IEC 60076-11:2018
(Main)Power transformers - Part 11: Dry-type transformers
Power transformers - Part 11: Dry-type transformers
IEC 60076-11:2018 applies to dry-type power transformers (including auto-transformers) having values of highest voltage for equipment up to and including 72,5 kV and at least one winding operating at greater than 1,1 kV. This document does not apply to:
- gas-filled dry-type transformers where the gas is not air;
- single-phase transformers rated at less than 5 kVA;
- polyphase transformers rated at less than 15 kVA;
- instrument transformers;
- starting transformers;
- testing transformers;
- traction transformers mounted on rolling stock;
- flameproof and mining transformers;
- welding transformers;
- voltage regulating transformers;
- small power transformers in which safety is a special consideration.
Where IEC standards do not exist for the transformers mentioned above or for other special transformers, this document may be applicable as a whole or in parts. This second edition cancels and replaces the first edition published in 2004 and constitutes a technical revision. The main changes with regard to the previous edition are as follows:
- Extension of the scope up to 72,5kV
- Enclosure management in regards of the performance
- Management of the dielectric and thermal features with altitude
- New climatic classes for a better adaptation of customers’ need
- Establishment of the relation between location and environmental classes
- For fire behaviour classes, limitation at 1000kVA and process of test more robust
- Introduction of Seismic class
- Recommendations for amorphous transformers
Keywords: dry-type transformers
The contents of the corrigendum of March 2019 and the Interpretation sheet 1 of July 2020 have been included in this copy.
Transformateurs de puissance - Partie 11 : Transformateurs de type sec
L'IEC 60076-11:2018 applique aux transformateurs de type sec (y compris les autotransformateurs) dont les valeurs de tension la plus élevée pour le matériel sont inférieures ou égales à 72,5 kV avec au moins un enroulement fonctionnant à plus de 1,1 kV. Le présent document ne s'applique pas aux:
- transformateurs de type sec avec un diélectrique gazeux autre que l'air;
- transformateurs monophasés de moins de 5 kVA;
- transformateurs polyphasés de moins de 15 kVA;
- transformateurs de mesure;
- transformateurs de démarrage;
- transformateurs d'essai;
- transformateurs de traction montés sur matériel roulant;
- transformateurs antidéflagrants et de mines;
- transformateurs de soudure;
- transformateurs de réglage de tension;
- petitstransformateurs de puissance pour lesquels la sécurité est spécialement à prendre en compte.
Lorsqu'il n'existe pas de norme IEC pour les transformateurs mentionnés ci-dessus ou pour d'autres transformateurs spéciaux, le présent document peut être appliquée en tout ou en partie. Cette deuxième édition annule et remplace la première édition publiée en 2004 dont elle constitue une révision technique.
Les principales modifications par rapport à l'édition précédente sont les suivantes:
- Extension du domaine d'application jusqu'à 72,5 kV
- Prise en compte des enveloppes en ce qui concerne les performances
- Prise en compte des caractéristiques diélectriques et thermiques en fonction de l'altitude
- Nouvelles classes climatiques pour une meilleure adaptation des besoins des clients
- Établissement de la relation entre l'emplacement et les classes d'environnement
- Pour les classes de comportement au feu, limitation à 1 000 kVA et processus d'essai plus robuste
- Introduction d'une classe sismique
- Recommandations pour les transformateurs amorphes
Mots-clés: transformateurs de type sec
Le contenu du corrigendum de mars 2019 et la feuille d'interprétation 1 de juillet 2020 (seulement en anglais) a été pris en considération dans cet exemplaire.
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Standards Content (Sample)
IEC 60076-11 ®
Edition 2.0 2018-08
REDLINE VERSION
INTERNATIONAL
STANDARD
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Power transformers –
Part 11: Dry-type transformers
IEC IEC 60076-11:2018-08 RLV(en)
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IEC 60076-11 ®
Edition 2.0 2018-08
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Power transformers –
Part 11: Dry-type transformers
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.180 ISBN 978-2-8322-5967-2
© IEC 2020
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
IEC 60076-11
Edition 2.0 2018-08
POWER TRANSFORMERS –
Part 11: Dry-type transformers
INTERPRETATION SHEET 1
This interpretation sheet has been prepared by IEC technical committee 14: Power
transformers.
The text of this interpretation sheet is based on the following documents:
DISH Report on voting
14/1052/DISH 14/1054/RVDISH
Full information on the voting for the approval of this interpretation sheet can be found in the
report on voting indicated in the above table.
___________
14.3.2 Temperature-rise test
Question
The independent certification body in Poland "Instytut Energetyki" carries out the testing of
transformers or its inspectors witness this testing at the manufacturers' premises. The
description of resistance measurement during the temperature rise test has caused a dispute
between a manufacturer and the inspector on where exactly the resistance should be
measured. The inspector requested that the resistance be measured on "winding lead exits"
inside the enclosure, while the manufacturer argued for the measurement to be made on
"winding terminals" which in its opinion were the bushings on the enclosure cover.
ICS 29.180
– 2 – IEC 60076-11:2018/ISH1:2020
© IEC 2020
Subclause 14.3.2.1 General, states:
The winding temperature rise shall be established by the rise in resistance method or
by superposition method. For the determination of the average winding temperature
rise the measured temperatures of the cooling air or of the water intake of the cooling
equipment shall be used.
For three-phase transformers, the resistance measurements shall be made between
the central and an outer phase line terminals.
NOTE When the temperature rise is performed it is advisable to measure the windings resistance close to the
windings.
Where should the measurements be made?
Interpretation
Testing of the winding resistance at transformer terminals (bushings) includes leadwork or
busbars and often also multiple connections. Because of this, the tested winding resistance
and its change due to heating is affected by the resistance of all these leads and connections.
