Use of FACTS and HVDC for Power
System Interconnection and
Grid Enhancement
Günther Beck, Wilfried Breuer,
Dusan Povh, Dietmar Retzmann,
Erwin Teltsch
Siemens Power Transmission and
Distribution (PTD),
Germany
1 / 33
0. Overview
Interconnection of power systems with either AC or DC links may offer important technical,
economical and environmental advantages. In the future of liberalised power markets, these
advantages will become even more important: pooling of large power stations, sharing of
spinning reserve, use of most economic energy resources, as well as ecological constraints:
nuclear power stations at selected locations, hydro energy from remote areas, solar energy
from steppes and deserts, and connection of large off-shore wind farms.
Examples of large interconnected systems are the Western and Eastern European systems
UCTE (installed capacity 530 GW) and IPS/UPS (315 GW), which are planned to be
interconnected in the future. Up to now, the power systems in China are more separated:
China with 7 large inter-provincial grids and India with 4 large regional grids. However,
interconnections by AC and increasingly by DC are in progress in Far East, too.
Since the 60s, FACTS (Flexible AC Transmission Systems) and HVDC (High Voltage Direct
Current) transmission have developed into a mature technology with high power ratings.
Transmission ratings of 3 GW over large distances with just one bipolar DC transmission
system are state of the art in many grids today. In China, however, there are new transmission
schemes in the planning phase with ratings of 4 - 6 GW (at +/- 800 kV DC and 1000 kV AC).
Reason for such high ratings is the need for bulk power transmission corridors with 20 GW
for system interconnection.
In general, for transmission distances above 700 km, DC transmission is more economical
than AC transmission (≥ 1000 MW). With submarine cables, transmission levels of up to 600
- 800 MW over distances of nearly 300 km have already been attained, and cable transmission
lengths of up to 1,300 km are in the planning stage. As a multi-terminal system, HVDC can
also be connected at several points with the surrounding AC networks. FACTS is applicable
in parallel connection (SVC, Static VAR Compensator – STATCOM, Static Synchronous
Compensator) or in series connection (FSC, Fixed Series Compensation - TCSC, Thyristor
Controlled Series Compensation – TPSC, Thyristor Protected Series Compensation) or in
combination of both (UPFC, Unified Power Flow Controller) to control load flow and to
improve dynamic conditions. Rating of SVCs is up to 800 MVAr, series FACTS devices are
implemented on 550 and 735 kV level to increase the line transmission capacity up to several
GW.
2 / 33
In the paper, benefits of FACTS and HVDC for system interconnection and for grid
enhancement are depicted, and preferences of applications are explained. Study and project
examples are given.
1. Development of Power Transmission
The development of power systems follows the requirements to transmit power from
generation to the consumers. With an increased demand for energy and the construction of
new generation plants, first built close and then at remote locations from the load centers, the
complexity of power systems has grown. This development is schematically shown in Fig. 1.
Use of new Technologies
Right of Way Problems, Transmission Bottlenecks
Power Consumption
per Capita
Least-Cost
Planning
High Energy Imports
Decentralized Power Supplies
More Investments in Distribution
Lifetime Extension, Monitoring
Increased Automation
Demand for Power Quality
System Interconnections
Long - Distance
Transmission
(HVAC, HVDC)
Introduction of
higher Voltage
Levels
Isolated small
Grids
Developing Countries
High Investments in Transmission Systems
Emerging Countries
Industrialized Countries
Fig. 1: Development of Power Systems and per Capita Consumption
To transport the energy from generation to consumers, the development of power systems
considers locations of expected load requirements on the one hand, and the suitable location
of power stations on the other hand. However, on a long-term basis, it can be expected that
the transmission systems will stagnate in their development, since an increasing part of power
generation will be transferred into the distribution or low voltage networks in the future [1, 3].
Since the load flows existing today can change considerably, this altering environment
decisively influences further development and optimization of transmission networks. The
ancillary functions required for smooth operation of the networks, such as frequency control,
load-flow control, reactive-power and voltage control, as well as the responsibility for system
3 / 33
security, are in the hands of the system operator. To support the operation and to increase the
reliability of heavily loaded networks, FACTS and HVDC need to be installed. Higher
investments into grid interconnections must be made to achieve cost benefits.
Based on a large number of studies on power system development in different world regions,
the following general trends can be expected:
 Increasing Power Demand - from
3,560 GW in 2000 to 5,700 GW in 2020
 Strong Environmental Constraints – Limitation
for Power Plant Expansions
 Natural Energy Resources far away from
Load Centers
 Severe Right of Way Constraints
¾ A strong Issue in many Countries, especially in Europe
As listed below, power system interconnections offer the necessary benefits regarding these
constraints. They are generally valid and do not depend on the kind of the interconnection.

Possibility to use larger and more economical
Power Plants

Reduction of the necessary Reserve Capacity in
the System

Utilization of most favorable Energy Resources

Flexibility of building new Power Plants at
favorable Locations

Increase of Reliability in the Systems

Reduction of Losses by an optimized System
Operation
With the size of interconnected systems, however, the technical and economical advantages
diminish and the required additional investments for system enlargements increase. In
addition to that, the transmission costs increase with the transmission distance. Considering
the current transmission costs of about 1-2 Cents per kWh and 1000 km, the advantages of the
energy taken from the interconnected systems over very long distances would not be
economical any more. The reasonable distance to transmit power still economically could be
therefore in the range of up to 3000 km. These conditions, however, could possibly change if
strong political efforts will support the use of renewable energy in remote areas in large scale,
independent from production and transmission costs. Strategies for the development of large
4 / 33
power systems go clearly in the direction of hybrid transmissions, consisting of HVDC and
HVAC interconnections among regional sub-systems. Such interconnected systems have
significant technical and reliability advantages [3-6].
Fig. 2 shows schematically such a hybrid system using HVDC and FACTS. Power exchange
in the neighboring areas of interconnected systems offering most advantages can be realized
by AC links, preferably including FACTS for increased transmission capacity and for stability
reasons. The transmission of larger power blocks over longer distances should, however, be
utilized by the HVDC transmissions directly to the locations of power demand. HVDC can be
realized as direct coupler without a DC line – the so-called Back-to-Back solution (B2) or as
point to point long distance transmission via DC line. The HVDC links can strengthen the AC
interconnections at the same time, in order to avoid possible dynamic problems which exist in
such huge interconnections [3, 6].
