IEC 62271-211:2014

IEC 62271-211 ®
Edition 1.0 2014-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
High-voltage switchgear and controlgear –
Part 211: Direct connection between power transformers and gas-insulated
metal-enclosed switchgear for rated voltages above 52 kV

Appareillage à haute tension –
Partie 211: Raccordements directs entre transformateurs de puissance et
appareillage sous enveloppe métallique à isolation gazeuse de tensions
assignées supérieures à 52 kV
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IEC 62271-211 ®
Edition 1.0 2014-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
High-voltage switchgear and controlgear –

Part 211: Direct connection between power transformers and gas-insulated

metal-enclosed switchgear for rated voltages above 52 kV

Appareillage à haute tension –

Partie 211: Raccordements directs entre transformateurs de puissance et

appareillage sous enveloppe métallique à isolation gazeuse de tensions

assignées supérieures à 52 kV
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX S
ICS 29.130.10 ISBN 978-2-8322-1534-0

– 2 – IEC 62271-211:2014 © IEC 2014
CONTENTS
FOREWORD . 4
1 General . 6
1.1 Scope . 6
1.2 Normative references . 6
2 Normal and special service conditions . 7
2.1 Normal service conditions . 7
2.2 Special service conditions . 7
3 Terms and definitions . 7
4 Rating. 8
4.1 Rated voltage (U ) . 8
r
4.2 Rated insulation level . 8
4.3 Rated frequency (f ) . 9
r
4.4 Rated continuous current (I ) and temperature rise . 9
r
4.5 Rated short-time withstand current (I ) and rated thermal short-time
k
current (I ) . 9
th
4.6 Rated peak withstand current (I ) and rated dynamic current (I ) . 9
p d
4.7 Rated duration of short-circuit (t ) and rated duration (t ) . 9
k th
4.8 Rated filling pressure p of gas for insulation . 9
re
5 Design and construction . 10
5.1 Limits of supply . 10
5.2 Pressure withstand requirements . 11
5.3 Gas and vacuum tightness . 11
5.4 Mechanical forces applied on the connection interface . 12
5.5 Mechanical forces applied on the bushing flange . 12
5.6 Horizontal and vertical displacement . 13
5.7 Vibrations . 13
6 Type tests . 14
6.1 General . 14
6.2 Dielectric tests . 14
6.2.1 Dielectric tests of bushing . 14
6.2.2 Dielectric tests of transformer connection in a single phase
enclosure . 14
6.2.3 Dielectric tests of transformer connection in a three phase
enclosure . 14
6.3 Cantilever load withstand tests. 14
6.4 Gas tightness tests . 15
7 Routine tests . 15
7.1 General . 15
7.2 External pressure test of the bushing . 15
7.3 Tightness tests . 15
8 Standard dimensions and tolerances . 15
8.1 Single-phase direct connection between oil-filled transformer and
switchgear . 15
8.2 Three-phase direct connection between oil-filled transformer and

switchgear . 15
8.3 Connection between gas-insulated transformer and switchgear . 16

8.4 Transformer tolerances . 16
8.5 Mounting of the transformer on its foundation . 16
9 Information to be given with enquiries, tenders and orders . 16
10 Transport, storage, erection, operation and maintenance . 16
Bibliography . 21

Figure 1 – Typical direct connection between power transformer and gas-insulated
metal-enclosed switchgear . 17
Figure 2 – Standard dimensions for typical direct connection between power
transformer and gas-insulated metal-enclosed switchgear . 18
Figure 3 – Transformer tolerances for a typical direct connection shown on the
example of a three-phase power transformer connected to a single-phase gas-
insulated metal-enclosed switchgear . 19
Figure 4 – Transformer tolerances for a typical direct connection shown on the
example of a three-phase power transformer connected to a three-phase gas-insulated
metal-enclosed switchgear up to 170 kV . 20

Table 1 – Moment and forces applied on the bushing flange and transformer . 13

– 4 – IEC 62271-211:2014 © IEC 2014
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
HIGH-VOLTAGE SWITCHGEAR AND CONTROLGEAR –

Part 211: Direct connection between power transformers and gas-
insulated metal-enclosed switchgear for rated voltages above 52 kV