Consequently, the derived winding temperature rise if measured at the transformer terminals
could be lower than if the winding resistance were tested directly on the winding lead exits.
That is why the standard suggests (in the NOTE) that measurement of the windings'
resistance be carried out close to the windings. That way, the accuracy of the indirect winding
temperature measurement by resistance is higher.
In the case of dry-type transformers without enclosures, it is possible to have access close to
the winding lead exits and not only to the transformer line terminals. Therefore,
measurements shall normally be made at such locations.
On the other hand, if the dry-type transformer is equipped with an enclosure, the resistance
measurement close to the winding lead exits requires opening the enclosure to have access
to carry out the test (hence, affecting the normal cooling efficiency of the unit). Nevertheless,
the advice to measure the resistance normally close to the winding lead exits holds. Limiting
the enclosure opening by using special through elements for the cabling and/or by closing the
required opening by temporary means as well as possible will minimize the impact on the
normal cooling efficiency.
– 2 – IEC 60076-11:2018 RLV © IEC 2018
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 Normal service conditions . 10
4.3 Electromagnetic compatibility (EMC) . 12
5 Rating and general requirements . 12
5.1 General . 12
5.2 Rated power . 12
5.2.1 General . 12
5.2.2 Operation Definition of the rated power with fans cooling or heat
exchangers . 13
5.2.3 Transformer IP00 (without enclosure) . 13
5.2.4 Operation in an Transformer with enclosure . 13
5.2.5 Preferred values of rated power . 14
5.2.6 Loading beyond rated power . 14
5.3 Provision for unusual service conditions . 14
5.4 Transportation and storage conditions . 15
5.4.1 Transport limitation . 15
5.4.2 Transport acceleration . 15
5.4.3 Temperature and environment conditions for transport and storage . 15
5.5 Rated voltage and rated frequency . 15
5.5.1 Rated voltage . 15
5.5.2 Rated frequency . 16
5.6 Operation at higher than rated voltage . 16
5.7 Highest voltage for equipment U and dielectric tests levels . 16
m
5.8 Identification according to cooling method . 16
5.8.1 General . 16
5.8.2 Identification symbols . 16
5.8.3 Arrangement of symbols . 17
5.9 Guaranteed temperature rise at rated conditions . 17
5.10 Additional information required for enquiry . 17
5.11 Sound level . 17
5.12 Components and materials . 17
6 Tappings . 17
7 Connections . 18
8 Ability to withstand short circuit . 18
9 Rating plate . 18
9.1 Rating plate fitted to the transformer . 18
9.2 Rating plate fitted to the transformer enclosure . 19
10 Temperature-rise limits . 19
10.1 Normal temperature-rise limits . 19
10.2 Reduced temperature rises for transformers designed for high cooling air
medium temperatures or special air cooling medium conditions . 20
10.3 High altitude temperature rise correction . 20
11 Insulation levels . 21
11.1 General . 21
11.2 Transformers for use at high altitudes . 22
12 Climatic, environmental and fire behaviour classes . 23
12.1 Climatic classes . 23
12.2 Environmental classes . 24
12.2.1 Transformers for indoor application with or without enclosure and for
outdoor application with enclosure . 24
12.2.2 Dry-type transformers without enclosure for outdoor application . 25
12.3 Fire behaviour classes . 25
12.4 Test criteria for climatic, environmental and fire behaviour classes . 25
13 Seismic . 26
13.1 General . 26
13.2 General seismic class approach . 27
13.2.1 Generalities . 27
13.2.2 The standard amplitude method . 27
13.2.3 The calculated amplitude method . 28
14 Test . 29
14.1 General requirements for tests . 29
14.2 Routine tests . 30
14.2.1 Measurement of winding resistance . 30
14.2.2 Measurement of voltage ratio and check of phase displacement . 30
14.2.3 Measurement of short-circuit impedance and load loss . 30
14.2.4 Measurement of no-load loss and current . 31
14.2.5 Separate-source AC withstand voltage test Applied voltage test (AV) . 31
14.2.6 Induced AC withstand voltage test Induced voltage withstand test(IVW) . 31
14.2.7 Partial discharge measurement . 31
14.3 Type tests . 33
14.3.1 Full wave lightning impulse test (LI) . 33
14.3.2 Temperature-rise test . 34
14.4 Additional procedure test (Special tests) . 38
14.4.1 Partial discharge measurement for transformers operated under a
single phase line-to-earth fault condition . 38
14.4.2 Measurement of sound level . 38
14.4.3 Short-circuit test. 39
14.4.4 Climatic tests . 39
Thermal shock test for C1 class transformers .
Thermal shock test for C2 class transformers .
