IEC 60633:1998/AMD2:2015

IEC 60633 ®
Edition 2.0 2015-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
A MENDMENT 2
AM ENDEMENT 2
Terminology for high-voltage direct current (HVDC) transmission

Terminologie pour le transport d'énergie en courant continu à haute tension
(CCHT)
IEC 60633:1998-12/AMD2:2015-07(en-fr)

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IEC 60633 ®
Edition 2.0 2015-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
A MENDMENT 2
AM ENDEMENT 2
Terminology for high-voltage direct current (HVDC) transmission

Terminologie pour le transport d'énergie en courant continu à haute tension

(CCHT)
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.200 ISBN 978-2-8322-2801-2

– 2 – IEC 60633:1998/AMD2:2015

© IEC 2015
FOREWORD
This amendment has been prepared by subcommittee 22F: Power electronics for electrical

transmission and distribution systems, of IEC technical committee 22: Power electronic
systems and equipment.
The text of this amendment is based on the following documents:

CDV Report on voting
22F/340/CDV 22F/350A/RVC
Full information on the voting for the approval of this amendment can be found in the report
on voting indicated in the above table.
The committee has decided that the contents of this amendment and the base 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• withdrawn,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.
___________
CONTENTS
Add the following new terms:
5.13  commutating voltage
5.14  controlled capacitor commutated converter
5.15  series capacitor converter

Replace the existing terms 6.12 and 6.18 as follows:
6.12  valve base electronics (VBE)
6.18  valve reactor
© IEC 2015
Add the following new terms:
6.21  valve module
6.22  redundant levels
6.23  valve anode terminal
6.24  valve cathode terminal
7.35  operating state
7.36  blocked state
7.37  valve voltage
Replace the existing terms 8.4 and 8.8 as follows:
8.4  bi-directional HVDC system
8.8  (asymmetric) monopolar (HVDC) system

Add the following new terms:
8.16  symmetrical monopole
8.17  rigid DC current bipolar system
8.18  symmetrical monopolar (HVDC) system
8.19  earth return
8.20  metallic return
8.21  series converter configuration
8.22  unitary connection
8.23  isolated generating system
8.24  point of common coupling (PCC)
8.25  point of common coupling – DC side (PCC-DC)

Replace the existing terms 9.1, 9.2 and 9.4 as follows:
9.1  AC (harmonic) filter
9.2  (DC) smoothing reactor
9.4  DC harmonic filter
Add the following new terms:
9.14  AC high frequency (HF) filter
9.15  DC high frequency (HF) filter
9.16  neutral bus switch (NBS)
9.17  neutral bus grounding switch (NBGS)

– 4 – IEC 60633:1998/AMD2:2015

© IEC 2015
Replace the existing terms 10.2 and 10.4 as follows:

10.2  DC voltage control mode

10.4  active power control mode

Add the following new terms:
10.8  AC voltage control mode

10.9  islanded network operation mode

10.10  SSTI damping control mode

Replace the existing term 11.8 as follows:
11.8  valve control unit (VCU)

Add the following new term:
11.9  integrated AC/DC system control

2 Normative references
Replace the first paragraph with the following new text.
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments)
applies.
Replace all existing dated references with undated references.
3.1 List of letter symbols
Replace, in line 2, the word "conventional" with the word "nominal" to read:

U   nominal no-load direct voltage
d0
3.3 List of abbreviations
Add the following abbreviation:
SSTI   sub-synchronous torsional interaction (see 10.10)
5 General terms related to converter circuits
5.4
(converter) arm
Replace the existing definition and note with the following new definition:
part of a bridge connecting two points of different potentials within a bridge, for example,
between an AC terminal and a DC terminal

© IEC 2015
Add, at the end of Clause 5 as modified by Amendment 1, the following new terms and

definitions:
5.13
commutating voltage
voltage which causes the current to commutate

[SOURCE: IEC 60500-551:1998, 551-16-02]

5.14
controlled capacitor commutated converter

converter in which controlled series capacitors are included between the converter

transformer and the valves
5.15
series capacitor converter
converter in which fixed series capacitors are inserted between the AC filter bus and the AC
network
6 Converter units and valves
6.1
converter (unit)
Replace the existing definition and note with the following new definition.
indivisible operative unit comprising all equipment between the point of common coupling on
the AC side (see 8.24) and the point of common coupling DC side (see 8.25), essentially one
or more converter bridges, together with one or more converter transformers, converter unit
control equipment, essential protective and switching devices and auxiliaries, if any, used for
conversion (see Figure 3)
6.3
valve
Delete the note.
6.6
thyristor module
Replace the existing definition and notes as follows:
part of a valve comprising a mechanical assembly of thyristors with their immediate auxiliaries
but without valve reactors
Note 1 to entry: Thyristor modules may be elements in the construction of a valve, and/or be interchangeable for
maintenance purposes.
6.9
(valve) thyristor level
Replace, in the existing definition, the words "comprised of" by the word "comprising".
6.10
valve support
Replace the existing definition with the following new definition and note:
that part of the valve which mechanically supports and electrically insulates the active part of
the valve from earth
Note 1 to entry: A part of a valve which is clearly identifiable in a discrete form to be a valve support may not
exist in all designs of valves.

