IEC 60633:1998

IEC 60633 ®
Edition 2.1 2009-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Terminology for high-voltage direct current (HVDC) transmission

Terminologie pour le transport d'énergie en courant continu à haute tension
(CCHT)
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IEC 60633 ®
Edition 2.1 2009-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
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
PRICE CODE
INTERNATIONALE
CL
CODE PRIX
ICS 29.200 ISBN 978-2-88910-240-2
– 2 – 60633 © IEC:1998+A1:2009

CONTENTS
FOREWORD.6

1 Scope.8

2 Normative references.8

3 Symbols and abbreviations .8

3.1 List of letter symbols.8

3.2 List of subscripts .9

3.3 List of abbreviations.9
4 Graphical symbols .9
5 General terms related to converter circuits .10
5.1 conversion.10
5.2 converter connection.10
5.3 bridge (converter connection) .10
5.4 (converter) arm.10
5.5 by-pass path.10
5.6 commutation.11
5.7 commutating group.11
5.8 commutation inductance.11
5.9 pulse number p.11
5.10 commutation number q .11
5.11 capacitor commutated converter .11
5.12 controlled series capacitor converter.11
6 Converter units and valves.12
6.1 converter (unit) .12
6.2 (converter) bridge.12
6.3 valve.12
6.4 main valve .12
6.5 by-pass valve .12
6.6 thyristor module.12
6.7 reactor module.13
6.8 valve section .13
6.9 (valve) thyristor level.13
6.10 valve support.13

6.11 valve structure.13
6.12 valve interface (electronics) (unit) .13
6.13 valve electronics.13
6.14 valve arrester .13
6.15 converter unit arrester .13
6.16 converter unit d.c. bus arrester .13
6.17 midpoint d.c. bus arrester .14
6.18 valve (anode) (cathode) reactor .14
6.19 converter transformer.14
6.20 by-pass switch.14
7 Converter operating conditions.14
7.1 rectifier operation; rectification.14
7.2 inverter operation; inversion.14

60633 © IEC:1998+A1:2009 – 3 –

7.3 forward direction; conducting direction (of a valve) .14

7.4 reverse direction; non-conducting direction (of a valve) .14

7.5 forward current.15

7.6 reverse current.15

7.7 forward voltage.15

7.8 reverse voltage.15

7.9 conducting state; on-state.15

7.10 valve voltage drop .15

7.11 non-conducting state; blocking state .15

7.12 firing.15

7.13 (valve) control pulse .15
7.14 (valve) firing pulse .15
7.15 converter blocking.16
7.16 converter deblocking.16
7.17 valve blocking.16
7.18 valve deblocking .16
7.19 phase control.16
7.20 (trigger) delay angle α (firing) delay angle α .16
7.21 (trigger) advance angle β (firing) advance angle β.16
7.22 overlap angle μ.16
7.23 extinction angle γ .16
7.24 hold-off interval.16
7.25 conduction interval.17
7.26 blocking interval; idle interval .17
7.27 forward blocking interval .17
7.28 reverse blocking interval .17
7.29 false firing .17
7.30 firing failure .17
7.31 commutation failure.17
7.32 short-circuit ratio (SCR) .17
7.33 effective short-circuit ratio (ESCR).17
7.34 triggering; gating.17
8 HVDC systems and substations .18
8.1 HVDC system.18
8.2 HVDC transmission system.18

8.3 unidirectional HVDC system.18
8.4 reversible HVDC system .18
8.5 (HVDC) (system) pole.18
8.6 (HVDC) (system) bipole .18
8.7 bipolar (HVDC) system .18
8.8 monopolar (HVDC) system .19
8.9 HVDC substation HVDC converter station .19
8.10 (HVDC) substation bipole.19
8.11 (HVDC) substation pole .19
8.12 HVDC transmission line .19
8.13 HVDC transmission line pole.19
8.14 earth electrode .19
8.15 earth electrode line .20

– 4 – 60633 © IEC:1998+A1:2009

9 HVDC substation equipment .20

9.1 a.c. filter.20

9.2 d.c. (smoothing) reactor.20

9.3 d.c. reactor arrester .20

9.4 d.c. filter.20

9.5 d.c. damping circuit .20

9.6 d.c. surge capacitor .20

9.7 d.c. bus arrester .20

9.8 d.c. line arrester .20

9.9 HVDC substation earth .20
9.10 (d.c.) neutral bus capacitor .21
9.11 (d.c.) neutral bus arrester .21
9.12 metallic return transfer breaker (MRTB) .21
9.13 earth return transfer breaker (ERTB).21
10 Modes of control .21
10.1 control mode .21
10.2 voltage control mode .21
10.3 current control mode.21
10.4 power control mode .21
10.5 reactive power control mode .21
10.6 frequency control mode .21
10.7 damping control mode .21
11 Control systems.22
11.1 (HVDC) control system .22
11.2 HVDC system control.22
11.3 (HVDC) master control.22
11.4 (HVDC system) bipole control .22
11.5 (HVDC system) pole control.22
11.6 (HVDC) substation control .22
11.7 converter unit control .22
11.8 valve control .23
12 Control functions.23
12.1 equal delay angle control; individual phase control .23
12.2 equidistant firing control.23
12.3 α control .23

