SIST EN 61378-1:2012

SLOVENSKI STANDARD
01-januar-2012
Konvertorski transformatorji - 1. del: Transformatorji za industrijsko uporabo
Converter transformers - Part 1: Transformers for industrial applications
Stromrichtertransformatoren - Teil 1: Transformatoren für industrielle Anwendungen
Transformateurs de conversion - Partie 1: Transformateurs pour applications
industrielles
Ta slovenski standard je istoveten z: EN 61378-1:2011
ICS:
29.180 Transformatorji. Dušilke Transformers. Reactors
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 61378-1
NORME EUROPÉENNE
November 2011
EUROPÄISCHE NORM
ICS 29.180 Supersedes EN 61378-1:1998 + corr. Nov.1998

English version
Convertor transformers -
Part 1: Transformers for industrial applications
(IEC 61378-1:2011)
Transformateurs de conversion -  Stromrichtertransformatoren -
Partie 1: Transformateurs pour Teil 1: Transformatoren für industrielle
applications industrielles Anwendungen
(CEI 61378-1:2011) (IEC 61378-1:2011)

This European Standard was approved by CENELEC on 2011-08-30. 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, Romania, Slovakia, Slovenia,
Spain, Sweden, Switzerland and the United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Management Centre: Avenue Marnix 17, B - 1000 Brussels

© 2011 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 61378-1:2011 E
Foreword
The text of document 14/686/FDIS, future edition 2 of IEC 61378-1, 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:
(dop) 2012-05-30
• latest date by which the document has
to be implemented at national level by
publication of an identical national
standard or by endorsement
(dow) 2014-08-30
• latest date by which the national
standards conflicting with the
document have to be withdrawn
This document supersedes EN 61378-1:1998 + corr. Nov.1998.

corr. Nov.1998:
• addition of winding connections (zig-zag, extended delta, etc.) with phase displacement (<30º);
• addition of transformers with more than one active part in the same tank;
• change of reference power definition (it is now based on fundamental component of the current);
• addition of considerations for guidelines for OLTC selection;
• addition of regulating transformer feeding converter transformer;
• addition of considerations about current sharing and hot spot temperature in high currentwindings for
various winding arrangements;
• addition of transductors used for d.c. voltage regulation together with diode rectifiers;
• improved old annexes with several calculation examples;
• addition of new annexes for special measurements setups.

Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such patent
rights.
__________
Endorsement notice
The text of the International Standard IEC 61378-1:2011 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 60076-4:2002 NOTE  Harmonized as EN 60076-4:2002 (not modified).
IEC 60076-5:2006 NOTE  Harmonized as EN 60076-5:2006 (not modified).
IEC 60076-10:2001 NOTE  Harmonized as EN 60076-10:2001 (not modified).
IEC 60146-1-3:1991 NOTE  Harmonized as EN 60146-1-3:1993 (not modified).
IEC 61378-2:2001 NOTE  Harmonized as EN 61378-2:2001 (not modified).
__________
- 3 - EN 61378-1:2011
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

The following referenced documents are indispensable for the application 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  When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD
applies.
Publication Year Title EN/HD Year

IEC 60050-421 1990 International electrotechnical vocabulary - -
(IEV) -
Chapter 421: Power transformers and
reactors
IEC 60076 Series Power transformers EN 60076 Series

IEC 60076-1 2011 Power transformers - EN 60076-1 2011
Part 1: General
IEC 60076-2 2011 Power transformers - EN 60076-2 2011
Part 2: Temperature rise for liquid-immersed
transformers
IEC 60076-3 2000 Power transformers - EN 60076-3 2001
+ corr. December 2000 Part 3: Insulation levels, dielectric tests and
external clearances in air
IEC 60076-6 2007 Power transformers - EN 60076-6 2008
Part 6: Reactors
IEC 60076-8 1997 Power transformers - - -
Part 8: Application guide
IEC 60076-11 2004 Power transformers - EN 60076-11 2004
Part 11: Dry-type transformers

IEC 60146 Series Semiconductor converters - General EN 60146 Series
requirements and line commutated converters

IEC 60146-1-1 2009 Semiconductor converters - General EN 60146-1-1 2010
requirements and line commutated
converters -
Part 1-1: Specification of basic requirements