System
G
System
A
System
B
System
C
System
D
System
E
System
F
Large
LargeSystem
SystemInterconnections,
Interconnections,using
usingHVDC
HVDCand FACTS
HVDC - Long Distance DC Transmission
HVDC B2B - via AC Lines
High Voltage AC Transmission & FACTS
DC – the Stability Booster and
“Firewall” against “Blackout”
“Countermeasures”
against large
Blackouts
Fig. 2: Large Power System Interconnections – Benefits of Hybrid Solutions
Long-term developments in power industry depend on expectations for future political,
financial and technical conditions. For the last decade, however, the developments have been
strongly driven by the globalization, leading to deregulation and liberalization. The world
markets have been gradually opened, with different speed in different countries. This
transition of economies brought many advantages, but also disadvantages in some fields. At
5 / 33
the same time, social and environmental aspects became more and more important, even if
they are, in some way, in contradiction with the globalization of the economy.
Investments in Power Industry
Generation
Transmission
~ 20 %
~ 40 %
Distribution
~ 40 %
Depending on
Grid Structure
Fig. 3: Investments in Power Industry
Fig. 3 shows the typical sharing of investments in power generation, transmission and
distribution. These values depend, however, on the specific structure of the systems. The
estimation of the requested investments in the power industry for the next 30 years is US$ 10
trillion, or roughly US$ 350 billion per year. Based on this, about US$ 70 billion per year
should be invested in power transmission [1].
Deregulated Markets:
Regulated Markets:
z
one Owner - the Utility
z
different Owners & Players
Generation
Transmission
³
can be
Distribution
or
-neck
for Cash-Flow &
Return on Investments
Fig. 4: Transmission Systems – The “VIPs” of the Power Market
6 / 33
Although the sharing of transmission investments is only 20 % of the total sum, its
importance is in fact high: transmission can be the key for cash-flow and return on
investments, or just a bottleneck causing limitations and supply interruptions. Thus,
transmission systems are the VIPs of the power market, as shown in Fig. 4.
60
GW
50
Worldwide installed HVDC
“Capacity”: 55 GW in 2005
40
30
An additional 48 GW are
expected from China
alone until 2020 !
20
10
This is 1.4 % of the Worldwide
installed Generation Capacity
0
1970
1980
1990
2000
2010
Sources: IEEE T&D Committee 2000 - Cigre WG B4-04 2003
Fig. 5: Development of DC Transmission: Worldwide installed Capacity
Fig. 5 shows the perspectives of DC transmission capacity worldwide. It can be seen that
China alone will be contributing significantly to this development because of its large
increase of economy (GDP) per year.
In Fig. 6 and 7, the transmission grid developments in China and India are depicted, leading
to very large hybrid interconnections with AC and DC solutions.
A large number of different FACTS and HVDC have been put into operation either as
commercial projects or prototypes. Fig. 8 gives an example of the Siemens applications
worldwide. Thus it appears that some areas are still “blank”, which is expected to change in
the future. In the figure, the number and the increase of large HVDC long-distance
transmission projects are also indicated.
The different technologies with FACTS and HVDC for grid enhancement using modern high
power electronics, as indicated in Fig. 8, are explained more detailed in the next sections.
7 / 33
Russian Power Grid
In total: 20 HVDC Interconnections
Initially:
Gezhouba-Shanghai
TianGuang
3G-ECPG I
GuiGuang I
3G-Guangdong
GuiGuang II
NECPG
NCPG
Wangqu Plant
Yangcheng Plant
NWCPG
SPPG
…
North Power Grid
plus
3 x B2B and
CCPG
Three Gorges
CSPG
ECPG
Center Power Grid
11 x HVDC
Long Distance
Transmissions
Jinshajiang
River
SCPG
Lanchangjiang
River
2005: 12 GW
2020: 60 GW
HPPG
South Power Grid
Tailand Power Grid
Sources: SP China, ICPS - 09/2001; State Grid Corp. China, 2003
Fig. 6: China goes Hybrid: AC plus 20 HVDC Interconnections
D E V E L O P M E N T O F N A T IO N A L G R ID
URI
P H A S E - III
(B y 2 0 1 2 )
W AGOORA
DULHASTI
R A VI S ATLU J
K IS H E N P U R
JU LLA N DHA R
TEHRI
MOGA
B A LLA B G AR H
(D E L H I R IN G )
C H IC K E N N E C K
A 'P U R
BHUTAN
M EERUT
H IS S A R
LU C K N O W
NR
B H IW A D I
30
G 'P U R
VARANASI
M ALA N PU R
S IN G R A U L I
MW
N A G D A B IN A
S IL IG U R I/B IR P A R A
KORBA
R A IP U R
CHANDRAPUR
1000M W
W
M
00
20
AM RAVATI
WR
DHABOL
L O N IK A N D
KOYNA
KARAD
ER
TALCHER
JEYPO RE
Source: Power Grid Corporation of India, 2003
G AZUW AKA
SR
X P LA N
W
V IJ A Y A W A D A
00
7 6 5 K V L IN E S
20
S IR S I
LEGEND
E X IS T IN G /
IX P L A N
NARENDRA
K A IG A
H IR M A
NER
K R IS H N A
NAGAR
R O U R KE LA B A N G L A
DESH
RAM AGUNDAM
KOLHAPUR
PONDA
BADARPUR
T IP A IM U K H
N .K .
