TECHNICAL REQUIREMENTS AND SPECIFICATIONS OF STATE-OF-THE-ART HVDC SWITCHING EQUIPMENT

683
TECHNICAL REQUIREMENTS
AND SPECIFICATIONS
OF STATE-OF-THE-ART
HVDC SWITCHING EQUIPMENT
JOINED WORKING GROUP
A3/B4.34
APRIL 2017

Members
C.M. Franck, Convenor CH R. Smeets, Secretary NL
A. Adamczyk UK H. Bahirat US
C. Bartzsch DE N.A. Belda NL
S. Bødal NO G. Chaffey UK
M. Distler DE R. Doche CA
W. Grieshaber FR M. Groβmann DE
H.-D. Hwang KO R. Iravani CA
H. Ito JP L.-R. Jänicke DE
S. Jia CN S. Kulkarni IN
B.-W. Lee KO L. Liljestrand SE
Z. Liu CN T. Matsumoto JP
G. Nikolic DE F. Page UK
C. Peng US M. Runde NO
M. Saeedifard US U. Steiger CH
K. Tahata JP P. Vinson FR
Y. Wu CN A. Yanushkevich NL
D. Yoshida JP J. Yuan FR
Corresponding Members
M. Heidari CA H. Mercure CA
S. Poirier CA L. Recksiedler US
J. Sneath CA P. Wang CA
JWG A3/B4.34
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TECHNICAL REQUIREMENTS AND
SPECIFICATIONS OF STATE-OF-THE-ART
HVDC SWITCHING EQUIPMENT
ISBN : 978-2-85873-386-6

TECHNICAL REQUIREMENTS AND SPECIFICATIONS OF STATE-OF-THE-ART HVDC SWITCHING EQUIPMENT
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EXECUTIVE SUMMARY
Background and motivation of the working group
In 2013, the “Grid Feasibility Study” (CIGRÉ TB 533, 2013) concluded that the “technical feasibility
of building a large scale HVDC Grid requires that a fault has to be isolated very fast before it
affects the DC voltage in other parts of the grid”. For this, “it is not sufficient to be able to break the
current at the converter stations. DC circuit breakers will have to be located at the terminations of
all transmission lines/cables…”. Based on this input it was decided to start a working group on HVDC
switchgear, clearly with circuit breakers (CB) as the main motivation, but also explicitly on other
HVDC switchgear. The key performance challenges are not only related to the equipment design,
but also associated with requirements from the system perspective. Thus, the working group was set
up as a joint working group (JWG) to involve experts from the “high voltage equipment community
(A3)” and the “power electronics community (B4)”.
The working group decided to work with the following objectives:
A) Review the technical requirements of HVDC switching equipment for different applications
such as multi-terminal HVDC systems and off-shore wind farm connections.
B) Investigate the technical capabilities and limitations of existing and projected switching
equipment mainly with mechanical operating drives and then foresee the future capability
of these HVDC switching equipment.
C) Facilitate the development of new HVDC switching equipment, by identifying the gaps
between existing performance specifications and future requirements.
Results of the working group
Like every other working group, the present JWG started with a literature review on the relevant
topics, in which more than 250 documents have been collected and evaluated. Despite the relatively
large number of documents, only a limited amount of relevant information could be found, and often
the same few arguments are simply repeated. Especially lacking was a clear overview on HVDC
switches (not designed for fault current interruption) for the aspects devices and specifications.
The next activity of the working group was the design of a comprehensive schematic single line
diagram of a potential HVDC substation to show where and for what purpose the different switching
equipment could be installed. This diagram is not to be understood as a suggestion for future
substations, rather as an instructive element to show an example where all elements are present and
so their functionality becomes clear. This basic scheme is then stringently used throughout the brochure
to explain the functionalities of each type of switchgear. For each switchgear, the station single line
diagram is reduced to a simplified one highlighting only the specific switchgear to explain its main
functionality and requirements.
It is customary nowadays that each HVDC project is a single vendor turnkey project. Every company
has internal evaluations of performance to match specific requirements. No standardized ratings are
available and publications on this topic are lacking completely. Also, almost no brochures or
catalogues are available as these components are not freely for sale outside of a specific turnkey
project (except disconnecting switches). Moreover, due to the limited number of projects, switchgear
development is often not more than a modification of existing (AC) switchgear. Thus, in contrast to
the situation with AC switchgear, it is important not to misinterpret the existing switchgear
performance specifications as the limit performance that these devices might have.
Another important contribution of the work of this JWG is a concise summary and overview of existing
HVDC switchgear, which was not available before. The working group classified the switchgear into
four categories: disconnecting -, earthing -, commutation switches and circuit breakers.
Each of the switches is described in a separate chapter with identical structure: first, the detailed
functionality and basic working principle together with a dedicated single line diagram is provided.
Then, an overview of existing switchgear from various projects is presented to give an impression of
the performance specifications. These should not be misinterpreted as a list of performance limits.
Finally, an overview of projected nearby-future installations (status end of 2016) and necessary

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updates of the performance requirements is given. This is done considering future HVDC multi-
terminal networks.
In the following, a short summary of the chapters of all switches is given:
HVDC disconnecting switches are available for all voltage and current ratings and are built in every
project in large numbers. Today, the switching duties are very limited (line or converter bank
discharging), but in the future multi-terminal networks, bus-transfer or even line-transfer requirements
could be demanded, similar to disconnecting switches in AC networks.
HVDC earthing switches are available for all voltage and current ratings as well, and are built in
every project in large numbers. In contrast to disconnecting switches, however, it is not expected that
the requirement specifications will change substantially in future projects, nor for multi-terminal
systems.
In today’s HVDC projects, HVDC transfer switches are the type of switchgear with the highest current
commutation duty and they can transfer currents up to a few thousand Ampere from and to metallic
and earth return. The devices typically make use of the passive oscillation principle and the
interruption chamber is based on existing or modified AC gas circuit breakers. Besides the required
upgrades for the new HVDC projects with higher current and voltage ratings, it is also expected that
the increasing number of projects facilitates improvements in the interrupter design especially for the
use in HVDC transfer switches. Compared to DC transfer switches that just use existing AC interrupter
units, a reduction in cost or overall footprint can then be expected.
HVDC by-pass switches are used in projects with series connected valve groups. They are used to
bypass single valve groups for maintenance or in case of fault to continue power transfer with
reduced voltage. These devices are also transfer switches, but it is unlikely that the future multi-
terminal networks will be built with transfer switches as it is uneconomical to operate the entire
network at reduced voltage if only one converter valve group needs to be taken out of service.
HVDC high-speed earthing switches (also called neutral bus earthing switches (NBES)) enable a quick
re-establishment of the earthing of the substation in case the electrode line becomes unavailable.
Not every project in operation today uses these switches as its usefulness depends strongly on the
system arrangement. The required current transfer capability depends on the maximum imbalance
earth return current. The requirement specifications of these switches in multi-terminal networks may
substantially increase, as the imbalance current is less controllable.
HVDC paralleling switches are used to parallel and de-parallel converters to a common power line.
These switches are applied in very few projects, so far. In the future multi-terminal projects, however,
these types of switches will be essential to switch converter stations to and from the energized
network. HVDC circuit breakers might be a logical choice and can perform this switching duty, but
due to the size and cost of HVDC circuit breakers, it is more likely that paralleling switches will be
used for these routine tasks.
The situation in the literature with respect to HVDC circuit breakers is currently very dynamic; even
though only a small number of multi-terminal DC systems will be commissioned in the foreseeable
future. Proposed analyses and solutions are diverse and often impractical, partly because of an
absence of requirement specifications. On the one hand, this area has only recently regained
considerable interest and is developing quickly. On the other hand, the situation is ambiguous
because experts from different communities and with diverse backgrounds focus on different aspects:
equipment designers focus on functionality of the circuit breakers while the system designers focus on
the functionality of the system. A typical example of this is the discussion on the required time to fault
clearance and the required size of additional DC side reactors used for limiting the rate of rise of
fault current. Whereas equipment designers see the advantage of fault current limitation, system
designers may appreciate a slower propagation of voltage collapse through the system but need
to consider the impact of (large) reactors on system stability. With respect to time to fault clearance:
the equipment designers typically compare the internal current commutation times, whereas the
system designers compare the times required until the system voltage starts to recover, which is the
moment when the peak fault current is reached and the fault current starts to decrease.