14.4.5 Environmental test . 41
14.4.6 Fire behaviour test . 44
14.4.7 Seismic test . 51
14.4.8 Special test for transformers equipped with amorphous core . 52
15 Tolerances . 53
16 Protection against direct contact . 53
17 Degrees of protection provided by enclosures . 53
– 4 – IEC 60076-11:2018 RLV © IEC 2018
18 Earthing terminal . 53
19 Information required with enquiry and order . 53
Annex A (informative) Installation and safety of dry-type transformers . 54
A.1 Manuals . 54
A.2 Installation . 54
A.2.1 General . 54
A.2.2 Intrinsic safety . 54
A.2.3 Installation precautions . 55
A.2.4 Installation design . 55
Annex B (informative) Environmental test for evaluation of outdoor transformers
without enclosure . 56
B.1 General . 56
B.2 Salt-fog and UV-radiation chamber test . 56
B.2.1 Test description . 56
B.2.2 Acceptance criteria: . 58
B.3 Core and clamp coating test . 58
B.3.1 Test description . 58
B.3.2 Acceptance criteria . 58
B.4 Field test . 58
B.4.1 Test description . 58
B.4.2 Acceptance criteria . 59
Annex C (normative) Cooling of transformer in naturally ventilated room . 60
C.1 Assumptions . 60
C.2 Data for the calculation of ventilation . 61
C.3 Output . 61
C.4 Numerical application for a 1 000 kVA transformer . 62
Annex D (normative) Calculation of the losses with different reference temperatures
and/or winding material . 63
Bibliography . 66
Figure 1 – Basic measuring circuit for the partial discharge test for a single-phase
transformer . 32
Figure 2 – Basic measuring circuit for the partial discharge test for a three-phase
transformer . 32
Figure 3 – Voltage application for routine partial discharge test . 33
Figure 4 – Example of back-to-back method – Single phase . 36
Figure 5 – Example of back-to-back method – Three-phase . 37
Figure 6 – Voltage application for special partial discharge test . 38
Figure 7 – Test chamber . 47
Figure 8 – Test chamber details . 48
Figure B.1 – Salt fog multi-parameter ageing cycle . 57
Figure C.1 – Heat dissipation in a natural ventilated room . 60
Table – Insulation levels based on European practice .
Table – Insulation levels based on North American practice .
Table 1 – Letter symbols . 16
Table 2 – Winding temperature-rise limits . 20
Table 3 – Test voltage levels . 22
Table 4 – Applied voltage level correction factor . 23
Table 5 – Sequence of tests . 26
Table 6 – Approximate acceleration level and performance level . 28
Table 7 – Ground acceleration level (AG) . 28
Table 8 – Recommended super elevation factors (K) . 29
Table 9 – Direction factors (D) . 29
Table 10 – Climatic class features . 39
Table 11 – Environmental classes . 43
Table 12 – Dimension of the chamber . 46
Table B.1 – Outdoor environmental classes . 56
– 6 – IEC 60076-11:2018 RLV © IEC 2018
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
POWER TRANSFORMERS –
Part 11: Dry-type transformers
FOREWORD
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This redline version of the official IEC Standard allows the user to identify the changes
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has been made. Additions are in green text, deletions are in strikethrough red text.
International Standard IEC 60076-11 has been prepared by IEC technical committee 14:
Power transformers.
This second edition cancels and replaces the first edition published in 2004 and constitutes a
technical revision.
The main changes with regard to the previous edition are as follows:
Extension of the scope up to 72,5kV
Enclosure management in regards of the performance
Management of the dielectric and thermal features with altitude
New climatic classes for a better adaptation of customers’ need
Establishment of the relation between location and environmental classes
For fire behaviour classes, limitation at 1 000 kVA and process of test more robust
Introduction of Seismic class
Recommendations for amorphous transformers
The text of this International Standard is based on the following documents:
FDIS Report on voting
14/964/FDIS 14/972/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.
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.
The contents of the corrigendum of March 2019 and the Interpretation sheet 1 of July 2020
have been included in this copy.
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.
– 8 – IEC 60076-11:2018 RLV © IEC 2018
POWER TRANSFORMERS –
Part 11: Dry-type transformers
1 Scope
This part of IEC 60076 applies to dry-type power transformers (including auto-transformers)
having values of highest voltage for equipment up to and including 36 72,5 kV and at least
one winding operating at greater than 1,1 kV. The standard applies to all construction
technologies.
This document does not apply to:
• gas-filled dry-type transformers where the gas is not air;
• single-phase transformers rated at less than 5 kVA;
• polyphase transformers rated at less than 15 kVA;
• instrument transformers (see IEC 60044 and IEC 60186);
• starting transformers;
• testing transformers;
• traction transformers mounted on rolling stock;
• flameproof and mining transformers;
• welding transformers;
• voltage regulating transformers;
• small power transformers in which safety is a special consideration.
Where IEC standards do not exist for the transformers mentioned above or for other special
transformers, this document may be applicable as a whole or in parts.
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 60050 (all parts), International electrotechnical vocabulary (IEV)
IEC 60068-3-3, Environmental testing – Part 3-3: Guidance – Seismic test methods for
equipments
IEC 60071 (all parts), Insulation co-ordination
IEC 60071-1, Insulation co-ordination – Part 1: Definitions, principles and rules
IEC 60071-2, Insulation co-ordination – Part 2: Application guidelines
IEC 60076-1:1993 2011, Power transformers – Part 1: General
Amendment 1 (1999)
IEC 60076-2, Power transformers – Part 2: Temperature rise for liquid-immersed transformers
IEC 60076-3:2013, Power transformers – Part 3: Insulation levels, dielectric tests and external
clearances in air
IEC 60076-5, Power transformers – Part 5: Ability to withstand short-circuit
IEC 60076-10, Power transformers – Part 10: Determination of sound levels
IEC 60076-12:2008, Power transformers – Part 12: Loading guide for dry-type power
transformers
IEC 60085, Electrical insulation – Thermal evaluation and classification of electrical insulation
designation
IEC 60270, High-voltage test techniques – Partial discharge measurements
IEC 60332-3-10, Tests on electric cables under fire conditions – Part 3-10: Test for vertical
flame spread of vertically-mounted bunched wires or cables – Apparatus
IEC 60529, Degrees of protection provided by enclosures (IP Code)
IEC 60721-3-4, Classification of environmental conditions – Part 3: Classification of groups of
environmental parameters and their severities – Section 4: Stationary use at non-
weatherprotected locations
IEC TS 60815-1, Selection and dimensioning of high-voltage insulators intended for use in
polluted conditions – Part 1: Definitions, information and general principles
IEC 60905:1987, Loading guide for dry-type power transformers
IEC 61330, High-voltage/low voltage prefabricated substations
IEC 61378-1, Converter transformers – Part 1: Transformers for industrial applications
IEC 62271-202, High-voltage switchgear and controlgear – Part 202: High-voltage/low-voltage
prefabricated substation
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
dry-type transformer
transformer of which the magnetic circuit and windings are not immersed in an insulating
liquid
– 10 – IEC 60076-11:2018 RLV © IEC 2018
3.2
totally enclosed dry-type transformer
transformer in an un-pressurised enclosure cooled by the circulation of the internal air having
no intentional exchange with external air
3.3
enclosed dry-type transformer
transformer in a ventilated enclosure cooled by the circulation of the external air
3.4
non-enclosed dry-type transformer
transformer supplied without a protective enclosure cooled by natural or forced air ventilation
4 Service conditions
4.1 General
The requirements of IEC 60076-1 apply to dry-type transformers only in so far as they are
referred to in this document.