S E O N I S IP A T
TAR AP U R A K O LA
PADGHE
K A TH ALGURI
M A R IA N I
KAHALGAON
V IN D H Y A CHAL
SATNA
K R IS H N A P A T N A M
4 0 0 K V L IN E S
H V D C B /B
C H IT T O O R
H V D C B IP O L E
M A N G A LO R E
B A N G A LO R E
HOSUR
SOUTH CHENNAI
S IN G A R P E T
CUDDALORE
K O Z H IK O D E
P U G A LU R
DW
KAYATHAR
EE
P
Fig. 7: Grid Extension in India - Hybrid AC plus DC
8 / 33
AN AND
HA
T R IV A N D R U M
R
NICOBA
KS
K A R A IK U D I
K AY AM KU LAM
ANDAM
LA
C O C H IN
D IH A N G D A M W E
M IS A
500M W
GANDHAR/
A M R E LI K AW A S
CHEGAON
VAPI
BHANDARA
P IP A V A V
B O IS A R
RANGANADI
B O N G A IG A O N
B 'S H A R IF
/B A R H
DEHGAM
TALA
PURNEA
M
L IM B D I
JETPUR
00
TEESTA
ARUN
M 'B A D
A LLAH A BA D
/U N N A O
AGRA
J A IP U R
S H IR O H I
ZERDA
Similar Perspectives
… as in China
X I P LAN
Lamar 2005
Virginia Smith 1987
Inez 1998
Spring Valley 1986
2 Dominion 2003
2 Marcy 2001-2003
Lugo 1985
3, 2 El Dorado
2006
Devers 2006
••
Nine Mile 2005
Dayton 2006
Porter 2006
Paul Sweet 1998
2 Adelanto 1995
•
•
• • •
• •
•••••• •
•
••• •• •
••
•
•• •
•
••
2 Midway 2004
3 Vincent 2000
Military Highway 2000
Eddy County 1992
Nopala 2006
La Pila 1999
Moyle MSC 2003
Brushy Hill 1988 Willington 1997
3 Montagnais 1993
Châteauguay 1984
Wien Südost 1993
2, 2 Gorakhpur
2, 2 Purnea
••
••
•
Dürnrohr 1983
•
.
2 Zem Zem 1983
•
•
• • ••
•
• •
•
•
Cano Limón 1997
Imperatriz 1999
Serra de Mesa 1999
Samambaia 2002
Acaray 1981
•
•
•
•
••
•
•
Baish 2005, •
•
Campina Grande 2000
Maputo 2003
Bom Jesus la Lapa 2002
•
••
2 Gooty 2003
Illovo
Athene
Impala
Muldersvlei 1997
2 Chuddapah 2003
•
2 Sabah 2006
• •
Kapal 1994
Barberton 2003
••
Limpio 2003
Atacama 1999
2 Hechi 2003
2, 2 Tian Guang 2003
3 Puti 2005
K.I. North 2004
Funil 2001
Ibiuna 2002
2 Yangcheng 2000
•
••
.
Samitah 2006
Iringa,
Shinyanga 2006
2006
Kanjin (Korea) 2002
•
2 Lucknow 2006
Fortaleza 1986
Ahafo 2006
Milagres 1988
Chinú 1998
1997
.
.•
Hoya Morena,
Jijona 2004
Welsh 1995
Laredo 2000 Benejama,
Seguin 1998 Saladas 2006
Kayenta 1990
Cerro Gordo 1999
3 Juile 2002
P. Dutra 1997
.
Ghusais,
Hamria,
Mankhool,
Satwa
Etzenricht 1993
Radsted 2006
Siems 2004
2 Pelham, 2 Harker,
2 Central, 1991-1994
Sullivan 1995
Jacinto 2000
•
2 Tecali 2002
Rejsby Hede 1997
Jember 1994
1994-1995
9 Powerlink,
Refurbishment
2007
•
Nebo 2007
Series
Status: 10-2005
Parallel
2 Kemps Creek 1989
Load Flow
FSC
SVC
B2B
NGH
MSC/R
UPFC
TPSC
STATCOM
CSC
TCSC
Flicker STATCOM
Plus 16 Projects for
HVDC Long Distance
Transmission …
8 alone between 2000 &
2005 in 4 Continents
Fig. 8: FACTS & HVDC worldwide – Example Siemens (ref. to Text)
2. Transmission Solutions with FACTS and HVDC
FACTS and HVDC use power electronic components and conventional equipment which can
be combined in different configurations for switching or controlling reactive power, and for
active power conversion. Conventional equipment (e.g. breakers, tap-changer transformers)
offer very low losses, but the switching speed is relatively slow. Power electronics can
provide high switching frequencies up to several kHz, but with an increase in losses. A view
on the different kinds of semiconductors is given in Fig. 9. In Fig. 10, the stepwise assembly
of the thyristors in modules and valve groups is shown.
Pellet of
LTT Thyristor
Pellet of
GTO / IGCT
Assembly of
Chips in IGBT
LTT = Light triggered Thyristor
IGCT = Insulated Gate commutated Thyristor
Fig. 9: High Power Semiconductors
9 / 33
IGBT = Insulated Gate bipolar Transistor
Valve Group - Example
Indoor for HVDC
Module
Thyristor
Valve Group - Example
Outdoor for FACTS
Module
Thyristor
Fig. 10: HVDC and FACTS - Advanced Power Electronics for High Voltage Systems
More Dynamics for better Power Quality:
z
Use of Power Electronic Circuits for Controlling P, V & Q
z
Parallel and/or Series Connection of Converters
Fast AC/DC and DC/AC Conversion
z
Transition from “slow” to “fast”
Thyristor
4-5 %
GTO
1-2 %
Switching
Frequency
> 1000 Hz
< 500 Hz
50/60 Hz
On-Off Transition 20 - 80 ms
Fig. 11: Use of Power Electronics for FACTS & HVDC Transient Performance and Losses
10 / 33
IGBT / IGCT
Losses
The dependency between transient performance and losses is depicted in Fig. 11. An example
of actual losses in a large HVDC project is given in section 5, Fig. 26.
Flexible AC Transmission Systems (FACTS) based on power electronics have been
developed to improve the performance of long distance AC transmission. The technology has
then been extended to the devices which can also control power flow. Excellent operating
experiences are available worldwide, and FACTS technology also became mature and
reliable.