IEC/TR 60146-1-2 2011 Semiconductor converters - General - -
requirements and line commutated
converters -
Part 1-2: Application guide
IEC/TR 60616 1978 Terminal and tapping markings for power - -
transformers
IEC 61378-1 ®
Edition 2.0 2011-07
INTERNATIONAL
STANDARD
colour
inside
Converter transformers –
Part 1: Transformers for industrial applications

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
XC
ICS 29.180 ISBN 978-2-88912-602-6

– 2 – 61378-1 © IEC:2011(E)
CONTENTS
FOREWORD . 6
1 Scope . 8
2 Normative references. 9
3 Terms, definitions and acronyms . 9
3.1 Terms and definitions . 9
3.2 Acronyms . 10
4 Classification . 11
4.1 General . 11
4.2 Normal service conditions . 11
4.3 Provision for unusual service conditions . 12
5 Ratings . 12
5.1 General . 12
5.2 Rated power at rated frequency and load capability . 12
5.3 Rated and service voltages . 13
5.3.1 Transformer energized from an a.c. power system . 13
5.3.2 Transformer energized from a converter/inverter with or without
variable frequency . 13
5.4 Rated current . 13
5.5 Phase displacement and terminal identification for three-phase transformer . 13
5.6 Rating plate . 14
5.7 Units with tertiary windings loaded with filter and compensation . 14
5.8 On load tap-changers . 15
6 Load loss and voltage drop in transformers and reactors . 15
6.1 General . 15
6.2 Determination of transformer load loss under distorted current loading . 15
6.3 Current sharing, losses and hot spot in high current windings . 19
6.4 Effect of geometrical winding arrangement and magnetic coupling between
windings on their eddy current losses due to harmonics in transformers with
three or more windings wound on the same core limb . 20
6.5 Losses in interphase transformers, current-balancing reactors, series-
smoothing reactors and transductors . 26
6.5.1 General . 26
6.5.2 Interphase transformers . 26
6.5.3 Current-balancing reactors . 26
6.5.4 Series-smoothing reactors . 26
6.5.5 Transductors . 26
6.6 Voltage drops in transformers and reactors . 27
6.6.1 General . 27
6.6.2 Transductors . 28
7 Tests for converter transformers . 29
7.1 General . 29
7.2 Measurement of commutating reactance and determination of the inductive
voltage drop . 30
7.2.1 Commutating reactance . 30
7.2.2 Inductive voltage regulation . 30
7.3 Measurement of voltage ratio and phase displacement . 31
7.4 Dielectric tests . 31

61378-1 © IEC:2011(E) – 3 –
7.4.1 General . 31
7.4.2 Dielectric test between interleaved valve windings . 31
7.5 Load loss test . 32
7.5.1 General . 32
7.5.2 Load loss measurement in rectifier transformers with transductors in
the same tank . 32
7.5.3 Test bus bars configuration for short circuit of high current valve
windings . 32
7.6 Temperature rise tests . 32
7.6.1 General . 32
7.6.2 Total loss injection . 33
7.6.3 Rated load loss injection . 33
7.6.4 Test of temperature rise on dry-type transformers . 35
8 On load noise level with transductors and/or IPT . 35
Annex A (informative) Determination of transformer service load loss at rated non-
sinusoidal converter current from measurements with rated transformer current
of fundamental frequency . 38
Annex B (informative) Short-circuit test currents and load losses in transformers for
single-way converters (total loss injection) . 56
Annex C (informative) Current sharing measurement in high current valve windings . 57
Annex D (informative) Examples of duty cycles . 66
Annex E (informative) Guidelines for design review . 67
Annex F (informative) Determination of loss in transformer tank due to magnetic field.
3D simulation and guidelines for tank losses evaluation and tank hotspot
calculation . 70
Annex G (informative) Short-circuit measurements of rectifier transformers equipped
with built in transductors . 71
Annex H (informative) Determination of the transformer voltage ratio and phase
displacement by the turn ratio measurements . 73
Annex I (informative) Phase displacement connections and terminal indications of
converter transformers . 78
Annex J (normative) Correlation between IEC 61378-1 and IEC 60146-1-1 ratings . 83
Bibliography . 90

