IEC/IEEE 60076-57-129:2017

IEC/IEEE 60076-57-129 ®
Edition 1.0 2017-11
INTERNATIONAL
STANDARD
Power transformers –
Part 57-129: Transformers for HVDC applications

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IEC/IEEE 60076-57-129 ®
Edition 1.0 2017-11
INTERNATIONAL
STANDARD
Power transformers –
Part 57-129: Transformers for HVDC applications

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.180 ISBN 978-2-8322-4447-0

– 2 – IEC/IEEE 60076-57-129:2017
 IEC/IEEE 2017
CONTENTS
FOREWORD . 6
1 Scope . 8
2 Normative references . 8
2.1 IEC references . 8
2.2 IEEE references . 9
3 Terms, definitions and symbols. 9
3.1 Terms and definitions . 9
3.2 Symbols . 10
4 Use of normative references . 11
5 General requirements . 11
5.1 General . 11
5.2 Service conditions . 11
5.2.1 General . 11
5.2.2 Temperature . 11
5.2.3 Load current . 11
5.2.4 AC voltage . 11
5.2.5 Direction of power flow . 11
5.3 Unusual service conditions . 12
5.4 Loading of transformer above rating . 12
6 Rating data . 12
6.1 General . 12
6.2 Rated voltage . 12
6.3 Rated current . 12
6.4 Rated frequency . 12
6.5 Rated power . 12
7 Losses . 13
7.1 General . 13
7.2 No-load loss . 13
7.3 Load loss under rated frequency conditions . 13
7.4 Load loss under service conditions . 13
7.5 Determination of hot-spot temperature . 14
8 Test requirements . 15
8.1 General . 15
8.1.1 Routine tests . 15
8.1.2 Type tests . 15
8.1.3 Special tests . 15
8.1.4 Commissioning tests . 15
8.2 Test applicability . 16
8.2.1 General . 16
8.2.2 DC withstand voltage test . 16
8.2.3 Polarity reversal test . 16
8.2.4 AC applied withstand test for valve side winding(s) . 16
8.3 Dielectric test voltage levels . 17
8.3.1 Line windings . 17
8.3.2 Valve windings . 17
8.4 Induced voltage level with partial discharge measurement . 18

 IEC/IEEE 2017
9 Tests . 18
9.1 General . 18
9.1.1 Applicable tests . 18
9.1.2 Test sequence . 18
9.1.3 Ambient temperature . 18
9.1.4 Assembly . 18
9.1.5 Converter transformers for connection to gas-insulated equipment . 19
9.2 Load loss and impedance measurements . 19
9.2.1 General . 19
9.2.2 Calculation procedure . 19
9.3 Switching impulse test . 20
9.4 Applied switching impulse test on the valve side winding . 20
9.5 Lightning impulse tests . 20
9.6 DC withstand voltage test . 20
9.6.1 Applicability . 20
9.6.2 Transformer test temperature . 20
9.6.3 Polarity . 20
9.6.4 Test procedure . 21
9.6.5 Acceptance criteria . 21
9.7 Polarity reversal test . 21
9.7.1 Applicability . 21
9.7.2 Transformer test temperature . 21
9.7.3 Test procedure . 21
9.7.4 Acceptance criteria . 22
9.8 Extended polarity-reversal test . 23
9.8.1 Applicability . 23
9.8.2 Transformer test temperature . 23
9.8.3 Test procedure . 23
9.8.4 Acceptance criteria . 25
9.9 AC applied voltage test for valve side winding(s) . 25
9.9.1 Test procedure . 25
9.9.2 Acceptance criteria . 25
9.10 AC applied voltage test on line side winding(s) . 25
9.11 AC induced voltage test with partial discharge measurement . 26
9.11.1 General . 26
9.11.2 Acceptance criteria . 26
9.12 Induced voltage test including running of oil pumps . 26
9.13 Temperature-rise test . 26
9.13.1 General . 26
9.13.2 Test procedure . 27
9.13.3 Tank surface temperature rise measurement . 28
9.14 Load current test . 28
9.15 Sound level measurement . 28
9.16 Insulation power-factor test . 29
9.17 Winding insulation resistance test . 29
9.18 Core insulation resistance test . 29
9.19 Short-circuit test . 29
9.20 Frequency Response Analysis (FRA) measurements . 29
9.21 Over-excitation test . 29

