IEC TR 62001-1:2021

IEC TR 62001-1 ®
Edition 2.0 2021-07
TECHNICAL
REPORT
colour
inside
High-voltage direct current (HVDC) systems – Guidance to the specification and
design evaluation of AC filters –
Part 1: Overview
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IEC TR 62001-1 ®
Edition 2.0 2021-07
TECHNICAL
REPORT
colour
inside
High-voltage direct current (HVDC) systems – Guidance to the specification and

design evaluation of AC filters –

Part 1: Overview
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.200 ISBN 978-2-8322-9986-9

– 2 – IEC TR 62001-1:2021  IEC 2021
CONTENTS
FOREWORD . 7
INTRODUCTION . 9
1 Scope . 10
2 Normative references . 10
3 Terms and definitions . 10
4 Outline of specifications of AC filters for HVDC systems . 11
4.1 General . 11
4.2 Boundaries of responsibility . 12
4.3 Scope of studies . 14
4.4 Scope of supply . 14
4.5 Technical data to be supplied by contractor . 15
4.6 Alternative proposals by bidders . 15
5 Permissible distortion limits . 16
5.1 General . 16
5.2 Voltage distortion . 17
5.2.1 General . 17
5.2.2 Definitions of performance criteria . 17
5.2.3 Discussion and recommendations . 18
5.2.4 Determination of limits . 18
5.2.5 Pre-existing harmonic levels . 21
5.2.6 Relaxed limits for short term and infrequent conditions . 22
5.2.7 Treatment of interharmonic frequencies . 22
5.3 Distortion limits pertaining to the HV and EHV network equipment . 23
5.3.1 HVAC transmission system equipment . 23
5.3.2 Harmonic currents in synchronous machines . 23
5.3.3 Nearby HVDC installations . 24
5.4 Telephone interference . 24
5.4.1 General . 24
5.4.2 Causes of telephone interference . 24
5.4.3 Definitions of performance criteria . 24
5.4.4 Discussion . 25
5.4.5 Determination of limits . 25
5.4.6 Pre-existing harmonic levels . 27
5.4.7 Limits for temporary conditions . 27
5.5 Special criteria . 28
6 Harmonic generation . 28
6.1 General . 28
6.2 Converter harmonic generation . 28
6.2.1 Idealized conditions . 28
6.2.2 Realistic conditions . 30
6.3 Calculation methodology . 32
6.3.1 General . 32
6.3.2 Harmonic currents for performance, rating and other calculations . 32
6.3.3 Combining harmonics from different converter bridges. 33
6.3.4 Consistent sets . 33
6.3.5 Harmonic generation for different DC power ranges . 34

6.4 Sensitivity of harmonic generation to various factors . 35
6.4.1 Direct current, control angle and commutation overlap . 35
6.4.2 Effect of asymmetries on characteristic harmonics . 35
6.4.3 Converter equipment parameter tolerances . 35
6.4.4 Tap steps . 36
6.4.5 Theoretically cancelled harmonics . 36
6.4.6 Negative and zero sequence voltages . 36
6.4.7 Converter transformer saturation . 37
6.4.8 Harmonic interaction across the converter . 37
6.4.9 Back-to-back systems . 38
6.5 Externally generated harmonics . 38
7 Filter arrangements . 38
7.1 Overview . 38
7.2 Advantages and disadvantages of typical filters . 39
7.3 Classification of filter types . 40
7.4 Tuned filters . 40
7.4.1 Single tuned filters . 40
7.4.2 Double tuned filters . 42
7.4.3 Triple tuned filters . 44
7.5 Damped filters . 45
7.5.1 Single tuned damped filters . 45
7.5.2 Double tuned damped filters . 48
7.6 Choice of filters . 49
8 Filter performance calculation . 50
8.1 Calculation procedure . 50
8.1.1 General . 50
8.1.2 Input data . 50
8.1.3 Methodology . 50
8.1.4 Calculation of converter harmonic currents . 51
8.1.5 Selection of filter types and calculation of their impedances . 52
8.1.6 Calculation of performance . 52
8.2 Detuning and tolerances . 53
8.2.1 General . 53
8.2.2 Detuning factors . 54
8.2.3 Resistance variations . 55
8.2.4 Modelling . 55
8.3 Network impedance for performance calculations . 55
8.3.1 General . 55
8.3.2 Network modelling using impedance envelopes . 56
8.3.3 Sector diagram . 57
8.3.4 Circle diagram . 58
8.3.5 Discrete polygons . 59
8.3.6 Zero-sequence impedance modelling . 61
8.3.7 Detailed modelling of AC network for performance calculation . 61
8.4 Outages of filter banks and sub-banks . 62
8.5 Considerations of probability . 63
8.6 Flexibility regarding compliance . 65
8.7 Ratings of the harmonic filter equipment . 65
9 Filter switching and reactive power management . 66