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The part of this technical brochure related to HVDC circuit breakers, therefore, starts with a chapter
on the technical framework for HVDC circuit breakers. It contains timing definitions, an analysis of
HVDC fault currents and system stability aspects. The timing definitions are important contributions
of this working group since this is a proposal for harmonization of nomenclature to avoid confusion
between equipment and system aspects of the HVDC circuit breakers, not only to be technology
neutral, but also to avoid confusion with respect to AC breakers and systems.
The section on HVDC fault currents provides an overview of the typical temporal development of
fault currents in different HVDC system configurations and qualitative descriptions of the salient
parameters. The section on system stability extends the discussion on the consequences of faults in
HVDC grids to aspects beyond the fault current interruption capability of circuit breakers, to thermal
overload aspects of converters, to problems related to voltage collapse in the DC system and effects
on the AC system of a DC side fault.
The introduction to the “building blocks” of HVDC circuit breakers is presented as a separate chapter.
A definition and explanation of components needed for the description of all types of circuit
breakers: semiconductor devices, surge arresters, residual current breakers to interrupt for example
the leakage current through parallel connected MOSA, mechanical switches (ultra-fast disconnectors),
and electromagnetic pulse drives.
Circuit breaker prototypes have been demonstrated to perform in the range of requirements the
origin of which, however, is mainly based on present day feasibility of component technology than
on the future system requirements. None of these have been put in service in practical MT HVDC
networks yet (up to 2016 where the working group finished this brochure), but no technical barriers
to application are expected.
Up to now, different topologies have specific advantages and disadvantages regarding speed, on-
state losses, cost, maximum current interruption capability or reliability/simplicity of components
used. Thus, the working group decided to describe the details of all prototypes that have been
successfully tested in a voltage and current range that is “within reach” of HVDC applications. These
devices are grouped into four categories according to their basic topology: using a passive
oscillating principle, a current oscillation scheme with active current injection, pure power-electronic
devices in the nominal current path, or built with a hybrid mechanical and power-electronic
combination. Fault current neutralization times ≪10 ms and interruption of peak fault currents of 8
– 16 kA have been demonstrated by several different prototypes. In all cases, these prototypes are
“modules” verified to operate at DC voltage in the range of 80 – 120 kV, to be combined in series
for application realistic future MTDC systems.
Following the chapters dedicated to each topology, a single chapter is dedicated to the comparison
and evaluation of these concepts. With the current lack of field experience, no unambiguous
conclusion and recommendation can be provided here, but the advantages and disadvantages
clearly show where the future research and development could make a substantial contribution.
Beyond the circuit breaker development, new extremely fast protection concepts need to be
developed as particularly important in order to fully exploit the short operation time of the circuit
breakers. The combined optimization of circuit breakers and system protection is very important for
future multi-terminal HVDC networks, as, in contrast to AC networks, HVDC circuit breakers strongly
interact with the network to achieve fault current interruption.
A defined goal of the working group is to facilitate the development of new HVDC switching
equipment by identifying the gap between existing performance and expected future requirements.
This is done separately and qualitatively (given the absence of MTDC systems) in each of the
individual switchgear chapters, but is also summarized in chapter 17. Special focus in this chapter is
on the maximum current breaking capability, maximum energy dissipation/handling capability,
transient interruption voltage, CB failures, and peak withstand current.
Every circuit breaker needs to be tested to demonstrate its performance, and suitable test circuits
need to be identified and testing procedures need to be agreed upon and eventually standardized.
So far, most of the above described prototypes have been tested with newly designed test circuits.
In the present brochure, an overview of the test circuits used in the literature is provided, and a first
comparative evaluation is made. This shall serve the purpose to start a community wide discussion,

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e.g. whether interruption tests should be made with DC currents or AC currents with a defined rate
of rise of fault current, whether the tests should be performed to demonstrate the internal current
interruption and energy absorption capability simultaneously or separately, etc.
An extensive bibliography gives reference to the most important recent publications relevant for this
working group and enables the interested reader to get further details on the various aspects of
these topics.
Recommendation for future work
Based on the extensive work done by the members of this JWG, knowledge gaps have been
identified and suggestions for the next steps and future work can be made:
Clear requirements beyond functional specifications need to be derived for HVDC CBs. Based on
detailed studies, specific values for the maximum fault neutralization times, maximum current
interruption capability, required speed of detection and selection of protection system, and others
should be provided. In addition, a joint working group could reflect on the question of finding the
optimum (or at least the best compromise) between protection system, system operation, and CB
performance limits. The questions like: “What is the optimum size of the series reactors required to
limit the rate-of-rise of fault currents”, “Does the protection system have to rely on local
measurements only or can a fast communication system be used?”, or “Is the pre-activation of circuit
breakers and the submission of intermediate trip signal of advantage or not?” need to be addressed.
Test methods for HVDC switchgear have not been defined yet. Besides the specific test methods and
test conditions, more fundamental questions such as “is it required to test the main functionalities
simultaneously or can these tasks be tested separately?”, “do technology independent tests make
sense or should each technology be stressed with its corresponding worst case condition?”,” what is
the minimum module size that can be defined to test a DC breaker appropriately?”, need to be
answered.
Beyond testing of circuit breakers, field experience (mainly from China) needs to be collected and
evaluated. Pilot installations have to be planned and set into operation. This should be accompanied
with dedicated measurement equipment to learn about real system stresses, the interaction between
circuit breakers and the system, and the performance of the installed switchgear.
Finally, for all HVDC switches (transfer switches, disconnecting switches, etc.), clear requirements
beyond the functional specifications should be derived through detailed studies.
Acknowledgements
The convenor would like to thank all members for their constant involvement, active contribution and
intense but constructive discussion. He is proud to present this document to the public and look forward
to its active use. If more multi-terminal systems, like the ones in China, are planned and taken into
operation in the next years (may be even multi-vendor projects) this brochure will prove its usefulness
in practical applications. The advent of novel products, methods or well-defined systems that enable
to define requirements more quantitatively may necessitate an update of this brochure in the future.

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TABLE OF CONTENTS
EXECUTIVE SUMMARY ............................................................................................................................... 3
TABLE OF CONTENTS ................................................................................................................................ 7
1 INTRODUCTION.............................................................................................................................21
2 SWITCHING IN DC SYSTEMS (BASICS) ....................................................................................25
2.1 INTRODUCTION.................................................................................................................................... 25
2.2 GENERAL REQUIREMENTS COMPARED TO HVAC DEVICES AND SYSTEMS ........................... 25
2.3 HVDC SWITCHES.................................................................................................................................. 25
2.3.1 Converter disconnecting switch (CD) and bypass disconnecting switch (BPD)................... 29
2.3.2 Filter disconnecting switch (FD)................................................................................................... 29
2.3.3 Substation disconnecting switch (SD) ......................................................................................... 29
2.3.4 Line disconnecting switch (LD) and pole line disconnecting switch (PLD)............................. 29
2.3.5 Line to neutral disconnecting switch (LND)................................................................................ 29
2.3.6 Neutral bus disconnecting switch (NBD).................................................................................... 29
2.3.7 Neutral bus earthing disconnecting switch (NBED).................................................................. 29
2.3.8 Electrode line disconnecting switch (ELD).................................................................................. 29
2.3.9 Substation pole paralleling disconnecting switch (SPPD)...................................................... 29
2.3.10 Pole line earthing switch (PLES).............................................................................................. 29
2.3.11 Neutral bus earthing switch (NBES) ....................................................................................... 29
2.3.12 Filter earthing switch (FES) ...................................................................................................... 30
2.3.13 Converter earthing switch (CES)............................................................................................. 30
2.3.14 Substation earthing switch (SES)............................................................................................. 30
2.3.15 Pole paralleling earthing switch (PPES)................................................................................ 30
2.3.16 Neutral bus switch (NBS).......................................................................................................... 30
2.3.17 Earth return transfer switch (ERTS) and metallic return transfer switch (MRTS)............. 30
2.3.18 Converter bypass switch (BPS)............................................................................................... 30
2.3.19 High-speed earthing switch (HSES)........................................................................................ 31
2.3.20 Paralleling switch (PS).............................................................................................................. 31
2.3.21 Circuit breaker (CB).................................................................................................................. 31
2.4 CURRENT ZERO CREATION SCHEMES.............................................................................................. 31
2.4.1 Arc voltage .................................................................................................................................... 31
2.4.2 Passive oscillation.......................................................................................................................... 32
2.4.3 Active current injection................................................................................................................. 32
2.5 CURRENT COMMUTATION................................................................................................................. 33
2.6 DISSIPATION OF THE ENERGY.......................................................................................................... 33
3 HVDC SYSTEM TOPOLOGIES.....................................................................................................35
3.1 INTRODUCTION TO HVDC SYSTEMS............................................................................................... 35
3.1.1 HVDC transmission connections................................................................................................... 38
3.2 POINT-TO-POINT CONNECTIONS................................................................................................... 38
3.2.1 Schemes of point-to-point HVDC connections.......................................................................... 38
3.2.2 Point-to-point HVDC projects...................................................................................................... 40
3.3 MULTI-TERMINAL RADIAL HVDC SYSTEMS...................................................................................... 44
3.3.1 Sardinia - Corsica – Italy 3 terminal link................................................................................. 44
3.3.2 Québec – New England 5 terminal link ................................................................................... 45

