IEC TR 62001-4:2021

IEC TR 62001-4 ®
Edition 2.0 2021-09
REDLINE VERSION
TECHNICAL
REPORT
colour
inside
High-voltage direct current (HVDC) systems – Guidance to the specification and
design evaluation of AC filters –
Part 4: Equipment
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IEC TR 62001-4 ®
Edition 2.0 2021-09
REDLINE VERSION
TECHNICAL
REPORT
colour
inside
High-voltage direct current (HVDC) systems – Guidance to the specification and
design evaluation of AC filters –
Part 4: Equipment
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.200 ISBN 978-2-8322-4531-6

– 2 – IEC TR 62001-4:2021 RLV © IEC 2021
CONTENTS
FOREWORD . 6
INTRODUCTION . 8
1 Scope . 9
2 Normative references. 9
3 Terms and definitions . 9
4 Steady state rating . 9
4.1 General . 9
4.2 Calculation method . 10
4.2.1 General . 10
4.2.2 AC system pre-existing harmonics . 11
4.2.3 Combination of converter and pre-existing harmonics . 12
4.2.4 Equipment rating calculations . 12
4.2.5 Application of voltage ratings. 16
4.3 AC network conditions . 17
4.4 De-tuning effects . 17
4.5 Network impedance for rating calculations . 17
4.6 Outages . 18
5 Transient stresses and rating . 18
5.1 General . 18
5.2 Switching impulse studies . 19
5.2.1 Energization and switching . 19
5.2.2 Faults external to the filter . 21
5.2.3 Faults internal to the filter . 22
5.2.4 Transformer inrush currents . 23
5.3 Fast fronted waveform studies . 23
5.3.1 General . 23
5.3.2 Lightning strikes . 23
5.3.3 Busbar flashover studies . 23
5.4 Insulation co-ordination . 23
6 Losses . 25
6.1 Background . 25
6.2 AC filter component losses . 25
6.2.1 General . 25
6.2.2 Filter/shunt capacitor losses . 26
6.3 Reactor and resistor losses . 27
6.3.1 General . 27
6.3.2 Filter resistor losses . 28
6.3.3 Shunt reactor losses . 28
6.4 Criteria for loss evaluation . 28
6.4.1 General . 28
6.4.2 Fundamental frequency AC filter busbar voltage . 29
6.4.3 Fundamental frequency and ambient temperature . 29
6.4.4 AC system harmonic impedance . 29
6.4.5 Harmonic currents generated by the converter . 30
6.4.6 Pre-existing harmonic distortion . 30
6.4.7 Anticipated load profile of the converter station . 31

7 Design issues and special applications . 31
7.1 General . 31
7.2 Performance aspects . 31
7.2.1 Low order harmonic filtering and resonance conditions with AC system . 31
7.2.2 Definition of interference factors to include harmonics up to 5 kHz . 32
7.2.3 Triple-tuned filter circuits . 33
7.2.4 Harmonic AC filters on tertiary winding of converter transformers . 34
7.3 Rating aspects . 35
7.3.1 Limiting high harmonic currents in parallel-resonant filter circuits . 35
7.3.2 Transient ratings of parallel circuits in multiple tuned filters . 35
7.3.3 Overload protection of high-pass harmonic filter resistors . 36
7.3.4 Back-to-back switching of filters or shunt capacitors . 36
7.3.5 Short time overload – reasonable specification of requirements . 36
7.3.6 Low voltage filter capacitors without fuses . 37
7.4 Filters for special purposes . 38
7.4.1 Harmonic filters for damping transient overvoltages . 38
7.4.2 Non-linear filters for low order harmonics/transient overvoltages . 38
7.4.3 Series filters for HVDC converter stations . 39
7.4.4 Re-tunable AC filters . 42
7.5 Impact of new HVDC station in vicinity of an existing station . 43
7.6 Redundancy issues and spares . 44
7.6.1 Redundancy of filters – Savings in ratings and losses . 44
7.6.2 Internal filter redundancy . 45
7.6.3 Spare parts . 45
8 Protection . 46
8.1 Overview. 46
8.2 General . 46
8.3 Bank and sub-bank overall protection . 48
8.3.1 General . 48
8.3.2 Short-circuit protection . 48
8.3.3 Overcurrent protection . 48
8.3.4 Thermal overload protection . 48
8.3.5 Differential protection . 49
8.3.6 Earth fault protection . 49
8.3.7 Overvoltage and undervoltage protection . 49
8.3.8 Special protection functions and harmonic measurements . 50
8.3.9 Busbar and breaker failure protection . 50
8.4 Protection of individual filter components . 50
8.4.1 Unbalance protection for filter and shunt capacitors . 50
8.4.2 Protection of low voltage tuning capacitors . 52
8.4.3 Overload protection and detection of filter detuning . 52
8.4.4 Temperature measurement for protection . 52
8.4.5 Measurement of fundamental frequency components . 52
8.4.6 Capacitor fuses . 53
8.4.7 Protection and rating of instrument transformers . 53
8.4.8 Examples of protection arrangements . 54
8.5 Personnel protection . 54
9 Audible noise . 57
9.1 General . 57