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
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
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Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
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with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
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interested IEC National Committees.
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between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
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5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
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services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
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expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
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 62271-211 has been prepared by subcommittee 17C: High-voltage
switchgear and controlgear assemblies, of IEC technical committee 17: Switchgear and
controlgear.
This first edition cancels and replaces the first edition of IEC/TR 61639:1996 and constitutes
a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) transfer from technical report to international standard;
b) the minimum voltage rating was changed from 72,5 kV to above 52 kV;
c) update of normative references;
d) definition of insulated junction including limit of supply;

e) definition of dielectric test of gas-insulated metal-enclosed switchgear for transformer
connection in a three phase enclosure;
f) addition of interface tolerances at transformer side;
g) addition of transformer tolerances in service;
h) addition of exceptional loads for bushings and flanges;
i) consideration of oil- and gas-insulated transformers;
j) inclusion of three-phase enclosed direct connections.
The text of this standard is based on the following documents:
FDIS Report on voting
17C/596/FDIS 17C/600/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.
A list of all parts in the IEC 62271 series, published under the general title High-voltage
switchgear and controlgear, 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.
The contents of the corrigendum 1 of August 2015 and corrigendum 2 of August 2017 have
been included in this copy.
– 6 – IEC 62271-211:2014 © IEC 2014
HIGH-VOLTAGE SWITCHGEAR AND CONTROLGEAR –

Part 211: Direct connection between power transformers and gas-
insulated metal-enclosed switchgear for rated voltages above 52 kV

1 General
1.1 Scope
This part of IEC 62271 is applicable to single and three phase direct connections between
gas-insulated metal-enclosed switchgear (GIS) for rated voltages above 52 kV and
transformer arrangements to establish electrical and mechanical interchange ability and to
determine the limits of supply of for the transformer connection.
Direct connections are immersed on one end in the transformer oil or insulating gas and on
the other end in the insulating gas of the switchgear.
Transformer arrangements are single-phase transformers with single-phase enclosed
arrangement, three-phase transformers with three single-phase enclosed arrangements or
three-phase transformers with a three-phase enclosed arrangement with three transformer
bushings.
The connection satisfies the requirements of IEC 62271-203 for gas-insulated metal-enclosed
switchgear, IEC 60076 for power transformer and IEC 60137 for completely immersed
bushings.
For the purpose of this international standard the term "switchgear" is used for "gas-insulated
metal-enclosed switchgear".
1.2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60076 (all parts), Power transformers
IEC 60137:2008, Insulated bushings for alternating voltages above 1 000 V
IEC 61936-1, Power installations exceeding 1 kV a.c. – Part 1: Common rules
IEC 62271-1:2007, High-voltage switchgear and controlgear – Part 1: Common specifications
IEC 62271-203:2011, High-voltage switchgear and controlgear – Part 203: Gas-insulated
metal-enclosed switchgear for rated voltages above 52 kV
IEC 62271-207, High-voltage switchgear and controlgear – Part 207: Seismic qualification for
gas-insulated switchgear assemblies for rated voltages above 52 kV

2 Normal and special service conditions
2.1 Normal service conditions
Subclauses 2.1 of IEC 62271-1:2007 and IEC 62271-203:2011 are applicable.
2.2 Special service conditions
Subclauses 2.2 of IEC 62271-1:2007 and IEC 62271-203:2011 are applicable.
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 62271-1, as well as
the following apply.
3.1
bushing
device that enables a conductor to pass through a transformer tank, and insulates the
conductor from it
Note 1 to entry: The means of attachment (flange or fixing device) to the tank forms part of the bushing.
[SOURCE: IEC 60050-471:2007, 471-02-01, modified – update of the definition]
3.2
completely immersed bushing
a bushing both ends of which are intended to be immersed in an insulating medium other than
ambient air (e.g. oil or gas)
[SOURCE: IEC 60050-471:2007, 471-02-04]
3.3
gas-insulated switchgear enclosure
part of gas-insulated metal-enclosed switchgear retaining the insulating gas under the
prescribed conditions necessary to maintain safely the highest insulation level, protecting the
equipment against external influences and providing a high degree of protection to personnel
[SOURCE: 3.103 of IEC 62271-203:2011]
3.4
main circuit end terminal
part of the main circuit of a gas-insulated metal enclosed switchgear forming part of the
connection interface
[SOURCE: 3.2 of IEC 62271-209:2007]
3.5
transformer connection enclosure
part of the gas-insulated metal-enclosed switchgear which houses one end of a completely
immersed bushing fitted on a power transformer and a main circuit end terminal
3.6
maximum operating gas pressure
maximum pressure of the gaseous insulating medium in which one end of the bushing is
immersed, when in operation, the switchgear-power transformer connection assembly carrying
its rated normal current at the maximum ambient air temperature