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3.3.3 Nan’ao Island 3 terminal VSC MTDC link................................................................................ 46
3.3.4 Zhoushan 5 terminal VSC MTDC link......................................................................................... 46
3.3.5 North-East Agra UHVDC Link..................................................................................................... 47
3.3.6 Planned MTDC projects ............................................................................................................... 49
3.3.7 Advantages and disadvantages of MTDC networks versus point-to-point schemes ....... 49
3.3.8 Specific switching equipment used for LCC radial HVDC systems...................................... 50
3.4 MULTI-TERMINAL MESHED HVDC SYSTEMS.................................................................................... 52
3.4.1 Advantages and challenges of meshed HVDC systems ........................................................ 53
3.4.2 Evolution towards meshed networks.......................................................................................... 54
3.4.3 Examples of meshed multi-terminal study topologies............................................................ 54
3.4.4 New requirements for switching equipment in meshed grids ............................................... 56
3.4.5 Fault currents on meshed networks............................................................................................ 57
3.4.6 Main differences between radial and meshed topologies for switching apparatus ...... 57
4 HVDC DISCONNECTING SWITCHES.........................................................................................59
4.1 INTRODUCTION.................................................................................................................................... 59
4.2 DESCRIPTION OF BASIC FUNCTIONALITY AND BASIC WORKING PRINCIPLE....................... 60
4.2.1 Switching requirements ................................................................................................................ 60
4.2.2 Design difference in creepage distance between AC DS and DC DS............................... 62
4.3 OVERVIEW OF EXISTING INSTALLATIONS, PRODUCTS, APPLICATIONS................................ 63
4.3.1 Japanese experience................................................................................................................... 63
4.3.2 Chinese experience ...................................................................................................................... 65
4.3.3 New Zealand experience ........................................................................................................... 66
4.3.4 Canadian experience .................................................................................................................. 67
4.3.5 Korean experience....................................................................................................................... 67
4.4 FUTURE REQUIREMENT........................................................................................................................ 68
4.4.1 Bus transfer .................................................................................................................................... 68
4.4.2 Line transfer at full load.............................................................................................................. 69
5 HVDC EARTHING SWITCHES......................................................................................................71
5.1.1 Pole Line Earthing Switch (PLES)................................................................................................. 72
5.1.2 Neutral Bus Earthing Switch (NBES)........................................................................................... 73
5.1.3 Filter Earthing Switch (FES).......................................................................................................... 74
5.1.4 Converter Earthing Switch (CES) ................................................................................................ 74
5.2 LIST OF PERFORMANCE SPECIFICATIONS OF HVDC EARTHING SWITCHES.......................... 74
5.4 OVERVIEW OF (NEAR) FUTURE INSTALLATIONS, PRODUCTS, APPLICATIONS,
REQUIREMENTS................................................................................................................................................. 78
6 HVDC TRANSFER SWITCHES.......................................................................................................79
6.1 INTRODUCTION.................................................................................................................................... 79
6.2.1 Basic functionality of HVDC transfer switches......................................................................... 81
6.2.2 Operating principle of transfer switches.................................................................................. 85
6.2.3 Transfer between operation modes.......................................................................................... 87
6.3 LIST OF PERFORMANCE SPECIFICATIONS FOR HVDC TRANSFER SWITCHES........................ 89
6.3.1 Rated operating current.............................................................................................................. 89
6.3.2 Maximum continuous current in system operation................................................................... 89

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6.3.3 Maximum commutation current................................................................................................... 89
6.3.4 Maximum continuous operating voltage................................................................................... 89
6.3.5 Operating sequence..................................................................................................................... 90
6.3.6 Time parameters........................................................................................................................... 90
6.4.1 Examples of existing transfer switch products: ....................................................................... 90
6.4.2 Examples of existing applications:............................................................................................ 98
6.4.3 Highest requirement during the last 5 years........................................................................... 98
REQUIREMENTS................................................................................................................................................. 99
6.5.1 Design of HVDC transfer switches in GIS................................................................................. 99
6.5.2 Special structural design for HVDC transfer switches............................................................ 99
7 BYPASS SWITCHES .................................................................................................................... 101
7.1 DESCRIPTION OF BASIC FUNCTIONALITY AND BASIC WORKING PRINCIPLE.....................101
7.1.1 Bypass switching operations.....................................................................................................104
7.2 LIST OF PERFORMANCE SPECIFICATIONS OF BYPASS SWITCHES.........................................109
7.3 OVERVIEW OF EXISTING INSTALLATIONS, PRODUCTS, APPLICATIONS..............................113
REQUIREMENTS...............................................................................................................................................116
8 HIGH-SPEED EARTHING SWITCHES ....................................................................................... 117
8.1.1 Bipolar operation mode with electrode return path............................................................117
8.1.2 Bipolar operation mode with dedicated metallic return path ...........................................118
8.1.3 Monopolar operation mode with electrode return path.....................................................119
8.1.4 Backup functionality for Neutral Bus Switch ..........................................................................119
8.2 LIST OF PERFORMANCE SPECIFICATION FOR HSES...................................................................121
8.2.1 Maximum continuous DC current and commutation current.................................................121
8.2.2 Maximum Continuous Operating Voltage..............................................................................121
REQUIREMENTS...............................................................................................................................................124
8.4.1 Future requirements due to VSC converter technologies.....................................................124
8.4.2 Future requirements due to HVDC grids.................................................................................124
9 PARALLELING SWITCHES.......................................................................................................... 125
9.1.1 Switching of converter stations / converter groups..............................................................125
9.1.2 Switching of DC lines/cables....................................................................................................128
9.2 LIST OF PERFORMANCE SPECIFICATIONS OF PARALLELING SWITCHES..............................130
REQUIREMENTS...............................................................................................................................................133
10 TECHNICAL FRAMEWORK FOR HVDC CIRCUIT BREAKERS ............................................... 135
10.1 WAVE TRACE DEFINITIONS..........................................................................................................135

