IEC TS 61463:2016

IEC TS 61463 ®
Edition 2.0 2016-07
TECHNICAL
SPECIFICATION
Bushings – Seismic qualification
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IEC TS 61463 ®
Edition 2.0 2016-07
TECHNICAL
SPECIFICATION
Bushings – Seismic qualification

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.080.20 ISBN 978-2-8322-3518-8

– 2 – IEC TS 61463:2016 © IEC 2016
CONTENTS
FOREWORD .4
INTRODUCTION .6
1 Scope .7
2 Normative references .7
3 Terms and definitions .7
4 Symbols and abbreviated terms .8
5 Methods of seismic qualification .9
6 Severities . 10
6.1 At the ground . 10
6.2 At the bushing flange . 10
7 Qualification by static calculation . 11
8 Qualification by dynamic analysis . 13
8.1 General . 13
8.2 Modal analysis using the time-history method . 14
8.3 Modal analysis using the RRS . 14
9 Qualification by vibration test . 14
9.1 General . 14
9.1.1 General . 14
9.1.2 Mounting . 15
9.1.3 External load . 15
9.1.4 Measurements . 15
9.1.5 Standard frequency range . 15
9.1.6 Test methods . 15
9.1.7 Testing . 17
9.2 Test on complete apparatus . 18
9.3 Test on the bushing mounted on a simulating support . 18
9.4 Test on the bushing alone . 18
10 Evaluation of the seismic qualification . 18
10.1 Combination of stresses . 18
10.2 Cantilever test . 19
10.3 Acceptance criteria . 19
11 Necessary exchange of information . 20
11.1 Information supplied by the apparatus manufacturer . 20
11.2 Information supplied by the bushing manufacturer . 20
Annex A (informative) Flow chart for seismic qualification . 23
Annex B (informative) Natural frequency and damping determination: Free oscillation
test . 24
B.1 Free oscillation test . 24
B.2 Sine sweep frequency search . 25
Annex C (informative) Static calculation method – Additional considerations . 26
C.1 General . 26
C.2 Effect of the first bending mode . 26
C.3 Determination of S . 26
c
C.4 Value of a . 26
bg
C.5 Typical seismic response of cantilever type structures . 27

C.6 Superelevation factor K . 29
Annex D (informative) Qualification by static calculation – Example on transformer
bushing . 33
D.1 Seismic ground motion . 33
D.2 Critical part of the bushing . 33
D.3 Static calculation . 33
D.3.1 General . 33
D.3.2 Seismic load . 34
D.3.3 Wind load . 35
D.3.4 Terminal load . 35
D.4 Guaranteed bending strength . 36
Annex E (informative) Center clamped bushings . 37
Bibliography . 40

Figure 1 – Example of model of the transformer system . 14
Figure 2 – RRS for ground mounted equipment – ZPA = 0,5 g [1] [2] . 17
Figure 3 – Response factor R . 21
Figure 4 – Test with simulating support according to 9.3 . 22
Figure 5 – Determination of the severity . 22
Figure A.1 – Flow chart for seismic qualification . 23
Figure B.1 – Typical case of free oscillations. 24
Figure B.2 – Case of free oscillations with beats . 25
Figure C.1 – Single degree of freedom system . 27
Figure C.2 – Structure at the flange of a bushing with cemented porcelain [5] [7] . 28
Figure C.3 – Spring stiffness C in function of cemented part geometry [5] [7] . 29
Figure C.4 – Superelevation factor due to the existence of transformer body and
foundation [5] . 30
Figure D.1 – Critical part of the bushing . 33
Figure D.2 – Forces affecting the bushing . 34
Figure D.3 – Porcelain diameters . 35
Figure E.1 – Failure process [6] . 37
Figure E.2 – Failure process, flow chart [5] [6] . 38
Figure E.3 – Stress profile during the opening process [6] . 38
Figure E.4 – Relation between compression and tensile stress in the bottom edge of
the porcelain due to the opening process [6] . 39

Table 1 – Ground acceleration levels . 10
Table 2 – Dynamic parameters obtained from experience on bushings with porcelain
insulators (f = natural frequency, d = damping) . 12
Table 3 – Dynamic parameters obtained from experience on bushings with composite
insulators (f = natural frequency, d = damping) . 12
Table 4 – Example of qualification level: AG5: ZPA = 0,5 g. 17
Table 5 – Response factor R . 21
Table C.1 – Examples of typical seismic responses . 31