– 8 – IEC 62271-211:2014 © IEC 2014
3.7
design pressure of the enclosure
relative pressure used to determine the design of the enclosure
Note 1 to entry: It is at least equal to the maximum operating gas pressure in the enclosure at the highest
temperature that the gas used for insulation can reach under specified maximum service conditions
[SOURCE: 3.113 of IEC 62271-203:2011, modified – update of the note to entry]
3.8
rated filling pressure p of gas for insulation
re
pressure (in Pa), for insulation, referred to the standard atmospheric air conditions of +20 °C
and 101,3 kPa, which may be expressed in relative or absolute terms, to which the assembly
is filled before being put into service
[SOURCE: 3.6.5.1 of IEC 62271-1:2007, modified – update of the term and the definition]
3.9
minimum functional pressure p for insulation
me
pressure (in Pa), for insulation, referred to the standard atmospheric air conditions of +20 °C
and 101,3 kPa, which may be expressed in relative or absolute terms at which and above
which the characteristics of the switchgear-power-transformer connection are maintained and
at which replenishment becomes necessary
[SOURCE: 3.6.5.5 of IEC 62271-1:2007, modified – update of the term and the definition]
3.10
insulated junction
all parts which are needed to insulate the transformer from the switchgear including but not
limited to the insulating flange
3.11
proctor density
moisture-density relationship of a soil for a given compactive effort depending on the amount
of water the soil contains during soil compaction of controlled magnitude
4 Rating
4.1 Rated voltage (U )
r
The rated voltage shall be the rated voltage of the switchgear, selected from the following
standard values:
72,5 kV – 100 kV – 123 kV – 145 kV – 170 kV – 245 kV – 300 kV – 362 kV – 420 kV – 550 kV
NOTE Values 800 kV and higher are not considered because there is little experience at this time.
4.2 Rated insulation level
The rated insulation level for the GIS part in the transformer connection enclosure shall be
selected from the values given in the product standard IEC 62271-203. The rated insulation
level for the transformer bushing shall be selected from the values given in the product
standard IEC 60137.
NOTE Transformers can be tested at other insulation level values, according to the relevant standard.
The rated insulation level for a direct connection has to fulfil at least the requirements of
IEC 62271-203.
4.3 Rated frequency (f )
r
Subclause 4.3 of IEC 62271-1:2007 applies.
4.4 Rated continuous current (I ) and temperature rise
r
The dimensions of the connection interfaces shown in Figure 2 allow a maximum value of
3 150 A for the rated continuous current. The connection interface is shown in Figure 1 as
parts 3 and 4.
The contact surfaces of the connection interface shall be silver-coated, copper-coated or bare
copper.
For the rated continuous current, the connection between switchgear and power transformer
shall be designed that the temperature of the transformer connection enclosure and the
temperature of the connection interface do not exceed the values given in 4.4.2 of
IEC 62271-203:2011.
4.5 Rated short-time withstand current (I ) and rated thermal short-time current (I )
th
k
For the rated short-time withstand current of the GIS part of the transformer connection 4.5 of
IEC 62271-1:2007 is applicable and for the rated thermal short-time current of the bushing 4.3
of IEC 60137:2008.
It is recommended to apply the same short-time currents for GIS and bushing.
4.6 Rated peak withstand current (I ) and rated dynamic current (I )
p d
For the rated peak withstand current of the GIS part of the transformer connection 4.6 of
IEC 62271-1:2007 is applicable and for the rated dynamic current of the bushing 4.4 of
IEC 60137:2008.
It is recommended to apply the same value for the rated peak withstand current for the GIS
and the rated dynamic current for the bushing.
4.7 Rated duration of short-circuit (t ) and rated duration (t )
k th
For the rated duration of the short-circuit current of the GIS part of the transformer connection