– 4 – IEC TR 62001-1:2021  IEC 2021
9.1 General . 66
9.2 Reactive power interchange with AC network . 66
9.2.1 General . 66
9.2.2 Impact on reactive compensation and filter equipment . 66
9.2.3 Evaluation of reactive power interchange . 67
9.3 HVDC converter reactive power capability . 68
9.4 Bank/sub-bank definitions and sizing . 68
9.4.1 General . 68
9.4.2 Sizing . 69
9.5 Hysteresis in switching points . 71
9.6 Converter Q-V control near switching points . 72
9.7 Operation at increased converter control angles . 72
9.8 Filter switching sequence and harmonic performance . 72
9.9 Demarcation of responsibilities . 73
9.9.1 General . 73
9.9.2 Customer . 73
9.9.3 Contractor . 74
10 Customer specified parameters and requirements . 74
10.1 General . 74
10.2 AC system parameters . 74
10.2.1 Voltage . 74
10.2.2 Voltage unbalance . 75
10.2.3 Frequency . 75
10.2.4 Short circuit level . 75
10.2.5 Filter switching . 75
10.2.6 Reactive power interchange . 76
10.2.7 System harmonic impedance . 76
10.2.8 Zero sequence data . 76
10.2.9 System earthing. 76
10.2.10 Insulation level . 76
10.2.11 Creepage distances . 76
10.2.12 Pre-existing voltage distortion . 76
10.3 Harmonic distortion requirements . 77
10.3.1 General . 77
10.3.2 Redundancy requirements . 77
10.4 Environmental conditions . 77
10.4.1 Temperature . 77
10.4.2 Pollution . 77
10.4.3 Wind . 77
10.4.4 Ice and snow loading (if applicable) . 78
10.4.5 Solar radiation . 78
10.4.6 Isokeraunic levels . 78
10.4.7 Seismic requirements . 78
10.4.8 Audible noise . 78
10.5 Electrical environment. 78
10.6 Requirements for filter arrangements and components. 79
10.6.1 Filter arrangements . 79
10.6.2 Filter capacitors . 79
10.6.3 Test requirements . 79

10.7 Protection of filters . 79
10.8 Loss evaluation . 79
10.9 Field measurements and verifications . 79
10.10 General requirements . 79
11 Future developments . 80
11.1 General . 80
11.2 Non-standard filter technology . 80
11.2.1 General . 80
11.2.2 Automatically tuned reactors . 80
11.2.3 Single-phase redundancy . 83
11.2.4 Stand-along active filters . 84
11.2.5 Compact design . 86
11.3 Other LCC converter technology . 86
11.3.1 General . 86
11.3.2 Series commutated converters . 86
11.3.3 Transformerless converters . 89
11.3.4 Unit connection . 89
11.4 Changing external environment . 90
11.4.1 Increased pre-existing levels of harmonic distortion . 90
11.4.2 Developments in communication technology . 90
11.4.3 Changes in structure of the power supply industry . 91
11.4.4 Focus on power quality . 91
11.4.5 Fewer large synchronous generators and more renewable and
distributed generation . 91
Annex A (informative) Alternative type of procurement procedure . 92
Annex B (informative) Formulae for calculating the characteristic harmonics of a
bridge converter . 93
Annex C (informative) Definition of telephone interference parameters . 95
C.1 General . 95
C.2 Criteria according to European practice . 95
C.3 Criteria according to North American practice . 96
C.4 Discussion . 98
Annex D (informative) Equivalent frequency deviation . 99
Annex E (informative) Reactive power management . 100
E.1 HVDC converter reactive power capability . 100
E.1.1 Steady-state capability . 100
E.1.2 Temporary capability . 102
E.2 Converter Q-V control near switching points . 103
E.3 Step change in voltage on switching a filter . 104
Bibliography . 106