4.2 Normal service conditions
4.2.1 General
Unless otherwise stated, the service conditions in 4.2.2 to 4.2.6 apply. When transformers are
required to operate outside the normal service conditions, de-rating in accordance with 11.2
and/or 11.3 applies.
a) Altitude:
A height above sea level not exceeding 1 000 m. See IEC 60076-1.
b) Temperature of cooling air and water:
The temperature of cooling air not exceeding:
40 °C at any time;
30 °C monthly average of the hottest month;
20 °C yearly average.
and not below:
–25 °C in the case of outdoor transformers;
–5 °C in the case of indoor transformers.
where the monthly and yearly averages are as defined in 3.12 of IEC 60076-1.
See IEC 60076-1.
For water cooled transformers, specification of the water (temperature, water flow, etc.)
has to be defined by agreement between manufacturer and purchaser if the temperature
of the water is different from that specified in IEC 60076-1 and IEC 60076-2
NOTE Liquids other than water can be used as a cooling medium then all technical data of the liquid has to
be defined by agreement between manufacturer and purchaser.
c) Wave-shape of supply voltage:
A supply voltage of which the waveshape is approximately sinusoidal.
NOTE This requirement is normally not critical in public supply systems but may have to be considered in
installations with considerable converter loading. In such cases, there is a conventional rule that the deformation
shall neither exceed 5 % total harmonic content nor 1 % even harmonic content, see IEC 61000-2-4. Also note the
importance of current harmonics for load loss and temperature rise, see IEC 61378-1.
A sinusoidal supply voltage with a total harmonic content not exceeding 5 % and an even
harmonic content not exceeding 1 %.
The purchaser shall specify the magnitude and frequency of any harmonic voltages
present in the supply that exceed these limits.
The manufacturer should take into account these harmonics in determination of additional
core losses and also regarding the saturation of the core.
d) Load current harmonic content:
At the enquiry stage the purchaser shall specify the magnitude and frequency of each of
the harmonic current components generated by the load.
The manufacturer shall consider the additional losses caused by harmonic currents in
calculating the temperature rise of the windings and the effects on the other metallic parts
of the transformer.
The manufacturer shall calculate the additional loss by using the method of IEC 61378-1
or by using a method like finite element by agreement between manufacturer and
purchaser.
If the total harmonic content of the load current exceeds 5 %, then the extra losses due to
these harmonic currents shall be taken into account by increasing the test current for the
temperature rise test. The temperature rise with these losses shall not exceed the
corresponding limit specified in Table 2 when tested in accordance with 14.3.2.
e) Symmetry of polyphase three-phase supply voltages:
For three-phase transformers, a set of three-phase supply voltages which are approximately
symmetrical.
See IEC 60076-1.
f) Installation environment:
This standard defines specific classes for environment:
1) for climatic conditions;
2) for humidity and pollution;
3) for fire behaviour;
4) for seismic disturbance;
5) environmental conditions within the following definitions according to IEC 60721-3-4:
i) biological conditions 4B1;
ii) chemically active substances 4C2;
iii) mechanically active substances 4S3;
iv) mechanical conditions 4M4.
g) For transformers intended to be installed indoors, some of these environmental conditions
might not be applicable.
h) Inrush current:
System inrush current limitations, if any, (maximum value, duration) shall be given at the
enquiry stage by the purchaser.
i) Frequency of energization:
If frequency of energization is greater than 24 times a year, then purchaser shall specify
the number of energizations per year at the enquiry stage.
j) Protection from water and liquids:
– 12 – IEC 60076-11:2018 RLV © IEC 2018
The transformer shall be protected against dripping water or flooding by water and other
liquids.
k) Special electrical and environmental conditions around the transformer:
IEC 60076-3 recommends general minimum clearances between transformer live parts
and conductive parts in the installation.
Any part of the installation made of insulation material becomes conductive when
moistened with rain water, salt water or other conductive liquids. Partial discharges in the
surroundings of the transformer can decrease the dielectric strength of the air.
Therefore the clearances between these installations parts and the live parts of the
transformer shall meet the clearances recommended in IEC 60076-3.
NOTE An agreement between purchaser and manufacturer is needed to reduce the clearances between
transformer live parts and conductive parts in the installation.
l) Level of vibration:
Vibrations of the structure where the transformer is to be installed shall be taken into
account when designing the transformer and special consideration shall be given in the
stress transferred to connection terminals.
The purchaser shall specify vibration spectrum at the enquiry stage. The procedure of
vibration test, if any, should be agreed at enquiry stage between purchaser and
manufacturer.
m) Corrosion protection:
Depending on the type of the installation, the purchaser should choose a protection class
defined in ISO 12944 or as agreed between purchaser and manufacturer.
n) Maintenance
The user shall follow the manufacturer guide line for maintenance and specially avoid an
accumulation of dust or pollution on the transformer by a regular cleaning.