Figure 1 – B6U or DB 6 pulse double bridge connection . 10
Figure 2 – DSS 6 pulse connection . 11
Figure 3 – Leakage fields for a three-winding transformer with closely coupled valve
windings. 22
Figure 4 – Leakage fields for a three-winding transformer with decoupled valve
windings. 23
Figure 5 – Leakage fields for a three winding transformer with loosely coupled double
concentric valve windings . 24
Figure 6 – Leakage fields for a three winding transformer with loosely coupled double-
tier valve windings . 25
Figure 7 – Typical transductor regulating curve (with max voltage drop at zero control
current) and tolerance band . 28
Figure A.1 – Cross-section of a winding strand . 40
Figure A.2 – Terminal identification for winding connection Y y0y6 . 43
Figure A.3 – Terminal identification for winding connection D d0y1 . 46

– 4 – 61378-1 © IEC:2011(E)
Figure A.4 – Valve current DB connection rectangular shape positive shape . 47
Figure A.5 – Valve current DB connection rectangular shape positive and negative
shape. 48
Figure A.6 – Valve current DSS connection rectangular shape . 52
Figure C.1 – Example of valve high current winding and measurement equipment
disposition . 58
Figure C.2 – Transformer windings arrangement . 59
Figure C.3 – Measurement circuit for the in-phase measurement . 60
Figure C.4 – Measurement circuit for the in-opposition measurement. 61
Figure C.5 – Measurements and comparison with the simulations made by finite
element method software for the in-phase current distribution . 63
Figure C.6 – Measurements and comparison with the simulations made by finite
element method software for the in-opposition current distribution . 65
Figure H.1 – Yd1 connection . 74
Figure H.2 – Yd11 connection . 74
Figure H.3 – Pd0+7,5 connection . 75
Figure H.4 – Oscilloscope connection . 76
Figure H.5 – Oscilloscope with phase B + 7,5° lag referring to phase A . 76
Figure H.6 – Oscilloscope with phase B – 7,5° lead referring to phase A . 77
Figure I.1 – Counterclockwise phase displacement . 78
Figure I.2 – Yd11 connection . 78
Figure I.3 – Yd1 connection . 78
Figure I.4 – Example I.1 phase displacement . 79
Figure I.5 – Example I.2 phase displacement . 79
Figure J.1 – DB connection ideal rectangular current blocks . 83
Figure J.2 – DSS Connection rectangular current blocks . 84

Table 1 – Connections and calculation factors . 36
Table A.1 – Specified harmonic currents and phase displacement in the valve windings . 41
Table A.2 – Resistance measurements at 20 °C winding temperature . 42
Table A.3 – Specified harmonic currents and phase displacement in the line and valve
windings. 45
Table A.4 – Measurements from test report . 46
Table A.5 – Resulting current harmonics . 48
Table A.6 – Resulting current harmonics . 49
Table A.7 – Resulting current harmonics . 50
Table A.8 – Detailed transformer load losses at rated tap position, with tertiary unloaded . 51
Table A.9 – Resulting current harmonics . 52
Table A.10 – Specified harmonic currents and phase displacement in the line and valve
windings. 53
Table A.11 – Resulting current harmonics . 54
Table A.12 – Detailed transformer load losses at rated tap position, with tertiary
unloaded . 55
Table C.1 – Measurements and comparison with the simulations made by finite element
method software for the in-phase current distribution . 62

61378-1 © IEC:2011(E) – 5 –
Table C.2 – Measurements and comparison with the simulations made by finite element
method software for the in-opposition current distribution . 64
Table D.1 – Examples of duty cycles for different applications . 66
Table H.1 – Single phase ratio measurements . 73
th
Table J.1 – Harmonics content up to 25 in DB 6 pulse connection (ideal rectangular
current waveshape) . 84
th
Table J.2 – Harmonics content up to 25 in DSS 6 pulse connection (ideal rectangular
current waveshape) . 85
Table J.3 – Calculation factor comparison example . 86
Table J.4 – Calculation factor comparison general factors . 87

– 6 – 61378-1 © IEC:2011(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
CONVERTER TRANSFORMERS –
Part 1: Transformers for industrial applications