– 4 – IEC TS 61463:2016 © IEC 2016
INTERNATIONAL ELECTROTECHNICAL COMMISSION
___________
BUSHINGS – SEISMIC QUALIFICATION

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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.
The main task of IEC technical committees is to prepare International Standards. In
exceptional circumstances, a technical committee may propose the publication of a Technical
Specification when
• the required support cannot be obtained for the publication of an International Standard,
despite repeated efforts, or
• The subject is still under technical development or where, for any other reason, there is
the future but no immediate possibility of an agreement on an International Standard.
Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
IEC 61463, which is a Technical Specification, has been prepared by subcommittee 36A:
Insulated bushings, of IEC technical committee 36: Insulators.
This second edition cancels and replaces the first edition published in 1996 and
Amendment 1:2000. This edition constitutes a technical revision.

This edition includes the following significant technical changes with respect to the previous
edition:
a) the seismic spectrum profile has been substituted with the one of IEEE Std 693-2005,
worldwide used as a reference;
b) the acceptance criteria have been reviewed and the maximum permissible stress for each
main material has been harmonized with the relevant IEC Standard for that material;
c) a load on the head has been prescribed when the bushing is subject to the vibration test;
d) the sine sweep test has been added as a method of search of resonance frequency,
worldwide used.
The text of this document is based on the following documents:
Enquiry draft Report on voting
36A/178/DTS 36A/179/RVC
Full information on the voting for the approval of this document can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC website under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• transformed into an International standard,
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

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.
– 6 – IEC TS 61463:2016 © IEC 2016
INTRODUCTION
As it is not always possible to define accurately the seismic severity at the bushing flange
level, IEC TS 61463, which is a Technical Specification, presents three alternative methods
of qualification. The three methods are equally acceptable. If the required response spectrum
(RRS) at the bushing flange is not known, a severity (in terms of acceleration values) based
on standard response spectra at the ground level may be used to carry out qualification
through one of the three methods described in this document.
When the environmental characteristics are not sufficiently known, qualification by static
calculation is acceptable. Where high safety reliability of equipment is required for a specific
environment, precise data are used, therefore qualification by dynamic analysis or vibration
test is recommended. The choice between vibration testing and dynamic analysis depends
mainly on the capacity of the test facility for the mass and volume of the specimen, and, also
if non-linearities are expected.
When qualification by dynamic analysis is foreseen, it is recommended that the numerical
model be adjusted by using vibration data (see Clause 5).
This document was prepared with the intention of being applicable to bushings whatever their
construction material and their internal configuration.The information contained, originally
directed to porcelain bushings, has been partially updated to include also composite
bushings.
BUSHINGS – SEISMIC QUALIFICATION

1 Scope
IEC TS 61463, which is a Technical Specification, is applicable to alternating current and
direct current bushings for highest voltages above 52 kV (or with resonance frequencies
placed inside the seismic response spectrum), mounted on transformers, other apparatus or
buildings. For bushings with highest voltages less than or equal to 52 kV (or with resonance
frequencies placed outside from the seismic response spectrum), due to their characteristics,
seismic qualification is not used as far as construction practice and seismic construction
practice comply with the state of the art.
This document presents acceptable seismic qualification methods and requirements to
demonstrate that a bushing can maintain its mechanical properties, insulate and carry current
during and after an earthquake.
The seismic qualification of a bushing is only performed upon request.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements 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 60068-2-47, Environmental testing – Part 2-47: Test – Mounting of specimens for
vibration, impact and similar dynamic tests
IEC 60068-2-57, Environmental testing – Part 2-57: Tests – Test Ff: Vibration – Time-history
and sine-beat method
IEC 60068-3-3:1991, Environmental testing – Part 3-3: Guidance – Seismic test methods for
equipments
IEC 60137, Insulated bushings for alternating voltages above 1 000 V
IEC 61462, Composite hollow insulators – Pressurized and unpressurized insulators for use
in electrical equipment with rated voltage greater than 1 000 V – Definitions, test methods,
acceptance criteria and design recommendations
IEC 62155, Hollow pressurized and unpressurized ceramic and glass insulators for use in
electrical equipment with rated voltages greater than 1 000 V
IEC 62217, Polymeric insulators for indoor and outdoor use – General definitions, test
methods and acceptance criteria
ISO 2041, Mechanical vibration, shock and condition monitoring – Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60068-3-3,
IEC 60137, IEC 61462, ISO 2041 and the following apply.