– 4 – IEC TR 62001-4:2021 RLV © IEC 2021
9.2 Sound active components of AC filters . 57
9.3 Sound requirements . 59
9.4 Noise reduction . 59
10 Seismic requirements . 60
10.1 General . 60
10.2 Load specification . 61
10.2.1 Seismic loads . 61
10.2.2 Additional loads . 62
10.2.3 Soil quality . 62
10.3 Method of qualification . 62
10.3.1 General . 62
10.3.2 Qualification by analytical methods . 62
10.3.3 Design criteria. 63
10.3.4 Documentation for qualification by analytical methods . 64
10.4 Examples of improvements in the mechanical design . 64
11 Equipment design and test parameters . 64
11.1 General . 64
11.1.1 Technical information and requirements . 64
11.1.2 Technical information to be provided by the customer . 65
11.1.3 Customer requirements . 65
11.1.4 Technical information to be presented by the bidders . 67
11.1.5 Ratings . 67
11.2 Capacitors . 68
11.2.1 General . 68
11.2.2 Design aspects . 68
11.2.3 Electrical data . 71
11.2.4 Tests . 72
11.3 Reactors . 72
11.3.1 General . 72
11.3.2 Design aspects . 73
11.3.3 Electrical data . 73
11.3.4 Tests . 74
11.4 Resistors . 75
11.4.1 General . 75
11.4.2 Design aspects . 75
11.4.3 Electrical data . 76
11.4.4 Tests . 77
11.5 Arresters . 78
11.5.1 General . 78
11.5.2 Design aspects . 79
11.5.3 Electrical data . 79
11.5.4 Arresters: tests . 80
11.6 Instrument transformers . 80
11.6.1 Voltage transformers . 80
11.6.2 Current transformers . 81
11.7 Filter switching equipment . 83
11.7.1 Filter switching equipment: Introduction General . 83
11.7.2 Design aspects . 83
11.7.3 Electrical data . 86

11.7.4 Test requirements . 87
Annex A (informative) Background to loss evaluation .
Annex A (informative) Example of seismic response spectra (from IEEE Std 693-2005) . 91
Bibliography . 92

Figure 1 – Circuit for rating evaluation . 10
th
Figure 2 – Inrush current into a 12/24 double-tuned filter . 20
th
Figure 3 – Voltage across the low voltage capacitor of a 12/24 double-tuned filter at
switch-on . 21
th
Figure 4 – Voltage across the HV capacitor bank of a 12/24 double-tuned filter under
fault conditions . 22
Figure 5 – Typical arrangements of surge arresters . 24
Figure 6 – Non-linear low order filter for Vienna Southeast HVDC station . 39
Figure 7 – Single-tuned series filter and impedance plot . 40
Figure 8 – Triple-tuned series filter and impedance plot . 40
Figure 9 – Mixed series and shunt AC filters at Uruguaiana HVDC station . 41
Figure 10 – Re-tunable AC filter branch . 43
Figure 11 – Example of a protection scheme for an unearthed shunt capacitor . 55
Figure 12 – Example of a protection scheme for a C-type filter . 56
Figure 13 – Electrical spectrum . 58
Figure 14 – Force spectrum . 58
Figure 15 – Comparison of internal, fuseless and external fused capacitor unit designs . 70
Figure A.1 – Seismic response spectra . 91

Table 1 – Typical losses in an all-film capacitor unit . 26
Table 2 – Electrical data for capacitors . 71
Table 3 – Electrical data for reactors . 74
Table 4 – Electrical data for resistors . 76
Table 5 – Electrical data for arresters . 80
Table 6 – Electrical data for current transformers . 82
Table 7 – Electrical data for filter switching equipment . 87
Table A.1 – Capitalized costs of the future losses .