12.4 minimum α control .24
12.5 γ control.24
12.6 minimum γ control.24
12.7 control order .24
12.8 current margin.24
12.9 voltage dependent current order limit (VDCOL) .24
12.10 pole (current) balancing .24

BIBLIOGRAPHY.35

Figure 1 – Graphical symbols .25
Figure 2 – Bridge converter connection .25
Figure 3 – Example of a converter unit .26

60633 © IEC:1998+A1:2009 – 5 –

Figure 4 – Commutation process at rectifier and inverter modes of operation.27

Figure 5 – Illustrations of commutation in inverter operation.28

Figure 6 – Typical valve voltage waveforms .29

Figure 7 – Example of an HVDC substation .30

Figure 8 – Example of bipolar two-terminal HVDC transmission system .31

Figure 9 – Example of a multiterminal bipolar HVDC transmission system
with parallel connected HVDC substations.31

Figure 10 – Example of a multiterminal HVDC transmission system

with series connected HVDC substations.32

Figure 11 – A simplified steady-state voltage-current characteristic
of a two-terminal HVDC system .32
Figure 12 – Hierarchical structure of an HVDC control system .33
Figure 13 – Capacitor commutated converter configurations .34

– 6 – 60633 © IEC:1998+A1:2009

INTERNATIONAL ELECTROTECHNICAL COMMISSION

___________
TERMINOLOGY FOR HIGH-VOLTAGE DIRECT CURRENT (HVDC)

TRANSMISSION
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,
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Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
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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 provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
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
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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 60633 has been prepared by subcommittee 22F: Power electronics

for electrical transmission and distribution systems, of IEC technical committee 22: Power
electronics.
This consolidated version of IEC 60633 consists of the second edition (1998) [documents
22F/49/FDIS and 22F/53/RVD] and its amendment 1 (2009) [documents 22F/153/CDV and
22F/163/RVC].
The technical content is therefore identical to the base edition and its amendment and has
been prepared for user convenience.
It bears the edition number 2.1.
A vertical line in the margin shows where the base publication has been modified by
amendment 1.
60633 © IEC:1998+A1:2009 – 7 –

The committee has decided that the contents of the base publication and its amendments will

remain unchanged until the maintenance result 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.
– 8 – 60633 © IEC:1998+A1:2009

TERMINOLOGY FOR HIGH-VOLTAGE DIRECT CURRENT (HVDC)

TRANSMISSION
1 Scope
This International Standard defines terms for high-voltage direct current (HVDC) power

transmission systems and for HVDC substations using electronic power converters for the

conversion from a.c. to d.c. or vice versa.
This standard is applicable to HVDC substations with line commutated converters, most
commonly based on three-phase bridge (double way) connections (see figure 2) in which
unidirectional electronic valves, e.g. semiconductor valves, are used.
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 60027 (all parts), Letter symbols to be used in electrical technology
IEC 60050-551:1998, International Electrotechnical Vocabulary – Part 551: Power electronics
IEC 60146-1-1:1991, General requirements and line commutated convertors – Part 1-1:
Specifications of basic requirements
IEC 60617-5:1996, Graphical symbols for diagrams – Part 5: Semiconductors and electron
tubes
IEC 60617-6:1996, Graphical symbols for diagrams – Part 6: Production and conversion of
electrical energy
3 Symbols and abbreviations
The list covers only the most frequently used symbols. For a more complete list of the symbols
which have been adopted for static converters see IEC 60027 and other standards listed in the
normative references and the bibliography.
3.1 List of letter symbols
U direct voltage (any defined value)
d
U
conventional no-load direct voltage
d0
ideal no-load direct voltage
U
di0
U rated direct voltage
dN
U line-to-line voltage on line side of converter transformer, r.m.s. value including
L
harmonics
U U
rated value of
LN L
U no-load phase-to-phase voltage on the valve side of transformer, r.m.s. value
ν0
excluding harmonics
60633 © IEC:1998+A1:2009 – 9 –

I direct current (any defined value)
d
I
rated direct current
dN
I current on line side of converter transformer, r.m.s. value including harmonics
L
I
I rated value of
LN L
I
current on valve side of transformer, r.m.s. value including harmonics

ν
α (trigger) delay angle
β (trigger) advance angle
γ extinction angle
μ overlap angle
p pulse number
q commutation number
3.2 List of subscripts
0 (zero) at no load
N rated value or at rated load
d direct current or voltage
i ideal
L line side of converter transformer
v valve side of converter transformer
max maximum
min minimum
n pertaining to harmonic component of order n
3.3 List of abbreviations
The following abbreviations are always in capital letters and without dots.
HVDC high-voltage direct current
MVU multiple valve (unit) (see 6.3.2)
SCR short-circuit ratio (see 7.32)
ESCR effective short-circuit ratio (see 7.33)
MTDC multiterminal HVDC transmission system (see 8.2.2)