4.2.6 Humidity
The relative humidity of the surrounding air shall be less than 93 %. No drops of water shall
be present on the surface of the coils.
4.3 Electromagnetic compatibility (EMC)
Transformers shall be considered as passive elements in respect to emission and immunity to
electromagnetic disturbances.
5 Rating and general requirements
5.1 General
The manufacturer shall assign ratings to the transformer, which shall be marked on the rating
plate, see Clause 9. These ratings shall be such that the transformer can deliver its rated
current under steady loading conditions without exceeding the limits of temperature rise
specified in Clause 10, assuming that the applied primary voltage is equal to the rated voltage
and that the supply is at rated frequency.
5.2 Rated power
5.2.1 General
The rated power refers to continuous loading. This is a reference value for guarantees and
tests concerning load losses, temperature rises and short-circuit impedance.
NOTE A two-winding transformer has only one value of rated power, identical for both windings. When the
transformer has rated voltage applied to the primary winding, and rated current flows through the terminals of that
winding, the transformer receives the relevant rated power for both windings.
The rated power corresponds to continuous duty; nevertheless, dry-type transformers
complying with this standard can be overloaded and guidance on overloads is given in
IEC 60905 IEC 60076-12.
5.2.2 Operation Definition of the rated power with fans cooling or heat exchangers
The transformer shall have an assigned rated power for each winding which shall be marked
on the rating plate. The transformer shall be fully rated when supplied in an enclosure. The
rated power refers to continuous loading. This is a reference value for guarantees and tests
concerning load losses and temperature rises and short-circuit impedance.
If different values of apparent power are assigned under different circumstances, for example
with different methods of cooling, the highest of these values is the rated power.
When additional cooling by means of fans is provided, the nominal rated power rating with
and without fans shall be subject to agreement between purchaser and supplier.
The rating plate shall indicate both the power rating without fans and the maximum power
rating with fan cooling.
5.2.3 Transformer IP00 (without enclosure)
The transformer shall have an assigned rated power for each winding which shall be marked
on the rating plate.
5.2.4 Operation in an Transformer with enclosure
For operation in an enclosure that is not provided or later provided by the manufacturer of the
transformer, see Annex D of IEC 61330 and IEC 60905.
This subclause defines rated power and the distance between enclosures and live parts when
the transformer is equipped with an enclosure.
Two cases are defined:
a) The transformer in an enclosure is manufactured, tested in the enclosure and then
delivered on site:
• The clearances between the live parts and the enclosure shall be defined by the
manufacturer. The dielectric tests shall be performed with the enclosure as a routine
test.
• If the clearance between the live part and the enclosure meets the requirement of
IEC 60076-3 the dielectric routine test shall be performed either with enclosure or
without enclosure.
• It is permitted to disassemble the enclosure for transp
...
IEC 60076-11 ®
Edition 2.0 2018-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Power transformers –
Part 11: Dry-type transformers
Transformateurs de puissance –
Partie 11: Transformateurs de type sec
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IEC 60076-11 ®
Edition 2.0 2018-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Power transformers –
Part 11: Dry-type transformers
Transformateurs de puissance –
Partie 11: Transformateurs de type sec
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.180 ISBN 978-2-8322-5910-8
– 2 – IEC 60076-11:2018 © IEC 2018
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 Normal service conditions . 10
4.3 Electromagnetic compatibility (EMC) . 11
5 Rating and general requirements . 12
5.1 General . 12
5.2 Rated power . 12
5.2.1 General . 12
5.2.2 Definition of the rated power with fans cooling or heat exchangers . 12
5.2.3 Transformer IP00 (without enclosure) . 12
5.2.4 Transformer with enclosure . 12
5.2.5 Preferred values of rated power . 13
5.2.6 Loading beyond rated power . 13
5.3 Provision for unusual service conditions . 13
5.4 Transportation and storage . 14
5.4.1 Transport limitation . 14
5.4.2 Transport acceleration . 14
5.4.3 Temperature and environment conditions for transport and storage . 14
5.5 Rated voltage and rated frequency . 15
5.5.1 Rated voltage . 15
5.5.2 Rated frequency . 15
5.6 Operation at higher than rated voltage . 15
5.7 Highest voltage for equipment U and dielectric tests levels . 15
m
5.8 Identification according to cooling method . 15
5.8.1 General . 15
5.8.2 Identification symbols . 15
5.8.3 Arrangement of symbols . 16
5.9 Guaranteed temperature rise at rated conditions . 16
5.10 Additional information required for enquiry . 16
5.11 Sound level . 16
5.12 Components and materials . 16
6 Tappings . 16
7 Connections . 17
8 Ability to withstand short circuit . 17
9 Rating plate . 17
9.1 Rating plate fitted to the transformer . 17
9.2 Rating plate fitted to the transformer enclosure . 18
10 Temperature-rise limits . 18
10.1 Normal temperature-rise limits . 18
10.2 Reduced temperature rises for transformers designed for high cooling
medium temperatures or special cooling medium conditions . 19
10.3 High altitude temperature rise correction . 19
11 Insulation levels . 19
11.1 General . 19
11.2 Transformers for use at high altitudes . 20
12 Climatic, environmental and fire behaviour classes . 21
12.1 Climatic classes . 21
12.2 Environmental classes . 21
12.2.1 Transformers for indoor application with or without enclosure and for
outdoor application with enclosure . 21
12.2.2 Dry-type transformers without enclosure for outdoor application . 22
12.3 Fire behaviour classes . 22
12.4 Test criteria for climatic, environmental and fire behaviour classes . 23
