IEC 60099-8:2011

Surge arresters - Part 8: Metal-oxide surge arresters with external series gap (EGLA) for overhead transmission and distribution lines of a.c. systems above 1 kV

IEC 60099-8:2011 covers metal-oxide surge arresters with external series gap (externally gapped line arresters (EGLA) that are applied on overhead transmission and distribution lines, only to protect insulator assemblies from lightning-caused flashovers. This standard defines surge arresters to protect the insulator assembly from lightning-caused overvoltages only. Designs with the EGLA's external series gap installed in parallel to an insulator are not covered by this standard.

Parafoudres - Partie 8: Parafoudres à oxyde métallique avec éclateur extérieur en série (EGLA) pour lignes aériennes de transmission et de distribution de réseaux à courant alternatif de plus de 1 kV

La CEI 60099-8:2011 concerne les parafoudres à oxyde métallique, de ligne avec éclateur extérieur en série (EGLA) utilisés sur les lignes aériennes de transmission et de distribution, uniquement pour protéger les ensembles isolateurs contre les contournements provoqués par la foudre. Cette norme définit des parafoudres destinés à protéger l'ensemble isolateur uniquement contre les surtensions provoquées par la foudre. Les conceptions avec des EGLA à éclateur extérieur en série montés en parallèle sur un isolateur ne sont pas couvertes par la présente norme.

General Information

• Status: Published
• Publication Date: 26-Jan-2011
• ICS: 29.240.10 - Substations. Surge arresters
• Technical Committee: TC 37 - Surge arresters
• Drafting Committee: MT 4 - TC 37/MT 4
• Current Stage: DELPUB - Deleted Publication
• Start Date: 14-Nov-2017
• Completion Date: 28-Feb-2017

Relations

• Revised: IEC 60099-8:2017 - Surge arresters - Part 8: Metal-oxide surge arresters with external series gap (EGLA) for overhead transmission and distribution lines of a.c. systems above 1 kV
• Effective Date: 05-Sep-2023

Standards Content (Sample)

IEC 60099-8 ®
Edition 1.0 2011-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Surge arresters –
Part 8: Metal-oxide surge arresters with external series gap (EGLA) for overhead
transmission and distribution lines of a.c. systems above 1 kV

Parafoudres –
Partie 8: Parafoudres à oxyde métallique avec éclateur extérieur en série (EGLA)
pour lignes aériennes de transmission et de distribution de réseaux à courant
alternatif de plus de 1 kV
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IEC 60099-8 ®
Edition 1.0 2011-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Surge arresters –
Part 8: Metal-oxide surge arresters with external series gap (EGLA) for overhead
transmission and distribution lines of a.c. systems above 1 kV

Parafoudres –
Partie 8: Parafoudres à oxyde métallique avec éclateur extérieur en série (EGLA)
pour lignes aériennes de transmission et de distribution de réseaux à courant
alternatif de plus de 1 kV
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX XB
ICS 29.240.10 ISBN 978-2-88912-312-4
– 2 – 60099-8  IEC:2011
CONTENTS
FOREWORD . 5

INTRODUCTION . 7

1 Scope . 8

2 Normative references . 8

3 Terms and definitions . 9

4 Identification and classification . 11

4.1 EGLA identification . 11

4.2 EGLA classification . 12
5 Standard ratings and service conditions . 12
5.1 Standard rated voltages . 12
5.2 Standard rated frequencies . 13
5.3 Standard nominal discharge currents . 13
5.4 Service conditions . 13
5.4.1 Normal service conditions . 13
5.4.2 Abnormal service conditions . 13
6 Requirements . 13
6.1 Insulation withstand of the SVU and the complete EGLA . 13
6.1.1 Insulation withstand of the housing of the SVU . 13
6.1.2 Insulation withstand of EGLA with shorted (failed) SVU . 13
6.2 Residual voltages . 14
6.3 High current duty . 14
6.4 Lightning discharge capability . 14
6.5 Short-circuit performance of the SVU . 14
6.6 Mechanical performance . 14
6.7 Weather aging of SVU . 15
6.8 Reference voltage of the SVU . 15
6.9 Internal partial discharges . 15
6.10 Coordination between insulator withstand and EGLA protective level . 15
6.11 Follow current interrupting . 15
6.12 Electromagnetic compatibility . 15
6.13 End of life . 16
7 General testing procedure . 16