MRTB metallic return transfer breaker (see 9.12)
ERTB earth return transfer breaker (see 9.13)
VDCOL voltage dependent current order limit (see 12.9)
4 Graphical symbols
Figure 1 shows the specific graphical symbols which are defined only for the purposes of this
standard. For a more complete list of the graphical symbols which have been adopted for static
converters, see IEC 60617-5 and IEC 60617-6.

– 10 – 60633 © IEC:1998+A1:2009

5 General terms related to converter circuits

For the purposes of this standard, the following terms and definitions apply.

NOTE For a more complete list of the terms which have been adopted for static converters, see IEC 60050(551)

and IEC 60146-1-1.
5.1
conversion
in the context of HVDC, the transfer of energy from a.c. to d.c. or vice versa, or a combination
of these operations
5.2
converter connection
electrical arrangement of arms and other components necessary for the functioning of the main
power circuit of a converter
5.3
bridge (converter connection)
double-way connection as illustrated on Figure 2, comprising six converter arms such that the
centre terminals are the phase terminals of the a.c. circuit, and that the outer terminals of like
polarity are connected together and are the d.c. terminals
NOTE The term “bridge” may be used to describe either the circuit connection or the equipment implementing that
circuit (see 6.2).
5.3.1
uniform bridge
bridge where all converter arms are either controllable or non-controllable
5.3.2
non-uniform bridge
bridge with both controllable and non-controllable converter arms
5.4
(converter) arm
part of an operative circuit used for conversion which is connected between an a.c. terminal
and a d.c. terminal, with the ability to conduct current in only one direction, defined as the
forward direction (see 7.3)
NOTE The main function of a converter arm is conversion; it may also perform additional functions such as
voltage limiting, damping, etc.
5.4.1
controllable converter arm
converter arm in which the start of forward conduction may be determined by an externally
applied signal
5.4.2
non-controllable converter arm
converter arm in which the start of forward conduction is determined solely by the voltage
applied to its terminals
5.5
by-pass path
low resistance path between the d.c. terminals of one or several bridges excluding the a.c.
circuit
NOTE The by-pass path may either constitute a unidirectional path, e.g. a by-pass arm (see 5.5.1), or a by-pass
pair (see 5.5.2), or it may constitute a bidirectional path, e.g. a by-pass switch (see 6.20).

60633 © IEC:1998+A1:2009 – 11 –

5.5.1
by-pass arm
unidirectionally conducting by-pass path connected only between d.c. terminals, commonly

used with mercury arc valve technology (not shown in figure 2)

5.5.2
by-pass pair
two converter arms of a bridge connected to a common a.c. terminal and forming a by-pass

path (see figure 2)
5.6
commutation
transfer of current between any two paths with both paths carrying current simultaneously
during this process
NOTE Commutation may occur between any two converter arms, including the connected a.c. phases, between a
converter arm and a by-pass arm, or between any two paths in the circuit.
5.6.1
line commutation
method of commutation whereby the commutating voltage is supplied by the a.c. system
5.7
commutating group
group of converter arms which commutate cyclically and independently from other converter
arms, i.e. the commutations are normally not simultaneous (see figure 2)
NOTE In the case of a bridge, a commutating group is composed of the converter arms connected to a common
d.c. terminal. In certain cases, e.g. when large currents and/or large commutation inductances are involved, the
commutation in the two commutating groups belonging to the same bridge need not be independent.
5.8
commutation inductance
total inductance included in the commutation circuit, in series with the commutating voltage
5.9
pulse number p
characteristic of a converter connection expressed as the number of non-simultaneous
symmetrical commutations occurring during one cycle of the a.c. line voltage
NOTE The pulse number of a bridge converter connection defined in 5.3 is always p = 6.
5.10
commutation number q
number of commutations during one cycle of the a.c. line voltage occurring in each commutat-
ing group
NOTE In a bridge converter connection, each commutating group has a commutation number q = 3.
5.11
capacitor commutated converter
converter in which series capacitors are included between the converter transformer and the
valves (see Figure 13a)
5.12
controlled series capacitor converter
converter in which series capacitors are inserted between the a.c. filter bus and the a.c.
network (see Figure 13b)
– 12 – 60633 © IEC:1998+A1:2009

6 Converter units and valves
6.1
converter (unit)
operative unit comprising 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)

NOTE If a converter unit comprises two converter bridges with a phase displacement of 30°, then the converter
unit forms a 12-pulse unit (see figure 7). The term “12-pulse group” is also used.