– 6 – IEC 60633:1998/AMD2:2015

© IEC 2015
6.11
valve structure
Replace the existing definition with the following new definition:

structural components of a valve, required in order to physically support the valve modules

6.12
valve interface (electronics) (unit)

Replace the existing term, definition and note as follows:

valve base electronics
VBE
electronic unit, at earth potential, providing the electrical to optical conversion between the
converter control system and the valves
Note 1 to entry: This note applies to the French language only.
6.13
valve electronics
Replace the existing definition with the following new definition:
electronic circuits at valve potential(s) which perform control and protection functions for one
or more valve levels
6.18
valve (anode) (cathode) reactor
Replace the existing term and definition as follows:
valve reactor
reactor(s) connected in series with the thyristors in a valve for the purpose of limiting the rate
of rise of current at turn-on and voltage during the off-state
Note 1 to entry: Valve reactors may be external to the entire valve or distributed within the valve.

Add, after 6.20, the following new terms and their definitions:
6.21
valve module
part of a valve comprising a mechanical assembly of thyristors with their immediate auxiliaries
and valve reactor(s)
6.22
redundant levels
maximum number of series connected thyristor levels in a valve that may be short-circuited
externally or internally during service without affecting the safe operation of the valve as
demonstrated by type tests, and which if and when exceeded, would require shutdown of the
valve to replace the failed levels or acceptance of increased risk of failures
6.23
valve anode terminal
valve terminal at which the forward current flows into the valve
6.24
valve cathode terminal
valve terminal at which the forward current flows out of the valve

© IEC 2015
7 Converter operating conditions

7.11
non-conducting state; blocking state

Replace the existing definition with the following new definition:

condition of a valve when all thyristors are turned off

7.16
converter deblocking
Delete from the definition the last words "by removing blocking action".
7.17
valve blocking
Delete from the definition the last words "by inhibiting the valve control pulses".
7.18
valve deblocking
Delete from the definition the last words "by removing the valve blocking action".
7.29
false firing
Replace the existing term and definiton as follows:
false firing
misfiring
firing of a valve at an unintended instant
Add, at the end of Clause 7 as modified by Amendment 1, the following new terms and their
definitions:
7.35
operating state
condition in which the HVDC substation is energized and the converters are operating at
nonzero active or reactive power output at the point of common coupling (PCC) to the AC
network
7.36
blocked state
condition in which all valves of the converter unit are blocked

7.37
valve voltage
difference in voltage between the valve anode terminal and valve cathode terminal
8 HVDC systems and substations
8.3
unidirectional HVDC system
Add the following note:
Note 1 to entry: Most HVDC systems are inherently bidirectional. However, some systems may be optimized to
transmit power in only one preferred direction. Such systems may still be considered as “bidirectional”.

– 8 – IEC 60633:1998/AMD2:2015

© IEC 2015
8.4
reversible HVDC system
Replace, in the term and in the note, the word "reversible" with the word "bidirectional" as

follows:
bidirectional HVDC system
HVDC system for the transfer of energy in either direction

Note 1 to entry: A multiterminal HVDC system is bidirectional if one or more substations are bidirectional.

8.6
(HVDC) (system) bipole
Replace the existing definition with the following new definition:
part of an HVDC system consisting of two independently operable HVDC system poles which,
during normal operation, exhibit opposite direct voltage polarities with respect to earth
8.7.1
bipolar earth return (HVDC) system
Delete the existing term and its definiton.
8.7.2
bipolar metallic return (HVDC) system
Delete the existing term and its definiton.
8.8
monopolar (HVDC) system
Replace the existing term with the following new term:
(asymmetric) monopolar (HVDC) system

8.8.1
monopolar earth return (HVDC) system
Delete the existing term and its definiton.
8.8.2
monopolar metallic return (HVDC) system
Delete the existing term and its definiton.

