SIST EN IEC 60076-22-7:2020

SLOVENSKI STANDARD
01-september-2020
Močnostni transformatorji - 22-7. del: Močnostni transformatorji in dušilke - Pribor
Power transformers - Part 22-7: Power transformer and reactor fittings - Accessories and
fittings
Ta slovenski standard je istoveten z: EN IEC 60076-22-7:2020
ICS:
29.180 Transformatorji. Dušilke Transformers. Reactors
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 60076-22-7

NORME EUROPÉENNE
EUROPÄISCHE NORM
June 2020
ICS 29.180
English Version
Power transformers - Part 22-7: Power transformer and reactor
fittings - Accessories and fittings
(IEC 60076-22-7:2020)
Transformateurs de puissance - Partie 22-7: Leistungstransformatoren - Teil 22-7: Zubehörteile von
Transformateur de puissance et bobines d'inductance - Leistungstransformatoren und Drosselspulen - Zubehörteile
Accessoires et équipements und Armaturen
(IEC 60076-22-7:2020) (IEC 60076-22-7:2020)
This European Standard was approved by CENELEC on 2020-06-11. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2020 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 60076-22-7:2020 E

European foreword
The text of document 14/1044/FDIS, future edition 1 of IEC 60076-22-7, prepared by IEC/TC 14
"Power transformers" was submitted to the IEC-CENELEC parallel vote and approved by CENELEC
as EN IEC 60076-22-7:2020.
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2021-03-11
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2023-06-11
document have to be withdrawn
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.

Endorsement notice
The text of the International Standard IEC 60076-22-7:2020 was approved by CENELEC as a
European Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standards
indicated:
IEC 60076-5 NOTE Harmonized as EN 60076-5
IEC 60076-6 NOTE Harmonized as EN 60076-6
IEC 60255-5:2000 NOTE Harmonized as EN 60255-5:2001 (not modified)

Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
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.
NOTE 1  Where an International Publication has been modified by common modifications, indicated by (mod), the relevant
EN/HD applies.
NOTE 2  Up-to-date information on the latest versions of the European Standards listed in this annex is available here:
www.cenelec.eu.
Publication Year Title EN/HD Year
IEC 60068-3-3 1991 Environmental testing - Part 3-3: Guidance EN 60068-3-3 1993
- Seismic test methods for equipments
IEC 60068-3-3 2019 Environmental testing - Part 3-3: EN IEC 60068-3-3 2019
Supporting documentation and guidance -
Seismic test methods for equipment
IEC 60076-1 -  Power transformers - Part 1: General EN 60076-1 -
IEC 60076-7 -  Power transformers -- Part 7: Loading - -
guide for oil-immersed power transformers
IEC 60255-27 -  Measuring relays and protection equipment EN 60255-27 -
- Part 27: Product safety requirements
IEC 60296 -  Fluids for electrotechnical applications - EN 60296 -
Unused mineral insulating oils for
transformers and switchgear
IEC 60529 -  Degrees of protection provided by - -
enclosures (IP Code)
IEC 60721-3-4 -  Classification of environmental conditions - EN IEC 60721-3-4 -
Part 3-4: Classification of groups of
environmental parameters and their
severities - Stationary use at non-
weatherprotected locations
ISO 3601-1 -  Fluid power systems - O-rings – Part 1: - -
Inside diameters, cross-sections,
tolerances and designation codes
ISO 7005-1 -  Pipe flanges – Part 1: Steel flanges for - -
industrial and general service piping
systems
ISO 12944-6 -  Paints and varnishes – Corrosion EN ISO 12944-6 -
protection of steel structures by protective
paint systems – Part 6: Laboratory
performance test methods
IEC 60076-22-7 ®
Edition 1.0 2020-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Power transformers –
Part 22-7: Power transformer and reactor fittings – Accessories and fittings

Transformateurs de puissance –

Partie 22-7: Transformateur de puissance et bobines d'inductance – Accessoires

et équipements
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.180 ISBN 978-2-8322-8284-7