6.2
(converter) bridge
equipment used to implement the bridge converter connection and the by-pass arm, if used
NOTE The term “bridge” may be used to describe either the circuit connection or the equipment implementing that
circuit (see 5.3).
6.2.1
anode (cathode) valve commutating group
equipment used to implement the converter arms of one commutating group of a bridge with
interconnected anode (cathode) terminals
6.3
valve
complete operative controllable or non-controllable valve device assembly, normally conducting
in only one direction (the forward direction), which can function as a converter arm in a
converter bridge
NOTE An example of a non-controllable valve device assembly is a semiconductor diode valve. An example of a
controllable valve device assembly is a thyristor valve.
6.3.1
single valve (unit)
single structure comprising only one valve
6.3.2
multiple valve (unit) (MVU)
single structure comprising more than one valve
NOTE Examples of multiple valve units are double valves, quadrivalves and octovalves with two, four and eight
series-connected valves respectively.
6.4
main valve
valve in a converter arm
6.5
by-pass valve
valve in a by-pass arm
6.6
thyristor module
part of a valve comprised of a mechanical assembly of thyristors with their immediate
auxiliaries, and reactors, if used
NOTE 1 Thyristor modules may be elements in the construction of a valve, and/or be interchangeable for
maintenance purposes.
NOTE 2 The deprecated term “valve module” has been used with an equivalent meaning.

60633 © IEC:1998+A1:2009 – 13 –

6.7
reactor module
part of a valve, being a mechanical assembly of one or more reactors, used in some valve

designs
NOTE Reactor modules may be elements in the construction of a valve.

6.8
valve section
electrical assembly, comprising a number of thyristors and other components, which exhibits

prorated electrical properties of a complete valve

NOTE This term is mainly used to define a test object for valve testing purposes.

6.9
(valve) thyristor level
part of a valve comprised of a thyristor, or thyristors connected in parallel, together with their
immediate auxiliaries, and reactor, if any
6.10
valve support
that part of the valve which mechanically supports and electrically insulates from earth the
active part of the valve which houses the valve sections
6.11
valve structure
physical structure holding the thyristor levels of a valve which is insulated to the appropriate
voltage above earth potential
6.12
valve interface (electronics) (unit)
electronic unit which provides an interface between the control equipment, at earth potential,
and the valve electronics or valve devices
NOTE 1 Valve interface electronics units, if used, are typically located at earth potential close to the valve(s).
NOTE 2 The term “valve base electronics” (VBE) has also been used for this unit.
6.13
valve electronics
electronic circuits at valve potential(s) which perform control functions
6.14
valve arrester
arrester connected across a valve (see figure 3)

6.15
converter unit arrester
arrester connected across the d.c. terminals of a converter unit (see figure 3)
6.16
converter unit d.c. bus arrester
arrester connected from the high-voltage d.c. bus of the converter unit to substation earth (see
figures 3 and 7)
– 14 – 60633 © IEC:1998+A1:2009

6.17
midpoint d.c. bus arrester
arrester connected between the midpoint of the two 6-pulse bridges of a 12-pulse converter

unit and substation earth (see figure 7)

NOTE In some HVDC substation designs, two twelve-pulse converter units are connected in series. In this case,

the midpoint d.c. bus arrester at the upper twelve-pulse converter unit is not connected to substation earth but to
the high-voltage d.c. bus of the lower twelve-pulse converter unit.

6.18
valve (anode) (cathode) reactor
reactor connected in series with the valve, commonly used with mercury arc technology

6.19
converter transformer
transformer through which energy is transmitted from an a.c. system to one or more converter
bridges or vice versa (see figure 3)
6.19.1
line side windings
converter transformer windings which are connected to the a.c. system
6.19.2
valve side windings
converter transformer windings which are connected to the a.c. terminals of one or more
converter bridges
6.20
by-pass switch
mechanical power switching device connected across the d.c. terminals of one or more
converter bridges to shunt the bridge(s) during the turn-off procedure of the bridge(s) and to
commutate current to the by-pass arm or a by-pass pair during the turn-on procedure of the
bridge(s) (see figure 3)
NOTE A by-pass switch may also be used for prolonged shunting of the bridge(s).
7 Converter operating conditions
7.1
rectifier operation; rectification
mode of operation of a converter or an HVDC substation when energy is transferred from the
a.c. side to the d.c. side
7.2
inverter operation; inversion
mode of operation of a converter or an HVDC substation when energy is transferred from the
d.c. side to the a.c. side
7.3
forward direction; conducting direction (of a valve)
the direction in which a valve is capable of conducting load current
7.4
reverse direction; non-conducting direction (of a valve)
the reverse of the conducting direction