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 61378-1 has been prepared by IEC technical committee 14: Power
transformers.
This second edition cancels and replaces the first edition published in 1997. It constitutes a
technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
• addition of winding connections (zig-zag, extended delta, etc.) with phase displacement
(<30º);
• addition of transformers with more than one active part in the same tank;
• change of reference power definition (it is now based on fundamental component of the
current);
• addition of considerations for guidelines for OLTC selection;
• addition of regulating transformer feeding converter transformer;

61378-1 © IEC:2011(E) – 7 –
• addition of considerations about current sharing and hot spot temperature in high current
windings for various winding arrangements;
• addition of transductors used for d.c. voltage regulation together with diode rectifiers;
• improved old annexes with several calculation examples;
• addition of new annexes for special measurements setups.
The text of this standard is based on the following documents:
FDIS Report on voting
14/686/FDIS 14/695/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of the IEC 61378 series can be found, under the general title Converter
transformers, on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until the
stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data related to
the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this standard may be issued at a later date.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this document using a colour printer.

– 8 – 61378-1 © IEC:2011(E)
CONVERTER TRANSFORMERS –
Part 1: Transformers for industrial applications

1 Scope
This Part of IEC 61378 deals with the specification, design and testing of power transformers
and reactors which are intended for integration within semiconductor converter plants; it is not
applicable to transformers designed for industrial or public distribution of a.c. power in general.
The scope of this International Standard is limited to application of power converters of any
power rating. Typical applications are: thyristor rectifiers for electrolysis; diode rectifiers for
electrolysis; thyristor rectifiers for large drives; thyristor rectifiers for scrap melting furnaces,
and diode rectifiers feeding inverters for variable speed drives. The standard also covers the
regulating unit utilized in such application as step down regulating transformers or
autotransformers. The valve winding highest voltage for equipment is limited to 36 kV.
This standard is not applicable to transformers for HVDC power transmission. These are high-
voltage transformers, and they are subjected to d.c. voltage tests.
The standards for the complete converter plant (IEC 60146 series, or other publications
dedicated to particular fields of application) may contain requirements of guarantees and tests
(such as insulation and power loss) for the whole plant, including the converter transformer and
possibly auxiliary transformers and reactor equipment. This does not relieve the application of
the requirements of this standard concerning the guarantees and tests applicable to the
converter transformer itself as a separate component before being assembled with the
remainder of the converter plant.
The guarantees, service and type tests defined in this standard apply equally to transformers
supplied as part of an overall converter package, or to those transformers ordered separately
but for use with converter equipment. Any supplementary guarantee or special verification has
to be specifically agreed in the transformer contract.
The converter transformers covered by this standard may be of the oil-immersed or dry-type
design. Unless specific exceptions are stated in this standard, the transformers comply with
IEC 60076 series for oil-immersed transformers, and with IEC 60076-11 for dry-type
transformers.
NOTE For some converter applications, it is possible to use common distribution transformers of standard design.
The use of such standard transformers in the special converter applications may require a certain derating. This
matter is not specifically covered in this standard, which deals with the requirements to be placed on specially
designed units. It is possible to estimate this derating from the formulae given in 5.1, and also from Clause 9 of
IEC 60076-8:1997.
This standard deals with transformers with one or more active parts installed in the same tank
like regulating (auto)transformer and one or two rectifier transformers. It also covers
transformers with transductors and/or one or more interphase transformers.
For any combination not listed above an agreement between the purchaser and manufacturer
is necessary regarding the determination and the measurement of the total losses.
This standard deals with transformers star Y and delta D and any other phase shifting
connections (like zig-zag, extended delta, polygon etc.). Phase shifting windings can be placed
on either the regulating or rectifier transformer.