4.7 of IEC 62271-1:2007 is applicable and for the rated duration of the bushing 4.3 of
IEC 60137:2008.
It is recommended to apply the same value for the rated duration of short circuit for the GIS
and the rated duration for the bushing.
4.8 Rated filling pressure p of gas for insulation
re
The rated filling pressure p (or density) of gas for insulating is assigned by the switchgear
re
manufacturer.
If SF is used as the insulating gas, the minimum functional pressure for insulation p , used
me
to determine the design of the transformer bushing insulation, shall be not more than
0,35 MPa (absolute) at 20 °C.
For higher rated lightning impulse withstand voltage (BIL) the minimum functional pressure
may be increased.
– 10 – IEC 62271-211:2014 © IEC 2014
If a gas different from SF or a gas mixture is used, the minimum functional pressure shall be
chosen to provide the same dielectric strength. The minimum functional pressure shall be
below the maximum operating pressure and design pressure of the enclosure.
5 Design and construction
5.1 Limits of supply
A typical direct connection is shown in Figure 1.
The limits of supply of the switchgear manufacturer and transformer manufacturer shall be
according to Figure 1.
To minimize circulating currents between the switchgear and the transformer, bonding
connections according to IEC 61936-1 shall be provided by the switchgear manufacturer
between the different single phase switchgear enclosures; capable of carrying continuously
the rated current of the transformer in normal operation. If circulating currents higher than
250 A are expected via the single-phase transformer connection enclosure, an insulated
junction between the GIS and the transformer is necessary, see Figure 1 Part 9.This applies
to the direct connection of three-phase and single-phase power transformers according
IEC 60076 series.
NOTE 1 The tank of a transformer is not designed to carry any considerable, undefined continuous circulating
currents. Practical experiences have shown that a load current of up to 1 250 A can be carried without additional
precautions in the enclosure of the interface between the GIS and the transformer. This is due to the fact that
approximately 80 % of the load current is carried by the bonding connection of the switchgear, to be installed
preferably at the end of the switchgear enclosure at the transformer. Thus, approximately 20 % of the load current,
therefore up to 250 A, could generate continuous circulating currents in the transformer enclosure. The
confirmation of the current value in the bonding connection and through the transformer enclosure can be made by
calculation.
NOTE 2 The user clarifies with the transformer manufacturer to confirm the maximum acceptable current via the
transformer encapsulation to avoid the insulated junction, if possible.
An insulated junction may be also needed to achieve isolation between the transformer tank
and the neighbouring earthed switchgear enclosures, and to achieve correct operation of the
user’s protection schemes for GIS and transformer faults.
The insulation level across the insulated junction shall be designed to withstand a power-
frequency test voltage of 5 kV, r.m.s., for 1 min.
To limit the very-fast-front transient ground potential rises which may occur when a switching
device operates, non-linear resistors may be connected in parallel with the insulated junction.
The number and the characteristics of the non-linear resistors shall be determined by the
switchgear manufacturer. [1]
According to this standard two different locations (shown in Figure 1) are acceptable for the
insulated junction
a) location “A” between the flange of the transformer connection enclosure, part 6 in
Figure 1, and the flange of the bushing, part 10 in Figure 1, or
b) location “B” between the transformer connection enclosure, part 6 in Figure 1, and the
next switchgear housing, part 14 in Figure 1.
If the insulated junction is needed, the standard dimensions in accordance with Clause 8 shall
be kept.
___________
Numbers in square brackets refer to the Bibliography.