60633 © IEC:1998+A1:2009 – 15 –

7.5
forward current
current which flows through a valve in the forward direction

7.6
reverse current
current which flows through a valve in the reverse direction

7.7
forward voltage
voltage applied between the anode and cathode terminals of a valve or an arm when the anode

is positive with respect to the cathode
7.8
reverse voltage
voltage applied between the anode and cathode terminals of a valve or an arm when the anode
is negative with respect to the cathode
7.9
conducting state; on-state
condition of a valve when the valve exhibits a low resistance (the valve voltage for this
condition is shown in figure 6)
7.10
valve voltage drop
voltage which, during the conducting state, appears across the valve terminals
7.11
non-conducting state; blocking state
condition of a valve when the valve exhibits a high resistance (see figure 6)
7.11.1
forward blocking state; off-state
non-conducting state of a controllable valve when forward voltage is applied between its main
terminals (see figure 6)
7.11.2
reverse blocking state
non-conducting state of a valve when reverse voltage is applied between its main terminals
(see figure 6)
7.12
firing
establishment of current in the forward direction in a valve

7.13
(valve) control pulse
pulse which, during its entire duration, allows the firing of the valve
7.14
(valve) firing pulse
pulse which initiates the firing of the valve, normally derived from the valve control pulse

– 16 – 60633 © IEC:1998+A1:2009

7.15
converter blocking
operation preventing fur
...

IEC 60633 ®
Edition 2.2 2015-07
CONSOLIDATED VERSION
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
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Terminology for high-voltage direct current (HVDC) transmission

Terminologie pour le transport d'énergie en courant continu à haute tension
(CCHT)
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IEC 60633 ®
Edition 2.2 2015-07
CONSOLIDATED VERSION
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
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 978-2-8322-2833-3

IEC 60633 ®
Edition 2.2 2015-07
CONSOLIDATED VERSION
REDLINE VERSION
VERSION REDLINE
colour
inside
Terminology for high-voltage direct current (HVDC) transmission

Terminologie pour le transport d'énergie en courant continu à haute tension
(CCHT)
– 2 – IEC 60633:1998+AMD1:2009
+AMD2:2015 CSV © IEC 2015
CONTENTS
FO REW O RD . 6
1 Scope . 8
2 Normative references. 8
3 Symbols and abbreviations . 8
3.1 List of letter symbols . 8
3.2 List of subscripts . 9
3.3 List of abbreviations . 9
4 Graphical symbols . 9
5 General terms related to converter circuits . 9
5.1 conversion . 10
5.2 converter connection . 10
5.3 bridge (converter connection) . 10
5.4 (converter) arm . 10
5.5 by-pass path . 10
5.6 commutation . 11
5.7 commutating group . 11
5.8 commutation inductance . 11
5.9 pulse number p . 11
5.10 commutation number q . 11
5.11 capacitor commutated converter . 11
5.12 controlled series capacitor converter . 11
5.13 commutating voltage . 12
5.14 controlled capacitor commutated converter . 12
5.15 series capacitor converter . 12
6 Converter units and valves . 12
6.1 converter (unit) . 12
6.2 (converter) bridge . 12
6.3 valve . 12
6.4 main valve . 13
6.5 by-pass valve . 13
6.6 thyristor module . 13
6.7 reactor module . 13
6.8 valve section . 13
6.9 (valve) thyristor level . 13
6.10 valve support . 13
6.11 valve structure . 13
6.12 valve interface (electronics) (unit) valve base electronics (VBE) . 13
6.13 valve electronics . 14
6.14 valve arrester . 14
6.15 converter unit arrester . 14
6.16 converter unit d.c. bus arrester . 14
6.17 midpoint d.c. bus arrester . 14
6.18 valve (anode) (cathode) reactor . 14
6.19 converter transformer . 14
6.20 by-pass switch . 14
6.21 valve module . 15

+AMD2:2015 CSV © IEC 2015
6.22 redundant levels . 15
6.23 valve anode ter m inal . 15
6.24 valve cathode terminal . 15
7 Converter operating conditions . 15
7.1 rectifier operation; rectification . 15
7.2 inverter operation; inve r s ion . 15
7.3 forward direction; conducting direction (of a valve) . 15
7.4 reverse direction; non-conducting direction (of a valve) . 15
7.5 forward current . 15
7.6 reverse current . 15
7.7 forward voltage . 15
7.8 reverse voltage . 16
7.9 conducting state; on-state . 16
7.10 valve voltage drop . 16
7.11 non-conducting state; blocking state . 16
7.12 firing . 16
7.13 (valve) control pulse . 16
7.14 (valve) firing pulse . 16
7.15 converter blocking . 16
7.16 converter deblocking . 16
7.17 valve blocking . 16
7.18 valve deblocking . 17
7.19 phase c ontr o l . 17
7.20 (trigger) delay angle α . 17
7.21 (trigger) advance angle β . 17
7.22 overlap angle μ . 17
7.23 extinction angle γ . 17
7.24 hold-off interval . 17
7.25 conduction interval . 17
7.26 blocking interval; idle interval . 17
7.27 forward blocking interval . 18
7.28 reverse blocking interval . 18
7.29 false firing . 18
7.30 firing failure . 18
7.31 commutation failure . 18
7.32 short-circuit ratio (SCR) . 18
7.33 effective short-circuit ratio (ESCR) . 18
7.34 triggering; gating . 18
7.35 operating state. 18
7.36 blocked state . 18
7.37 valve voltage . 18
8 HVDC systems and substations . 19
8.1 HVDC system . 19
8.2 HVDC transmission system . 19
8.3 unidirectional HVDC system . 19
8.4 reversible bidirectional HVDC system . 19
8.5 (HVDC) (system) pole . 19
8.6 (HVDC) (system) bipole . 19
8.7 bipolar (HVDC) system . 19