7.1 Measuring equipment and accuracy . 16
7.2 Test samples . 16
8 Type tests . 16
8.1 General . 16
8.2 Insulation withstand tests on the SVU housing and on the EGLA with failed
SVU . 17
8.2.1 General . 17
8.2.2 Insulation withstand test on the SVU housing . 17
8.2.3 Insulation withstand tests on EGLA with failed SVU . 18
8.3 Residual voltage tests . 19
8.3.1 General . 19
8.3.2 Procedure for correction and calculation of inductive voltages . 19
8.3.3 Lightning current impulse residual voltage test . 20

60099-8  IEC:2011 – 3 –
8.3.4 High current impulse residual voltage test . 21

8.4 Standard lightning impulse sparkover test . 21

8.5 High current impulse withstand test . 22

8.5.1 Selection of test samples . 22

8.5.2 Test procedure . 22

8.5.3 Test evaluation . 22

8.6 Lightning discharge capability test . 23

8.6.1 Selection of test samples . 23

8.6.2 Test procedure . 23

8.6.3 Test parameters for the lightning impulse discharge capability test . 23

8.6.4 Measurements during the lightning impulse discharge capability test . 24
8.6.5 Rated lightning impulse discharge capability. 24
8.6.6 List of rated charge values . 24
8.7 Short-circuit tests . 24
8.7.1 General . 24
8.7.2 Preparation of the test samples . 25
8.7.3 Mounting of the test sample . 26
8.7.4 High-current short-circuit tests . 27
8.7.5 Low-current short-circuit test . 29
8.7.6 Evaluation of test results . 29
8.8 Follow current interrupting test . 34
8.8.1 General . 34
8.8.2 "Test method A" . 34
8.8.3 "Test method B" . 36
8.9 Mechanical load tests on the SVU . 38
8.9.1 Bending test . 38
8.9.2 Vibration test . 47
8.10 Weather aging tests . 48
8.10.1 General . 48
8.10.2 Sample preparation . 48
8.10.3 Test procedure . 48
8.10.4 Test evaluation . 48
8.10.5 Additional test procedure for polymer (composite and cast resin)
housed SVUs. 48
9 Routine tests . 49

9.1 General . 49
10 Acceptance tests . 50
10.1 General . 50
10.2 Reference voltage measurement of SVU . 50
10.3 Internal partial discharge test of SVU . 50
10.4 Radio interference voltage (RIV) test . 50
10.5 Test for coordination between insulator withstand and EGLA protective level . 51
10.5.1 General . 51
10.5.2 Front-of-wave impulse sparkover test . 51
10.5.3 Standard lightning impulse sparkover test . 51
10.6 Follow current interrupting test . 52
10.6.1 General . 52
10.6.2 Test procedure . 52
10.6.3 Test sequence . 52

– 4 – 60099-8  IEC:2011
10.6.4 Test evaluation . 52

10.7 Vibration test on the SVU with attached electrode . 52

10.7.1 Test procedure and test condition . 53

10.7.2 Test evaluation . 53

Annex A (informative) Example of a test circuit for the follow current interrupting test . 54

Annex B (normative) Mechanical considerations . 55

Bibliography . 60

Figure 1 – Configuration of an EGLA with insulator and arcing horn . 7

Figure 2 – Examples of SVU units . 32
Figure 3 – Short-circuit test setup . 33
Figure 4 – Example of a test circuit for re-applying pre-failing circuit immediately
before applying the short-circuit test current . 34
Figure 5 – Thermo-mechanical test . 43
Figure 6 – Example of the test arrangement for the thermo-mechanical test and
direction of the cantilever load . 44
Figure 7 – Test sequence of the water immersion test . 45
Figure A.1 – Example of a test circuit for the follow current interrupting test . 54
Figure B.1 – Bending moment – Multi-unit SVU . 55
Figure B.2 – SVU unit . 57
Figure B.3 – SVU dimensions . 58

Table 1 – EGLA classification – “Series X” and “Series Y“ . 12
Table 2 – Steps of rated voltages (r.m.s. values) . 12
Table 3 – Type tests (all tests to be performed without insulator assembly) . 17
Table 4 – Test requirements . 30
Table 5 – Required currents for short-circuit tests . 31
Table 6 – Acceptance tests . 50
Table 7 – Virtual steepness of wave front of front-of-wave lightning impulses . 51

60099-8  IEC:2011 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________
SURGE ARRESTERS –
Part 8: Metal-oxide surge arresters with external series gap (EGLA)

for overhead transmission and distribution lines

of a.c. systems above 1 kV
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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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 60099-8 has been prepared by IEC technical committee 37: Surge
arresters.
The text of this standard is based on the following documents:
FDIS Report on voting
37/370/FDIS 37/377/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.