Add, after 8.15, the following new terms and their definitions:
8.16
symmetrical monopole
part of an HVDC system consisting of all the equipment in the HVDC substations and the
interconnecting transmission lines, if any, which during normal operation exhibits equal and
opposite direct voltage polarities with respect to earth but without series connection of
converters in each converter station
Note 1 to entry: The term “symmetrical monopole” is used even though there are two polarities with DC voltages,
because with only one converter it is not possible to provide the redundancy which is normally associated with the
term “bipole”.
8.17
rigid DC current bipolar system
bipolar HVDC system without neutral connection between both converter stations

© IEC 2015
Note 1 to entry: Since only two (pole) conductors exist, no unbalance current between both poles is possible. In

case of interruption of power transfer of one converter pole, the current of the other pole has also to be interrupted
(at least for a limited time to allow reconfiguration of the DC circuit).

8.18
symmetrical monopolar (HVDC) system

HVDC system with only one symmetrical monopole

8.19
earth return
operation mode in which the return current path between neutrals of the HVDC substations is

through the earth
8.20
metallic return
operation mode in which the return current path between neutrals of the HVDC substations is
through a dedicated conductor
Note 1 to entry: The metallic return conductor may be either a dedicated neutral conductor or another high
voltage conductor.
8.21
series converter configuration
converter configuration which consists of two or more converters connected in series on DC
side and located in the same substation and connected to the same AC and DC transmission
system
8.22
unitary connection
HVDC system where only one generator is directly connected to an HVDC system through a
specific converter and without any other AC component except for an assigned step-up
transformer
8.23
isolated generating system
HVDC system in which several generators are directly connected to one HVDC converter
through one or more specifically assigned step-up transformers but without any other AC
network connection
8.24
point of common coupling
PCC
point of interconnection of the HVDC converter station to the adjacent AC system

Note 1 to entry: This note applies to the French language only.
8.25
point of common coupling – DC side
PCC-DC
point of interconnection of the HVDC converter station to the DC transmission line
Note 1 to entry: This note applies to the French language only.

– 10 – IEC 60633:1998/AMD2:2015

© IEC 2015
9 HVDC substation equipment
9.1
a.c. filter
Replace the term and its definiton as follows:

AC (harmonic) filter
filter designed to reduce the harmonic voltage at the AC bus and the flow of harmonic current

into the associated AC system and to prevent amplification of background harmonics on the

AC system (see figure 7)
9.2
d.c. (smoothing) reactor
Replace the existing term with the following new term:
(DC) smoothing reactor
9.4
d.c. filter
Replace the existing term with the following new term:
DC harmonic filter
9.13
earth return transfer breaker (ERTB)
Add, below the existing term, the following equivalent term:
earth return transfer switch (ERTS)

Add, after 9.13, the following new terms and their definitions:
9.14
AC high frequency (HF) filter
filter on the AC side of a converter, designed to prevent converter-generated high frequency
(HF) harmonics from penetrating into the AC system
9.15
DC high frequency (HF) filter
filter on the DC side of a converter, designed to prevent converter-generated high frequency
(HF) harmonics from penetrating into the DC system

Note 1 to entry: DC high frequency filters may be located at the high-voltage or low-voltage (neutral) terminals of
the converter.
9.16
neutral bus switch (NBS)
switching device used to transfer DC current from a fault on the neutral bus into the metallic
or earth return path
Note 1 to entry: This note applies to the French language only.
9.17
neutral bus grounding switch (NBGS)
switching device used to transfer DC current from a fault on the neutral bus or neutral
conductor into station ground
Note 1 to entry: This note applies to the French language only.

© IEC 2015
10 Modes of control
10.1
control mode
Replace the existing definition with the following new definition and note:

manner in which a converter unit, pole or HVDC substation is controlled in order to maintain

one or more electrical quantities at desired values

Note 1 to entry: The desired values may change with time or as a function of measured quantities and defined

priorities.
10.2
voltage control mode
Replace the existing term and definition with the following new term and its definition:
d.c. voltage control mode
control of the DC voltage in an HVDC substation
10.4
power control mode
Replace the existing term and definition with the following new term and its definition:
active power control mode
control of the active power exchanged between an HVDC substation and the connected AC
network
10.6
frequency control mode
Replace the existing definition with the following new definition:
control of the frequency of the connected AC network by varying the active power exchanged
between an HVDC substation and the connected AC network
10.7
damping control mode
Replace the existing definition with the following new definition:
supplementary control mode providing the damping of power oscillations in one or more
connected AC networks
Add, after 10.7, the following new terms and definitions:
10.8
AC voltage control mode
control of the AC voltage of the AC network connected to an HVDC substation
10.9
islanded network operation mode
control mode in which the HVDC substation is connected to an islanded AC network
10.10
SSTI damping control mode
...