– 4 – IEC 60633:1998+AMD1:2009
+AMD2:2015 CSV © IEC 2015
8.8 (asymmetric) monopolar (HVDC) system . 20
8.9 HVDC substation . 20
8.10 (HVDC) substation bipole . 20
8.11 (HVDC) substation pole . 20
8.12 HVDC transmission line . 20
8.13 HVDC transmission line pole . 20
8.14 earth electrode . 21
8.15 earth electrode line . 21
8.16 symmetrical monopole . 21
8.17 rigid DC current bipolar system . 21
8.18 symmetrical monopolar (HVDC) system . 21
8.19 earth return . 21
8.20 metallic return. 21
8.21 series converter configuration . 21
8.22 unitary connection . 21
8.23 isolated generating system . 22
8.24 point of common coupling . 22
8.25 point of common coupling – DC side . 22
9 HVDC substation equipment . 22
9.1 a.c. AC (harmonic) filter . 22
9.2 d.c. (DC) (smoothing) reactor. 22
9.3 d.c. reactor arrester . 22
9.4 d.c. DC harmonic filter . 22
9.5 d.c. damping circuit . 22
9.6 d.c. surge capacitor . 22
9.7 d.c. bus arrester . 22
9.8 d.c. line arrester . 23
9.9 HVDC substation earth . 23
9.10 (d.c.) neutral bus capacitor . 23
9.11 (d.c.) neutral bus arrester . 23
9.12 metallic return transfer breaker (MRTB) . 23
9.13 earth return transfer breaker (ERTB) . 23
9.14 AC high frequency (HF) filter . 23
9.15 DC high frequency (HF) filter . 23
9.16 neutral bus switch (NBS) . 23
9.17 neutral bus grounding switch (NBGS) . 23
10 Modes of control . 24
10.1 control mode . 24
10.2 d.c.voltage control mode . 24
10.3 current control mode . 24
10.4 active power control mode . 24
10.5 reactive power control mode . 24
10.6 frequency control mode . 24
10.7 damping control mode . 24
10.8 AC voltage control mode . 24
10.9 islanded network operation mode . 24
10.10 SSTI damping control mode . 24
11 Control systems . 25
11.1 (HVDC) control system . 25

+AMD2:2015 CSV © IEC 2015
11.2 HVDC system control . 25
11.3 (HVDC) master control. 25
11.4 (HVDC system) bipole control . 25
11.5 (HVDC system) pole control . 25
11.6 (HVDC) substation control . 25
11.7 converter unit control . 25
11.8 valve control unit (VCU) . 26
11.9 integrated AC/DC system control . 26
12 Control functions. 26
12.1 equal delay angle control; individual phase control . 26
12.2 equidistant firing control . 27
12.3 α control . 27
12.4 minimum α control . 27
12.5 γ control. 27
12.6 minimum γ control . 27
12.7 control order . 27
12.8 current margin . 27
12.9 voltage dependent current order limit (VDCOL) . 27
12.10 pole (current) balancing . 27
Bibliography . 38

Figure 1 – Graphical symbols . 28
Figure 2 – Bridge converter connection . 29
Figure 3 – Example of a converter unit . 29
Figure 4 – Commutation process at rectifier and inverter modes of operation . 30
Figure 5 – Illustrations of commutation in inverter operation . 31
Figure 6 – Typical valve voltage waveforms . 32
Figure 7 – Example of an HVDC substation . 33
Figure 8 – Example of bipolar two-terminal HVDC transmission system . 34
Figure 9 – Example of a multiterminal bipolar HVDC transmission system with parallel
connected HVDC substations . 34
Figure 10 – Example of a multiterminal HVDC transmission system with series connected
HVDC substations . 35
Figure 11 – A simplified steady-state voltage-current characteristic of a two-terminal
HVDC system . 35
Figure 12 – Hierarchical structure of an HVDC control system . 36
Figure 13 – Capacitor commutated converter configurations . 37

– 6 – IEC 60633:1998+AMD1:2009
+AMD2:2015 CSV © IEC 2015
INTERNATIONAL ELECTROTECHNICAL COMMISSION
___________
TERMINOLOGY FOR HIGH-VOLTAGE DIRECT CURRENT (HVDC)
TRANSMISSION
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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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.
This consolidated version of the official IEC Standard and its amendments has been
prepared for user convenience.
IEC 60633 edition 2.2 contains the second edition (1998-12) [documents 22F/49/FDIS and
22F/53/RVD], its amendment 1 (2009-05) [documents 22F/153/CDV and 22F/163/RVC] and
its amendment 2 (2015-07) [documents 22F/340/CDV and 22F/350A/RVC].
In this Redline version, a vertical line in the margin shows where the technical content is
modified by amendments 1 and 2. Additions and deletions are displayed in red, with
deletions being struck through. A separate Final version with all changes accepted is
available in this publication.