– 6 – 60099-8  IEC:2011
A list of all parts of IEC 60098 series, under the general title Surge arresters can be found on

the IEC website.
The committee has decided that the contents of this publication will remain unchanged until

the stability 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.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this document using a colour printer.

60099-8  IEC:2011 – 7 –
INTRODUCTION
This part of IEC 60099 applies to the externally gapped line arrester (EGLA)

This type of surge arrester is connected directly in parallel with an insulator assembly. It
comprises a series varistor unit (SVU), made up from non-linear metal-oxide resistors

encapsulated in a polymer or porcelain housing, and an external series gap, see Figure 1.

The purpose of an EGLA is to protect the parallel-connected insulator assembly from

lightning-caused overvoltages. The external series gap, therefore, should spark over only due

to fast-front overvoltages. The gap should withstand all power-frequency and slow-front

overvoltages occurring on the system.
In the event of SVU failure, the external series gap should be able to isolate the SVU from the
system.
EGLA
Tower arm
Insulator assembly
S
(insulator assembly,
Series varistor unit V
with/without arcing horns
U or grading elements)
External series gap
(without an insulator
Conductor
in parallel)
IEC  2896/10
Figure 1 – Configuration of an EGLA with insulator and arcing horn

– 8 – 60099-8  IEC:2011
SURGE ARRESTERS –
Part 8: Metal-oxide surge arresters with external series gap (EGLA)

for overhead transmission and distribution lines

of a.c. systems above 1 kV
1 Scope
This part of IEC 60099 covers metal-oxide surge arresters with external series gap (externally
gapped line arresters (EGLA) that are applied on overhead transmission and distribution lines,
only to protect insulator assemblies from lightning-caused flashovers.
This standard defines surge arresters to protect the insulator assembly from lightning-caused
overvoltages only. Therefore, and since the metal-oxide resistors are not permanently
connected to the line, the following items are not considered for this standard:
• switching impulse sparkover voltage;
• residual voltage at steep current and switching current impulse;
• thermal stability;
• long-duration current impulse withstand duty;
• power-frequency voltage versus time characteristics of an arrester;
• disconnector test;
• aging duties by power-frequency voltage.
Considering the particular design concept and the special application on overhead
transmission and distribution lines, some unique requirements and tests are introduced, such
as the verification test for coordination between insulator withstand and EGLA protective
level, the follow current interrupting test, mechanical load tests, etc.
Designs with the EGLA's external series gap installed in parallel to an insulator are not
covered by this standard.
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 60060-1:1989, High-voltage test techniques – Part 1: General definitions and test
requirements
IEC 60060-2:1994, High-voltage test techniques – Part 2: Measuring systems
IEC 60068-2-11:1981, Environmental testing – Part 2: Tests. Test kA: Salt mist
IEC 60068-2-14:2009, Environmental testing – Part 2-14: Tests – Test N: Change of
temperature
IEC 60099-4:2009, Surge arresters – Part 4: Metal-oxide surge arresters without gaps for a.c.
systems
60099-8  IEC:2011 – 9 –
IEC 60270:2000, High-voltage test techniques – Partial discharge measurements

IEC 60507:1991, Artificial pollution tests on high-voltage insulators to be used on a.c.

systems
IEC/TS 60815-1:2008, Selection and dimensioning of high-voltage insulators intended for use

in polluted conditions – Part 1: Definitions, information and general principles

IEC 62217:2005, Polymeric insulators for indoor and outdoor use with a nominal voltage