13 Seismic . 23
13.1 General . 23
13.2 General seismic class approach . 24
13.2.1 Generalities . 24
13.2.2 The standard amplitude method . 24
13.2.3 The calculated amplitude method . 25
14 Test . 26
14.1 General requirements for tests . 26
14.2 Routine tests . 27
14.2.1 Measurement of winding resistance . 27
14.2.2 Measurement of voltage ratio and check of phase displacement . 27
14.2.3 Measurement of short-circuit impedance and load loss . 27
14.2.4 Measurement of no-load loss and current . 28
14.2.5 Applied voltage test (AV) . 28
14.2.6 Induced voltage withstand test (IVW) . 28
14.2.7 Partial discharge measurement . 28
14.3 Type tests . 30
14.3.1 Full wave lightning impulse test (LI) . 30
14.3.2 Temperature-rise test . 31
14.4 Special tests . 34
14.4.1 Partial discharge measurement for transformers operated under a
single phase line-to-earth fault condition . 34
14.4.2 Measurement of sound level . 35
14.4.3 Short-circuit test. 35
14.4.4 Climatic tests . 35
14.4.5 Environmental test . 37
14.4.6 Fire behaviour test . 39
14.4.7 Seismic test . 45
14.4.8 Special test for transformers equipped with amorphous core . 46
15 Tolerances . 46
16 Protection against direct contact . 47
17 Degrees of protection provided by enclosures . 47
18 Earthing terminal . 47
19 Information required with enquiry and order . 47
Annex A (informative) Installation and safety of dry-type transformers . 48
A.1 Manuals . 48
– 4 – IEC 60076-11:2018 © IEC 2018
A.2 Installation . 48
A.2.1 General . 48
A.2.2 Intrinsic safety . 48
A.2.3 Installation precautions . 48
A.2.4 Installation design . 49
Annex B (informative) Environmental test for evaluation of outdoor transformers
without enclosure . 50
B.1 General . 50
B.2 Salt-fog and UV-radiation chamber test . 50
B.2.1 Test description . 50
B.2.2 Acceptance criteria: . 52
B.3 Core and clamp coating test . 52
B.3.1 Test description . 52
B.3.2 Acceptance criteria . 52
B.4 Field test . 52
B.4.1 Test description . 52
B.4.2 Acceptance criteria . 53
Annex C (normative) Cooling of transformer in naturally ventilated room . 54
C.1 Assumptions . 54
C.2 Data for the calculation of ventilation . 55
C.3 Output . 55
C.4 Numerical application for a 1 000 kVA transformer . 56
Annex D (normative) Calculation of the losses with different reference temperatures
and/or winding material . 57
Bibliography . 60
Figure 1 – Basic measuring circuit for the partial discharge test for a single-phase
transformer . 29
Figure 2 – Basic measuring circuit for the partial discharge test for a three-phase
transformer . 29
Figure 3 – Voltage application for routine partial discharge test . 30
Figure 4 – Example of back-to-back method – Single phase . 33
Figure 5 – Example of back-to-back method – Three-phase . 33
Figure 6 – Voltage application for special partial discharge test . 35
Figure 7 – Test chamber . 41
Figure 8 – Test chamber details . 42
Figure B.1 – Salt fog multi-parameter ageing cycle . 51
Figure C.1 – Heat dissipation in a natural ventilated room . 54
Table 1 – Letter symbols . 15
Table 2 – Winding temperature-rise limits . 18
Table 3 – Test voltage levels . 19
Table 4 – Applied voltage level correction factor . 20
Table 5 – Sequence of tests . 23
Table 6 – Approximate acceleration level and performance level . 25
Table 7 – Ground acceleration level (AG) . 26
Table 8 – Recommended super elevation factors (K) . 26
Table 9 – Direction factors (D) . 26
Table 10 – Climatic class features . 35
Table 11 – Environmental classes . 38
Table 12 – Dimension of the chamber . 40
Table B.1 – Outdoor environmental classes . 50
– 6 – IEC 60076-11:2018 © IEC 2018
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
POWER TRANSFORMERS –
Part 11: Dry-type transformers
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
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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 60076-11 has been prepared by IEC technical committee 14:
Power transformers.
This second edition cancels and replaces the first edition published in 2004 and constitutes a
technical revision.
The main changes with regard to the previous edition are as follows:
• Extension of the scope up to 72,5kV
• Enclosure management in regards of the performance
• Management of the dielectric and thermal features with altitude
• New climatic classes for a better adaptation of customers’ need
• Establishment of the relation between location and environmental classes
• For fire behaviour classes, limitation at 1 000 kVA and process of test more robust
• Introduction of Seismic class
• Recommendations for amorphous transformers
The text of this International Standard is based on the following documents:
FDIS Report on voting
14/964/FDIS 14/972/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.
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.
The contents of the corrigendum of March 2019 have been included in this copy.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
considered to be useful for the correct
that it contains colours which are
understanding of its contents. Users should therefore print this document using a
colour printer.
– 8 – IEC 60076-11:2018 © IEC 2018
POWER TRANSFORMERS –
Part 11: Dry-type transformers
1 Scope
This part of IEC 60076 applies to dry-type power transformers (including auto-transformers)
having values of highest voltage for equipment up to and including 72,5 kV and at least one
winding operating at greater than 1,1 kV.
This document does not apply to:
• gas-filled dry-type transformers where the gas is not air;
• single-phase transformers rated at less than 5 kVA;
• polyphase transformers rated at less than 15 kVA;
• instrument transformers;
• starting transformers;
• testing transformers;
• traction transformers mounted on rolling stock;
• flameproof and mining transformers;
• welding transformers;
• voltage regulating transformers;
• small power transformers in which safety is a special consideration.
Where IEC standards do not exist for the transformers mentioned above or for other special
transformers, this document may be applicable as a whole or in parts.