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 IEC/IEEE 2017
10 Dielectric tests on transformers that have been in service . 29
11 Sound levels . 30
11.1 General . 30
11.2 Determination of service sound levels . 30
11.3 Guaranteed sound levels . 30
12 Bushings . 30
12.1 General . 30
12.2 Line side winding bushings . 31
12.3 Valve side winding bushings . 31
13 Tap-changer . 31
13.1 General . 31
13.2 Current wave shape . 31
13.3 Consecutive operation of tap-changers . 31
14 High-frequency modelling . 31
15 Tolerances . 32
15.1 General . 32
15.2 Short-circuit impedance tolerances . 32
16 Rating plate . 32
Annex A (informative) In service overloading of HVDC converter transformers used
with current commutated valves (either mercury arc valves or thyristors) . 34
A.1 General . 34
A.2 Overloading in service . 34
A.3 Temperature rise test for demonstrating normal loading condition . 36
A.4 Temperature rise test for demonstrating planned overload conditions . 36
Annex B (informative) HVDC converter transformers for use with voltage source
converters . 38
B.1 General . 38
B.2 Converter transformer stressed with only fundamental voltage and current . 38
B.3 Converter transformers stressed with direct voltage, fundamental voltage
and fundamental current . 39
B.4 Converter transformer stressed with the valves connected directly to the
converter transformer . 40
B.5 Summary of stresses . 41
Annex C (informative) Design review . 42
C.1 General . 42
C.2 Topics . 42
Annex D (informative) Transformer specification content . 44
D.1 General . 44
D.2 Data to be provided by the purchaser. 44
D.3 Data to be provided by the manufacturer. 45
Annex E (informative) Audible sound of converter transformers . 47
E.1 General . 47
E.2 Technical reference . 47
E.3 Current harmonics . 47
E.4 Voltage harmonics . 47
E.5 DC bias current . 48
E.6 Derivation of service sound power levels . 48
E.7 Sound level guarantee . 48

 IEC/IEEE 2017
Annex F (informative) Determination of transformer service load loss at rated non-
sinusoidal converter current from measurements with rated transformer current of
fundamental frequency . 49
F.1 General . 49
F.2 Alternative method for calculation of the winding eddy loss enhancement
factor . 50
Bibliography . 52

Figure 1 – Double reversal test voltage profile . 22
Figure 2 – Extended polarity reversal test alternative 1 . 24
Figure 3 – Extended polarity reversal test alternative 2 . 24
Figure A.1 – Example of an overload diagram . 36
Figure B.1 – Configuration with no additional stresses on the converter transformer . 39
Figure B.2 – Configuration with multi-level VSC HVDC converter station applied in a
monopolar scheme with DC overhead line transmission . 40
Figure B.3 – Configuration with VSC valves connected directly to the converter
transformer . 41
Figure F.1 – Cross-section of a winding strand . 51

Table 1 – Routine, type and special tests . 15
Table A.1 – Example of an overload table . 35