– 2 – IEC 60076-22-7:2020  IEC:2020
CONTENTS
FOREWORD . 6
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 9
4 Service conditions . 10
4.1 General . 10
4.2 Corrosion protection . 10
4.3 Resistance to ambient conditions . 10
4.4 Insulating liquid characteristics . 10
5 General requirements for routine and type test . 10
6 Accessories and fittings . 10
6.1 Thermometer pockets . 10
6.1.1 General . 10
6.1.2 Identification and nameplate . 11
6.1.3 Test . 11
6.1.4 Dimensions of thermometer pockets . 11
6.2 Earthing terminal . 12
6.2.1 General . 12
6.2.2 Dimensions of different earth terminals . 12
6.3 Draining plug . 15
6.3.1 General . 15
6.3.2 Materials . 15
6.3.3 Dimensions of different devices . 15
6.4 Air vent and liquid draining device . 17
6.4.1 General . 17
6.4.2 Materials . 17
6.4.3 Dimensions of different devices . 18
6.5 Wheel assembly – General requirements . 18
6.6 Dehydrating breathers . 18
6.6.1 General . 18
6.6.2 Common requirements . 19
6.6.3 Additional requirements for conventional manual replacement types . 19
6.6.4 Additional aspects for self-regenerating types . 22
6.6.5 Tests . 25
6.7 Butterfly valves . 26
6.7.1 General . 26
6.7.2 Requirements and characteristics . 26
6.7.3 Valve components . 26
6.7.4 Assembly arrangements and dimensions . 27
6.7.5 Performances . 28
6.7.6 Tests . 29
6.7.7 Supply conditions . 30
6.8 Junction terminal boxes . 30
6.8.1 General . 30
6.8.2 Degree of protection . 30
6.8.3 Function of the junction terminal box . 30

IEC 60076-22-7:2020  IEC:2020 – 3 –
6.8.4 General construction . 30
6.8.5 Overall dimensions . 31
6.8.6 Preferred functional and manufacturing characteristics of the box . 31
6.8.7 Preferred functional and manufacturing characteristics of the terminals . 31
6.8.8 Performance . 31
6.8.9 Tests . 32
6.9 Sampling device . 33
6.9.1 General . 33
6.9.2 Requirements and characteristics . 33
6.9.3 Tests . 35
Annex A (informative) Earthing pad current capacity calculation . 37
A.1 Theory . 37
A.2 Application to earthing pads . 38
Annex B (informative) Wheel assembly . 40
B.1 Introduction to wheel selection . 40
B.2 Theory of contact . 40
B.2.1 Maximum load . 40
B.2.2 Traction force . 41
B.3 Wheel dimensions and gauges . 42
B.3.1 Pitch and gauge . 42
B.3.2 Non-flanged wheel . 42
B.3.3 Flanged wheel . 44
Annex C (informative) Sizing of conventional types of dehydrating breather – Guide for
calculation of breather size . 50
Annex D (normative) Butterfly valve types . 52
D.1 Butterfly valve types A1, A2 and A3 assembled by welding on tank wall . 52
D.2 Butterfly valve types B1 and B3 assembled between tank wall and pipeline

and on pipeline . 54
D.3 Butterfly valves types C1 and C2 assembled on pipeline . 57
Annex E (normative) Gaskets and gasket seats . 60
E.1 General . 60
E.2 Gasket seats and gaskets for butterfly valve types A1, A2, A3, C1 and C2 . 60
E.3 Gasket seats and gaskets for butterfly valve types B1 and B2 . 61
Annex F (informative) Terminal boxes – Preferred mounting dimensions . 62
Bibliography . 63

Figure 1 – Thermometer pocket with female (left) and male (right) thread . 11
Figure 2 – Earth terminal type B1 . 13
Figure 3 – Earth terminal type B2 . 13
Figure 4 – Earth terminal type B3 . 13
Figure 5 – Earth terminal type B4 . 14
Figure 6 – Earth terminal type B5 . 14
Figure 7 – Earth terminal type B6 . 14
Figure 8 – Earth terminal type B7 . 15
Figure 9 – Draining plug type C1 (bolted type) . 16
Figure 10 – Draining plug type C2 . 16
Figure 11 – Draining device type C3 . 17