61378-1 © IEC:2011(E) – 9 –
2 Normative references
The following referenced documents are indispensable for the application 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 60050-421:1990, International Electrotechnical Vocabulary (IEV) – Chapter 421: Power
transformers and reactors
IEC 60076 (all parts), Power transformers
IEC 60076-1:2011, Power transformers – Part 1: General
IEC 60076-2:2011, Power transformers – Part 2: Temperature rise for liquid-immersed transformers
IEC 60076-3:2000, Power transformers – Part 3: Insulation levels, dielectric tests and external
clearances in air
IEC 60076-6:2007, Power transformers – Part 6: Reactors
IEC 60076-8:1997, Power transformers – Part 8: Application guide
IEC 60076-11:2004, Power transformers – Part 11: Dry-type transformers
IEC 60146 (all parts), Semiconductor converters – General requirements and line commutated
converters
IEC 60146-1-1:2009, Semiconductor converters – General requirements and line commutated
converters – Part 1-1: Specifications of basic requirements
IEC/TR 60146-1-2:2011, Semiconductor converters – General requirements and line
commutated converters – Part 1-2: Application guide
IEC/TR 60616:1978, Terminal and tapping markings for power transformers
3 Terms, definitions and acronyms
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60050-421,
IEC 60076-1 and IEC 60146-1-1, as well as the following apply.
3.1.1
polygon connection
P
the winding connection in which each phase winding consists of two parts in which phase
displaced voltages are induced. One part of each phase is connected in series to the other part
of a different phase and then closed in a delta (see Annex I)
3.1.2
extended delta connection
E
the winding connection in which each phase winding consists of two parts in which phase
displaced voltages are induced. One part of each phase is delta connected and it is then
connected to its appropriate line terminal through the other part (see Annex I)

– 10 – 61378-1 © IEC:2011(E)
3.1.3
phase shifting angle
Γ
the angle with sign, expressed in degrees and decimal of degrees, which needs to be added to
the nearest clock number to obtain the phase displacement
3.1.4
transductor
device consisting of one or more ferromagnetic cores with windings, by means of which an a.c.
or d.c. current or voltage can be varied by an independent voltage or current, utilizing
saturation phenomena in the magnetic circuit
NOTE The French term transducteur magnétique (English: transductor) should not be confused with the more
general French term transducteur (English: transducer). The use of the term transducteur in the sense of
transducteur magnétique is permissible when no ambiguity is possible.
[IEC 60050-431:1980, 431-01-01]
3.1.5
interphase transformer
an electromagnetic device enabling the operation in parallel of two or more phase displaced
commutating groups through inductive coupling between the windings placed on the same core
[IEC 60050-551:1998, 551-14-16]
3.1.6
line side
transformer winding connected to the a.c. network
3.1.7
valve side
transformer winding connected to the converter
3.2 Acronyms
B6U 6-pulse double bridge connection (see Figure 1 below)
DB double bridge connection (see Figure 1 below)
NOTE The transformer windings can be star or delta connected.
+
1V 2v
2u
2v
2u
1U
2w
1W 2w
-
IEC  1720/11
Figure 1 – B6U or DB 6 pulse double bridge connection
DSS double star with interphase transformer (see Figure 2 below)

61378-1 © IEC:2011(E) – 11 –
2u
2v
2v
w
2u
1V
2w
2n
1U 3u
3n
w
1W
3u 3v
+
3w
3v
2n
3n
-
IEC  1721/11
Figure 2 – DSS 6 pulse connection
IPT see definition 3.1.5
SR see definition 3.1.4
FFT fast fourier transformation
4 Classification
4.1 General
Classification of converters and converter applications are given in 4.1 of IEC 60146-1-1:2009
and in 4.1 of IEC/TR 60146-1-2:2011. From the aspect of transformer design, it is important to
distinguish between
– applications with essentially sinusoidal voltage across the transformer, and
– applications with non-sinusoidal voltage where the transformer primary is energized from a
converter circuit for a.c. power control or variable frequency conversion.
It is also important to distinguish between
– applications characterized by a continuous load, such as electrolysis, d.c. arc furnace etc.,
and
– applications with short-time cyclic or irregular load variation, such as reversible mill-motor
drives, etc.
Information about the converter application should be supplied in the transformer specification.
This is detailed further in following subclauses of this standard.
4.2 Normal service conditions
Normal service conditions for the transformer are in accordance with IEC 60076-1, IEC 60076-
2, IEC 60076-11 and IEC 60146-1-1.
Any deviation of the a.c. voltage from the rated voltage value or tapping voltage value,
sinusoidal wave shape or three-phase symmetry should be within the limits of immunity class
B, according to 5.4 of IEC 60146-1-1:2009. If the converter transformer is supplied with non-
sinusoidal voltage, inverter or frequency converter application, it is necessary that information
on the range of variation of service voltage shape and frequency variation shall be submitted in