+AMD2:2015 CSV © IEC 2015
International Standard IEC 60633 has been prepared by subcommittee 22F: Power electronics
for electrical transmission and distribution systems, of IEC technical committee 22: Power
electronics.
The committee has decided that the contents of the base publication and its amendments 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.
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 60633:1998+AMD1:2009
+AMD2:2015 CSV © IEC 2015
TERMINOLOGY FOR HIGH-VOLTAGE DIRECT CURRENT (HVDC)
TRANSMISSION
1 Scope
This International Standard defines terms for high-voltage direct current (HVDC) power
transmission systems and for HVDC substations using electronic power converters for the
conversion from a.c. to d.c. or vice versa.
This standard is applicable to HVDC substations with line commutated converters, most
commonly based on three-phase bridge (double way) connections (see figure 2) in which
unidirectional electronic valves, e.g. semiconductor valves, are used.
2 Normative references
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.
IEC 60027 (all parts), Letter symbols to be used in electrical technology
IEC 60050-551:1998, International Electrotechnical Vocabulary – Part 551: Power electronics
IEC 60146-1-1:1991, General requirements and line commutated convertors – Part 1-1:
Specifications of basic requirements
IEC 60617-5:1996, Graphical symbols for diagrams – Part 5: Semiconductors and electron
tubes
IEC 60617-6:1996, Graphical symbols for diagrams – Part 6: Production and conversion of
electrical energy
3 Symbols and abbreviations
The list covers only the most frequently used symbols. For a more complete list of the symbols
which have been adopted for static converters see IEC 60027 and other standards listed in the
normative references and the bibliography.
3.1 List of letter symbols
U direct voltage (any defined value)
d
U conventional nominal no-load direct voltage
d0
U ideal no-load direct voltage
di0
U rated direct voltage
dN
U line-to-line voltage on line side of converter transformer, r.m.s. value including
L
harmonics
U U
rated value of
LN L
U r.m.s. value
no-load phase-to-phase voltage on the valve side of transformer,
ν0
excluding harmonics
+AMD2:2015 CSV © IEC 2015
I direct current (any defined value)
d
I
rated direct current
dN
I current on line side of converter transformer, r.m.s. value including harmonics
L
I
I rated value of
LN L
I
current on valve side of transformer, r.m.s. value including harmonics
ν
α (trigger) delay angle
β (trigger) advance angle
γ extinction angle
μ overlap angle
p pulse number
q commutation number
3.2 List of subscripts
0 (zero) at no load
N rated value or at rated load
d direct current or voltage
i ideal
L line side of converter transformer
v valve side of converter transformer
max maximum
min minimum
n pertaining to harmonic component of order n
3.3 List of abbreviations
The following abbreviations are always in capital letters and without dots.
HVDC high-voltage direct current
MVU multiple valve (unit) (see 6.3.2)
SCR short-circuit ratio (see 7.32)
ESCR effective short-circuit ratio (see 7.33)
MTDC multiterminal HVDC transmission system (see 8.2.2)
MRTB metallic return transfer breaker (see 9.12)
ERTB earth return transfer breaker (see 9.13)
VDCOL voltage dependent current order limit (see 12.9)
SSTI sub-synchronous torsional interaction (see 10.10)
4 Graphical symbols
Figure 1 shows the specific graphical symbols which are defined only for the purposes of this
standard. For a more complete list of the graphical symbols which have been adopted for static
converters, see IEC 60617-5 and IEC 60617-6.
5 General terms related to converter circuits
For the purposes of this standard, the following terms and definitions apply.