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10.1.1 Transient Interruption Voltage (TIV) ....................................................................................135
10.1.2 Transient Interruption Voltage Peak (Peak TIV)................................................................135
10.1.3 Prospective Fault Current ......................................................................................................135
10.1.4 Peak fault Current ..................................................................................................................135
10.2 TIMING DEFINITIONS.....................................................................................................................135
10.2.1 Introduction...............................................................................................................................136
10.2.2 Definitions.................................................................................................................................137
10.2.3 Nominal current interruption .................................................................................................139
10.3 HVDC FAULT CONDITIONS..........................................................................................................140
10.3.1 Short-circuit current conditions..............................................................................................141
10.3.2 DC fault in LCC systems.........................................................................................................142
10.3.3 DC fault in VSC systems.........................................................................................................144
10.3.4 Pole-to-earth fault in VSC HVDC systems..........................................................................145
10.3.5 Pole-to-pole faults in VSC HVDC systems..........................................................................146
10.3.6 Comparison .................................................................................................................................148
10.3.7 Mixed AC/DC fault................................................................................................................148
10.3.8 Influence of reactors...............................................................................................................149
10.4 SYSTEM STABILITY..........................................................................................................................150
10.4.1 AC system stability .................................................................................................................150
10.4.2 Continued converter operation under a DC fault.............................................................152
10.4.3 Insulation coordination ...........................................................................................................154
10.4.4 Converter current withstand..................................................................................................156
10.4.5 Auto-reclose.............................................................................................................................156
11 BUILDING BLOCKS OF HVDC CIRCUIT BREAKERS............................................................... 159
11.1 SEMICONDUCTOR DEVICES.........................................................................................................159
11.1.1 Wide Band Gap Devices......................................................................................................160
11.2 SURGE ARRESTERS .........................................................................................................................162
11.3 RESIDUAL CURRENT BREAKER ......................................................................................................164
11.4 MECHANICAL SWITCH – ULTRA-FAST DISCONNECTOR.......................................................164
11.5 ELECTROMAGNETIC ACTUATORS ..............................................................................................165
12 PASSIVE OSCILLATION HVDC CIRCUIT BREAKERS.............................................................. 169
12.1 DESCRIPTION OF BASIC FUNCTIONALITY AND BASIC WORKING PRINCIPLE.................169
12.2 EXAMPLE TOPOLOGY 1...............................................................................................................170
12.4 TOPOLOGY BASED ON POWER ELECTRONICS.....................................................................171
12.5 OVERVIEW OF PERFORMANCE SPECIFICATIONS OF TESTED PROTOTYPES ...................172
13 ACTIVE CURRENT INJECTION HVDC CIRCUIT BREAKERS................................................... 173
13.1 DESCRIPTION OF BASIC FUNCTIONALITY AND BASIC WORKING PRINCIPLE.................173
13.4 EXAMPLE TOPOLOGY 3 - ALTERNATIVE SCHEME..................................................................177
13.6 OVERVIEW OF PERFORMANCE SPECIFICATIONS OF TESTED PROTOTYPES ...................182

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14 POWER ELECTRONIC HVDC CIRCUIT BREAKERS................................................................. 183
14.1 OVERVIEW.......................................................................................................................................183
14.2 TYPICAL OPERATION.....................................................................................................................183
14.3 POWER ELECTRONIC CIRCUIT BREAKER CONCEPT 1............................................................185
14.3.1 Status of the circuit breaker..................................................................................................185
14.3.2 Intrinsic limits.............................................................................................................................186
14.4 OTHER PROPOSED TOPOLOGIES..............................................................................................186
14.5 FAULT CURRENT INTERRUPTION TIMING..................................................................................187
15 MECHANICAL AND POWER ELECTRONIC HYBRID HVDC CIRCUIT BREAKERS.............. 189
15.1 HYBRID CIRCUIT BREAKER CONCEPT 1 .....................................................................................191
15.1.2 Intrinsic Limits............................................................................................................................194
16 COMPARISON OF DIFFERENT HVDC CIRCUIT BREAKER PRINCIPLES .............................. 201
16.1 INTRODUCTION..............................................................................................................................201
16.2 INTERNAL CURRENT COMMUTATION TIME..............................................................................202
16.3 INTERRUPTION CAPABILITY..........................................................................................................203
16.4 ON-STATE LOSSES.........................................................................................................................203
16.5 RATE OF RISE OF FAULT CURRENT .............................................................................................204
16.6 INSTALLATION COSTS...................................................................................................................204
16.7 EXPECTED USAGE OF CIRCUIT BREAKERS IN FUTURE MTDC VSC SYSTEMS.....................205
16.7.1 Passive oscillation HVDC circuit breaker............................................................................205
16.7.2 Active current injection HVDC circuit breaker ...................................................................205
16.7.3 Power Electronic HVDC circuit breaker ..............................................................................205
16.7.4 Mechanical and power electronic hybrid HVDC circuit breaker...................................205
16.8 PROTECTION TIMING....................................................................................................................205
17 GAPS BETWEEN REQUIREMENT AND EXISTING PERFORMANCE SPECIFICATIONS .... 209
17.1 INTRODUCTION..............................................................................................................................209
17.2 HVDC CIRCUIT BREAKER ...............................................................................................................209
17.2.1 HVDC CB Operation Delay (internal current commutation time)...................................210
17.2.2 HVDC CB Maximum Current Breaking Capability...........................................................211
17.2.3 HVDC CB Maximum Energy Dissipation/Handling Capability......................................211
17.2.4 HVDC CB Transient Interruption Voltage ...........................................................................212
17.2.5 HVDC CB Failure.....................................................................................................................212
17.2.6 Peak Withstand Current........................................................................................................212
17.3 NON-BREAKING SWITCHING EQUIPMENT .............................................................................212

12
18 TEST METHODS AND TEST CIRCUITS FOR HVDC SWITCHGEAR ..................................... 215
18.1 TEST METHODS AND TEST CIRCUITS OF HVDC CIRCUIT BREAKERS ...................................215
18.1.1 Introduction...............................................................................................................................215
18.1.2 Review of HVDC circuit breaker tests and test circuits for LCC application ...............215
18.1.3 Recent tests of HVDC circuit breakers ................................................................................217
18.1.4 Candidate test circuits for HVDC circuit breakers............................................................221
18.2 MRTS TEST........................................................................................................................................227
19 BIBLIOGRAPHY/REFERENCES................................................................................................... 229

13
Figures and Illustrations
Figure 2.1: Schematic HVDC circuits with switches performing a current interruption (left) and a
current commutation from one circuit to an existing parallel circuit (right). For higher system voltages
and large current ratings only the latter type of devices is commercially available (Kanngiesser,
1989). Us is counter voltage generated by switching equipment........................................................... 26
Figure 2.2: Example of HVDC side switchgear arrangement for one pole in an HVDC substation.
(Expanded version of a figure in (CIGRÉ WG 13/14.08, 1989) ) See Table 2-1and text for
explanations of abbreviations and duties................................................................................................... 27
Figure 2.3: Process of fault interruption by generating a counter voltage........................................... 31
Figure 2.4: Circuit breaker with passive oscillation circuit........................................................................ 32
Figure 2.5: Circuit breaker with active current injection scheme. ............................................................ 32
Figure 2.6: Current commutation by opening a switch in one branch .................................................... 33
Figure 3.1 Principle diagram of (a) LCC-HVDC converter station, (b) VSC-HVDC 2/3-level converter
station, and (c) VSC-HVDC multilevel converter station............................................................................ 37
Figure 3.2: Schematic diagrams of point-to-point HVDC transmission systems.................................... 40
Figure 3.3: Schematic diagram of the Kii-channel HVDC link.................................................................. 43
Figure 3.4: Existing configuration of the Skagerak system SK1, SK2 and SK3 ................................... 44
Figure 3.5: New bipolar configuration of SK3 and SK4 (the Xs in the plot of SK4 indicate the switching
arrangement needed to reverse polarity, see also text) (Kjærgaard, et al., 2012). ........................ 44
Figure 3.6: Sardinia-Corsica-Italy three terminal link............................................................................... 45
Figure 3.7: Schematic diagram of the SACOI link including the Corsica tapping station with its high
speed reversing switches................................................................................................................................. 45
Figure 3.8: Québec - New England radial MTDC link.............................................................................. 46
Figure 3.9: Zhoushan 5 terminal VSC project in China.............................................................................. 47
Figure 3.10: 800 kV North-East Agra UHVDC Link in India.................................................................... 48
Figure 3.11: North-East Agra UHVDC Link.................................................................................................. 48
Figure 3.12: Single-line diagram for MTDC bipole terminal showing paralleling switches .............. 51
Figure 3.13: Closing operation of a PS on a multi-terminal network..................................................... 51
Figure 3.14 Example of an HVDC Grid System having a meshed and radial structure (CENELEC,
2012).................................................................................................................................................................. 52
Figure 3.15 View of meshed DC grid overlaying the AC network (Hertem & Ghandhari, 2010) .. 52
Figure 3.16 Multiple point-to-point HVDC schemes (left) and HVDC grid (right) (Andersen, 2014)
............................................................................................................................................................................. 53
Figure 3.17 CIGRE B4 DC Test System (CIGRE TB 604, December 2014)........................................... 55
Figure 3.18 Examples of different offshore grid configurations (OffshoreGrid, 2011) ................... 56
Figure 3.19: Zhangbei 500 kV flexible DC grid project ......................................................................... 56
Figure 3.20 Principal components in a simple meshed network with three converters, disconnecting
switches (DS), DC circuit breakers (HVDC CB) and power-flow controllers (PFC)................................ 57
Figure 4.1: Single-line diagram of a bipolar LCC HVDC transmission system with disconnecting
switches............................................................................................................................................................... 59
Figure 4.2: Current transfer operation of BPD ........................................................................................... 61
Figure 4.3: Voltage difference across the group D DS ............................................................................ 62
Figure 4.4: DC 500 kV DS with closing resistor and its closing operation sequence .......................... 62
Figure 4.5: HVDC DS switching tests............................................................................................................. 64
Figure 4.6: Three terminal MTDC network model ...................................................................................... 68
Figure 4.7: Bus transfer simulation model.................................................................................................... 69
Figure 5.1: Example of interlocking device for AC earthing - and disconnecting switch................... 71
Figure 5.2: Earthing switches in a typical HVDC system........................................................................... 72
Figure 5.3: Neutral Bus earthing switch (left) and Line Neutral earthing switch (right) ...................... 73
Figure 6.1: HVDC system configurations (a) Bipolar (b) Monopolar earth return (c) Monopolar metallic
return (d) Monopolar metal and earth return combined operation modes........................................... 79
Figure 6.2: HVDC transfer switches in a substation ................................................................................... 81
Figure 6.3: Earth fault at three different locations.................................................................................... 82
Figure 6.4: Equivalent circuits of earth faults.............................................................................................. 82
Figure 6.5: Equivalent circuit relative to MRTS and ERTS operation ...................................................... 83