Fig. 12 shows the principal configurations of FACTS devices. Main shunt connected FACTS
application is the Static Var Compensator with line-commutated thyristor technology, where
the maximum switching frequency in each phase element is limited by the “driving” system
frequency.
z
SVC - Static Var Compensator (Standard for Parallel Compensation)
z
STATCOM - Static Synchr. Compensator (Fast SVC, Flicker Compensation)
z
FSC - Fixed Series Compensation
z
TCSC - Thyristor Controlled Series Compensation
z
TPSC - Thyristor Protected Series Compensation
z
GPFC - Grid Power Flow Controller (FACTS-B2B)
z
UPFC – Unified Power Flow Controller
SVC / STATCOM
FSC
GPFC/UPFC
/ UPFC
AC
AC
AC
AC
AC
60 Hz
60 Hz
60 Hz
60 Hz
60 Hz
AC
50 or 60 Hz
/ TPSC
TCSC/TPSC
Fig. 12: FACTS - Flexible AC Transmission Systems: Support of Power Flow
A further development is STATCOM using voltage sourced converters. Both devices provide
fast voltage control, reactive power control and power oscillation damping features (POD). As
an option, SVC can control unbalanced system voltages. The developments of FACTS
technologies are depicted in Fig. 13. Static Var Compensation is mainly used to control
system voltage. There are hundreds of these devices in operation worldwide. For decades, it
has been a well developed technology, and the demand on SVC is further increasing.
Fixed series compensation is widely used to improve the stability by reducing the
transmission angle in long distance transmissions. A huge number of these applications are in
operation. If system conditions are more complex, Thyristor Controlled Series Compensation
11 / 33
is used. TCSC has already been applied in different projects for load-flow control, stability
improvement and to damp oscillations in interconnected systems.
Response Time
Breaker Delay
2 - 3 Cycles
1st Generation
2nd Generation
1- 2 Cycles
V-Control
3rd Generation
I-Control:
< 1 Cycle
Mechanically
Switched Devices
Thyristor Controlled
Components
Slow VARs
VSC Technology
GTO, IGBT, IGCT
Fast VARs
Fig. 13: FACTS – Technology Developments
Special FACTS devices are UPFC (Unified Power Flow Controller) and GPFC (Grid Power
Flow Controller) [2, 5]. UPFC combines a shunt connected STATCOM with a series
connected STATCOM (= S3C, Solid State Series Compensator), which can exchange energy
via a coupling capacitor. The CSC (Convertible Synchronous Compensator) in Fig. 8 uses a
UPFC which can be switched over into different applications with either two STATCOMs or
two S³Cs. GPFC is a special DC back-to-back link, which is designed for fast power and
voltage control at both terminals. In this manner, GPFC is a “FACTS Back-to-Back”, which
is less complex and expensive than the UPFC.
For most applications in AC transmission systems and for network interconnections, SVC,
FSC, TCSC and GPFC/B2B are fully sufficient to match the essential requirements of the
grid. STATCOM and UPFC are tailored solutions for special needs.
The basic configurations of HVDC are depicted in Fig. 14 and 15. HVDC operates as power
flow controller; it “forces P to flow”. In hybrid system configurations with synchronous
frequencies over the whole grid, HVDC offers a highly effective control of power flow. In
addition to that, in case of system faults, HVDC can either support the grid recovery, or it can
automatically split the systems like a “Firewall”, which is very helpful for Blackout
12 / 33
prevention in case of cascading events [3]. For bipolar applications, a second set of converters
with negative voltage plus coupling transformers is provided.
Power & Voltage Control
Fault Current Blocking
Back-to-Back - the short Link ...
Filters
Filters
fA = 50 Hz
Rating LDT:
130
130≤≤ kV
kV ≤≤ 800
800
300
300≤≤MW
MW≥≥ 4000
4000
B2B - Rating:
Example
fB = 60 Hz
... or with Cable/Line - the
Long Distance
Transmission
13,8
13,8 ≤≤ kV
kV ≤≤ 550
550
≤
MW
30
30 ≤ MW≤≤1200
1200
up to 1000 - 4000 km
Fig. 14: High Voltage DC Transmission – Basic Configurations
HVDC - High Voltage DC Transmission: It forces P to flow
z
Standard with Thyristors (Line-commutated Converter)
z
AC/DC and DC/AC conversion by Power Electronics
z
HVDCPLUS (Voltage-Sourced Converter - VSC)
z
HVDC can be combined with FACTS
z
V-Control included
HVDC-LDT - Long Distance Transmission
B2B - The Short Link
Back-to-Back Station
AC
60 Hz
AC
50 Hz
Submarine Cable Transmission
AC
AC
DC Cable
Long Distance OHL Transmission
AC
AC
DC Line
Fig. 15: HVDC - High Voltage DC Transmission: It forces P to flow
For system interconnections, an additional benefit of the HVDC is its incorporated faultcurrent limitation feature. HVDCPLUS is the preferred technology for interconnection of
islanded grids to the power system, such as off-shore wind farms. This technology provides
the so-called “Black Start” feature by use of voltage sourced converters. Voltage sourced
13 / 33
converters do not have the need of a “driving” system voltage; they can build up a 3 phase AC
voltage via the DC voltage at the cable end, supplied from the converter at the main grid.
3. Phase Shifting Transformer versus HVDC and FACTS
Phase shifting transformers have been developed for transmission system enhancement in
steady state system conditions. The operation principle is voltage source injection into the line
by a series connected transformer, which is fed by a tapped shunt transformer, very similar to
the UPFC, which uses VSC-Power Electronics for coupling of shunt and series transformer.
This way, overloading of lines and loop-flows in Meshed Systems and in parallel line
configurations can be eliminated. However, the speed of phase shifting transformers for
changing the phase angle of the injected voltage via the taps is very slow: typically between 5
and 10 s per tap, which sums up for 1 minute or more, depending on the number of taps.
As a rule of thumb for successful voltage or power-flow restoration under transient system
conditions, a response time of approx. 100 ms is necessary with regard to voltage collapse
phenomena and “First Swing Stability” requirements. Such fast reaction times can easily be
achieved by means of FACTS and HVDC controllers. Their response times are fully suitable
for fast support of the system recovery. Therefore, dynamic voltage and load-flow restoration
is clearly reserved to power electronic devices like FACTS and HVDC.
In conclusion, phase shifting transformers and similar devices using mechanical taps can only
be applied for very limited tasks with slow requirements under steady state system conditions.
4. FACTS Technologies and Applications
In this section, a more detailed description of FACTS technologies is given. Fig. 16 and 17
show the full range of applications, including actual ratings and voltage levels of today’s
solutions, as listed in Fig. 8.