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, Environmental testing – Part 3-3: Guidance – Seismic test methods for
equipments
IEC 60071-1, Insulation co-ordination – Part 1: Definitions, principles and rules
IEC 60071-2, Insulation co-ordination – Part 2: Application guidelines
IEC 60076-1:2011, Power transformers – Part 1: General
IEC 60076-2, Power transformers – Part 2: Temperature rise for liquid-immersed transformers
IEC 60076-3:2013, Power transformers – Part 3: Insulation levels, dielectric tests and external
clearances in air
IEC 60076-5, Power transformers – Part 5: Ability to withstand short circuit
IEC 60076-10, Power transformers – Part 10: Determination of sound levels
IEC 60076-12:2008, Power transformers – Part 12: Loading guide for dry-type power
transformers
IEC 60085, Electrical insulation – Thermal evaluation and designation
IEC 60270, High-voltage test techniques – Partial discharge measurements
IEC 60332-3-10, Tests on electric cables under fire conditions – Part 3-10: Test for vertical
flame spread of vertically-mounted bunched wires or cables – Apparatus
IEC 60529, Degrees of protection provided by enclosures (IP Code)
IEC 60721-3-4, Classification of environmental conditions – Part 3: Classification of groups of
environmental parameters and their severities – Section 4: Stationary use at non-
weatherprotected locations
IEC TS 60815-1, Selection and dimensioning of high-voltage insulators intended for use in
polluted conditions – Part 1: Definitions, information and general principles
IEC 61378-1, Converter transformers – Part 1: Transformers for industrial applications
IEC 62271-202, High-voltage switchgear and controlgear – Part 202: High-voltage/low-voltage
prefabricated substation
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
dry-type transformer
transformer of which the magnetic circuit and windings are not immersed in an insulating
liquid
3.2
totally enclosed dry-type transformer
transformer in an un-pressurised enclosure cooled by the circulation of the internal air having
no intentional exchange with external air
3.3
enclosed dry-type transformer
transformer in a ventilated enclosure cooled by the circulation of the external air
– 10 – IEC 60076-11:2018 © IEC 2018
3.4
non-enclosed dry-type transformer
transformer supplied without a protective enclosure cooled by natural or forced air ventilation
4 Service conditions
4.1 General
The requirements of IEC 60076-1 apply to dry-type transformers only in so far as they are
referred to in this document.
4.2 Normal service conditions
a) Altitude:
See IEC 60076-1.
b) Temperature of cooling air and water:
See IEC 60076-1.
For water cooled transformers, specification of the water (temperature, water flow, etc.)
has to be defined by agreement between manufacturer and purchaser if the temperature
of the water is different from that specified in IEC 60076-1 and IEC 60076-2
NOTE Liquids other than water can be used as a cooling medium then all technical data of the liquid has to
be defined by agreement between manufacturer and purchaser
c) Wave-shape of supply voltage:
A sinusoidal supply voltage with a total harmonic content not exceeding 5 % and an even
harmonic content not exceeding 1 %.
The purchaser shall specify the magnitude and frequency of any harmonic voltages
present in the supply that exceed these limits.
The manufacturer should take into account these harmonics in determination of additional
core losses and also regarding the saturation of the core.
d) Load current harmonic content:
At the enquiry stage the purchaser shall specify the magnitude and frequency of each of
the harmonic current components generated by the load.
The manufacturer shall consider the additional losses caused by harmonic currents in
calculating the temperature rise of the windings and the effects on the other metallic parts
of the transformer.
The manufacturer shall calculate the additional loss by using the method of IEC 61378-1
or by using a method like finite element by agreement between manufacturer and
purchaser.
If the total harmonic content of the load current exceeds 5 %, then the extra losses due to
these harmonic currents shall be taken into account by increasing the test current for the
temperature rise test. The temperature rise with these losses shall not exceed the
corresponding limit specified in Table 2 when tested in accordance with 14.3.2.
e) Symmetry of three-phase supply voltages:
See IEC 60076-1.
f) Installation environment:
This standard defines specific classes for environment:
1) for climatic conditions;
2) for humidity and pollution;
3) for fire behaviour;
4) for seismic disturbance;
5) environmental conditions within the following definitions according to IEC 60721-3-4:
i) biological conditions 4B1;
ii) chemically active substances 4C2;
iii) mechanically active substances 4S3;
iv) mechanical conditions 4M4.
g) For transformers intended to be installed indoors, some of these environmental conditions
might not be applicable.
h) Inrush current:
System inrush current limitations, if any, (maximum value, duration) shall be given at the
enquiry stage by the purchaser.
i) Frequency of energization:
If frequency of energization is greater than 24 times a year, then purchaser shall specify
the number of energizations per year at the enquiry stage.
j) Protection from water and liquids:
The transformer shall be protected against dripping water or flooding by water and other
liquids.
k) Special electrical and environmental conditions around the transformer:
IEC 60076-3 recommends general minimum clearances between transformer live parts
and conductive parts in the installation.
Any part of the installation made of insulation material becomes conductive when
moistened with rain water, salt water or other conductive liquids. Partial discharges in the
surroundings of the transformer can decrease the dielectric strength of the air.
Therefore the clearances between these installations parts and the live parts of the
transformer shall meet the clearances recommended in IEC 60076-3.
NOTE An agreement between purchaser and manufacturer is needed to reduce the clearances between
transformer live parts and conductive parts in the installation.
l) Level of vibration:
Vibrations of the structure where the transformer is to be installed shall be taken into
account when designing the transformer and special consideration shall be given in the
stress transferred to connection terminals.