14
Figure 6.6: Diagram of Kii Channel HVDC Link.......................................................................................... 84
Figure 6.7: Oscillograms of an actual lightning fault on the overhead transmission line ................... 85
Figure 6.8: Conceptual diagram of a transfer switch (cf. also Figure 12.1) ........................................ 85
Figure 6.9: Photographs of a DC transfer switch prototype with passive oscillation current zero
creation scheme in a test set-up..................................................................................................................... 86
Figure 6.10: Measured wave traces of a transfer switch......................................................................... 87
Figure 6.11: Bipolar configuration in normal operation ........................................................................... 88
Figure 6.12: The operating sequence of transfer switches when a fault occurs on pole 1................ 88
Figure 6.13 Steps of pole 2 switch from the earth return to the metallic return.................................. 89
Figure 6.14: The structure of ±800 kV HVDC transfer switch prototype (Peng, et al., 2012)......... 90
Figure 6.15: Circuit of a double-breaker passive oscillation DC transfer switch ................................ 91
Figure 6.16: Measured waveforms of the interruption test (Peng, et al., 2012)................................. 91
Figure 6.17: Diagram of Hokkaido-Honshu HVDC Link............................................................................ 91
Figure 6.18: The MRTS in the Hokkaido-Honshu link ................................................................................. 92
Figure 6.19: Typical waveforms of EMTP analysis based on customer specified values................... 93
Figure 6.20: The configuration of a MRTS in a converter station ........................................................... 96
Figure 6.21: Photo of the MRTS in Jeju....................................................................................................... 96
Figure 6.22: A gas-insulated 320 kV DC switchgear................................................................................ 99
Figure 7.1: Series connected converters, with HVDC bypass switches (BPS) and bypass disconnecting
switch (BPD) in parallel..................................................................................................................................101
Figure 7.2: Series connected converters, without bypass disconnecting switches (BPD) in parallel to
the converters ..................................................................................................................................................102
Figure 7.3: Voltage distribution across the four switching units of high- and low-voltage HVDC bypass
switches for converters of 800 kV having two valve groups and thus 200 kV across each switching
unit.....................................................................................................................................................................103
Figure 7.4: Normal operation: the current flows through both valve groups. ....................................105
Figure 7.5: In bypass pair mode.................................................................................................................105
Figure 7.6: Valve group bypassed.............................................................................................................106
Figure 7.7: With closed BPS and BPD........................................................................................................106
Figure 7.8: For longer time operation, the BPS and CDs are opened.................................................106
Figure 7.9: During operation with reduced voltage (one valve group bypassed)............................108
Figure 7.10: During commutation process from BPD to BPS...................................................................108
Figure 7.11: Completed commutation from BPD to BPS. ........................................................................108
Figure 7.12: During commutation process from BPS to valve group. ...................................................108
Figure 7.13: After successful current commutation from BPS back to the valve group.....................109
Figure 7.14: High-voltage segment (400 – 800 kV) HVDC bypass switch during high-voltage test.
...........................................................................................................................................................................111
Figure 7.15: Low-voltage segment (0 – 400 kV) HVDC bypass switch during high-voltage test..112
Figure 8.1: Bipolar operation mode with electrode return path...........................................................118
Figure 8.2: bipolar operation mode with dedicated metallic return....................................................118
Figure 8.3: Current flow (red) in monopolar operation mode before (left) and after (right) a fault of
the electrode path (green)............................................................................................................................119
Figure 8.4: Earth fault and subsequent current sharing between electrode line (blue) and fault path
(green) ..............................................................................................................................................................120
Figure 8.5: NBS isolates the faulted converter pole................................................................................120
Figure 8.6: Equivalent circuit diagram for HSES switching requirements (indices N-neutral bus, EL-
electrode line, E-earth path, EE-earth electrode).....................................................................................121
Figure 8.7 – HSES in project New Zealand Pole 3 - Haywards converter station............................123
Figure 8.8: HSES in the project Skagerrak 4 – Kristiansand converter station ..................................123
Figure 9.1: Four-terminal system equipped with HVDC paralleling switches (PS).............................126
Figure 9.2: Rigid-bipolar configuration with HVDC paralleling switches (PS) and bypass switches
(BPS)..................................................................................................................................................................128
Figure 9.3: Example arrangement of DC line/ cable paralleling switches for a bipolar HVDC scheme
...........................................................................................................................................................................128
Figure 9.4: Example arrangement for parallel operation of separate bipolar HVDC schemes....130
Figure 9.5: DC paralleling switches installed at Manitoba Hydro’s Bipole I and Bipole II..............131

15
Figure 9.6: 800 kV PS during factory tests (Skytt, et al., September 2015).....................................132
Figure 10.1: Schematic of a fault interruption process with current through (solid thick line) and
voltage across the HVDC CB (dashed lines) as a function of time........................................................136
Figure 10.2: Schematic of a nominal current interruption process with current through (solid thick line)
and TIV, the voltage across the HVDC CB (dashed thick line) as a function of time.........................140
Figure 10.3: Single line diagram of HVDC system in case of a DC fault ...........................................141
Figure 10.4: Example of representative fault current development....................................................141
Figure 10.5: Short-circuit current characteristics in rectifier (left) and inverter when a fault occurs in
a LCC system ...................................................................................................................................................143
Figure 10.6: Voltage characteristics in rectifier (left) and inverter when a fault occurs in a LCC system
...........................................................................................................................................................................144
Figure 10.7: Fault current in half and full bridge cells............................................................................144
Figure 10.8: HVDC system configurations .................................................................................................144
Figure 10.9: Pole-to-earth fault current paths in a VSC HVDC system ...............................................145
Figure 10.10: Current and voltage during pole-to-earth fault in a low impedance earthed monopolar
VSC HVDC system..........................................................................................................................................145
Figure 10.11: Voltage during pole-to-earth fault in a high impedance earthed monopolar VSC HVDC
system................................................................................................................................................................146
Figure 10.12: Current and voltage during pole-to-earth fault in a bipolar VSC HVDC system....146
Figure 10.13: Pole-to-pole fault current paths in a MMC VSC HVDC system ...................................147
Figure 10.14: current and voltage during a pole-to-pole fault in a VSC HVDC symmetric monopole
system................................................................................................................................................................147
Figure 10.15: Current and voltage during a pole-to-pole fault in a bipolar VSC HVDC system..148
Figure 10.16: Comparison of fault current behavior in different system configurations..................148
Figure 10.17: Current in AC (left) and DC systems during a mixed fault ...........................................149
Figure 10.18: Effect of a DC reactor (DCL) on fault current waveform..............................................150
Figure 10.19: Temporary DC pole-to-earth voltage profiles in a DC grid. The time and voltage limits
depend on technology and topology of the DC grid. The scales are used for illustration only (CIGRÉ
TB 657, 2011).................................................................................................................................................152
Figure 10.20: Example of DC voltage behavior across a four terminal DC network after a fault
occurrence (Tahata, et al., 2014)................................................................................................................153
Figure 10.21: Relationship between DC reactor value and DC CB fault clearing time interval at
remote terminal (240 km away from the fault)........................................................................................154
Figure 10.22: Equivalent for DC current breaking ..................................................................................155
Figure 11.1: Hybrid CB (left) and circuit breaker with oscillation principle (right). ..........................159
Figure 11.2: Application voltage of different semiconductor materials (Madjour, 2014). .............161
Figure 11.3: Variation of on-state resistance vs. breakdown voltage (Semiconductor Today, 2012)
...........................................................................................................................................................................162
Figure 11.4: Possible SiC application voltages and devices (Singh, 2011) .......................................162
Figure 11.5: Device ratings possible future trend as given by EPRI (Adapa, 2014)........................162
Figure 11.6: Parallel surge arresters for protection of series compensation......................................163
Figure 11.7: DC circuit breaker and surge arrester for transient overvoltage protection (5) and
system source voltage and inductance and a permanent fault.............................................................163
Figure 11.8: Current-voltage characteristic of a surge arrester...........................................................164
Figure 11.9: Ultra-fast disconnector in closed position (left) and open position (right)....................165
Figure 11.10: Separating forces acting on two permanent magnets or on two coils with a common
current through them ......................................................................................................................................166
Figure 11.11: Configuration of high-speed electromagnetic repulsion operating mechanism........166
Figure 11.12: Double sided coil actuator (left) and Thomson actuator (right) (Bissal, et al., 2015)
...........................................................................................................................................................................167
Figure 11.13: Electrical diagram of the drive for the Thomson actuator and the moving armature
acting on the mechanical switch (Bissal, et al., 2012)..............................................................................167
Figure 11.14: Coil and armature for a Thomson actuator (Bissal, et al., 2015)................................168
Figure 11.15: Examples of coil currents, forces and velocities for a Thomson coil actuator and a
double sided coil actuator (Bissal, et al., 2012).......................................................................................168
Figure 12.1: Passive oscillation interruption principle .............................................................................169