Fig. 18 shows a site view of one of the 27 SVCs, which have been installed in the UK to
overcome transmission bottlenecks caused by deregulation [3]. The SVC control functions,
including options for specific tasks, such as unbalance control (not necessary in UK), are also
indicated in the figure. An increasing number of SVCs are also going to be installed in other
continents. In Fig. 19, an example of an SVC in South America is given. The SVC was
implemented to improve system stability of the large transmission grid. The installed
containerized solution offers additional benefits, such as reduction in installation and
14 / 33
commissioning time, as well as space and cost savings compared to conventional building
technologies.
MSC / MSR
SVC
Mechanical Switched
Capacitors / Reactors
STATCOM
Static Var
Compensator
Static Synchronous
Compensator
Switchgear
Thyristor Valve(s)
GTO/IGBT Valves
Capacitors
Control & Protection
Control & Protection
Reactors
Transformer
Transformer
Capacitors
DC Capacitors
Reactors
52 ≤ kV ≤ 800
50 ≤ MVAr ≤ 500
~
52 ≤ kV ≤ 800
50 ≤ MVAr ≤ 800
52 ≤ kV ≤ 800
50 ≤ MVAr ≤ 800
~
~
Fig. 16: FACTS for Parallel Compensation
FSC
TPSC
Fixed Series
Compensation
Thyristor Protected
Series Compensation
Thyristor Controlled
Series Compensation
Capacitors
Capacitors
Capacitors
Protection
Protection
Control & Protection
Arresters
Circuit Breakers
Thyristor Valves
Thyristor Valves
Circuit Breakers
Circuit Breakers
220 ≤ kV ≤ 800
200 ≤ MVAr ≤ 800
220 ≤ kV ≤ 800
100 ≤ MVAr ≤ 500
220 ≤ kV ≤ 800
100 ≤ MVAr ≤ 200
~
~
~
ILim
Fig. 17: FACTS for Series Compensation
15 / 33
TCSC
α
„
„
„
„
Voltage Control
Reactive Power Control
Power Oscillation Damping
Unbalance Control (Option)
Benefits:
o Improvement of Voltage Quality
o Increased Stability
Fig. 18: SVC Pelham, NGC, UK - 400 kV/14 kV, -75/+150 MVAr
Valves &
Control
Benefits:
o Improvement of Voltage Quality
o Increased Stability
o Avoidance of Outages
Fig. 19: SVC Bom Jesus da Lapa, Enelpower, Brazil - 500 kV, +/-250 MVAr
Containerized Solution
In Fig. 20-21, the features and cost savings of series compensation due to grid enhancement
are summarized. The mentioned SSR (sub-synchronous resonances) topic is a critical issue
for large thermal generators with long shafts [7]. The flexibility of modern FACTS
technologies under extremely harsh environmental conditions is indicated in Fig. 21-22: the
operating range for FSC begins at -500 C, for TCSC it can reach up to +850 C. This is
16 / 33
necessary due to the outdoor installation on high voltage potential, with the isolated platform
mounted directly in series with the transmission line.
Fixed Series Compensation:

~
~
Increase of Transmission
Capacity
Controlled Series Compensation:
Damping of Power Oscillations
 Load-Flow Control
 Mitigation of SSR

TCSC/TPSC
α
FSC
Fig. 20: FACTS - Application of Series Compensation
„ Current Control
„ Impedance Control
„ Power Oscillation
Damping (POD)
„ Mitigation of SSR
(Option)
Up to 500 POD
Operations per day
for saving the
System Stability
A System Outage of
24 h hours would
cost 840,000 US $ *
* 25 US $/MWh x 1400 MW x 24 hrs
> + 60 o C
Benefits:
o Increase of Transmission Capacity
up to 85 o
o Improvement of System Stability
Fig. 21: 500 kV TCSC Serra da Mesa, Furnas/Brazil – Essential for Transmission
- 50 o C
Poste Montagnais, Canada - FSC
Fig. 22: FSC at EHV 735 kV plus harsh Environment
17 / 33
For Thyristor Protected Series Compensation TPSC, innovative developments in ThyristorTechnology have been applied: Light-triggered Thyristors (now state of the art for FACTS
and HVDC) by means of a special heat-sink to enable a very fast self-cooling of the valves
within half a second only. By these means, TPSC is fully suitable for multiple fault
conditions, as it is often the case under hot climate conditions due to brush-fires leading to
repetitive line faults. In the TPSC, the thyristor replaces the conventional MOV (zinc oxide
arrester) for fast capacitor protection against over voltages due to short-circuit currents.
During faults, the MOV heats up heavily. Due to an upper temperature limit, the MOV must
cool down before the next current stress can be absorbed. Cool-down requires a substantial
amount of time, time constants of several hours are typical. During this time, the series
compensation must be taken out of service (bypass-breaker closed) and consequently the
power transfer on the related line needs to be reduced dependent on the degree of
compensation, leading to a significant loss in transmission capacity. Thus it appears that by
using the TPSC with fast cooling-down time instead of conventional series compensation with
MOV, a significant amount of money for each application can be saved.
Fig. 23 shows a site-view of one of the 5 TPSCs, installed at 500 kV in California, USA (ref.
to Fig. 8).
TPSC Technology:


Outdoor Valves on a Platform
LTT Thyristors, self-cooled
Fig. 23: TPSCs Vincent and Midway/USA: 5 TPSC Systems at 500 kV fully proven in Practice
In Fig. 24, two projects with series compensation in China are presented. The picture a) gives
a view of one phase element of the two Pingguo TCSCs. The 3D view b) demonstrates how
18 / 33
easily series compensation can be mounted to the existing line: when the installation is
finished (besides the line), a line interruption and a jumper connection to the platform is
made, with an actual power transmission interruption of only 1-3 days.
b)
a)
Commercial Operation in June 2006
Enhancement of Chinas “Central Transmission Corridor”
Fig. 24: China goes ahead – Transmission Enhancement with FACTS
a) Photo of Pingguo TCSC, commissioned in June 2003
b) 3D View on Fengjie 500 kV Fixed Series Compensation, China
2x 600 MVAr, Line Compensation Level 35%
5. HVDC for Interconnection and Transmission Optimization
During the developments of East-West Grid interconnection in Europe, three B2B projects
have initially been installed. One of them is shown in Fig. 25. All 3 projects led to fast and
more than full return on investments by energy trading. With the upcoming synchronous
extension of UCTE, however, they were taken out of service.