– 6 – IEC TR 62001-4:2021 RLV © IEC 2021
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
HIGH-VOLTAGE DIRECT CURRENT (HVDC) SYSTEMS –
GUIDANCE TO THE SPECIFICATION AND DESIGN
EVALUATION OF AC FILTERS –
Part 4: Equipment
FOREWORD
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This redline version of the official IEC Standard allows the user to identify the changes
made to the previous edition IEC TR 62001-4:2016. A vertical bar appears in the margin
wherever a change has been made. Additions are in green text, deletions are in
strikethrough red text.
IEC TR 62001-4 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
change with respect to the previous edition:
a) general updating of the document to reflect changes in practice;
b) Annex A deleted as its content is covered by IEC 61803.
The text of this Technical Report is based on the following documents:
Draft Report on voting
22F/615/DTR 22F/622B/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 publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
– 8 – IEC TR 62001-4:2021 RLV © IEC 2021
INTRODUCTION
The IEC TR 62001 series is structured in four 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, design issues and special
applications, 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 HVDC systems with
voltage sourced converters (VSC)
This part concerns specific issues of AC filter design related to high-voltage direct current
(VSC) systems with voltage sourced converters (HVDC).

HIGH-VOLTAGE DIRECT CURRENT (HVDC) SYSTEMS –
GUIDANCE TO THE SPECIFICATION AND DESIGN
EVALUATION OF AC FILTERS –
Part 4: Equipment
1 Scope
This part of IEC TR 62001, which is a Technical Report, provides guidance on the basic data
of AC side filters for high-voltage direct current (HVDC) systems and their components such
as ratings, power losses, design issues and special applications, protection, seismic
requirements, equipment design and test parameters.
This document covers AC side filtering for the frequency range of interest in terms of
harmonic distortion and audible frequency disturbances. It excludes filters designed to be
effective in the power line carrier (PLC) and radio interference spectra.
It concerns the conventional AC filter technology and LCC (line-commutated converter) HVDC
converters but much of this applies to any filter equipment for VSC (voltage sourced
converter) HVDC.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• ISO Online browsing platform: available at https://www.iso.org/obp
• IEC Electropedia: available at http://www.electropedia.org/
4 Steady state rating
4.1 General
The calculation of the steady state ratings of the harmonic filter equipment is the
responsibility of the contractor. Clause 4 gives guidance on the calculation of equipment
rating parameters and the different factors to be considered in the studies. It is the
responsibility of the customer to provide the appropriate system and environmental data and
also to clarify the operational conditions, such as filter outages and network contingencies,
which need to be taken into account.