– 4 – IEC 60076-22-7:2020  IEC:2020
Figure 12 – Air venting and liquid draining type D1 (M6) and D2 (M12) . 18
Figure 13 – Breather connecting flanges . 20
Figure 14 – Overall dimensions . 21
Figure 15 – Sampling device NF C 52-132 . 34
Figure 16 – Sampling device DIN 42568 . 35
Figure B.1 – Contact surface between a wheel and a plane . 40
Figure B.2 – Traction force . 41
Figure B.3 – Pitch and gauge . 42
Figure B.4 – Non-flanged wheel assembly type W1 . 43
Figure B.5 – Wheel assembly type W1, top view of longitudinal and cross pitch . 43
Figure B.6 – Vignole type rail profile . 44
Figure B.7 – Burbach rail profile. 45
Figure B.8 – Wheel and rail positions . 45
Figure B.9 – Single wheel flanged type W2 . 46
Figure B.10 – Example of round shape wheel profile . 46
Figure B.11 – Double wheel flanged type W3 . 47
Figure B.12 – Cross side track . 47
Figure B.13 – Single side track . 48
Figure B.14 – Concentric double tracks . 48
Figure B.15 – Parallel double tracks . 49
Figure D.1 – Assembly layout of butterfly valves, type A1, A2 and A3 . 52
Figure D.2 – Butterfly valves, type A1, A2 and A3 . 53
Figure D.3 – Assembly layout of butterfly valves type B1 and B2 between tank wall
and pipeline . 54
Figure D.4 – Assembly layout of butterfly valves type B1 and B2 on pipeline . 54
Figure D.5 – Butterfly valves, type B1 . 55
Figure D.6 – Butterfly valves, type B2 . 56
Figure D.7 – Assembly layout of butterfly valves type C1 and C2 on pipeline . 57
Figure D.8 – Butterfly valves, type C1 . 58
Figure D.9 – Butterfly valves, type C2 . 59
Figure F.1 – Dimensions of terminal boxes size A, B, C and D . 62

Table 1 – Preferred dimensions for thermometer pockets . 12
Table 2 – Maximum current for earth terminals . 15
Table 3 – Dimensions of draining plug type C2 . 17
Table 4 – Typical size classes of breathers . 21
Table 5 – Making and breaking capacity – Self regenerating breather . 24
Table 6 – Dielectric strength of switches – Power frequency . 24
Table 7 – Dielectric strength of switches – Impulse . 24
Table 8 – Maximum admissible leakage value . 29
Table 9 – Dimensions of sampling device in Figure 15 . 34
Table 10 – Dimensions of sampling device in Figure 16 . 35
Table A.1 – Material data for current capacity calculation . 39

IEC 60076-22-7:2020  IEC:2020 – 5 –
Table A.2 – Maximum permissible current for standard earthing pads, during 0,5 s . 39
Table B.1 – W1 wheel assembly dimensions . 43
Table B.2 – Wheel W1 pitches . 44
Table B.3 – Rail resting surface . 45
Table B.4 – Flanged single wheel dimensions . 46
Table B.5 – Flanged double wheel dimensions . 47
Table B.6 – Rail gauge for cross side track . 48
Table B.7 – Rail gauges for single track . 48
Table B.8 – Rail gauges for concentric tracks . 49
Table B.9 – Rail gauges for parallel tracks . 49
Table C.1 – Mass of water, in grams, contained in one cubic metre of air . 51
Table D.1 – Dimensions of butterfly valves, types A1, A2 and A3 . 53
Table D.2 – Dimensions of butterfly valves, type B1 . 55
Table D.3 – Dimensions of butterfly valves, type B2 . 56
Table D.4 – Dimensions of butterfly valves type C1 . 58
Table D.5 – Dimensions of butterfly valves, type C2 . 59
Table E.1 – Gasket seat dimensions and gasket types and dimensions for butterfly
valves types A1, A2, A3, C1 and C2. 60
Table E.2 – Gasket seats dimensions and gasket types and dimensions for butterfly

valves types B1 and B2. 61
Table F.1 – Dimensions of terminal boxes size A, B, C and D . 62