The low losses of the thyristor technology in comparison with VSC devices (ref. to Fig. 11),
are depicted in Fig. 26 for the Etzenricht installation shown in Fig. 25. Similar – and even
lower – losses have been achieved with the new HVDC installations. Especially in very large
DC transmission projects with 3 GW and more, minimal losses are an important issue for the
investors.
19 / 33
HVDC B2B - as
Interconnector or
Power-Flow
Controller: Etzenricht,
an Example from
Germany
System Data:
Rated Power:
DC Voltage:
DC Current:
AC Voltage:
600 MW
160 kV DC
3750 A
420 kV
Fig. 25: Etzenricht, one of the initial Steps for East-West System Interconnection in
Europe with 3 B2Bs – now replaced by synchronous Links (ref. to Text)
8000 kW of
Losses equals
1.33% of 600MW
3%
3%
4%
Auxiliaries
Smoothing Reactor
Filter Circuits
37%
Converter Valves
53%
Converter Transformers
this sums up
to …
Total B2B Losses: close to 1 % only
Fig. 26: HVDC Losses – Example B2B Etzenricht
After the Blackout in the United States, new projects with high voltage power electronics are
smoothly coming up. Siemens PTD has been awarded a contract by Neptune Regional
20 / 33
Transmission System LLC (RTS) in Fairfield, Connecticut, to construct an HVDC
transmission link between Sayreville, New Jersey and Long Island, New York. Neptune RTS
was established to develop and commercially operate power supply projects in the United
States. By delivering a complete package of supply, installation, service and operation from a
single source, Siemens is providing seamless coverage for the customer’s needs. The
availability of this combined expertise fulfills the prerequisites for financing these kinds of
complex supply projects through the free investment market. Siemens and Neptune RTS
developed the project over three years to prepare it for implementation. In addition to
providing technological expertise, studies, and engineering services, Siemens also supported
its customer in the project’s approval process. In Fig. 27, highlights of this innovative project
are depicted.
Ed Stern, President of Neptune RTS: “High-Voltage Direct-Current
Transmission will play an increasingly important Role, especially as it
becomes necessary to tap Energy Reserves whose Sources are far away from
the Point of Consumption”
Customer:
Neptune RTS
End User:
Long Island Power
Authority (LIPA)
Location:
New Jersey: Sayreville
Long Island: Duffy Avenue
Project
Development:
Supplier:
NTP-Date:
07/2005
PAC:
07/2007
Consortium
Siemens / Prysmian
Transmission:
Sea Cable
Power rating:
600/660 MW monopolar
Transmission dist.:
82 km DC Sea Cable
23 km Land Cable
Fig. 27: New HVDC Cable Link Neptune RTS, USA
Another highlight of HVDC project development is shown in Fig. 28. Basslink HVDC
provides a submarine cable link across the Bass Strait between Tasmania and the state of
Victoria on the Australian mainland. Basslink Pty Ltd. was specially formed by National Grid
Transco (the world's largest independent transmission network operator) to run the project
titled Basslink. The advantages of this link lie on both sides of the water: gaining access to the
Australian electricity market, Tasmania can supply Victoria at peak load times with power
from hydro generating plants. Tasmania can top up its base load from the mainland grid and
21 / 33
also secure the base load in drought periods, when reduced hydro power is available. In
addition to that, Tasmania plans to set up wind farms to improve the production of electrical
power from regenerative sources further, ref. to Fig. 28.
Benefits
of HVDC
Clean & Low Cost Energy
over Long Distance – suitable
for Peak-Load Demand
Improvement of Power
Quality
Improvement of local
Infrastructures
System Data:
Rating
500 MW
Voltage
400 kV DC
Thyristor
8 kV LTT
Transmission
length
370 km
HVDC Cable
(400 kV / 1500 mm2)
FO Cable
(12 Fibers)
Metallic Return
Cable (12/20 kV /
1400 mm2)
Cable Laying Vessel
“Giulio Verne“
Fig. 28: Innovative Transmission Technologies for long Distances - Basslink HVDC
The Basslink HVDC project shows that HVDC is fully suitable to match complex
transmission requirements even under environmental sensitive conditions. In Fig. 29 it is
shown that a combination of land cable, sea cable and overhead line was selected to match
both environmental constraints and cost issues.
For a long time, China has been benefiting from HVDC transmission by connecting clean and
low cost energy sources to the remote load centers, as indicated in Fig. 30 for the Tian-Guang
project (1800 MW) in South China. In Fig. 31 it is shown that a project termination for GuiGuang I (3000 MW) could be achieved 6 months ahead of schedule, which provides a large
amount of additional return on investments to the customer.
22 / 33
McGaurans
Beach
Loy Yang
3.2 km
57.4 km
6.4 km
Five Mile
Bluff
295 km
1.7 km
Georgetown
8.9 km
2.1 km
Bass Strait
Converter
Station
Underground
Cable
Underground
Cable
Converter
Station
Sea Cable
500 kV
Substation
Transition
Station
Transition
Station
220 kV
Substation
Fig. 29: Basslink HVDC - Optimization of the Transmission System
Operated by:
South China Electric
Power JVC (SCEP)
The Task: Connection of Hydro
Generation to Remote Load Centers
System Data:
Rating
1800 MW
Voltage +/-500 kVDC
Thyristor
8 kV
Line Length 960 km
Tian Hydro Station
Guangzhou Beijiao
Tianshengqiao
Benefits
Use of Clean &
Low Cost
Energy
Fig. 30: HVDC Long Distance Transmission Tian-Guang
As a follow-up of the Gui-Guang I project, which is in full commercial operation, a new
contract for Gui-Guang II has been awarded to Siemens and its local partners with equal
transmission capacity of 3000 MW. Examples of system studies for projects with HVDC and
FACTS for system stability improvement in China and other continents are depicted in the
next section.