The purchaser shall specify vibration spectrum at the enquiry stage. The procedure of
vibration test, if any, should be agreed at enquiry stage between purchaser and
manufacturer.
m) Corrosion protection:
Depending on the type of the installation, the purchaser should choose a protection class
defined in ISO 12944 or as agreed between purchaser and manufacturer.
n) Maintenance
The user shall follow the manufacturer guide line for maintenance and specially avoid an
accumulation of dust or pollution on the transformer by a regular cleaning.
4.3 Electromagnetic compatibility (EMC)
Transformers shall be considered as passive elements in respect to emission and immunity to
electromagnetic disturbances.
– 12 – IEC 60076-11:2018 © IEC 2018
5 Rating and general requirements
5.1 General
The manufacturer shall assign ratings to the transformer, which shall be marked on the rating
plate, see Clause 9. These ratings shall be such that the transformer can deliver its rated
current under steady loading conditions without exceeding the limits of temperature rise
specified in Clause 10, assuming that the applied primary voltage is equal to the rated voltage
and that the supply is at rated frequency.
5.2 Rated power
5.2.1 General
The rated power refers to continuous loading. This is a reference value for guarantees and
tests concerning load losses, temperature rises and short-circuit impedance.
NOTE A two-winding transformer has only one value of rated power, identical for both windings. When the
transformer has rated voltage applied to the primary winding, and rated current flows through the terminals of that
winding, the transformer receives the relevant rated power for both windings.
The rated power corresponds to continuous duty; nevertheless, dry-type transformers
complying with this standard can be overloaded and guidance on overloads is given in
IEC 60076-12.
5.2.2 Definition of the rated power with fans cooling or heat exchangers
The transformer shall have an assigned rated power for each winding which shall be marked
on the rating plate. The rated power refers to continuous loading. This is a reference value for
guarantees and tests concerning load losses and temperature rises.
If different values of apparent power are assigned under different circumstances, for example
with different methods of cooling, the highest of these values is the rated power.
When additional cooling by means of fans is provided, the rated power without fans shall be
subject to agreement between purchaser and supplier.
5.2.3 Transformer IP00 (without enclosure)
The transformer shall have an assigned rated power for each winding which shall be marked
on the rating plate.
5.2.4 Transformer with enclosure
This subclause defines rated power and the distance between enclosures and live parts when
the transformer is equipped with an enclosure.
Two cases are defined:
a) The transformer in an enclosure is manufactured, tested in the enclosure and then
delivered on site:
• The clearances between the live parts and the enclosure shall be defined by the
manufacturer. The dielectric tests shall be performed with the enclosure as a routine
test.
• If the clearance between the live part and the enclosure meets the requirement of
IEC 60076-3 the dielectric routine test shall be performed either with enclosure or
without enclosure.
• It is permitted to disassemble the enclosure for transportation reasons. In this case the
dis-assembled clearances between the live parts and the enclosure shall meet the
requirements of IEC 60076-3.
• There shall be no reduction (de-rating) of the rated power.
b) Transformer and enclosure are delivered on site separately, or later:
• There are two methods to determine the thermal performance of enclosure:
– The de-rating of the rated power is determined by IEC 62271-202. Then the
thermal class of enclosure shall be declared by the manufacturer of the enclosure
(seller of the package).
– The enclosure is calculated using Annex C of this document.
• The clearance between the live part and the enclosure shall meet the requirement of
IEC 60076-3.
• Enclosure shall have a rating plate and the manufacturer of the enclosure or seller of
the package is responsible for determining the rated power of the transformer with the
enclosure.
5.2.5 Preferred values of rated power
The preferred values shall be in accordance with IEC 60076-1 starting from 50 kVA.
5.2.6 Loading beyond rated power
The loading guides for dry-type transformers in IEC 60076-12 and the requirements in
IEC 60076-1 shall apply.
5.3 Provision for unusual service conditions
The purchaser shall identify in his enquiry any service conditions not covered by the normal
service conditions in 4.2. Examples of such conditions are:
• high or low ambient temperature outside the limits prescribed in 4.2;
• restricted ventilation;
• altitude in excess of the limit prescribed in 4.2;
• damaging fumes and vapours;
• steam;
• humidity in excess of the limit prescribed in 4.2;
• dripping water;
• salt spray;
• conductive pollution;
• excessive and abrasive dust;
• high harmonic content of the load current prescribed in 4.2;
• distortion of the supply voltage waveform prescribed in 4.2;
• fast transient overvoltage over the limits prescribed in 11.1;
• associated power factor correction and method of capacitor switching to limit inrush
current;
• superimposed DC current;
• seismic qualification which would otherwise require special considerations in the design;
• extreme mechanical shock and vibrations;
• transport and storage conditions not covered by the normal condition described in 5.7;
– 14 – IEC 60076-11:2018 © IEC 2018
• solar radiation;
• regular frequent energization in excess of 24 times per year;
• regular frequents short-circuits;
• V/Hz in excess of IEC 60076-1;
• if a generator step-up transformer is intended to be used in back-feed mode when not
connected to the generator without protection on the lower voltage side;
• corrosion protection, according to the type of installation;
• environment (see 4.2), the purchaser should choose classes of protection in ISO12944 or
by agreement between purchaser and manufacturer;
• load rejection conditions for generator transformers more severe than those given in
IEC 60076-1.
Transformer specification for operation under such abnormal conditions shall be subject to
agreement between the manufacturer and purchaser.
Supplementary requirements, within defined limits, for the rating and testing of transformers
designed for other than normal service conditions listed in 4.2, such as high temperature of
cooling air or altitude above 1 000 m, are given in 10.2 and 10.3.
5.4 Transportation and storage
5.4.1 Transport limitation
If transport size or weight limits apply, these shall be stated in the enquiry.
If any other special conditions apply during transportation, they shall be stated in the enquiry.
5.4.2 Transport acce
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