16
Figure 12.2: (A) Conceptual view and (B) circuit diagram of the 500 kV topology 1 circuit breaker
...........................................................................................................................................................................170
Figure 12.3: Schematic of the 500 kV topology 2 HVDC circuit breaker ..........................................171
Figure 12.4: Configuration (left); experimental result (middle); switching details (right)...............172
Figure 13.1: Basic operating principle of a HVDC circuit breaker with active current injection principle
(Franck, 2011).................................................................................................................................................173
Figure 13.2: Configuration and interruption of active injection scheme HVDC CB (Tahata, et al., 2014)
...........................................................................................................................................................................174
Figure 13.3: DC current interruption phenomenon by active injection scheme...................................175
Figure 13.4: Testing configuration of a HVDC circuit breaker (Tahata, et al., 2014)......................176
Figure 13.5: Voltage and current characteristics during DC 16 kA (left) and DC 5 kA (right)
interruption. The HVDC circuit breaker trips 2 ms after test current starts to flow (Tahata, et al., 2014)
...........................................................................................................................................................................176
Figure 13.6: Schematic circuit diagram of a HVDC circuit breaker with active current injection
principle (Eriksson, et al., 2014) ..................................................................................................................177
Figure 13.7: Breaker current and counter voltage during fault current test 10 kA. The breaker is
tripped approximately 1 ms after the test current starts to flow (Eriksson, et al., 2014)................177
Figure 13.8: (a) Monopole layout of current injection circuit breaker (b) Bipolar layout of current
injection circuit breaker (Wang & Marquardt, 2013) ............................................................................178
Figure 13.9: Detailed layout of current injection DC circuit breaker (Wang & Marquardt, 2013)
...........................................................................................................................................................................178
Figure 13.10: (a) Simulation results for the input current and voltage (b) Simulation results for the
output VI current and voltage (Wang & Marquardt, 2014).................................................................179
Figure 13.11: Active injection HVDC Circuit breaker (Kim, et al., 2016)............................................179
Figure 13.12: Current interrupting operation steps of HVDC CB (Kim, et al., 2016).......................180
Figure 13.13: Experimental result of current interruption (Kim, et al., 2016) ....................................181
Figure 14.1: Power electronic circuit breaker: (1) power electronic switching component, (2) energy
dissipation and overvoltage protection MOSA element and (3) residual current breaker.............184
Figure 14.2: The voltages and currents within the power electronic HVDC circuit breaker; a) line
current and voltage (as seen at the non-faulted side of the CB), b) currents through the CB branches
– I1 (blue) through the PE element and I2 (green) through the MOSA..................................................184
Figure 14.3: High-current test circuit of IGBT modules (Häfner & Jacobson, 2011).........................185
Figure 14.4: Maximum stress tests on the BIGTs (Rahimo, et al., 2014)..............................................186
Figure 14.5: Proposed power electronic DC circuit breaker topologies: (i) bi-directional IGBT based
module (Häfner & Jacobson, 2011), (ii) full bridge IGBT cell (Zhou, et al., 2015), (iii) GCT based
module (Meyer, et al., 2005) and (iv) example of thyristor based forced commutation breaker
(Meyer, et al., 2004).....................................................................................................................................187
Figure 15.1: Simplified sketch of a hybrid circuit breaker. ...................................................................190
Figure 15.2: Line current and voltage upstream the circuit breaker..................................................190
Figure 15.3: The currents through the three branches of the DC circuit breaker in Figure 15.1. ...191
Figure 15.4: Hybrid HVDC circuit breaker concept 1.............................................................................192
Figure 15.5: Different states of current interruption in hybrid breaker concept 1. Upper: normal
conduction; centre: commutation into main breaker; bottom: counter voltage generation in arrester.
...........................................................................................................................................................................192
Figure 15.6: Current interruption and current limiting mode (Häfner & Jacobson, 2011)...............193
Figure 15.7: Current interruption test showing the current through and voltage across the main
breaker (Derakhshanfar, et al., 2014).......................................................................................................194
Figure 15.8: Building blocks for the hybrid high-voltage DC circuit breaker concept 2..................194
Figure 15.9: Electrical diagram for the hybrid high-voltage DC circuit breaker concept 2
(Grieshaber, et al., 2014). ...........................................................................................................................195
Figure 15.10: Current interruption stages of hybrid HVDC CB concept 2..........................................196
Figure 15.11: Superimposed oscillogram with prospective (green) and interrupted current (blue) and
current in the surge arrester (red), voltage across the circuit breaker (violet, right axis) (Grieshaber,
et al., 2014).....................................................................................................................................................197
Figure 15.12: Schematic of the full-bridge based hybrid HVDC breaker concept 3 (left). A zoom into
the full-bridge sub-module is shown on the right......................................................................................198

17
Figure 15.13: Switching sequence with current flow indicated by a bold line. In steady state "closed"
position (top left) the current flows through the main branch. During interruption the current is briefly
transferred into the transfer branch (top right and then bottom left) and the absorber branch (bottom
right) and eventually the breaker reaches steady state "open" position (bottom right)..................198
Figure 15.14: Test result with current (blue, left y-axis) and voltage (green, right y-axis) across the
CB (Zhou, et al., 2015). .................................................................................................................................199
Figure 16.1: Example of HVDC circuit breaker topologies (MS: Making Switch, PE: Power Electronic
switch)................................................................................................................................................................202
Figure 16.2: Timing sequence for a breaker without pre-activations and/or a protection system with
only one trip order.........................................................................................................................................206
Figure 16.3: Timing sequence for a breaker with pre-activation in a protection system with multiple
orders (see also Figure 10.1, which includes relevant waveshapes)....................................................206
Figure 16.4: Fault neutralization time as a function of the selection time for different CB technologies.
...........................................................................................................................................................................207
Figure 18.1: Hybrid HVDC circuit breaker test circuit (Callavik, et al., 2012) ..................................218
Figure 18.2: Verification of current interruption and counter voltage build-up capability of the main
breaker (Callavik, et al., 2012) ..................................................................................................................218
Figure 18.3 HVDC circuit breaker test circuit (two superposed L-C circuits) (Grieshaber & Penache,
2014)................................................................................................................................................................219
Figure 18.4 Interruption test results using superposition of high-frequency LC circuit on low frequency
LC circuit (Grieshaber & Penache, 2014)..................................................................................................220
Figure 18.5: Test circuit of the sub-module and control unit (Zhou, et al., 2015) ..............................220
Figure 18.6: A test circuit with ideal DC source........................................................................................221
Figure 18.7: Test circuit using AC generator(s).........................................................................................223
Figure 18.8: Test circuit by charged reactor method..............................................................................224
Figure 18.9: Test circuit by charged capacitor.........................................................................................224
Figure 18.10: Prospective fault currents of test circuits (Smeets, et al., October, 2015).................225
Figure 18.11: (a) current; (b) voltage across breaker; (c) source voltage and (d) arrester energy at
fault clearance with hybrid HVDC CB in the basic test circuits. In the 16,7 Hz circuit, the fault initiation
angle (time) is 4,3 ms before voltage peak, in the 50 Hz circuit this is 1,44 ms before voltage peak.
...........................................................................................................................................................................226
Figure 18.12: Diagram of commutation test circuit..................................................................................227
Figure 18.13: Oscillograms of commutation test results..........................................................................227