23 / 33
View of the Thyristor-Module
Rating:
Voltage:
3000 MW
± 500 kV
Contract: Nov. 1, 2001
Project terminated 6 Months
ahead of Schedule by Sept. 2004
Thyristor: 5" LTT with integrated
Overvoltage Protection
Fig. 31: HVDC Long Distance Transmission Gui-Guang I
6. System Studies for large Transmission Projects with HVDC and FACTS
Fig. 32-33 give an example of a large power system simulation of the Chinese grid [2], in
which both FACTS and HVDC have been integrated for grid interconnection and point to
point long distance transmission in a hybrid way.
Nayong
Anshun
Conv. Stat.
Guizhou
Guiyang
Guangxi
Huishui
Anshun
HVDC GuiGuang
Anshun
Hydro Power Station
Thermal Power Station
Luoping
Lubuge
HVDC Converter
Station
TCSC
Guangdong
FSC
Hechi
TSQ-I
TSQ
Conv. Stat.
Baise
Beijiao
Conv. Stat.
Yantan
Liuzhou
TCSC & FSC
Pingguo Laibin
Beijiao
Zhengcheng
Wuzhou
Luodong
Pingguo
FSC
Zhaoqing
HVDC TSQ
Yunnan
Gaomin
Yulin
Guangxi
Nanning
Fig. 32: Use of HVDC and FACTS in a hybrid System in China
24 / 33
Guangzhou
Hezhou
Liudong
TSQ-II
Zhaoqing
Conv. Stat.
Because of the long transmission distances, the system experiences severe power oscillations
after faults, close to the stability limits. In the recordings in Fig. 33 (upper part) oscillations
are depicted. The first case given is HVDC transmitting power in constant power mode, see
curve a. It can be seen that strong power oscillations occur. If, however, damping control of
HVDC Gui-Guang is activated (curve b ), the oscillations are damped very effectively. Using
series compensation with two TCSCs and two FSCs at Pingguo substation, the stability of the
overall system can be further increased (curve c ). The lower part of Fig. 33 shows that
without HVDC, the Pingguo TCSCs need more actions for damping: 1a) compared to 2a)-b).
Without series compensation and without HVDC damping, such a large power system would
be unstable in case of fault contingencies, thus leading to severe outages (Blackout) [3].
1500
Power flow in one line
Huishui -Hechi (MVA)
1200
Dynamic Results
a – without Power Modulation
b – with Power Modulation
of HVDC Control
900
600
300
b
0
Flow in one Line
b Power
a
-300
-600
c – further Improvements with
Pingguo TCSC/FSC
-900
0
c
Huishui-Hechi (MW)
a
5
10
15
Time (s)
POD Output Signal (pu) TCSC 1 (= TCSC 2)
1a)
More Action of TCSC required
HVDC not active
POD Output Signal (pu) TCSC 1 (= TCSC 2)
2a)
Less Action of TCSC required
HVDC active
POD Output Signal HVDC (%)
2b)
Fast and strong Action of HVDC with POD
Fig. 33: China - Benefits of active Damping with HVDC & FACTS
25 / 33
Time / s
20
Similar studies have been carried out for large transmission projects worldwide. An example
of such studies is described in the following.
With the Mead-Adelanto and the Mead-Phoenix Transmission Project (MAP/MPP), a major
500 kV transmission system extension has been carried out to increase the power transfer
opportunities between Arizona and California, USA. The extension includes two main series
compensated 500 kV line segments and two equally rated Static Var Compensators, supplied
by Siemens, at the Adelanto and Marketplace substations - ref to Fig. 34. The SVCs enabled
the integrated operation of the already existing highly compensated EHV AC system and two
large HVDC systems. The SVC installation was an essential prerequisite for the overall
system stability at an increased power transfer rate.
Upgrade of a large AC
and DC Transmission
System with 2 SVCs
& FSCs
ƒ Increase of Transmission Capacity
ƒ Improvement of System Stability
Each SVC: 388 MVAr for
Voltage and POD Control
Fig. 34: HVDC plus SVC: Mead-Adelanto - USA
An example of the intensive project testing with computer and real-time simulator facilities is
given in Fig. 35 for a fault application at Marketplace 500 kV bus. The figure shows the
computer test results with both SVCs active. The influence of the HVDC can be seen from
26 / 33
the DC voltage E dc. Figure a) is with both SVCs only in voltage control mode (PSDC
blocked); Figure b) shows an improved damping with the PSDC function enabled.
E dc Adelanto (volts)
1100
1.4
1.2
1000
1.0
900
0.8
800
Design by Computer Studies
0.6
700
Adel Bsvc (Mvar)
a)
Mkplc 500kV Bus Vlt (pu)
400
400
200
200
0
0
Mkplc Bsvc (Mvar)
1100
Mkplc 500kV Bus Vlt (pu)
E dc Adelanto (volts)
1.4
1.2
1000
1.0
900
0.8
800
0.6
700
400
a) Both SVCs in Voltage Control Mode
b) Both SVCs in Coordinated Voltage
& Power Oscillation Damping
Control Mode
Mkplc Bsvc (Mvar)
Adel Bsvc (Mvar)
400
200
200
0
0
0
10
Time (sec)
20
0
10
20
Time (sec)
b)
Fig. 35: Mead-Adelanto Studies – Comparison of SVC Voltage- and POD-Control Mode
In Fig. 36, a new FACTS application with SVC in combination with HVDC in Germany is
shown [2]. It is actually the first high voltage FACTS controller in the German network.
Reason for the SVC installation at Siems substation nearby the landing point of the Baltic
Cable HVDC were unforeseen right of way restrictions in the neighboring area, where an
initially planned new tie-line to the strong 400 kV network for connection of the HVDC was
denied. Therefore, with the existing reduced network voltage of 110 kV (see the dotted black
lines in Fig. 36, only a limited amount of power transfer of the DC link was possible since its
commissioning in 1994, in order to avoid repetitive HVDC commutation failures and voltage
problems in the grid. In an initial first step for grid access improvement, an additional
transformer for connecting the 400 kV HVDC AC bus with the 110 kV bus (see the figure)
was installed. Finally, in 2003 with the new SVC, equipped with a fast coordinated control,
the HVDC could fully increase its transmission capacity up to the design rating of 600 MW.
In addition to this measure, a new cable to the 220 kV grid was installed, to increase the
system strength with regard to performance improvement of the HVDC controls. In Fig. 37, a
photo of the Siems SVC in Germany is given.