– 8 – IEC TS 61463:2016 © IEC 2016
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp

3.1
critical cross-section
section of the bushing that is most likely to fail during an earthquake
3.2
response spectrum
plot of the maximum response to a defined input motion of a family of single-degree-of-
freedom bodies at a specified damping ratio
[SOURCE: IEC 60068-2-57:2013, 3.18, modified — The words "as a function of their natural
frequencies and at a specified damping ratio" has been replaced by "at a specified damping
ratio".]
3.3
rigid equipment
equipment whose natural frequency is greater than 33 Hz is considered rigid for the purpose
of this technical specification
3.4
standard frequency range
predominant frequencies of a typical earthquake
Note 1 to entry: This range is generally between 0,3 Hz and 33 Hz.
Note 2 to entry: This range is sufficient to determine the critical frequencies of the equipment and for its testing.
In certain cases the test frequency range may be extended or reduced dependent on the critical frequencies
present, but this shall be justified.
3.5
zero period acceleration
high frequency asymptotic value of acceleration of a response spectrum (above the cut-off
frequency of 33 Hz)
Note 1 to entry: This acceleration corresponds to the maximum acceleration of the time history used to derive the
spectrum.
4 Symbols and abbreviated terms
a equivalent maximum acceleration to the centre of gravity of the bushing during the
bg
seismic event
a maximum acceleration of the bushing flange
f
a maximum acceleration of the ground resulting from the motion of a given earthquake
g
NOTE a is equal to the zero period acceleration (ZPA) of Figure 2.

g
d damping of the bushing
d distance between the centre of gravity of the part of the bushing which is under
p
consideration and the critical cross-section
f first natural frequency of the bushing
K superelevation factor between ground and bushing flange: factor accounting for the
change in the acceleration from the ground to the flange due to the amplification by
foundation, buildings and structure
m mass of the part of the bushing which is under consideration
p
M bending moment at the critical cross-section of the part of the bushing considered,
s
due to an earthquake
R response factor derived from the required response spectrum (RRS) as the ratio
between the response acceleration and the ZPA (see Figure 3)
RRS required response spectrum: response spectrum specified by the user
S coefficient established to take into account the effects of both multifrequency
c
excitation and multimode response
S spectral acceleration
a
ZPA zero period acceleration (see a )
g
5 Methods of seismic qualification
Seismic qualification should demonstrate the ability of a bushing to withstand seismic
stresses and to maintain its required function without failure, during and after an earthquake
of a specified severity (see Clause 6).
As bushings are mounted on apparatus or buildings, the seismic qualification of the bushing
must consider the behaviour of the system on which the bushing is fixed. In the seismic
qualification of a bushing, all parts should be included, which contribute to the stresses in the
critical cross-sections during a seismic event, for example the conductor and inner spacer in
gas insulated bushings.
Three methods and combinations thereof are described in this document:
– qualification by static calculation (Clause 7);
– qualification by dynamic analysis (Clause 8);
– qualification by vibration test (Clause 9).
A combination of the methods may be used
– to qualify a bushing which cannot be qualified by testing alone (e.g. because of size
and/or complexity of the apparatus),
– to qualify a bushing already tested under different seismic conditions, and
– to qualify a bushing similar to a bushing already tested but which includes modifications
influencing the dynamic behaviour (e.g. change in the length of insulators or in the mass).
Vibrational data (damping, critical frequencies, stresses of critical elements as a function of
input acceleration) for analysis can be obtained by
a) a dynamic test on a similar bushing,
b) a dynamic test at reduced test level, and
c) determination of natural frequencies and damping by other tests such as free oscillation
tests or sine sweep tests (see Annex B).
The methods result in the value of M which is determined for each part of the bushing on

s
either side of the flange. The stress due to this moment should be combined with the other
stresses acting in the bushing, and it should be demonstrated that the bushing withstands the
combined stress (Clause 10).
The different methods of seismic qualification are illustrated in the flow chart given in Annex
A.
– 10 – IEC TS 61463:2016 © IEC 2016
6 Severities
6.1 At the ground
The ground acceleration depends upon the seismic conditions of the site where the
apparatus is to be located. When it is known, it should be prescribed by the relevant
specification. Otherwise, the severity level should be selected from Table 1.
Table 1 – Ground acceleration levels
Description of earthquake
Ground
acceleration
ZPA = a Richter UBC
b
General Intensity MSK RRS
reference 2 a
m/s scale magnitude zone
g
c
AG2 Light to medium 2 (0,2 g) 1 to 2 Figure 1
< 5,5 < VIII
earthquakes
c
AG3 Medium to strong 3 (0,3 g) 5,5 to 7,0 3 VIII to IX Figure 1
earthquakes
AG5 Strong to very strong 5 (0,5 g) 4 Figure 1
> 7,0 > IX
earthquakes
a
Approximate Uniform building code zone (International conference of building officials).
b
MSK (Medvedev-Sponheuer-Karnik) corresponds to modified Mercalli intensity scale.
c
Values for AG2 and AG3 are obtained by multiplying the values from Figure 2 by 2/5 and 3/5 respectively.