Figure 1 – Idealized current waveforms on the AC side of converter transformer . 29
Figure 2 – Realistic current waveforms on the AC side of converter transformer
including effect of non-idealities . 30
Figure 3 – Comparison of harmonic content of current waveform under idealized and

realistic conditions . 31
Figure 4 – Typical variation of characteristic harmonic magnitude with direct current . 34
Figure 5 – Single tuned filter and frequency response . 41

– 6 – IEC TR 62001-1:2021  IEC 2021
Figure 6 – Double tuned filter and frequency response . 42
Figure 7 – Triple tuned filter and frequency response . 44
nd
Figure 8 – 2 order damped filter and frequency response . 46
rd
Figure 9 – 3 order damped filter and frequency response . 46
Figure 10 – C-type filter and frequency response . 47
Figure 11 – Double tuned damped filter and frequency response . 48
Figure 12 – Circuit model for filter calculations . 51
Figure 13 – AC system impedance general sector diagram, with minimum impedance . 58
Figure 14 – AC system impedance general sector diagram, with minimum resistance . 58
Figure 15 – AC system impedance general circle diagram, with minimum resistance . 59
Figure 16 – Example of harmonic impedances for harmonics of order 2 to 4 . 60
Figure 17 – Example of harmonic impedances for harmonics of order 5 to 8 . 60
Figure 18 – Example of harmonic impedances for harmonics of order 9 to 13 . 61
Figure 19 – Example of harmonic impedances for harmonics of order 14 to 49 . 61
Figure 20 – Illustration of basic voltage quality concepts with time/location statistics
covering the whole system (adapted from IEC TR 61000-3-6:2008) . 64
Figure 21 – Example of range of operation where specifications on harmonic levels are

not met for a filter scheme solution . 65
Figure 22 – Branch, sub-bank and bank definition . 69
Figure 23 – Typical switching sequence . 73
Figure 24 – Reactive power components. 74
Figure 25 – Design principle of a self-tuned reactor using DC control current in an
orthogonal winding . 82
Figure 26 – Control principle for self-tuned filter . 82
Figure 27 – One method of switching a redundant single phase filter . 84
Figure 28 – Various possible configurations of series compensated HVDC converters . 88
Figure E.1 – Capability diagram of a converter under different control strategies . 100
Figure E.2 – Converter capability with γ = 17°, γ = 40°, α = 5°, α = 35°
min max min max
and U = 1,2U . 101
diomax dioN
Figure E.3 – Reactive power absorption of a rectifier as a function of α with
U = U , d = 9,4 % and d = 0,2 % . 103
dio dioN x r
Figure E.4 – Reactive power absorption of a inverter as a function of γ with
U = U , d = 9,4 % and d = 0,2 % . 103
dio dioN x r
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
HIGH-VOLTAGE DIRECT CURRENT (HVDC) SYSTEMS –
GUIDANCE TO THE SPECIFICATION AND DESIGN
EVALUATION OF AC FILTERS –
Part 1: Overview
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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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.
IEC TR 62001-1 has been prepared by subcommittee 22F: Power electronics for electrical
transmission and distribution systems, of IEC technical committee 22: Power electronic systems
and equipment. It is a Technical Report.
This second edition cancels and replaces the first edition published in 2016. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) general updating of the document to reflect changes in practice;
b) 10.2.4 on fuseless capacitors has been transferred to IEC TR 62001-4;
c) Clause 11 on future developments has been expanded;
d) 10.3.3 and Annex F on voltage sourced converters have been deleted as their content is
covered by IEC TR 62543.
– 8 – IEC TR 62001-1:2021  IEC 2021
The text of this Technical Report is based on the following documents:
DTR Report on voting
22F/614/DTR 22F/623A/RVDTR
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this Technical Report is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/standardsdev/publications.
A list of all parts in the IEC TR 62001 series, published under the general title High-voltage
direct current (HVDC) systems – Guidance to the specification and design evaluation of AC
filters, 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 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 document 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.