18
Tables
Table 0-1 List of abbreviations and acronyms........................................................................................... 19
Table 2-1: Classification and duties (simplified) of HVDC switchgear.................................................. 28
Table 3-1: Voltage, temperature and power levels for different cable technologies....................... 38
Table 3-2: Examples of point-to-point LCC HVDC projects outside China........................................... 41
Table 3-3: Examples of point-to-point LCC HVDC projects in China.................................................... 41
Table 3-4: Examples of point-to-point VSC HVDC projects.................................................................... 42
Table 3-5: Overview of the Kitahon and Kii-channel HVDC links........................................................... 43
Table 3-6: Examples of planned radial MTDC projects........................................................................... 49
Table 4-1: Major switching duties of HVDC DS applied to a bipolar LCC HVDC system................. 60
Table 4-2: Specifications of HVDC DSs....................................................................................................... 63
Table 4-3: Specifications of HVDC DS in Japan........................................................................................ 64
Table 4-4: Specifications of HVDC DS used in Yunnan-Guangdong project in China........................ 65
Table 4-5: Specifications of HVDC DS used in Hami - Zhengzhou project in China ........................... 65
Table 4-6: Specifications of HVDC DS used in Sanxia - Guangdong project in China ..................... 66
Table 4-7: Specifications of HVDC DS used in Cook Straight project in New Zealand..................... 66
Table 4-8: Specifications of HVDC DS used in MT-LCC HVDC project in Canada............................. 67
Table 4-9: Specifications of HVDC DS used in Jeju - Jindo project in South Korea ........................... 67
Table 4-10: Bus transfer operation simulation results ............................................................................... 68
Table 4-11: Line transfer full load condition simulation results ............................................................... 69
Table 5-1: Summary of earthing switches ................................................................................................... 75
Table 6-1: Ratings of the MRTS applied on Hokkaido-Honshu link........................................................ 92
Table 6-2: Parameters of the oil circuit breaker........................................................................................ 93
Table 6-3: Parameters of the trigger gap.................................................................................................. 93
Table 6-4: Parameters of commutation capacitor ..................................................................................... 94
Table 6-5: Parameters of the MOSA........................................................................................................... 95
Table 6-6: The DC transfer Switches in a test lab ..................................................................................... 97
Table 6-7: The DC transfer Switches in a test lab ..................................................................................... 97
Table 6-8: Performance of HVDC transfer switches in different HVDC transmission systems........... 98
Table 6-9: Highest requirement of the years 2010-2014 (Liljestrand & Steiger, 2014).................. 98
Table 7-1: Requirements for the high-voltage segment of BPS in selected installations..................110
Table 7-2: Requirements for low-voltage segment BPS in selected installations...............................111
Table 7-3: Voltage requirements for HVDC bypass switches in selected installations.....................112
Table 7-4: Mozambique, Project Cahora Bassa, mid 1970s.................................................................113
Table 7-5: Canada, Project Nelson River Bipole 1, mid 1970’s vintage (bypass switches were
replaced in mid-2010’s). Courtesy of Manitoba Hydro.........................................................................114
Table 7-6: Canada, Project Nelson River Bipole 2, mid 1980s............................................................114
Table 7-7: China, Project Nouzhadu-Guangdong, mid 2000s .............................................................115
Table 7-8: Japan, GIS HVDC bypass switch during test........................................................................115
Table 8-1: Overview of requirements of some existing HSES...............................................................122
Table 11-1: Semiconductor Losses Comparison........................................................................................160
Table 11-2: Properties of interest for wide band gap and other semiconductor materials...........161
Table 12-1: Summary of passive oscillation principle HVDC circuit breaker specifications............172
Table 13-1: Overview of HVDC active current injection circuit breakers...........................................182
Table 14-1: Summary of advantages and disadvantages of power electronic HVDC circuit breakers
...........................................................................................................................................................................183
Table 15-1: Advantages and disadvantages of mechanical and semiconductor switches..............189
Table 16-1: HVDC circuit breaker comparison summary.......................................................................201
Table 16-2: Circuit breaker Internal Current Commutation Time Comparison...................................202
Table 16-3: Circuit breaker interruption capability comparison..........................................................203
Table 16-4: Circuit breaker on-state losses comparison ........................................................................203
Table 16-5: rate of rise of fault current....................................................................................................204
Table 16-6: Circuit breaker installation costs comparison .....................................................................204

19
Table 0-1 List of abbreviations and acronyms
Abbreviation/Acronyms Definition
BPD Bypass Disconnecting Switch
BPS Bypass Switch
BTB Back-to-back
CB Circuit Breaker
CD Converter Disconnecting Switch
CES Converter Earthing Switch
DMR Dedicated Metallic Return
DNR Dedicated Neutral Return
ELD
EMTP
Electrode Line Disconnecting Switch
Electro-Magnetic Transient Program
ERTS Earth Return Transfer Switch
FD Filter Disconnecting Switch
FES Filter Earthing Switch
GTO Gate Turn-off Thyristor
HSES High-Speed Earthing Switch
HVAC High-Voltage Alternating Current
HVDC High-Voltage Direct Current
HVDC CB High-voltage Direct Current Circuit Breaker
IGBT Insulated Gate Bipolar Transistor
ITIV Initial Transient Interruption Voltage
LCC Line Commutated Converter
LD Line Disconnecting Switch
LIWV Lightning Impulse Withstand Voltage
LND
LPD
Line to Neutral Disconnecting Switch
Line Pole Disconnecting Switch
MMC Modular Multi-Level Converter
MOSA Metal Oxide Surge Arrester
MOV Metal Oxide Varistor
MRTS Metallic Return Transfer Switch
MT Multi-terminal
MTDC Multi-terminal HVDC
NBD Neutral Bus Disconnecting Switch
NBED Neutral Bus Earthing Disconnecting Switch
NBES Neutral Bus Earthing Switch
NBS Neutral Bus Switch
O-C-O Open-Close-Open

20
PLES Pole Line Earthing Switch
PPES Pole Paralleling Earthing Switch
PS Paralleling Switch
PWM Pulse Width Modulation
SD Substation Disconnecting Switch
SES Substation Earthing Switch
SIWV Switching Impulse Withstand Voltage
SPPD Substation Pole Paralleling Disconnecting Switch
TIV
TRV
Transient Interruption Voltage
Transient Recovery Voltage
VCB Vacuum Circuit Breaker
VI Vacuum Interrupter
VSC Voltage Source Converter
XLPE Cross-Linked Polyethylene