– 10 – IEC 60633:1998+AMD1:2009
+AMD2:2015 CSV © IEC 2015
NOTE – For a more complete list of the terms which have been adopted for static converters, see IEC 60050(551)
and IEC 60146-1-1.
5.1
conversion
in the context of HVDC, the transfer of energy from a.c. to d.c. or vice versa, or a combination
of these operations
5.2
converter connection
electrical arrangement of arms and other components necessary for the functioning of the main
power circuit of a converter
5.3
bridge (converter connection)
double-way connection, as illustrated in Figure 2, comprising six converter arms which are
connected such that the centre terminals are the phase terminals of the a.c. circuit, and that
the outer terminals of like polarity are connected together and are the d.c. terminals
NOTE – The term “bridge” may be used to describe either the circuit connection or the equipment implementing that
circuit (see 6.2).
5.3.1
uniform bridge
bridge where all converter arms are either controllable or non-controllable
5.3.2
non-uniform bridge
bridge with both controllable and non-controllable converter arms
5.4
(converter) arm
part of an operative circuit used for conversion which is connected between an a.c. terminal and a d.c. terminal,
with the ability to conduct current in only one direction, defined as the forward direction (see 7.3)

NOTE – The main function of a converter arm is conversion; it may also perform additional functions such as
voltage limiting, damping, etc.
part of a bridge connecting two points of different potentials within a bridge, for example,
between an AC terminal and a DC terminal
5.4.1
controllable converter arm
converter arm in which the start of forward conduction may be determined by an externally
applied signal
5.4.2
non-controllable converter arm
converter arm in which the start of forward conduction is determined solely by the voltage
applied to its terminals
5.5
by-pass path
low resistance path between the d.c. terminals of one or several bridges excluding the a.c.
circuit
NOTE – The by-pass path may either constitute a unidirectional path, e.g. a by-pass arm (see 5.5.1), or a by-pass
pair (see 5.5.2), or it may constitute a bidirectional path, e.g. a by-pass switch (see 6.20).

+AMD2:2015 CSV © IEC 2015
5.5.1
by-pass arm
unidirectionally conducting by-pass path connected only between d.c. terminals, commonly
used with mercury arc valve technology (not shown in figure 2)
5.5.2
by-pass pair
two converter arms of a bridge connected to a common a.c. terminal and forming a by-pass
path (see figure 2)
5.6
commutation
transfer of current between any two paths with both paths carrying current simultaneously
during this process
NOTE – Commutation may occur between any two converter arms, including the connected a.c. phases, between a
converter arm and a by-pass arm, or between any two paths in the circuit.
5.6.1
line commutation
method of commutation whereby the commutating voltage is supplied by the a.c. system
5.7
commutating group
group of converter arms which commutate cyclically and independently from other converter
arms, i.e. the commutations are normally not simultaneous (see figure 2)
NOTE – In the case of a bridge, a commutating group is composed of the converter arms connected to a common
d.c. terminal. In certain cases, e.g. when large currents and/or large commutation inductances are involved, the
commutation in the two commutating groups belonging to the same bridge need not be independent.
5.8
commutation inductance
total inductance included in the commutation circuit, in series with the commutating voltage
5.9
pulse number p
characteristic of a converter connection expressed as the number of non-simultaneous
symmetrical commutations occurring during one cycle of the a.c. line voltage
NOTE – The pulse number of a bridge converter connection defined in 5.3 is always p = 6.
5.10
commutation number q
number of commutations during one cycle of the a.c. line voltage occurring in each commutat-
ing group
NOTE – In a bridge converter connection, each commutating group has a commutation number q = 3.
5.11
capacitor commutated converter
converter in which series capacitors are included between the converter transformer and the
valves (see Figure 13a)
5.12
controlled series capacitor converter
converter in which series capacitors are inserted between the a.c. filter bus and the a.c.
network (see Figure 13b)
– 12 – IEC 60633:1998+AMD1:2009
+AMD2:2015 CSV © IEC 2015
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)
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)
NOTE – If a converter unit comprises two converter bridges with a phase displacement of 30°, then the converter
unit forms a 12-pulse unit (see figure 7). The term “12-pulse group” is also used.
6.2
(converter) bridge
equipment used to implement the bridge converter connection and the by-pass arm, if used
NOTE – The term “bridge” may be used to describe either the circuit connection or the equipment implementing that
circuit (see 5.3).
6.2.1
anode (cathode) valve commutating group
equipment used to implement the converter arms of one commutating group of a bridge with
interconnected anode (cathode) terminals
6.3
valve
complete operative controllable or non-controllable valve device assembly, normally conducting
in only one direction (the forward direction), which can function as a converter arm in a
converter bridge
NOTE – An example of a non-controllable valve device assembly is a semiconductor diode valve. An example of a
controllable valve device assembly is a thyristor valve.
6.3.1
single valve (unit)
single structure comprising only one valve
6.3.2
multiple valve (unit) (MVU)
single structure comprising more than one valve
NOTE – Examples of multiple valve units are double valves, quadrivalves and octovalves with two, four and eight
series-connected valves respectively.

+AMD2:2015 CSV © IEC 2015
6.4
main valve
valve in a converter arm
6.5
by-pass valve
valve in a by-pass arm
6.6
thyristor module
part of a valve comprised of comprising a mechanical assembly of thyristors with their
immediate auxiliaries, and reactors, if used 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.
NOTE 2 – The deprecated term “valve module” has been used with an equivalent meaning.
6.7
reactor module
part of a valve, being a mechanical assembly of one or more reactors, used in some valve
designs
NOTE – Reacto
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