid
transfer of the arc onto surrounding equipment. A weight or mechanical load is applied to the
bottom of the string by a second insulated conductor. The supply and return circuits are
connected perpendicular to these conductors, at a distance from the string of one to two times
the arcing distance of the string.
The distances between the insulator string and the grounded structures shall be sufficient to
avoid transfer of the arc onto the structures. The distance from the conductors to the ground
plane shall be at least 1 m.
The value of the load applied to the string shall be at least 5 kN.
The fittings used to connect the conductors to the string shall be of appropriate size and
shape to match the end fittings of the string under test.
8.3 Test current
The characteristics of the test current shall be in accordance with Clause 5.
8.4 Supply and return circuit conditions
The supply and return circuits shall both be unbalanced (see Clause 6 and Figure 3).
8.5 Arc initiation
The arc shall be initiated by fusible wire of a low resistance material (e.g. silver, aluminium,
copper) with a maximum total cross-section of 1 mm . If more than one wire is used, they
shall be twisted together in parallel.
NOTE If there are problems in initiating the arc, a larger diameter fusible wire may be used. However, it should be
noted that this can have an adverse effect on the test result due to reduced initial arc mobility and deposition of
metal on the insulator surface.
The fusible wire shall be attached to the metal of top and bottom fittings of the insulator string
preferably by a single point contact or alternatively by wrapping. The wire shall follow the
arcing distance of the string, as shown in Figure 3. If the string does not have metal end
fittings, the wire shall be attached to the closest point on the mating fitting of the test
arrangement.
Whenever possible, (cap and pin, long rod, composite insulator strings) the plane of the fuse
wires shall have an angle of 45° to the supply and return conductors.
The attachment point of the fusible wire shall be moved to an adjacent quadrant for each
successive test.
8.6 Ambient conditions
If the test is performed outdoors, the wind velocity and all other ambient conditions
(atmospheric pressure, rain, humidity and temperature) shall be recorded. For tests performed
indoors, atmospheric pressure, humidity and temperature shall be recorded.
As the wind has an influence on the arc movement, the tests may be carried out in a test
chamber or, when performed outdoors, shall be carried out in calm weather whenever
possible. To enable efficient comparison of lower current power arc tests (<10 kA), a
maximum wind speed of 5 m/s is allowed.

– 16 – 61467 © IEC:2008
Annex E gives an explanation of the importance of wind on power arc tests.
Other atmospheric conditions are considered to have no significant influence on the results.
8.7 Test series and characteristics of the power arcs
The test series for short strings consists of three successive tests where in each a short string
is tested with one short-circuit application only. The entire short string is changed after each
arc application. Table 3 gives the currents and durations of the tests in the series.
Table 3 – Test series for short insulator strings
a a
Test circuit Short-circuit current Number and duration of tests
(see Table 1) (test sequence)
D I = 12 kA One of t = 0,1 s
n n
D I = 12 kA One of t = 0,1 s
n n
D I = 12 kA One of t = 0,1 s
n n
a
Alternatively, and after agreement between the interested parties, the tests may be
carried out at 6 kA for 0,2 s.

The mechanical load on the string shall be maintained for 5 min after the application of the
arc.
61467 © IEC:2008 – 17 –
Ceiling or supporting structure
Insulating plate
Return
I = I
R1 n
One to two times
the arcing
distance of the
string
Insulating sleeve
Wrapped or single
point contact
Fusible
wire
Wrapped or single
point contact
One to two times
the arcing
distance of the
string
Insulating sleeve
Supply
I = I
S1 n
≥ 5 kN
IEC  1312/08
Figure 3 – Mounting arrangement for short strings

– 18 – 61467 © IEC:2008
9 Test report
In order to harmonize the format of the test reports, the information to be included in the test
documentation shall appear in the following sequence:
a) an appropriate front sheet;
b) complete details of ratings assigned by the applicant for the tests;
c) a list of the tests performed and, if appropriate, a list of persons witnessing the tests, as
well as the circulation of the test documentation.
The remainder of the test document can be arranged to suit the convenience of the testing
laboratory. The preferable format for the report is given in Annex G.
10 Evaluation of results
10.1 General remark
This clause sets forth criteria, to be used as guidelines only, for evaluating the effects on
operational reliability of the insulator set or string.
The evaluation consists of two parts. A visual examination is performed first, followed by a
series of analytical tests to determine the suitability of the insulators to continue in service.
For tests on insulator sets, the visual examination also includes all mechanical components
and fittings of the insulator set; this information is recorded for use by other relevant product
standards as necessary. The criteria for evaluation of these fittings and connections are
beyond the scope of this standard.
10.2 Visual examination
A thorough visual examination, including photographs, shall record all significant damage
sustained by the insulator units, fittings, protective fittings, and conductor(s):
– Metallic insulator components and all load-bearing fittings shall be examined and
photographed for arc damage that could have an effect on their mechanical strength. This
includes partial melting, arc puddling, and metallic evaporation.
– Metallic components that are galvanized shall be examined for damage to the coating that
could sustain future corrosion.
– Metallic components that carry significant levels of surface electrical stress shall be
examined for localized contour changes which might induce excessive corona and radio
noise.
10.3 Porcelain or glass insulators
In addition to the visual examination for damage to the hardware components of insulators,
porcelain or glass insulators shall be examined for damage to the insulating component.
Damage to the insulating component can include the following:
– partial or complete breakage of sheds;
– burning or scaling of the insulating surfaces.
Ringing of the sheds of cap and pin insulators can be helpful as a preliminary means of
detecting possible internal dielectric fractures in porcelain insulators. However, this method is
somewhat subjective, and can be used only as a preliminary assessment before performing
the analysis outlined in Table 4.

61467 © IEC:2008 – 19 –
10.4 Composite insulators
In addition to visual examination for hardware damage, composite insulators shall be
examined for damage to the insulating element. Damage to the insulating element can include
the following:
– surface changes such as discoloration, erosion or arc plasma deposits;
– splitting or puncture of individual sheds;
– major housing damage which allows exposure of the fibreglass rod, loss of seal at end
fittings or joints, or exudation of sealing grease, where used.
10.5 Acceptance criteria
The acceptance criteria is that the insulator set or string shall be operationally safe after the
conclusion of the test series. The operational safety conditions shall be verified both for the
mechanical and electrical behaviour, in accordance with the criteria defined in Table 4 below.
Special care shall be taken in judging the test results.
Table 4 – Test assessment criteria
Assessment criteria
Criteria or test to be performed
Insulator sets Short strings
Insulator separation during the test Not permitted Not permitted
a
Burning, breaking of sheds or ribs, glaze Permitted Permitted
removal, melting of galvanized surfaces
Exposure of the fibreglass core Not permitted Not permitted
(composite insulators only)
Dry power frequency flashover to check All units shall be tested and All
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