– 12 – 61378-1 © IEC:2011(E)
the specification. It is also important that information is given regarding the d.c. component of
the applied voltage cycle.
4.3 Provision for unusual service conditions
In addition to the unusual service conditions to be specified for power transformers, in case of
transformers with more than two windings, each loading combination of the windings is to be
clearly specified. Each loading combination shall include the respective current harmonic
components.
Examples of this type of unusual service conditions are no or reduced load on tertiary
compensation winding or on one valve winding.
5 Ratings
5.1 General
IEC 60076-1 applies, with the following additions and explanations.
Transformers for converter application are loaded with non-sinusoidal current, and sometimes
work with non-sinusoidal voltage. Even the frequency may vary considerably in certain
applications.
The rating of the transformers on which the tests will be conducted and to which the
corresponding guarantees are related is expressed in sinusoidal quantities of fundamental
frequency in steady state.
The following subclauses provide guidance as to how to determine the transformer rating when
the details of the converter and other information about the loading are available.
5.2 Rated power at rated frequency and load capability
The rated power of the converter transformer line side winding is based on the fundamental
frequency components of voltage and current, hence the rated three-phase power is:
S = 3× U × I (1)
R 1
where
U is the r.m.s. value of the fundamental component of the line-to-line voltage;
I is the r.m.s. value of the fundamental component of the rated line side current. This
fundamental component is calculated from an ideal rectangular waveshape current (see
Table 1).
The rated power S and line current I shall be used for guaranteed load losses and short
R
circuit impedance.
The rated power of the valve windings S is equal to the rated power of the line winding
V
multiplied by a factor which is a function of number of valve windings and type of rectifier
(single or double way). This factor is defined in Table 1.
The thermal design and cooling system of the transformers shall be determined after allowance
is made for the increased losses due to harmonics (including d.c. components) by means of an
equivalent thermal current to be used in temperature rise test (see Clause 6).
In case of cyclic loading, the load variation pattern shall be included by the purchaser in the
transformer specification.
61378-1 © IEC:2011(E) – 13 –
5.3 Rated and service voltages
5.3.1 Transformer energized from an a.c. power system
For a converter transformer connected to an a.c. power system, the rated voltage shall be as
specified in 5.4 of IEC 60076-1:2011 and in IEC 60076-8.
5.3.2 Transformer energized from a converter/inverter with or without variable
frequency
For a converter application with a considerably distorted transformer voltage, the rated voltage
shall be the r.m.s value of the sinusoidal fundamental component derived from the Fourier
series analysis of the maximum continuous service voltage.
For applications with such a distorted transformer voltage, or with variable frequency,
information shall be given in the specification concerning the applied voltage under various
service conditions.
NOTE For the above applications, the amplitude of flux density in the magnetic circuit is the determining
parameter, and not the amplitude of a non-sinusoidal voltage. The value of flux is determined by the voltage-time
integral over a half-cycle. This value will be the maximum value in continuous service. If short-time higher values of
the voltage-time integral exist, they should also be included in the specification, to permit checking against possible
overfluxing.
5.4 Rated current
The rated current of the transformer is the r.m.s. value of the fundamental component of
current corresponding to rated power according to 5.2.
5.5 Phase displacement and terminal identification for three-phase transformer
The definition of phase displacement is described in 3.10.6 of IEC 60076-1:2011.
Whenever the ‘clock number’ notation outlined in the Clause 7 of IEC 60076-1:2011 is not
sufficient to identify the phase displacement; the nearest clock number shall be used followed
by the value with sign of the angle Γ which has to be added to obtain the exact phase
displacement. The indication of the sign of the Γ has to follow the definition of the leading and
lagging displacement included in 3.10.6 of IEC 60076-1:2011 (see Annex I).
The terminal identification of a converter transformer shall also include the information
regarding the sequence of the commutating valve. Therefore the terminals are expressed by a
code of three symbols as described below.
First symbol: Number, that refers the different winding systems (with 1 for line
side winding).
Second symbol:   Letter, that refers the sequence of the phases according to the IEC
60616.
Third symbol (optional):  “+” or “–“ that refers to which polarity of the rectifier the terminal is
connected to.
Examples of different type of connections, phase displacement and te
...