– 6 – IEC/IEEE 60076-57-129:2017
 IEC/IEEE 2017
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
POWER TRANSFORMERS –
Part 57-129: Transformers for HVDC 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
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IEEE Standards documents are developed within IEEE Societies and Standards Coordinating Committees of the
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IEC collaborates closely with IEEE in accordance with conditions determined by agreement between the two
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terms of that agreement.
2) The formal decisions 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
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and Standards Coordinating Committees has been reached, is determined by a balanced ballot of materially
interested parties who indicate interest in reviewing the proposed standard. Final approval of the IEEE
standards document is given by the IEEE Standards Association (IEEE-SA) Standards Board.
3) IEC/IEEE Publications have the form of recommendations for international use and are accepted by IEC
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5) IEC and IEEE do not provide any attestation of conformity. Independent certification bodies provide conformity
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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 implementation of this IEC/IEEE Publication may require use of
material covered by patent rights. By publication of this standard, no position is taken with respect to the
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 IEC/IEEE 2017
International Standard IEC/IEEE 60076-57-129 has been prepared by IEC technical
committee 14: Power transformers, in cooperation with the Transformers Committee of the
IEEE Power & Energy Society , under the IEC/IEEE Dual Logo Agreement.
This publication cancels and replaces the first edition of IEC 61378-2 published in 2001 and
IEEE Std C57.129™ published in 2007.
This publication is published as an IEC/IEEE Dual Logo standard.
The text of this standard is based on the following IEC documents:
FDIS Report on voting
14/904/FDIS 14/907/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.
International standards are drafted in accordance with the rules given in the ISO/IEC
Directives, Part 2.
A list of parts of the 60076 International Standard, published under the general title Power
transformers, can be found on the IEC website.
The IEC Technical Committee and IEEE Technical Committee have decided that the contents
of this publication will remain unchanged until the stability date indicated on the IEC website
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 publication may be issued at a later date.

______________
A list of IEEE participants can be found at the following URL: http://standards.ieee.org/downloads/60076/60076-
57-129-2017/60076-57-129-2017_wg-participants.pdf

– 8 – IEC/IEEE 60076-57-129:2017
 IEC/IEEE 2017
POWER TRANSFORMERS –
Part 57-129: Transformers for HVDC applications

1 Scope
This part of 60076 International Standard specifies requirements of liquid-immersed three-phase
and single-phase converter transformers for use in high voltage direct current (HVDC) power
transmission systems including back-to-back applications. It applies to transformers having
two, three or multiple windings.
This document does not apply to
– converter transformers for industrial applications (see IEC 61378-1 or IEEE Std
C57.18.10);
– converter transformers for traction applications (see IEC 60310).
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.
2.1 IEC references
IEC 60050-421, International Electrotechnical Vocabulary – Chapter 421: Power transformers
and reactors (available at http://www.electropedia.org)
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 60076-18, Power transformers – Part 18: Measurement of frequency response
IEC 60076-10, Power transformers – Part 10: Determination of sound levels
IEC 60137, Insulated bushings for alternating voltages above 1 000 V
IEC 60214-1, Tap-changers – Part 1: Performance requirements and test methods
IEC 60270, High voltage test techniques – Partial discharge measurements
IEC/IEEE 65700-19-03, Bushings for DC application