The selected qualification level should be in accordance with expected earthquakes of
maximum ground motions for the site location, for which certain structures, systems and
components are designed to remain functional. These structures are those essential to
assure proper function, integrity and safety of the total system (S type earthquakes,
according to IEC 60068-3-3).
For qualification, it should be assumed that
– the horizontal movements as described in Table 1 act in any direction
– the severities of the vertical accelerations are 50 % of the horizontal (if a different value is
used, a justification shall be provided), and
– both directions may reach their maximum values simultaneously.
The ground motion can be described by natural time histories when known, or by artificial
time histories, which should comply with the RRS; this is used as input for dynamic analysis
or vibration test on the complete apparatus.
NOTE Information on the correlation between seismic qualification levels, seismic zone and seismic scales is
given in IEC 60721-2-6 [1] and IEC 60068-3-3.
6.2 At the bushing flange
The severity at the bushing flange (see Figure 5) may be available from the manufacturer of
the apparatus and structures (i.e. transformers, gas insulated apparatuses (GIS), building) in
terms of RRS or maximum acceleration (a ). Where no information is available, the following
f
simplified formula is used in order to establish an acceleration value at the flange of the
bushing.
a = K × a
f g
The superelevation factor K can be
_____________
Numbers in square brackets refer to the Bibliography.

– calculated by finite element analysis including soil interaction or any other careful
modelling, or
– derived from results from calculations or tests on comparable apparatus or structures, or
– taken from typical values obtained from experience.

So far, very little experience is reported. Unless more background information is available, K
should be assumed to be 1 for through-wall bushings, 1,5 for GIS bushings and for
transformer bushings directly mounted on the transformer cover, and 2 for transformer
bushings mounted on a turret. If the mounting configuration on the transformer is not known,
K will be assumed as 1,5.
See also IEC 60068-3-3:1991, Table 4.
7 Qualification by static calculation
This method is valid for rigid equipment. It may be extended to flexible equipment, such as a
bushing, taking into consideration the response factor R, as an alternative to the method by
analysis. This allows simpler evaluation with increased conservatism.
Using the static calculation method, the bending moment in the critical cross-section of the
part of the bushing under consideration is calculated from an equivalent acceleration of the
centre of gravity of that part (a ):
bg
M = a × d × m
s bg p p
This acceleration, a , is calculated from the flange acceleration a by multiplication with a
bg f
coefficient S and the response factor R (see Annex C):
c
a = a × S × R
bg f c
The value of S depends on the natural frequency f of the mounted bushing:
c 0
f ≤ 8 Hz S = 1,5
0 c
8 < f < 33 Hz S = 1 + 0,5 × (33 – f ) / (33-8)
0 c 0
f ≥ 33 Hz S = 1,0
0 c
If the natural frequency f is not known, the conservative value S = 1,5 should be used.
0 c
The value R can be established by one of the following methods.
a) From the spectrum at the bushing flange (if available).
b) When the spectrum at the bushing flange is not known, the spectrum at the ground
(Figure 2) may be used assuming that the levels at all frequencies are equally amplified
(K factor) from the ground to the flange. For such cases, the values of R are summarized
in Figure 3. The value of R is derived from the RRS (Figure 2 and Table 4) by dividing the
spectrum values with the ZPA value of asymptotic acceleration.
In order to correctly use the R values, it is necessary to know the first natural frequency f
and the damping d % of the bushing mounted on its supporting structure. The natural
frequency can either be calculated as indicated for the superelevation factor or found by a
free oscillation test as described in Annex B.
c) R may be assumed to be equal to 2,5 when information for frequency f and damping d %
of the bushing mounted on a transformer is not available. The value of 2,5 corresponds to
the frequency range 1,1 Hz to 8 Hz and 5 % damping ratio (ref. to Figure 3 and Table 5).