> 1 000 V – General definitions, test methods and acceptance criteria

ISO 3274, Geometric product specifications (GPS) – Surface texture: Profile method –
Nominal characteristics of contact (stylus) instruments
ISO 4287, Geometrical Product Specifications (GPS) – Surface texture: Profile method –
Terms, definitions and surface texture parameters
ISO 4892-1, Plastics – Methods of exposure to laboratory light sources – Part 1: General
Guidance
ISO 4892-2, Plastics – Methods of exposure to laboratory light sources – Part 2: Xenon-arc
sources
ISO 4892-3, Plastics – Methods of exposure to laboratory light sources – Part 3: Fluorescent
UV lamps
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
externally gapped line arrester
EGLA
arrester designed for installation on overhead lines to protect an insulator assembly from
lightning-caused fast-front overvoltages only
NOTE This is accomplished by rising the sparkover level of the external series gap to a level that isolates the
arrester from power-frequency overvoltages and from the worst case slow-front overvoltages due to switching and
fault events expected on the line to which it is applied.
3.2
series varistor unit
SVU
non-linear metal-oxide resistor part, contained in a housing, which must be connected with an
external series gap to construct the complete arrester
NOTE The series varistor unit may include several units.
3.3
section of an EGLA
complete, suitably assembled part of a complete EGLA necessary to represent the behaviour
of a complete EGLA with respect to a particular test
3.4
section of an SVU
complete, suitably assembled part of an SVU unit necessary to represent the behaviour of an
SVU with respect to a particular test

– 10 – 60099-8  IEC:2011
3.5
unit of an SVU
completely housed part of an SVU which may be connected in series and/or in parallel with

other units of an SVU to construct, in combination with the external series gap, an EGLA of

higher voltage and/or current rating

3.6
rated voltage of an EGLA
U
r
maximum permissible r.m.s. value of power-frequency voltage between the EGLA terminals,
at which it is designed to operate correctly

NOTE 1 The rated voltage is used as a reference parameter for the specification of operating and current
interrupting characteristics.
NOTE 2 Different to the rated voltage of gapless (line) arresters, the rated voltage of an EGLA is a voltage that
may be applied continuously.
3.7
reference voltage of an SVU
U
ref
peak value of power-frequency voltage divided by √2, which should be applied to the SVU to
obtain the reference current
NOTE The reference voltage of a multi-unit SVU is the sum of the reference voltages of the individual units.
3.8
reference current of an SVU
I
ref
peak value (the higher peak value of the two polarities if the current is asymmetrical) of the
resistive component of a power-frequency current used to determine the reference voltage of
the SVU
NOTE 1 The reference current should be high enough to make the effects of stray capacitances at the measured
reference voltage of the SVU units negligible. It is to be specified by the manufacturer.
NOTE 2 Depending on the nominal discharge current of the EGLA, the reference current will be typically in the
range of 0,05 mA to 1,0 mA per square centimetre of metal-oxide resistor area for a single column SVU.
3.9
rated short-circuit current of an SVU
I
s
r.m.s. value of the highest short-circuit current under which the SUV will not fail in a manner
that causes violent shattering of the housing and under which self-extinguishing of open
flames (if any) will occur within a defined period of time

3.10
residual voltage of an EGLA
peak value of voltage that appears across the terminal-to-terminal length of the EGLA
including series gap and connection leads during the passage of discharge current
3.11
residual voltage of an SVU
peak value of voltage that appears between the terminals of the SVU during the passage of
discharge current
3.12
surface leakage current of an SVU
current that flows on the surface of the SVU

60099-8  IEC:2011 – 11 –
3.13
follow current
I
follow
the current immediately following an impulse through an EGLA with the power-frequency

voltage as the source
3.14
specified long-term load of an SVU

SLL
mechanical force perpendicular to the longitudinal axis of an SVU, allowed to be continuously
applied during service without causing any mechanical damage to the SVU

3.15
specified short-term load of an SVU
SSL
greatest mechanical force perpendicular to the longitudinal axis of an SVU, allowed to be
applied during service for short periods and for relatively rare events (for example, short-
circuit current loads and extreme wind gusts) without causing any mechanical damage to the
SVU
3.16
mean breaking load of an SVU
MBL
the average breaking load for porcelain or cast resin-housed SVUs determined from tests
3.17
high current impulse
peak value of discharge current having a 4/10 or 2/20 impulse shape, which is used to test the
withstand capability of the SVU on extreme lightning occasions
3.18
salt deposit density
SDD
the amount of salt in the deposit on a given surface of the SVU housing, divided by the area
of this surface; generally expressed in mg/cm²
3.19
verification test for coordination between insulator withstand and EGLA protective level
test used to verify that the EGLA will exhibit correct sparkover operation and clamp the
overvoltage caused by lightning considerably lower than the flashover voltage of the parallel-
connected insulator assembly
3.20
vibration withstand test
test to verify that the SVU and its connectors can withstand the specified mechanical vibration
levels
4 Identification and classification
4.1 EGLA identification
An EGLA shall be identified by the following minimum information, which shall appear on a
nameplate permanently attached to the arrester:
• rated voltage U in kV;
r
• rated frequency in Hz, only if it is less than 48 Hz or larger than 62 Hz;
• classification series information (examples: "X1", "Y2");