 IEC/IEEE 2017
2.2 IEEE references
IEEE Std C57.12.00™, IEEE Standard for General Requirements for Liquid-Immersed
Distribution, Power, and Regulating Transformers
IEEE Std C57.12.10™, IEEE Standard Requirements for Liquid-Immersed Power
Transformers
IEEE Std C57.12.80™, IEEE Standard Terminology for Power and Distribution Transformers
IEEE Std C57.12.90™, IEEE Standard Test Code for Liquid-Immersed Distribution, Power, and
Regulating Transformers
IEEE Std C57.19.00™, IEEE Standard General Requirements and Test Procedures for Power
Apparatus Bushings
IEEE Std C57.113™, IEEE Recommended Practice for Partial Discharge Measurement in
Liquid-Filled Power Transformers and Shunt Reactors
IEEE Std C57.131™, IEEE Standard Requirements for Tap Changers
IEEE Std C57.149™, IEEE Guide for the Application and Interpretation of Frequency
Response Analysis for Oil-Immersed Transformers
3 Terms, definitions and symbols
For the purposes of this document, the terms and definitions given in IEC 60050-421 and
IEC 60076-1 apply to IEC specified transformers for HVDC applications. For IEEE specified
transformers for HVDC applications, the terms and definitions given in IEEE Std C57.12.80
apply. For all transformers for HVDC applications, the following apply and take precedence.
NOTE Where the term oil is used in the text, it is understood to be the insulating liquid in the transformer.
ISO, IEC and IEEE 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
• IEEE Standards Dictionary Online: available at
http://ieeexplore.ieee.org/xpls/dictionary.jsp
3.1 Terms and definitions
3.1.1
valve side winding
winding connected to the converter
3.1.2
line side winding
winding connected to the AC network
Note 1 to entry: In other standards, valve side can be denoted as DC side and line side can be denoted as AC
side.
– 10 – IEC/IEEE 60076-57-129:2017
 IEC/IEEE 2017
3.2 Symbols
f rated frequency and also the fundamental frequency
f frequency at harmonic order number h
h
F loss adjustment factor at harmonic h
h
frequency ≥ 150 Hz used to determine the distribution of eddy current losses
f
x
F enhancement factor for stray losses in structural parts
SE
enhancement factor for winding eddy losses
F
WE
h harmonic order number
I equivalent sinusoidal r.m.s. current of rated frequency, giving the winding losses,
eq
used in temperature rise test
th
I magnitude of the h harmonic current in the transformer
h
I square root of the sum of the square of the fundamental and harmonic currents up to
LN
th
the 49 harmonic for a particular loading condition and associated harmonic current
spectra. I = I (49 is the highest harmonic to be evaluated).
LN h
∑
h=1
NOTE I equals I for the nominal load condition but it can also be used for other load conditions (e.g.
LN r
overload).
I rated current, r.m.s. value of the nominal in-service load current, including
r
harmonics, in the winding under consideration calculated in the same way as I
LN
above. Used as a basis for the definition of rated impedance.
I R ohmic losses at rated current
r
I load loss test current at frequency f
x x
k ratio of the current I to the rated current I
h h r
K windings enhancement loss p.u. at fundamental frequency due to eddy losses
WE
N number of six-pulse bridges in series from the neutral of the DC line to the rectifier
bridge connected to the transformer
P total load losses at fundamental frequency (50 Hz or 60 Hz) and rated current
1r
P load loss used in determining guaranteed total losses
LLG
P calculated total load loss under service conditions
LLT
P total service load loss
N
P total no-load loss
NL
P stray losses in structural parts (excluding windings) at fundamental frequency and
SE1r
rated current
P total loss under service conditions (used for temperature rise test)
TL
P eddy losses in windings at fundamental frequency and rated current
WE1r
P load loss measured at frequency f
x x
R DC resistance of windings including internal leads
S rated power
R
U AC separate source test voltage for the valve windings (r.m.s. value)
AC
U DC withstand test voltage for the valve windings
DC
U highest DC voltage per valve bridge
dm
U highest system voltage of the line winding
m
U polarity reversal test voltage (DC voltage) for the valve windings
pr
U rated voltage
r
U maximum phase-to-phase AC operating voltage of the valve windings of the
vm
converter transformer
 IEC/IEEE 2017
4 Use of normative references
This document can be used with either the IEC or IEEE normative references, but the
references shall not be mixed. The purchaser shall include in the enquiry and order which
normative references are to be used. If the choice of normative references is not specified,
then IEC standards shall be used except for HVDC converter transformers intended for
installation in North America where IEEE standards shall be used.
5 General requirements
5.1 General
All the requirements in IEC 60076-1 or IEEE Std C57.12.00 and IEEE Std C57.12.10 are valid
unless specific requirements are given in this document. In case of conflicting requirements,
this document shall prevail.
5.2 Service conditions
5.2.1 General
Converter transformers in this document shall comply with the service conditions stated in
IEC 60076-1 or IEEE Std C57.12.00, except where it is clearly not applicable to converter
transformers or when other requirements are specified herein. It is assumed that the
transformer operates in an approximately symmetrical three-phase system, unless otherwise
stated.
5.2.2 Temperature
If any part of the transformer (for example, the valve bushings) protrudes into the valve hall,