Independent of the existence of an insulated junction, bonding connections between the
single-phase enclosures of the switchgear need be provided by the switchgear manufacturer
in accordance with IEC 61936-1 and IEC 62271-203.
Bonding connections always need to be provided between single-phase enclosed direct
connection arrangements of single-phase, two-phase or three-phase transformers.
Bonding connections need not be provided for a three-phase transformer with a three-phase
enclosed direct connection arrangement.
In the case of not having an insulated junction, bonding connections shall be designed not
exceeding the permitted value of circulating current via the transformer tank as specified in
this clause.
Without an insulated junction the bonding connection shall be made at the end of the
transformer connection enclosure towards the bushing, i.e. location marked “A” in Figure 1.
With an insulated junction, in case of location marked “A” in Figure 1 the bonding connection
shall be made at the end of the transformer connection enclosure towards the bushing.
In case of location marked “B” in Figure 1 the bonding connection shall be made at the end of
the switchgear housing towards the bushing.
The transformer, including the bushing, shall be able to withstand very fast transient voltages
which are generated by the switchgear.
If an insulated junction is applied, its design shall be also able to withstand the same value of
the very fast transient voltages generated by the switchgear.
NOTE 3 Alternatively to the insulating junction an insulating spacer can be used.
5.2 Pressure withstand requirements
The maximum operating gas pressure used to determine the mechanical strength of the
bushing shall be at least 0,85 MPa (absolute) at 20 °C.
The transformer connection enclosure and all pressurized connected parts shall satisfy the
requirements provided in 5.103 of IEC 62271-203:2011 for the design pressure determined by
the switchgear manufacturer as specified in 5.103.2 of IEC 62271-203:2011.
The design pressure of the transformer connection enclosure may be lower than the maximum
operating gas pressure which is used to determine the mechanical strength of the bushing.
5.3 Gas and vacuum tightness
Subclause 5.15 of IEC 62271-203:2011 is applicable with the following addition:
For conditions up to the maximum occurring gas operating pressure, the bushing shall prevent
insulating media, gas, diffusing into the transformer.
The bushing shall prevent entering insulating media, gas or oil, into the GIS.
The bushing shall be capable of withstanding the vacuum conditions when the transformer
connection enclosure is evacuated, as part of the gas filling process and shall be capable of
withstanding the vacuum conditions when the transformer is evacuated as part of its gas or oil
filling process.
– 12 – IEC 62271-211:2014 © IEC 2014
In the case of a gas-insulated transformer the gas compartment of the transformer shall be
completely separated and managed independently from the switchgear.
5.4 Mechanical forces applied on the connection interface
Normal loads applicable to bushings at the connection interface (part 3 and 4 in Figure 1) are
given in IEC 60137:2008, Table 1, level I (see operating loads); the minimum normal load
however shall not be less than 2 kN, acting either transversely or axially to the connection
interface.
Table 1 of IEC 60137:2008 gives values for bushing installed up to 30° from the vertical.
If higher normal loads are to be expected at the connection interface, then the higher loads
shall be selected from IEC 60137:2008, Table 1, Level II (heavy load).
For exceptional such as short current or seismic loads use cantilever test load level II of
Table 1 in IEC 60137:2008.
For seismic requirements, it is necessary to carry out seismic calculation in order to identify
the location of mechanical reinforcements, see IEC 62271-207.
It is the responsibility of the switchgear manufacturer to ensure that this specified force is not
exceeded or agrees with the bushing manufacturer that the bushing shall withstand the higher
forces.
The selection of the appropriate bushing is under the responsibility of the transformer
manufacturer taking into account the maximum occurring short circuit forces between phase
and ground, respectively also between phases in the case of a three-phase enclosure at both
ends of the bushing.
In the case of different withstand currents of the GIS respectively the transformer, the higher
withstand currents apply.
5.5 Mechanical forces applied on the bushing flange
In addition to the maximum operating gas pressure specified in 5.2, the flange of the bushing
attached to the transformer connection enclosure is subjected, in service, to the following
normal loads:
– part of the weight of the switchgear not supported by the switchgear's own supporting
structures;
– part of the wind load, if applicable, not supported by the switchgear's own supporting
structures;
– expansion or contraction stresses due to the temperature variations of the transformer
tank.
The precise evaluation of these thermal stresses of the transformer tank shall be based on
the thermal expansion factor of the material of the transformer tank, taking into account the
lowest occurring ambient temperature (i.e. transformer out of service) and the occurring
average maximum temperature the transformer tank will have in operation (i.e. normally 90 °C
at a reference temperature of 20 °C). The thermal expansion factor of the material of the
transformer shall be considered for mild steel with 12E-6 / K. Concerning the expansion-
contraction of the transformer one cycle per day can be assumed.
NOTE 1 Variations of height or position due to draining the transformer oil and evacuating the transformer tank
are not considered, assuming that the switchgear and the transformer are not connected together when these
operations are performed.
Other expansion-contraction cycles need to be provided to the GIS manufacturer by the user.