– 12 – 60099-8  IEC:2011
• rated short-circuit current I in kA;
s
• manufacturer’s name or trade mark;

• year of manufacture;
• serial number (at least for arresters for U > 52 kV);
m
• lightning discharge capability (only charge value) in C; example: "8 C".

Information on required gap spacing including tolerances shall be given in an appropriate

way, for example in the manual.

4.2 EGLA classification
EGLAs are classified by their nominal discharge currents and their high current impulse
withstand capabilities as per Table 1, and they shall meet at least the test requirements and
performance characteristics specified in Table 3. These arresters have no operating duties for
slow-front surges and power-frequency overvoltages.
Table 1 – EGLA classification – “Series X” and “Series Y“
Series X Series Y
Class name X1 X2 X3 X4 Class name Y1 Y2 Y3 Y4
Nominal discharge 5 5 10 20 Nominal discharge 5 10 15 20
current (kA), 8/20 current (kA), 2/20
High current impulse 40 65 100 100 High current impulse 10 25 40 65
(kA), 4/10 (kA), 2/20
NOTE 1 "Series X" corresponds to the classification used in IEC 60099-4. A nominal discharge current of
8/20 wave shape and a high current impulse of 4/10 wave shape are used in IEC and in IEEE standards.
"Series Y" corresponds to the classification applied e.g. in Japan on shielded line applications. Specification
of wave shape 2/20 both for the nominal discharge current and for the high current impulse is based on this
special application.
NOTE 2 According to service conditions, other high current impulse values than those specified in this table
may be applied.
5 Standard ratings and service conditions
5.1 Standard rated voltages
Standard values of rated voltages (r.m.s. values) are specified in Table 2 in equal voltage
steps within specified voltage ranges.

Table 2 – Steps of rated voltages (r.m.s. values)
Range of rated voltages (kV) Steps of rated voltage (kV)
3 - 30 1
> 30 - 54
> 54 - 96
> 96 - 288 12
> 288 - 396
> 396
NOTE Other values of rated voltage may be acceptable, provided they are multiples of 6.

60099-8  IEC:2011 – 13 –
5.2 Standard rated frequencies

The standard rated frequencies are 48 Hz to 62 Hz.

5.3 Standard nominal discharge currents

The standard nominal discharge currents for 8/20 or 2/20 shapes are: 5 kA, 10 kA, 15 kA and
20 kA.
5.4 Service conditions
5.4.1 Normal service conditions

EGLAs which conform to this standard shall be suitable for normal operation under the
following normal service conditions:
a) ambient air temperature within the range of –40 ºC to +40 ºC;
b) altitude not exceeding 1000 m;
c) frequency of the a.c. power supply not less than 48 Hz and not more than 62 Hz;
d) power-frequency voltage applied continuously between the terminals of the EGLA not
exceeding its rated voltage;
e) mechanical conditions: not specified (see NOTE);
f) wind speed: not specified (see NOTE);
g) pollution conditions: pollution by dust, smoke, corrosive gases, vapours or salt may occur;
pollution does not exceed “heavy” as defined in IEC/TS 60815-1.
NOTE It is recognized that mechanical and environmental issues are important for service, but due to the large
variety of possible installation configurations it is not possible to provide standard values for items e) and f).
5.4.2 Abnormal service conditions
Surge arresters subject to other than normal application or service conditions may require
special consideration in design, manufacture or application. The use of this standard in case
of abnormal service conditions shall be subject to agreement between the manufacturer and
the purchaser.
6 Requirements
6.1 Insulation withstand of the SVU and the complete EGLA
6.1.1 Insulation withstand of the housing of the SVU