INTRODUCTION
The IEC TR 62001 series is structured in five parts:
IEC TR 62001-1 – Overview
This part concerns specifications of AC filters for high-voltage direct current (HVDC) systems
with line-commutated converters, permissible distortion limits, harmonic generation, filter
arrangements, filter performance calculation, filter switching and reactive power management
and customer specified parameters and requirements.
IEC TR 62001-2 – Performance
This part deals with current-based interference criteria, field measurements and verification.
IEC TR 62001-3 – Modelling
This part addresses the harmonic interaction across converters, pre-existing harmonics,
AC network impedance modelling, simulation of AC filter performance.
IEC TR 62001-4 – Equipment
This part concerns steady-state and transient ratings of AC filters and their components, power
losses, audible noise, design issues and special applications, filter protection, seismic
requirements, equipment design and test parameters.
IEC TR 62001-5 – AC side harmonics and appropriate harmonic limits for high-voltage direct
current (HVDC) systems with voltage sourced converters (VSC)
This document concerns specific issues of AC filter design related to VSC HVDC systems.
Parts 1 to 4 are written with focus on line commutated converters.

____________
Under preparation. Stage at the time of publication: IEC/RPUB 62001-5:2021.

– 10 – IEC TR 62001-1:2021  IEC 2021
HIGH-VOLTAGE DIRECT CURRENT (HVDC) SYSTEMS –
GUIDANCE TO THE SPECIFICATION AND DESIGN
EVALUATION OF AC FILTERS –
Part 1: Overview
1 Scope
This part of IEC 62001, which is a Technical Report, deals with the specification and design
evaluation of AC side harmonic performance and AC side filters for HVDC schemes. It is
intended to be primarily for the use of the utilities and consultants who are responsible for
issuing the specifications for new HVDC projects and evaluating designs proposed by
prospective suppliers.
This document provides guidance on the specifications of AC filters for high-voltage direct
current (HVDC) systems with line-commutated converters and filter performance calculation.
The scope of this document covers AC side filtering for the frequency range of interest in terms
of harmonic distortion and audible frequency disturbances. Where the term "HVDC converter"
or "HVDC station" is referred to without qualification, in this document, it is understood to refer
to LCC technology. It excludes filters designed to be effective in the power line carrier (PLC)
and radio interference spectra.
The bulk of this document concentrates on the "conventional" AC filter technology and LCC
(line-commutated converter) HVDC. Voltage sourced converter (VSC) specific issues are
discussed in CIGRE Technical Brochure 754 [1] and in IEC TR 62001-5 [2].
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
specification
document which defines the overall system requirements for an AC filter and the AC system
environment in which it operates
Note 1 to entry: Such a document is normally issued by utilities to the prospective HVDC manufacturers. It also
ensures the uniformity of proposals and sets guidelines for the evaluation of bids.
Note 2 to entry: The term as used here does not refer to the detailed engineering specifications relating to individual
items of equipment, which are prepared by the HVDC manufacturer as a result of the filter design process.
Note 3 to entry: The specification defines the technical basis for a contract between two parties: the customer (3.2)
and the contractor (3.3).
____________
Numbers in square brackets refer to the Bibliography.

