SIST EN IEC 60076-11:2019

SLOVENSKI STANDARD
01-januar-2019
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SIST EN 60076-11:2005
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Power transformers - Part 11: Dry-type transformers
Leistungstransformatoren - Teil 11: Trockentransformatoren
Transformateurs de puissance - Partie 11: Transformateurs de type sec
Ta slovenski standard je istoveten z: EN IEC 60076-11:2018
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 60076-11

NORME EUROPÉENNE
EUROPÄISCHE NORM
October 2018
ICS 29.180 Supersedes EN 60076-11:2004
English Version
Power transformers - Part 11: Dry-type transformers
(IEC 60076-11:2018)
Transformateurs de puissance - Partie 11: Transformateurs Leistungstransformatoren - Teil 11: Trockentransformatoren
de type sec (IEC 60076-11:2018)
(IEC 60076-11:2018)
This European Standard was approved by CENELEC on 2018-09-19. 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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, 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
© 2018 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 60076-11:2018 E

European foreword
The text of document 14/964/FDIS, future edition 2 of IEC 60076-11, prepared by IEC/TC 14 "Power
transformers" was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2019-06-19
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2021-09-19
document have to be withdrawn
This document supersedes EN 60076-11:2004.
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 60076-11:2018 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 60721-2-6:1990 NOTE Harmonized as HD 478.2.6 S1:1993 (not modified)
ISO 12944-2 NOTE Harmonized as EN ISO 12944-2
ISO 12944 (series) NOTE Harmonized as EN ISO 12944 (series)

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 -  Environmental testing - Part 3-3: Guidance -  EN 60068-3-3 -
Seismic test methods for equipments
IEC 60071-1 -  Insulation co-ordination - Part 1: Definitions,  EN 60071-1 -
principles and rules
IEC 60071-2 -  Insulation co-ordination – Part 2: Application  EN IEC 60071-2 -
guidelines
IEC 60076-1 2011 Power transformers - Part 1: General  EN 60076-1 2011
IEC 60076-2 -  Power transformers - Part 2: Temperature rise  EN 60076-2 -
for liquid-immersed transformers
IEC 60076-3 2013 Power transformers - Part 3: Insulation levels,  EN 60076-3 2013
dielectric tests and external clearances in air
IEC 60076-5 -  Power transformers - Part 5: Ability to withstand  EN 60076-5 -
short circuit
IEC 60076-10 -  Power transformers - Part 10: Determination of  EN 60076-10 -
sound levels
IEC 60076-12 2008 Power transformers - Part 12: Loading guide for  - -
dry-type power transformers
IEC 60085 -  Electrical insulation - Thermal evaluation and  EN 60085 -
designation
IEC 60270 -  High-voltage test techniques - Partial discharge  EN 60270 -
measurements
IEC 60332-3-10 -  Tests on electric cables under fire conditions -  EN IEC 60332-3- -
Part 3-10: Test for vertical flame spread of 10
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  EN 60721-3-4 -
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  EN 61378-1 -
insulators intended for use in polluted
conditions - Part 1: Definitions, information and
general principles
IEC 61378-1 - Converter transformers - Part 1: Transformers  EN 61378-1 -
for industrial applications
IEC 62271-202 -  High-voltage switchgear and controlgear - Part  EN 62271-202 -
202: High-voltage/ low-voltage prefabricated
substation
ISO 12944-6 -  Paints and varnishes - Corrosion protection of  EN ISO 12944-6 -
steel structures by protective paint systems -
Part 6: Laboratory performance test methods

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

IEC 60076-11:2018 © IEC 2018 – 3 –
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

IEC 60076-11:2018 © IEC 2018 – 5 –
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
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 60076-11 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

IEC 60076-11:2018 © IEC 2018 – 7 –
• 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.
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 60076-11:2018 © IEC 2018 – 9 –
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;
IEC 60076-11:2018 © IEC 2018 – 11 –
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.
IEC 60076-11:2018 © IEC 2018 – 13 –
• 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 abrasi
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