– 12 – IEC TS 61463:2016 © IEC 2016
d) R may be assumed to be equal to 2,9 when information for frequency f and damping d %
of the bushing mounted on a GIS structure is not available. The value of 2,9 corresponds
to the frequency range 1,1 Hz to 8 Hz and 3 % damping ratio (ref. to Figure 3 and Table
5).
Different R values can be agreed between purchaser and manufacturer if justified.
Collected data show that the first natural frequency of a mounted bushing is lower than that
of the bushing itself. Reported natural frequencies show a great variation, while the damping
ratios lie within a limited range (see Table 2 and Table 3).
An example of the application of the method for bushings mounted on a transformer is given
in Annex D.
Table 2 – Dynamic parameters obtained from experience
on bushings with porcelain insulators (f = natural frequency, d = damping)
Highest voltage of equipment
Type of 123 kV to 170 kV 245 kV to 362 kV 420 kV to 550 kV 800 kV to 1 200 kV
mounting
f d f d f d f d
0 0 0 0
[%] [%] [%] [%]
[Hz] [Hz] [Hz] [Hz]
Bushing alone
(mounted on a 15 to 35 2 to 4 10 to 24 2 to 4 3 to10 2 to 5 1.5 to 5 2 to 6
rigid structure)
Bushing mounted
on a transformer 5 to 20 3 to 6 5 to 15 5 3 to 8 5 1 to 4 5
tank
Bushing mounted
4 to 12 3 to 5 4 to 10 – 3,5 to 10 – 4 to 5 1,5 to 3
on a GIS
Bushing mounted
– – – – – – – –
on a building
NOTE 1 In the case of special dissipating systems, higher damping ratios can be obtained.
NOTE 2 Additional data will be included in this table based on experience of the practical application of this
technical specification.
Table 3 – Dynamic parameters obtained from experience on
bushings with composite insulators (f = natural frequency, d = damping)
Highest voltage of equipment
Type of 123 kV to 170 kV 245 kV to 362 kV 420 kV to 550 kV 800 kV to 1 200 kV
mounting
f d f d f d f d
0 0 0 0
[Hz] [%] [Hz] [%] [Hz] [%] [Hz] [%]
Bushing alone
(mounted on a 14 to 18 1.5 to 2 5,5 to 13 1 to 3,5 3.5 to6,5 1 to 4
rigid structure)
Bushing mounted
on a transformer
tank
Bushing mounted
10 4 to 5,5 1 to 4
on a GIS
Bushing mounted
on a building
NOTE 1 In the case of special dissipating systems, higher damping ratios can be obtained.
NOTE 2 An empty space means that data are not yet available. Additional data or ranges of values will be
included in this table based on experience of the practical application of this technical specification.