3.2
customer
organization which is purchasing the HVDC converter station, including the AC filters
Note 1 to entry: The term "customer" is taken to cover similar terms which may be used in specifications, such as
owner, client, buyer, utility, user, employer and purchaser, and also covers a consultant representing the customer.
3.3
contractor
organization which has the overall responsibility for delivery of the HVDC converter station,
including the AC filters, as a system
Note 1 to entry: The contractor may in turn contract one or more sub-suppliers of individual items of equipment.
Note 2 to entry: The term "contractor" is taken to cover similar terms which may be used in specifications, such as
manufacturer, or supplier.
Note 3 to entry: Where the context clearly refers to the pre-contract stage of a project, the word "bidder" has been
used instead of "contractor", to indicate a prospective contractor, or tenderer.
3.4
branch
arm
set of components (capacitor, inductor, resistor), either in singular or interconnected
arrangement, which may be isolated off load for maintenance
SEE: Figure 22
Note 1 to entry: In interconnected arrangement, it forms a smallest tuned filter unit.
3.5
sub-bank
one or more branches which can be switched (connected or disconnected) on load for reactive
power control
SEE: Figure 22
Note 1 to entry: The switch does not necessarily need to have fault clearing capability.
3.6
bank
one or more sub-banks which can be switched together by a circuit breaker
SEE: Figure 22
4 Outline of specifications of AC filters for HVDC systems
4.1 General
When installing an HVDC converter station in an AC system, the way in which it may affect the
quality of power supply in that system is always an important issue. One of the main power
quality topics is that of harmonic performance.
The AC side current of an HVDC converter has a highly non-sinusoidal waveform, and, if
allowed to flow in the connected AC system, might produce unacceptable levels of distortion.
AC side filters are therefore required as part of the total HVDC converter station, in order to
reduce the harmonic distortion of the AC side current and voltage to acceptably low levels.

– 12 – IEC TR 62001-1:2021  IEC 2021
HVDC converters also consume substantial reactive power, a large proportion of which is
normally supplied locally within the converter station. Shunt connected AC filters appear as
capacitive sources of reactive power at fundamental frequency, and normally in conventional
HVDC schemes the AC filters are used to compensate most or all of the reactive consumption
of the converter. Additional shunt capacitors and reactors may also be used to ensure that the
desired reactive balance is maintained within specified limits under defined operational
conditions.
The design of the AC filters therefore normally has to satisfy these two requirements of
harmonic filtering and reactive power compensation, for various operational states and load
levels. Optimization of this design is the task of the AC filter designer, and the constraints under
which the design is made are defined in the specification.
The AC filters form a substantial part of a conventional HVDC converter station. The
fundamental reactive power rating of the AC filters (including shunt capacitors where applicable)
at each converter station has typically been in the range of 50 % to 60 % of the active power
rating of the scheme. Together with the required switchyard equipment, the AC filters can
occupy over half of the total land requirements of an HVDC scheme. The cost of manufacture,
installation and commissioning of the AC filter equipment is significant, being typically in the
approximate range of 10 % of the total station costs. In addition, the filter design studies can
be extensive and may have an impact on many other aspects of station design (see [1], [4], [5])
and on the total project schedule. Once in operation, the AC filters will continue to have a major
importance due to requirements for switching, maintenance, component spares, and reliability.
It is therefore important that the way in which the requirements for the AC filters are specified
is such as to allow the design to be optimized in terms of all the above factors, while fulfilling
the essential functions of disturbance mitigation and reactive power compensation.
In general, this document assumes that the purchase of an HVDC converter station, including
AC filters, will be made on a turnkey or similar basis, such as has been the case for the majority
of HVDC schemes to date. The discussions herein of aspects such as provision of technical
information, allocation of risks and so on therefore apply principally to such an all-inclusive
approach. If the alternative approach of specifying and purchasing equipment item by item were
adopted, then these aspects of the document would have to be reconsidered in the context of
the particular scheme, although the purely technical content of the document would still be
applicable.
Most specifications for HVDC projects are issued in a final format after definition of the details
of the project by the customer and possibly consultants. An alternative approach which has
been used is discussed in Annex A.
4.2 Boundaries of responsib
...