21
1 INTRODUCTION
The global trend of increasing interest and investment in HVDC projects has also manifested itself in
a considerable activity within CIGRÉ regarding HVDC, in particular HVDC grids. In 2013, WG B4.52
concluded [TB 533] that HVDC grids are in principle feasible, but several challenges must be
addressed and solved. To address these challenges, further working groups have been launched.
Two examples of these are: “Grid Codes” (WG B4.56, [TB 657]) and “Grid protection and control”
(JWG B4/B5.59).
When planning and building HVDC grids, the issues of system stability and equipment stresses are
the most fundamental ones. All equipment needs to be designed (and tested) to comply with the
anticipated stresses. This applies to all components. The present joint working group (JWG
A3/B4.34) is mainly focused on switching equipment having mechanical subcomponents for one or
more switching function(s).
Today, a broad number of different switchgear is involved in each HVDC project, but so far no
standardization for HVDC switchgear exists. Performance specifications are derived for each
individual (typically point-to-point) project. Moreover, the HVDC schemes are always single-vendor
solutions, thus the performance specifications are not as publicly known as from AC projects and are
almost never part of the tender. It is not possible to compare the performance specifications of
equipment from different projects. It is only possible to give an overview on typical HVDC switchgear
and variety of specifications.
Most HVDC switchgear today are based on AC switchgear with a few appropriate adaptations.
Consequently, the given performance specifications should not be misinterpreted as limit
performances of these devices. This is very much in contrast to AC switchgear, where the devices
have reached their individual limit performance after years of development and progressive
improvement.
In this context, the objectives of JWG A3/B4.34 “Technical Requirements and Specifications of State-
of-the-Art DC switching equipment” are formulated as:
1. Review the technical requirements of DC switching equipment for different applications such as
multi-terminal DC systems and off-shore wind farm connections.
2. Investigate the technical capabilities and limitations of existing and projected switching
equipment mainly with mechanical operating drives and then foresee the future capability of
these DC switching equipment.
3. Facilitate the development of new DC switching equipment by identifying the gaps between
existing performance specifications and future requirements.
Although grid protection and HVDC circuit breakers are presently the most discussed topics, the
working group included also other switchgear. These types of switchgear, which are already applied
in existing point-to-point projects, outweigh the circuit breakers in numbers by far and it is foreseen
that they will remain equally important in future HVDC grids. As an example, HVDC paralleling
switches will be used to connect and disconnect converters from the grid under normal operating
conditions, even though CB could be used as well. This is different in AC systems, where the costs and
size of CBs is not as much higher than other types of switchgear.
The joint working group JWG A3/B4.34 started its operation early 2014 and held its final meeting
in August 2016. The working group was built from experts of both CIGRÉ study committees, the high-
voltage equipment study committee A3 and the power electronics study committee B4. The
competences of the experts are wide, covering experience from working for manufacturers, utilities,
consultants, and in academia. Despite the growing interest in HVDC and HVDC grids, still there is a
lack of publicly accessible literature and documented field experience in the areas of requirement
specifications for HVDC switchgear (even on the basic methods used to derive these specifications)
and the existing performance specifications. It was essential that the experts collected this information
in the framework of this working group and strived to compile and pass on these information in a
format as structured as possible.

22
The present technical brochure is the result of these endeavors and it is believed that it constitutes an
unprecedented overview on existing HVDC switchgear.
The idea behind the structure of this brochure is as follows:
The first two chapters introduce the reader to the topic of switching in HVDC in the form of an
overview. It starts with the theoretical basics, explaining also the fundamental differences between
current interruption and current commutation duties. Based on a generic HVDC substation that
contains nearly all different types of HVDC switchgear, the different duties of HVDC switchgear and
the nomenclature are introduced.
The following chapters give a more detailed overview on the different types of HVDC switchgear.
They are all structured similarly, starting with a detailed description of the working principle, the
basic requirements and the switching principles. Then, an extensive overview on existing switchgear
is given, partly with illustrative pictures and detailed performance specifications, and partly in the
form of a table with a variety of installed examples. Most chapters conclude with the attempt of
providing an outlook towards future requirements, in particular in HVDC grids. The problem here is
that these grids practically do not exist, let alone switching equipment designed to serve in these
grids. Therefore, inevitably, this outlook is of preliminary and rather general nature, but it should
mainly serve the purpose of stimulating further investigations in this direction. Investigations with a
view to determine more precisely the requirement specifications, but also to improve the performance
of HVDC switchgear are required. The sequence of appearance of the different switchgear in this
TB is according to increasing switching complexity: starting with disconnecting and earthing switches,
continuing to transfer switches and finally to circuit breakers.
Chapter 4 is devoted to disconnecting switches, Chapter 5 to earthing switches. Chapter 6 contains
different transfer switches, such as the metal return transfer breaker, the earth return transfer switch,
and the neutral bus switch. The bypass switch, high-speed earthing switch (also called neutral bus
earthing switch), and paralleling switch are also transfer switches, but are dealt with in separate
Chapters 7, 8 and 9 respectively.
The second part of the brochure is devoted to circuit breakers. These are by far the most discussed
type of switchgear today, but only prototypes have been presented and tested up to now (for use
in VSC based grids). During the working group discussions, it became evident that even the basic
nomenclature varied between experts, in particular between the A3 and B4 communities. Chapter
10 is thus devoted to harmonization and summarizes and defines the basic requirements such as
timing, fault currents, and system stability.
Chapter 11 describes the basic building blocks that each circuit breaker topology requires, such as
the energy absorption elements, fast operating mechanisms, power-electronic devices and residual
current breakers.
Chapters 12 - 15 describe the different circuit breaker topologies: those building on current zero
creation by passive oscillation principles, by oscillation principles with active current injection, pure
power electronic, and hybrid mechanical and power electronic based circuit breakers, respectively.
A comparison of advantages and disadvantages of these different topologies, based on existing
prototypes, is given in Chapter 16.
Chapter 17 then presents a comparison between existing and required performance of all types of
switchgear and can be seen as the condensed summary of the preceding Chapters. As stated above,
the identification of these gaps shall stimulate further research and development.
Inevitably, multi-vendor grids will only be possible after certain standards and grid codes have been
defined and the equipment has been appropriately tested. An overview of the state-of-the art in
testing HVDC circuit breakers is given in Chapter 18.
The present JWG A3/B4.34 tried to harmonize and complement as much as possible with other
activities. The most relevant ones to name here are:
 CENELEC (the European Committee for electrotechnical standardization) established a
working group “Technical Guidelines for First HVDC Grids” which was working on a first set

23
of functional specifications of the main equipment and HVDC Grid Controllers. This work has
led to a follow-up group
 CENELEC Working Group TC8x WG06, which aims at creating clear functional specifications
for many aspects of HVDC Grid Systems.
 CIGRÉ WG B4.56 - Guidelines for the preparation of “connection agreements” or “Grid
Codes” for HVDC grids. With relevance for HVDC switchgear, this working group deals with
the derivation of technical performance specifications: the short-circuit currents that have to
be expected in HVDC grid and the DC-side harmonics that may exist in the HVDC grid
(injected by the converters connected to the grid).
 JWG B4/B5.59 - Control and Protection of HVDC Grids. In this group, potentially several
aspects that influence the required performance of HVDC switchgear will be investigated:
the use of converters with fault current blocking capability, methods to slow down the
progression of the DC voltage collapse after a DC-side fault, and the entire HVDC Grid
protection system e.g. the measurement, fault detection and interruption devices.
 B4.57 and B4.58 have jointly developed a multi-terminal HVDC (MTDC) network, which can
be used to investigate requirements for HVDC switchgear. The model is not aimed at transient
studies, but can suitably be extended for protection studies and the calculation of transient
current and voltage stresses.
 IEC TC 115 WG9 is drafting a standard on HVDC power system requirements for DC side
equipment (including DC switchgear but excluding DC circuit breakers)
 IEC TC 17A started an ad hoc WG 4 to investigate the market relevance of DC switchgear
and the need for standardization
 Various Chinese national standards have been issued:
GB/T 25307 (2010) on HVDC bypass switches
GB/T 25309 (2010) on HVDC transfer switches
GB/T 25091 (2010) on HVDC disconnecting- and earthing switches
A GB standard on HVDC circuit breakers is being drafted
 The EU (European Union) project PROMOTioN: Progress on Meshed HVDC Offshore
Transmission Networks (https://www.promotion-offshore.net/), started 2016 on working to
overcome technological hurdles set by lack of experience with protection systems, multi-
vendor interoperability and HVDC circuit breakers as well as by high converter costs.
Despite the advancements of JWG A3/B4.34 and ongoing efforts of other groups, there is still
a lot of work to be done to define the stresses to which equipment in the HVDC grid will be
exposed. This work can continue in working groups of different organizations.

24

TECHNICAL REQUIREMENTS AND SPECIFICATIONS OF STATE-OF-THE-ART HVDC SWITCHING EQUIPMENT

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