– 6 – IEC 60076-22-7:2020  IEC:2020
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
POWER TRANSFORMERS –
Part 22-7: Power transformer and reactor fittings –
Accessories and fittings
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, Technical Reports,
Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their
preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with
may participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. IEC collaborates closely 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
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence between
any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
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
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
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 60076-22-7 has been prepared by IEC technical committee 14:
Power transformers.
The text of this International Standard is based on the following documents:
FDIS Report on voting
14/1044/FDIS 14/1048/RVD
Full information on the voting for the approval of this International Standard can be found in the
report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 60076 series, published under the general title Power transformers,
can be found on the IEC website.

IEC 60076-22-7:2020  IEC:2020 – 7 –
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 8 – IEC 60076-22-7:2020  IEC:2020
POWER TRANSFORMERS –
Part 22-7: Power transformer and reactor fittings –
Accessories and fittings
1 Scope
This part of IEC 60076-22 applies to a selection of accessories and fittings mounted on liquid
immersed power transformers according to IEC 60076-1 and reactors according to IEC 60076-6
with or without conservator for indoor or outdoor installation. It outlines the service conditions
and the mechanical requirements that are common to all the accessories and fittings.
This document also outlines the operation requirements specific to each device as well as the
preferred dimensions relevant for interchangeability and the type and routine test to be
performed.
This document covers an exhaustive selection of the accessories and fittings that are currently
used on transformers or reactors.
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 60068-3-3:2019, Environmental testing – Part 3-3: Supporting documentation and
guidance – Seismic test methods for equipment
IEC 60068-3-3:1991, Environmental testing – Part 3-3: Guidance – Seismic test methods for
equipments
IEC 60076-1, Power transformers – Part 1: General
IEC 60076-7, Power transformers – Part 7: Loading guide for mineral-oil-immersed power
transformers
IEC 60296, Fluids for electrotechnical applications – Unused mineral insulating oils for
transformers and switchgear
IEC 60529, Degrees of protection provided by enclosures (IP Code)
IEC 60721-3-4, Classification of environmental conditions – Part 3-4: Classification of groups
of environmental parameters and their severities – Stationary use at non-weatherprotected
locations
IEC 60255-27, Measuring relays and protection equipment – Part 27: Product safety
requirements
ISO 3601-1, Fluid power systems – O-rings – Part 1: Inside diameters, cross-sections,
tolerances and designation codes

IEC 60076-22-7:2020  IEC:2020 – 9 –
ISO 7005-1, Pipe flanges – Part 1: Steel flanges for industrial and general service piping
systems
ISO 12944-6, Paints and varnishes – Corrosion protection of steel structures by protective paint
systems – Part 6: Laboratory performance test methods
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
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
thermometer pocket
facility mounted on the transformer or reactor cover or pipework or any liquid filled compartment,
intended to house a thermal sensor to measure the insulating liquid temperature
3.2
earthing terminal
terminal provided on the transformer or reactor tank or cooler support structure or any other
part that needs to be grounded and intended for the electric connection with the earthing
network
3.3
draining plug
facility intended to drain the insulating liquid from liquid filled compartments
3.4
air vent
facility for venting the air or gas trapped within the transformer tank and pipework
3.5
wheel assembly
device suitable for movement of the transformer in different directions using rails
3.6
dehydrating breather
device linking the air space at the top of the tank of a liquid immersed transformer with the
outside air to absorb the humidity of the breathed air
3.7
butterfly valve
device designed to isolate any component or accessory mounted on the transformer liquid
system
3.8
junction terminal box
device designed to make low-voltage, low-current, insulated and liquid-tight electrical
connections between the inside and outside of a liquid filled compartment
3.9
sampling valve
device used to take samples of the insulating liquid