– 10 – IEC TR 62001-4:2021 RLV © IEC 2021
4.2 Calculation method
4.2.1 General
Steady state rating of filter equipment for an LCC HVDC system is based on a solution of the
following circuit which represents the HVDC converter, the filter banks and the AC supply
system. See Figure 1.
NOTE The symbols used in this figure are explained in the key to Formula (1).
Figure 1 – Circuit for rating evaluation
The harmonic current flowing in the filter is the summation of two components, the
contribution from the HVDC converter and the contribution from the AC supply network.
Using the principle of superposition, Formula (1) and Formula (2) can be used to evaluate the
contribution to the harmonic filter current of order n from these two sources.
a) HVDC converter:
Z
i sn
II⋅  (1)
fcnn
ZZ+
sfnn
where
i
I is the filter harmonic current from the converter;
fn
I is the converter harmonic current;
cn
I is the system harmonic current;
sn
is the filter harmonic impedance;
Z
fn
Z is the network harmonic impedance.
sn
b) AC supply network:
U
ii n
o
I =   (2)
fn
ZZ+
sfnn
where
ii
I is the filter harmonic current from the system;
fn
U is the existing system harmonic voltage.
on
The definition of network impedance is described in 4.5.
=
To solve Formula (1) and Formula (2), the following independent variables need to be known.
• The harmonic current (I ) produced by the rectifier or inverter of the HVDC station. It is
cn
calculated for all harmonics (see IEC TR 62001-1 [1] or CIGRE Technical Brochure 754
[2] for VSC using a harmonic voltage source). This evaluation should consider the worst-
case operating conditions which can occur in steady state conditions, i.e. for periods in
excess of 1 min. The extreme tolerance range of key parameters, for example converter
transformer impedances or operating range of the tap changer, needs to be taken into
account. Harmonic interaction phenomena as discussed in IEC TR 62001-3 [3] should also
be taken into account.
• The pre-existing system harmonic voltage, as discussed in 4.2.2.
• The harmonic impedance of AC network (Z ), as discussed in IEC TR 62001-1 [1]. Note
sn
i ii
that different values of Z can be defined for the calculation of I and I , depending on
sn fn fn
how the pre-existing harmonic distortion is specified (see 4.2.3).
The harmonic impedance of the filter (Z ) needs to take account of the de-tuning and
fn
tolerance factors discussed in 4.4.
In the case of an HVDC link connecting two AC systems of different fundamental frequencies,
and particularly if the link is a back-to-back station, both converters may generate currents on
their AC sides at frequencies other than harmonics of the fundamental. The fundamental
frequencies may either be nominally different, for example 50 Hz and 60 Hz, or may be
nominally identical but differ at times by up to 1 Hz or 2 Hz. This additional generated
distortion (interharmonics) will be at frequencies which are harmonics of the fundamental
frequency of the remote AC system, and will be transferred across the link. Interharmonics
may give rise to specific problems not found with true harmonics, such as
a) interference with ripple control systems, and
b) light flicker due to the low frequency amplitude modulation caused by the beating of a
harmonic frequency with an adjacent interharmonic.
th
EXAMPLE A 10 Hz flicker due to the interaction of a 650 Hz 13 harmonic of a 50 Hz system with 660 Hz
th
11 harmonic penetration from a 60 Hz system.
The effect of interharmonics (see IEC TR 62001-1 [1]), although small, should also be taken
into account in the calculation of filter component rating.
4.2.2 AC system pre-existing harmonics
It is important that the effects of pre-existing harmonic distortion on the AC system are
included in the filter rating calculations. Conventionally, In many early HVDC projects this was
accommodated not by direct calculation as shown in 4.2.1 but by creating an arbitrary margin
of a 10 % to 20 % increase in converter harmonic currents (I ). However, such an approach
cn
rd th th
may not adequately reflect the low order harmonic distortion (typically 3 , 5 and 7 ) which
exists on many power systems. As modern converter stations produce only small amounts of
such low order harmonics, a simple enhancement of the magnitude may not adequately reflect
their potential contribution to filter ratings.
To model a multiplicity of harmonic current sources in a detailed network model is impractical
for the purposes of filter design. Therefore, it is proposed that Often a Thévenin equivalent
voltage source is modelled behind the AC system impedance, as shown in Figure 1, to create
an open circuit voltage distortion at the filter busbar, i.e. the level of distortion prior to
connection of the filters. The magnitude of the individual harmonic voltages can be based on
measurements or on the performance limits, but limited by a value of total harmonic distortion.
This approach provides a more realistic assessment of the contribution to equipment rating
caused by ambient distortion levels.
___________
1 Numbers in square brackets refer to the Bibliography.