The housing of the SVU shall withstand a lightning impulse voltage of
a) for "Series X": 1,4 times the residual voltage at the nominal discharge current
b) for "Series Y": 1,13 times the residual voltage at high current impulse, but not less than
1,3 times the residual voltage at nominal discharge current
NOTE The factor of 1,4 in case a) covers variations in atmospheric conditions and discharge currents up to three
times the nominal discharge current.
6.1.2 Insulation withstand of EGLA with shorted (failed) SVU
The EGLA shall have the following insulation withstand performance:
a) the EGLA shall withstand the specified switching impulse withstand voltage level of the
system even if the SVU has been shorted due to overloading (failure);

– 14 – 60099-8  IEC:2011
b) the EGLA shall be able to withstand the maximum temporary overvoltages phase to

ground for their maximum durations even if the SVU has been shorted due to overloading

(failure).
6.2 Residual voltages
The purpose of the measurement of residual voltages is to obtain the maximum residual

voltages for a given design for all specified currents and wave shapes. These are derived

from the type test data and from the maximum residual voltage at a lightning impulse current

used for routine tests as specified and published by the manufacturer.

The maximum residual voltage of a given EGLA design for any current and wave shape is

calculated from the residual voltage of SVU sections tested during type tests multiplied by a
specific scale factor plus a calculated inductive voltage drop across the SVU, the gap and
connection leads. The scale factor is equal to the ratio of the declared maximum residual
voltage, as checked during the routine tests, to the measured residual voltage of the sections
at the same current and wave shape.
The value of the residual voltage of the EGLA at nominal discharge current and at high
current impulse, respectively, multiplied by a factor as given in 6.1.1, shall be lower than the
minimum flashover voltage of the insulator assembly to be protected.
6.3 High current duty
The capability of the SVU for discharging operations shall be demonstrated by injecting two
high current impulses.
6.4 Lightning discharge capability
The capability of the metal-oxide resistors to withstand lightning discharges having current
waveforms with durations of several tens of microseconds for arresters applied on shielded
lines and several hundreds of microseconds for arresters on unshielded lines shall be
demonstrated. The related test also covers effects of multiple lightning strikes.
6.5 Short-circuit performance of the SVU
The manufacturer shall claim a short-circuit rating of the SVU. The short-circuit currents
according to this rating shall not cause violent shattering of the SVU, and any open flames
shall self-extinguish in a given time.
NOTE The gap is not subject of the short-circuit tests on the SVU, and its short-circuit performance should be
verified separately. The gap should be able to maintain its mechanical integrity after having been subjected to the
rated short-circuit current of the EGLA, and its sparkover voltage should not be decreased.

6.6 Mechanical performance
For the EGLA to be mounted on transmission towers or poles, mechanical performance to
withstand tensile, bending and/or vibration loads due to wind pressure, conductor vibration
abnormal load during installation work and moisture ingress shall be demonstrated.
The applicable values of tensile and bending loads shall be agreed between the manufacturer
and the purchaser.
The SVU shall be able to withstand the vibration load to be expected in service.
NOTE The complete EGLA including gap assembly and mounting structure should be able to withstand at least
the same mechanical stress.
60099-8  IEC:2011 – 15 –
6.7 Weather aging of SVU
The SVU must be able to withstand the environmental stress expected in service.

Environmental tests demonstrate by accelerated test procedures that the sealing mechanism

and the exposed metal combinations of the SVU are not impaired by environmental

conditions. For SVUs with polymer (composite and cast resin) housings, resistance to UV
radiation has to be demonstrated in addition.

NOTE A revision of the UV test is currently under consideration by Cigré WG D1.14.

6.8 Reference voltage of the SVU

The reference voltage (U ) of the SVU shall be measured at the reference current on
ref
sections and units when required. The measurement shall be performed at an ambient
temperature of 20 °C ± 15 K, and the actual temperature shall be recorded.
NOTE As an acceptable approximation, the instantaneous value of the current at the instant of voltage peak may
be taken to correspond to the peak value of the resistive component of current.
6.9 Internal partial discharges
The level of internal partial discharges in the SVU in the tests according to 9.1 and 10.3 shall
not exceed 10 pC.
6.10 Coordination between insulator withstand and EGLA protective level
The correct coordination between flashover characteristics of the insulator assembly, the
sparkover voltage of the EGLA with front-of-wa
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