– 10 – IEC 60076-22-7:2020  IEC:2020
4 Service conditions
4.1 General
The service conditions set out in IEC 60076-1:2011, 4.2 represent the normal scope of
operation of the accessories and fittings specified in this document.
For any unusual service conditions that require special consideration in the design of the
devices and equipment, see IEC 60076-1:2011, 5.5. Device specification for operation under
such unusual service conditions shall be subject to agreement between the purchaser and
manufacturer.
4.2 Corrosion protection
The materials used for the construction of the accessories and fittings or the surface treatment
shall be resistant to the insulating liquid and suitable to withstand the environmental conditions.
Unless otherwise specified, minimum withstand level of the parts exposed to the environment
shall be C4 medium durability according to ISO 12944-6.
Parts intended to be welded and earthing pads shall not be painted.
Unless otherwise specified, screws exposed to the environment shall be stainless steel,
consistent with the minimum corrosion class C4 medium durability.
4.3 Resistance to ambient conditions
The materials used for the construction of the accessories and fittings shall be UV resistant;
windows and sight glasses shall not become opaque over the life of the accessory.
4.4 Insulating liquid characteristics
This Subclause 4.4 concerns only the accessories and fittings that are in contact with the
insulating liquid.
If not otherwise specified, the insulating liquid is a mineral liquid according to IEC 60296 and
the operating temperature shall be in accordance with IEC 60076-7.
If the insulating liquid is not a mineral liquid then the purchaser shall indicate the operating
temperature.
5 General requirements for routine and type test
Unless otherwise specified, tests shall be made at an ambient temperature between 10 °C and
40 °C.
All measuring instruments used for the tests shall have traceable accuracy and be subject to
periodic calibration.
6 Accessories and fittings
6.1 Thermometer pockets
6.1.1 General
The thermometer pocket shall provide at all times a separation between the insulating liquid
and the sensor; the thermometer pocket shall be designed to withstand the vacuum and
pressure tests defined by IEC 60076-1:2011, 11.8, 11.9, 11.10 and 11.11, for transformer tanks.

IEC 60076-22-7:2020  IEC:2020 – 11 –
When the thermometer pocket is not in use, the opening shall be plugged to avoid contamination
by moisture, dust and any other undesired particles.
The thermometer pocket shall be designed to avoid damage to the thermometer pocket or to
the temperature sensing equipment due to the thermal expansion of the heat transfer medium.
There shall be good thermal transfer of the thermometer pocket material and the filling medium.
6.1.2 Identification and nameplate
No requirement.
6.1.3 Test
The thermometer pocket is not tested individually, but as a component of the transformer or
reactor during type or routine testing.
6.1.4 Dimensions of thermometer pockets
Figure 1 and Table 1 give the preferred solutions for thermometer pockets.
The protective plug or cap is not specified by this document.
Dimensions in millimetres
Figure 1 – Thermometer pocket with female (left) and male (right) thread

– 12 – IEC 60076-22-7:2020  IEC:2020
Table 1 – Preferred dimensions for thermometer pockets
Dimensions in millimetres
Thermometer
Type A min B min B max C min D max Thread ØT
pockets with
A1 20 20 165 30 G1
Female thread F 17 16 155 30 M22 × 1,5
U 13 12,4 12,5 166 30 M22 × 1,5
Male thread A2 20 20 120 30 G ¾

6.2 Earthing terminal
6.2.1 General
Earthing terminals shall be stainless steel grade 304L minimum and positioned clear of ground
level. The pad shall be selected to withstand the maximum prospective earth fault currents.
Prior to connection to earth, any non-conductive coating shall be removed at threads, contact
points, and contact surfaces.
The terminal shall be identified by the letter "E" either on the terminal itself or on its vicinity.
For the calculation of the maximum current of the earthing pads shown in Table 2, the cross
section of the earthing element is used; the welding on the tank is considered to have a minimum
cross section equivalent to the cross section of the pad. For earth terminal B7, a 5 mm welding
seam along the complete circumference is considered. For a stud type earthing element, the
core thread is used.
The terminal shall ensure electrical continuity with the transformer tank.
The welding materials and methods for connecting the pads to the tank shall be capable of
withstanding the maximum temperatures indicated in Table A.1 for each type of pad without
detriment.
The maximum current values detailed in Table 2 are related only to the earthing pad and its
connection to the tank; earthing connections to the pad should be suitably rated to match these
values.
Table 2 shows the short-circuit current carrying capacity of the earth terminals. Table 2 is based
on an initial temperature of 40 °C and a final temperature of 300 °C and a short circuit duration
of 0,5 s, considering that the transformer protections will trip the current earlier than this value.
The values in Table 2 have been established considering the material properties as found in
literature and an adiabatic temperature rise.
For additional information, see Annex A.
6.2.2 Dimensions of different earth terminals
Figure 2 to Figure 8 show the preferred solutions.