8 Qualification by dynamic analysis
8.1 General
For dynamic analysis, the whole structure, the apparatus and the ground conditions including
foundations, with the mounted bushing, should be modelled by finite elements or other
mathematical modelling technique, taking into consideration the specific values of elasticity
and damping of all elements as well as the relevant masses. The structure may be assumed
to behave linearly and elastically except special seismic equipment (see 10.3, c)), which
should be modelled with its actual properties. The linear values used should correspond to
the values expected at the seismic load level.
Natural frequencies of the bushing, the rocking motion of the foundation and responses at the
top of the bushing are influenced by the mass of the foundation, by the spring constant and
by the damping coefficient of soil. When the natural frequency of the bushing and the one of
the rocking motion are coincident, resonant phenomena occur and high response at the top
of the bushing can be produced.
If then the condition of the soil is not good (soft), the modeling of the total transformer system
(soil – foundation – transformer body – turret – bushing, refer to Figure 1) will be necessary.
The model in Figure 1 is an example of the whole system [3].
m
m
m
Bushing
m
Sleeve
m
m
K ,C
1 1
K ,C
2 2
Bushing turret
m
K ,C
3 3
Transformer body
m
Foundation
K ,C
HS HS
m
Soil
K ,C
RS RS
K ,C
K ,C
H H
R R
IEC
Symbols
mi: mass
K ,C : Rotational spring constant and damping coefficient at joint
i i
K ,C : Horizontal spring constant and damping coefficient at the bottom of foundation
H H
K ,C : Rotational spring constant and damping coefficient at the bottom of foundation
R R
K ,C : Horizontal spring constant and damping coefficient at the side of foundation
HS HS
– 14 – IEC TS 61463:2016 © IEC 2016
K ,C : Rotational spring constant and damping coefficient at the side of foundation
RS RS
Figure 1 – Example of model of the transformer system
From the calculation, the stresses in the critical cross-section of the bushing can be found.
A dynamic analysis may be performed on a bushing alone if the flange severity is already
known.
The general procedure is to establish, using experimental data, a mathematical model as the
previous shown of the structure in order to assess its dynamic characteristics and then to
determine the response, using either of the methods described in 8.2 and 8.3. Other methods
may be used if they can be justified.
8.2 Modal analysis using the time-history method
When the time-history method is used for seismic analysis, the ground motion acceleration
time-histories shall comply with the RRS (see Figure 2). Two types of superimposition may
generally be applied depending on the complexity of the problem:
– separate calculation of the maximum responses due to each of the three directions (x and
y in the horizontal, and z in the vertical direction) of the earthquake motion. The effects of
each single horizontal direction and the vertical direction shall be then combined by taking
2 2 1/2 2 2 1/2
the square root of the sum of the squares, i.e. (x + z ) and (y + z ) .
max max max max
The greater of these two values is used for the combination of the stresses of the
bushing;
– simultaneous calculation of the maximum responses assuming one of the seismic
horizontal directions and the vertical direction (x with z) and, thereafter, calculation of
max
the other horizontal direction and the vertical direction (y with z) . This means that, after
max
each step of calculation, all values (force, stresses) are superimposed algebrically. The
greater of these two values is used for the combination of the stresses of the bushing.
8.3 Modal analysis using the RRS
When the RRS method is used for seismic analysis, the procedure of combining the stresses
is described for an orthogonal system of co-ordinates in the main axes of the bushing and
with x and y in the horizontal and z in the vertical direction. The maximum values of stresses
in the bushing for each of the three directions x, y and z are obtained by superimposing the
stresses calculated for the various modal frequencies in each of these directions by taking
the square root of the sum of the squares. The maximum values in the x and z direction —
and in the y and z direction — are obtained by taking the square root of the sum of the
2 2 1/2 2 2 1/2
squares (x + z ) and (y + z ) . The greater value of these two cases (x, z)
max max max max
or (y, z) is used for the combination of the stresses of the bushing.
9 Qualification by vibration test
9.1 General
9.1.1 General
Three different approaches can be applied:
– test on the complete apparatus (bushing mounted on the real apparatus);
– test on the bushing mounted on a simulating support;
– test on the bushing alone.
The procedure for qualification by test shall be in accordance with IEC 60068-2-57 and
IEC 60068-3-3. The tests shall be made at the ambient air temperature of the test location

and this temperature shall be recorded in the test report. After the vibration test, the bushing
shall pass a routine test according to IEC 60137.
9.1.2 Mounting
General mounting requirements are given in IEC 60068-2-47. The specimen should be
mounted as in service including dampers (if any).
NOTE For more detailed guidance in the case of equipment normally used with vibration isolators, see A.5 of
IEC 60068-2-6:2007 [2].
The orientation and mounting of the specimen during conditioning should be prescribed by
the relevant standard. They are the only condition for which the specimen is considered as
complying with the requirements of the standard, unless adequate justification can be given
for extension to an untested condition (for instance, if it is proved that the effects of gravity
do not influence the behaviour of the specimen).
9.1.3 External load
Generally, electrical and environmental service loads cannot be simulated during the seismic
test. This applies also to possible internal pressure of the bushing due to safety requirements
of the test laboratory.
During vibrational test, the following weight shall be added to the HV bushing terminal:
• For U greater than 420 kV: 11 kg
m
• For U less or equal to 420 kV: 7 kg
m
These weights represent the lower range of weight associated with conductor connections
hardware and part of the weight of conductors connected to the bushing.
Other masses could be agreed between parts.
NOTE For combination of seismic and service loads to be taken into account during static or dynamic analysis,
see Clause 10.
9.1.4 Measurements
Measurements shall be performed in accordance with 5.2 of IEC 60068-3-3:1991, and should
include
– acceleration at both ends of the bushing and at the centre of gravity,
– displacement of the top of the bushing, and
– strains on critical cross-sections.
9.1.5 Standard frequency range
The frequency range shall be 0,3 Hz to 33 Hz.
9.1.6 Test methods
9.1.6.1 General
The following test methods with their waveforms shall be used to comply with RRS:
– time-history; or
– sine-beat; or
– other waveforms, for example sine wave (requiri
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