– 12 – IEC TR 62001-4:2021 RLV © IEC 2021
IEC TR 61001-3 [3] contains a detailed discussion on alternative ways of handling pre-
existing harmonics.
4.2.3 Combination of converter and pre-existing harmonics
i ii
As there is no fixed vectorial relationship between I and I , it is proposed one option is that
fn fn
that these individual contributions to filter rating are summated on root sum square (RSS)
basis at each harmonic:
i 2 ii 2
I II+     (3)
fn ffnn
Alternatively, the general summation law from IEC 61000-3-6 [4] may be used.
For pre-existing harmonics of relatively low magnitude, RSS summation is reasonable, as
some harmonics may be in phase and others not, and as these relationships will vary with
time and operating conditions.
Alternatively, linear addition would provide greater security against the possibility of the
contributions at a significant frequency being approximately in phase, but would entail an
increase in cost, particularly if used for the voltage rating of the high voltage capacitors.
Linear addition should be considered for any pre-existing individual harmonic of such
magnitude that linear addition would significantly affect the current rating of the components.
Otherwise, if in practice the two sources were in phase for a period of time, the filter could trip
on overcurrent protection. If linear addition is to be used, care should be taken to ensure that
the conditions under which the two currents are calculated are consistent, i.e. the calculated
currents can occur simultaneously in practice.
4.2.4 Equipment rating calculations
4.2.4.1 General
nd th
The total filter current is derived as in 4.2.3 for each harmonic order from 2 to 50 inclusive
of significant magnitude. Traditionally for LCC HVDC systems, the maximum harmonic order
was generally taken as 49 or 50. However with the increasing prevalence of high power
electronic equipment, higher values of the maximum harmonic order may be considered. For
LCC it is important that this range is covered to ensure that any resonance conditions
between the filters and the AC network and between different filters are inherently considered.
th
Harmonics above the 50 order are unlikely to have a significant impact on the total rating
values and can be ignored.
The calculation of I for each connected filter allows the spectrum of harmonic currents in
fn
each branch of the filter to be evaluated. From this current data, individual element ratings
can be calculated.
4.2.4.2 Capacitors
From the spectrum of currents in the capacitor bank (I ), the total RSS current can be
fcn
calculated as
n=49
II= ( )
∑
c fcn
n−1
=
n=N
II=    (4)
( )
∑
c fcn
n −1
( )
This current is used for capacitor fuse design, and both maximum and minimum values are
required.
Typically, the capacitor unit bushings are the limiting factor for capacitor unit current. The
magnitudes of the spectrum of most significant harmonic currents should be specified.
As the voltage rating of the high-voltage capacitors is the most significant factor in
determining the total cost of the AC filters, the question of which formula is used to derive this
rating should be carefully considered. There have been many discussions among utilities,
consultants and manufacturers in the past regarding this point. The most conservative
assumption in deriving a total rated voltage would be to assume that AC system resonance
occurs at all harmonics and that all harmonics are in phase. However, the use of this
assumption for an HVDC filter capacitor would result in an expensive design with a large
margin between rated voltage and what would be experienced in reality. In practice,
amplification due to filter-AC system resonance may take place at some harmonic
frequencies, but not at most. Similarly, some harmonics may be in phase under some
operating conditions, but in general the harmonics have an unpredictable phase relationship.
Other approaches have therefore been formulated by HVDC users and manufacturers in an
attempt to ensure an adequate design at a reasonable cost.
The issue is therefore one of perceived risk against cost, and due to the diversity of existing
opinions it is not possible to give a clear recommendation here. Various approaches are
discussed below. All have been used successfully in practice on different HVDC schemes.
In the most conservative approach, the maximum voltage (U ) can be calculated as an
m
arithmetic sum of the individual harmonics and the fundamental, that is
n=49
U IX⋅
m ∑ fcn fcn
n=1
n=N
U IX⋅      (5)
∑
m fcnnfc
n=1
where
X is the harmonic impedance of order n of the capacitor bank.
fcn
However, such an evaluation, especially when based on simultaneous resonance between the
filters and the AC system at all harmonics, is overly pessimistic, as it assumes that all
harmonics are in phase, and will result in an expensive capacitor design.
A more realistic method is to use Formula (5) but to assume that only a limited number of
harmonics are considered to be in resonance (e.g. the two largest contributions) and all other
harmonics are evaluated against an open-circuit system or fixed impedance. However, this
method still assumes that all harmonics are in phase, which will not be the case in practice.
In a further approach, all harmonics are assumed to be in resonance, but Formula (5) is
modified such that only the fundamental and largest harmonic components are summed
arithmetically. All other harmonic components of voltage are summed on an RSS basis and
added arithmetically to the sum of fundamental and largest harmonic components to evaluate
U . This "quasi-quadratic" summation thus takes account of the natural phase angle diversity
m
between individual harmonic components:
=
=
– 14 – IEC TR 62001-4:2021 RLV © IEC 2021
n=49
U=UU++ U
∑
m 1 no n
n=2
n=N
U =UU+ + U   (6)
m1 no ∑ n
n=2
where
U is the fundamental component;
U is the largest component of all harmonic voltages;
no
U is the individual harmonic components of order n excluding the largest component.
n
The above may be taken a step further by addin
...