IEC 60076-22-7:2020  IEC:2020 – 13 –
Dimensions in millimetres
Figure 2 – Earth terminal type B1
Dimensions in millimetres
Figure 3 – Earth terminal type B2
Dimensions in millimetres
Figure 4 – Earth terminal type B3

– 14 – IEC 60076-22-7:2020  IEC:2020
Dimensions in millimetres
Figure 5 – Earth terminal type B4
Dimensions in millimetres
Figure 6 – Earth terminal type B5
Dimensions in millimetres
Figure 7 – Earth terminal type B6

IEC 60076-22-7:2020  IEC:2020 – 15 –
Dimensions in millimetres
Figure 8 – Earth terminal type B7
Table 2 – Maximum current for earth terminals
Short-circuit current
Cross section S
Earth terminal type capability
mm
kA
B1 Ø30 M12 594 31,5
B2 5 mm × 30 mm 150 8,0
B3 M12 76 4,0
B4 60 mm × 10 mm 600 31,5
B5 120 mm × 10 mm 1 200 63,0
B6 110 mm × 10 mm 1 100 58,0
B7 51 mm × 89 mm 1 400 74,0
6.3 Draining plug
6.3.1 General
Draining plugs are used on all insulating liquid compartments, for the complete draining of the
liquid contained inside.
They shall be positioned in the lowest part of the compartment.
They shall not leak in operation.
6.3.2 Materials
The welded parts shall be made of carbon steel, screws and screwed parts shall be brass or
stainless steel, and protective caps shall be metallic.
6.3.3 Dimensions of different devices
Figure 9 to Figure 11 show the preferred solutions, to be chosen according to the liquid volume
to be drained. Table 3 shows the dimensions of the draining plugs shown in Figure 10.

– 16 – IEC 60076-22-7:2020  IEC:2020
Dimensions in millimetres
Figure 9 – Draining plug type C1 (bolted type)
Dimensions in millimetres
Figure 10 – Draining plug type C2

IEC 60076-22-7:2020  IEC:2020 – 17 –
Table 3 – Dimensions of draining plug type C2
Dimensions in millimetres
d
Size d a b c d d d 5
1 2 3 4
mm
mm mm mm
mm mm mm
min
C2-A 22 67 6 46 M24 × 1,5 30 46 18,5
C2-B 31 93 10 65 M33 × 1,5 40 65 26
C2-C 40 115 10 80 M42 × 1,5 52 80 33,8

Figure 11 – Draining device type C3
6.4 Air vent and liquid draining device
6.4.1 General
Air vents are used on insulating liquid compartments, for the venting of the air or gas contained
inside. When used as an air vent they shall be positioned in the highest part of the compartment.
Draining devices are used on insulating liquid compartments for draining small amounts of liquid.
When used as a draining plug, they shall be positioned at the lowest part of the compartment.
Air vents and liquid draining devices shall not leak in operation.
6.4.2 Materials
The welded parts shall be made of carbon steel, screws and screwed parts shall be brass or
stainless steel, and protective caps shall be metallic.

– 18 – IEC 60076-22-7:2020  IEC:2020
6.4.3 Dimensions of different devices
Figure 12 shows the preferred solution, to be chosen according to the gas volume to be vented
or the oil volume to be drained.
Dimensions in millimetres
Type D1 (M6) Type D2 (M12)
Figure 12 – Air venting and liquid draining type D1 (M6) and D2 (M12)
6.5 Wheel assembly – General requirements
Each wheel assembly shall be suitable for movement in at least two perpendicular directions
and be able to be secured in the selected position.
Each wheel assembly shall be designed to accept a device for blocking the wheels with chocks.
Each wheel assembly shall be capable of bearing 120 % of the maxim
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