the maximum temperature in the valve hall shall be specified in addition to the normal ambient
temperature.
NOTE The maximum air temperature in the valve hall is normally between 40 °C and 60 °C depending on the
technology used
5.2.3 Load current
The currents flowing through the transformers contain harmonics. Residual DC currents may
also flow through the windings. The purchaser shall provide the manufacturer with the
harmonic content and the magnitude of the residual DC currents in the enquiry.
The harmonic content should preferably be given by listing a number of typical operating
conditions.
5.2.4 AC voltage
The voltage applied to the line side winding shall be approximately sinusoidal (e.g., maximum
total harmonic distortion of 5 % with no individual harmonic exceeding 1 %), and the phase
voltages supplying a poly-phase transformer shall be approximately equal in magnitude and
time displacement.
5.2.5 Direction of power flow
Unless otherwise specified, the transformer shall be designed for both rectifier and inverter
operation.
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 IEC/IEEE 2017
5.3 Unusual service conditions
Conditions other than those described in 5.2 are considered unusual and shall be specified by
the purchaser. Special attention on sources of DC current also needs to be considered.
NOTE Sources of DC current could be currents induced by geomagnetic storms and by fundamental frequency
currents in DC lines.
5.4 Loading of transformer above rating
Any requirements for loading beyond rated power or at other than rated conditions shall be
specified by the purchaser. The loading of HVDC transformers above nameplate rating shall
not be made without consultation with the supplier.
NOTE Converter transformers are normally designed for a specific installation and are coordinated with the
capabilities of the valves and other DC components. If the station is to be operated above its rated capacity, a
detailed thermal study would be needed to determine the capability of all the affected terminal equipment. Detailed
information about the transformer design and capabilities at both fundamental and harmonic currents would be part
of the study.
6 Rating data
6.1 General
The rating characteristics of the transformer are expressed in steady-state sinusoidal
quantities of current and voltages at rated fundamental frequency. The guaranteed losses,
impedances and sound level shall correspond to these values. For a general list of rating data
see IEC 60076-1 or IEEE Std C57.12.00.
6.2 Rated voltage
The rated voltage is the r.m.s. value of the fundamental component of the phase-to-phase
(line-to-line) voltage.
NOTE For single-phase transformers intended to be connected in star to form a three-phase bank or to be
connected between the line and the neutral of a three phase system, the rated voltage is indicated as the phase-to-
phase voltage, divided by √3 , for example 400 / √3 kV.
6.3 Rated current
The rated current is the square root of the sum of the square of the fundamental and harmonic
th
currents up to the 49 harmonic for the nominal loading condition
I = I
r h
∑ (1)
h=1
(49 is the highest harmonic to be evaluated).
6.4 Rated frequency
The rated frequency is the fundamental frequency of either 50 Hz or 60 Hz for which the
transformer is designed.
6.5 Rated power
The rated three-phase power is the product of , the rated voltage and the rated current.
S = 3 ×U × I (2)
R r r
 IEC/IEEE 2017
7 Losses
7.1 General
The total losses of a converter transformer shall be the sum of the no-load loss and the load
loss at a specific service condition. The guaranteed losses shall be within the tolerances of
IEC 60076-1:2011, Table 1 or IEEE Std C57.12.00.
The standard reference temperatures for the losses of converter transformers shall be the
ones given in IEC 60076-1 or IEEE Std C57.12.00.
7.2 No-load loss
No-load loss and no-load current are measured in the same way as for conventional AC
transformers according to IEC 60076-1 or IEEE Std C57.12.90. This shall be the guaranteed
no-load loss.
NOTE The harmonic voltages and DC bias currents have an effect on no-load loss and no-load current. However,
in practice the differences due to this effect can be disregarded in comparison to the total losses of the
transformer.
7.3 Load loss under rated frequency conditions
The load loss shall be measured in accordance with IEC 60076-1 or IEEE Std C57.12.90.
7.4 Load loss under service conditions
The currents flowing through the windings of converter transformers contain certain harmonics
whose magnitudes depend on the parameters of the converter station. The determination of
actual load loss in service cannot be deduced from one single load loss measurement. The
procedure to determine the load loss in accordance with this document includes two load loss
measurements and certain assumptions on loss distribution and a specific calculation scheme
(see 9.2).
The determination of actual load loss in service is more complicated due to harmonic effects.
The harmonic spectrum for the temperature rise test and the harmonic spectrum to be used
for load loss evaluation shall be clearly defined by the purchaser. The spectrum for load loss
evaluation may be different from the one specified for temperature rise tests; the latter
representing a worst case operating condition.
To determine the losses under service conditions, the following assumptions are made:
– eddy and stray losses are proportional to the square of the current;
– winding eddy losses
...