These loads result in the simultaneous application, at the centre of the bushing flange, of:
– a bending moment M ;
– a shearing force F ;
t
– a tensile or compressive force F .
a
The bushing and the transformer shall be capable of withstanding, in service, the values of
M , F and F specified in Table 1, and it shall be the responsibility of the switchgear

0 t a
manufacturer to ensure that these values are not exceeded.
Exceptional loads, such as a short circuit, installation or seismic, shall be 200 % of the given
normal loads in Table 1.
NOTE 2 Forces on the transformer flange of the bushing imposed by switchgear enclosure as given in Table 1 are
significantly higher than those forces imposed by outdoor immersed bushings in accordance with IEC 60137 of
equivalent rating. These forces depend on the layout of the switchgear, with or without compensating elements on
the switchgear or transformer side.
NOTE 3 The requirement concerning the ratio between normal and exceptional load is in accordance with the
ratio of the operational and cantilever test loads in IEC 60137:2008, Table 1.
Table 1 – Moment and forces applied on the bushing flange and transformer
Rated voltage Bending moment M Shearing force F Tensile or compressive
0 t
force F
a
kV kN
kNm kN
52 to 100 5 7 4
123 to 170 10 10 5
245 to 300 20 14 7
362 to 550 40 20 10
For seismic requirements, it is necessary to carry out seismic calculation in order to identify
the location of mechanical reinforcements, see IEC 62271-207.
5.6 Horizontal and vertical displacement
Relative displacement between the foundations of the transformer and the switchgear shall be
avoided by appropriate civil engineering design.
A maximum relative vertical settlement of 5 mm between switchgear and transformer
foundation shall be considered in the design of a direct connection occurring during operation.
The ground below the transformer and switchgear foundation shall be compacted to achieve
100 % proctor density in order to obtain a maximum settlement of 5 mm between the
switchgear and transformer foundation.
Relative displacements of the different foundations caused by seismic activity are not covered
by this standard. Relative turning or tilting of the foundations is excluded as well, since such
is considered occurring only during seismic activity.
NOTE Most of the vertical settlement of a transformer foundation can be avoided, if the transformer remains
seated upon its foundation for 2 weeks filled with oil without being connected to the switchgear.
5.7 Vibrations
The vibrations generated inside the energized transformer are transmitted by the oil and the
tank wall of the transformer to the bushing rigidly fixed on this wall and to the switchgear. The
switchgear manufacturer and the transformer manufacturer shall agree to take into account

– 14 – IEC 62271-211:2014 © IEC 2014
these vibrations. The transformer may generate vibrations at frequencies which are multiple of
the network frequency.
6 Type tests
6.1 General
The testing of the bushing and the switchgear shall be performed in accordance with
IEC 60137 and IEC 62271-203 respectively, with the following additions.
6.2 Dielectric tests
6.2.1 Dielectric tests of bushing
The dielectric type tests of the bushing shall to be performed in an enclosure filled with
insulating gas at the minimum pressure specified in 4.8.
If a shield is an integral part of the bushing design, it shall be mounted in its service position
during the tests.
A cylindrical extension piece having a diameter equal to d in Figure 2 may be attached to the
exposed termination top for the tests, if required by the bushing manufacturer.
The bushing end shall be surrounded by an earthed metal cylinder, the diameter of which
shall not exceed d in Figure 2. The minimum length of the metal cylinder shall be in

accordance with the dimension l given in Figure 2.
To qualify single bushings for use in a three phase encapsulated system (i.e. assembled on a
common plate) calculations shall demonstrate that the dielectric withstand capability is equal
or higher compared to a single phase system. Phase-to-phase stress and phase-to-earth
stress have to be considered.
6.2.2 Dielectric tests of transformer connection in a single phase enclosure
The transformer connection enclosure and main circuit end terminal shall be subjected to the
dielectric type tests. Dielectric type test can be performed without the bushing but with a test
cylindrical extension piece having a diameter equal to d in Figure 2.
as
The dielectric type tests shall be performed at the minimum functional pressure p
me
specified in 4.8.
6.2.3 Dielectric tests of transformer connection in a three phase enclosure
If the calculation of a three phase arrangement shows higher stresses than in a single phase
arrangement, the design has to be modified or the arrangement has to be type-tested. The
calculation respectively type test results shall be available upon request.
6.3 Cantilever load withstand tests
To demonstrate compliance with 5.4, the bushing shall be tested in accordance with 8.9 of
IEC 60137:2008, Table 1, applying the shown test loads, however with a minimum test load of
4 kN.
To demonstrate withstand to the bending moment specified in Table 1, an additional test shall
be performed as follows.
The bushing shall be assembled as far as necessary for the test, but there shall not be any
internal gas pressure. It shall be installed vertically with its transformer-side-flange rigidly

fixed to a suitable device. The bushing end for gas immersion intended for connection to the
switchgear shall be mounted in a tank as for normal operation, at ambient temperature. The
tank shall be filled with an appropri
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