27 / 33
Initially planned Connection
Grid Access
2
denied
1994
1
Now, the HVDC
can operate at
full Power
Rating
2
2
Final Solution: new
SVC with TCR & TSC
100 MVar ind.
200 MVar cap.
2003
1 Initial Step for Grid Access
Enhancement
2 and a new 220 kV Cable
Fig. 36: The Problem – no Right of Way for 400 kV AC Grid Access of
Baltic Cable HVDC
Essential for
enhanced Grid
Access of the HVDC
Fig. 37: The Solution – the first HV SVC in the German Grid at Siems Substation
In the same way as in the previous project cases, intensive studies, first with computer and
then with real-time simulator by using the physical SVC controls and simplified models for
the HVDC, have been carried out prior to commissioning.
28 / 33
In conclusion of the previous sections, Table 1 summarizes the impact of FACTS and HVDC
on load flow, stability and voltage quality when using different devices. Evaluation is based
on a large number of studies and experiences from projects.
Principle
Devices
Scheme
Impact on System Performance
Load Flow
Variation of the
Line
Impedance:
Series
Compensation
FSC
Stability
Voltage
Quality
z
zzz
z
z
zzz
z
zz
zzz
z
(Mechanically
Switched Capacitor /
Reactor)
{
z
zz
SVC
{
zz
zzz
{
zz
zzz
HVDC (B2B, LDT)
zzz
zzz
zz
UPFC
zzz
zzz
zzz
(Fixed Series
Compensation)
TPSC
(Thyristor
Protected Series
Compensation)
TCSC
(Thyristor
Controlled Series
Compensation)
MSC/R
Voltage
Control:
Shunt
Compensation
(Static Var
Compensator)
STATCOM
(Static Synchronous
Compensator)
Load-Flow
Control
(Unified Power
Flow Controller)
Based on Studies & practical Experience
Table 1: FACTS & HVDC – Overview of Functions & “Ranking”
Influence:
{
z
zz
zzz
no or low
small
medium
strong
7. Innovative Transmission Solutions using High Voltage Power Electronics
Increasing generation in high load density networks on the one hand, and interconnections
among the systems on the other hand, increase the short-circuit power. If the short-circuit
current rating of the equipment in the system is exceeded, the equipment must be uprated or
replaced, which is a very cost- and time-intensive procedure. Short-circuit current limitation
offers clear benefits in such cases. Limitation by passive elements, e.g. reactors, is a well
29 / 33
known practice. It reduces, however, the system stability, and there is an impact on the loadflow.
By combining the previously mentioned 500 kV TPSC application with an external reactor
(see Fig. 38), whose design is determined by the allowed short-circuit current level, this
device can also be used very effectively as short-circuit current limiter (SCCL, ref. to [4, 7]).
SCCL
TPSC
+
The new Idea !
Reactor
AC
AC
Bus 2
Bus 1
Thyristor Protected
Series Compensation
Use of proven Technology
Fig. 38: SCCL - an Innovative FACTS Solution using TPSC
This new device operates with zero impedance in steady-state conditions, and in case of shortcircuit it is switched within a few ms to the limiting-reactor impedance.
Risk of Voltage Collapse
 Fault
Current Limitation
¾ Conventional Solution: Reactor
¾ The new FACTS Solution: SCCL
Difficult or impossible at
High Voltage Levels
¾ Future Option: High-Temperature Superconducting FCL
 Fault
Current Interruption
¾ Is-Limiter
¾ Electronic Devices (“Small FACTS”)
SCCL: no Constraints
Fig. 39: FCL - Principles and Applications
30 / 33
Not available for HV
Levels and Constraints
on Protection Coordination
Fig. 39 gives a brief overview on today’s solutions for fault-current limitation, including the
new SCCL. Basically, there are two methods for fault-current reduction: limitation and
interruption. The constraints and benefits of the different solutions are indicated in the figure.
Fig. 40 shows the basic function and the operating principle of the SCCL, including a 3-D
view of the SCCL. In comparison with the TPSC site photo, it can be seen that the TPSC is
just complemented by an additional reactor for the current limitation. Further details on the
SCCL solution are described in [7].
Thyristor Valve Housing
Capacitor Bank
To Bus 1
BYPASS
Breaker
Communication
Reactor
Just one additional X !
To Bus 2
Impedance
X
Fast Increase of Coupling Impedance
Zero Ohm for best Load Flow
t
Fig. 40: SCCL - Short-Circuit Current Limitation with FACTS
8. Market and Reliability Issues
Table 2 summarizes the market expectations for FACTS and HVDC solutions today and in
the future. The market for series compensation, for SVC and for B2B for load-flow control is
actually large today and, as a result of liberalization and deregulation in the power industry, is
developing fast in the future. The market in the HVDC long distance transmission field is
further progressing fast. A large number of high power long distance transmission schemes
using either overhead lines or submarine cables projects have been put into operation or are in
the stage of installation.
31 / 33
MSC/R
zzz
SVC
zzz
STATCOM
z
FSC
zzz
TCSC / TPSC
zz
Combined Device
UPFC
z
Power Transmission
HVDC
zzz
Shunt Compensation
Series Compensation
Excellent Market
Upcoming Market
Small Market
zzz
zz
z
Table 2: Markets for FACTS and HVDC
Illovo SVC
1995
1996
1997
1998
Availability (%)
99.9
99.45
100
100
Forced and
deferred Outages
2
5
2
1
Off-line
Maintenance
0h
80h00
102h26
162h00
On-line
Maintenance
10h15
2h00
3h00
0
MDT in hrs
2h13
9h40
36h40
1h00
Athene SVC
1995
1996
1997
1998
Availability (%)
99.78
99.71
99.92
99.77
Forced and
deferred Outages
4
9
1
2
Off-line
Maintenance
4h00
81h00
62h00
60h15
On-line
Maintenance
1h00
0
0
0
MDT in hrs
4h40
3h20
4h40
10h30
Recordings from NATAL SVCs / RSA (2 TCR & 3 Filter)
Guarantied Availability: 98 - 99 %
Table 3: Availability of Power Electronics – Example FACTS: close to 100 %- same
for HVDC
Concerning reliability of high voltage power electronics, Table 3 gives an example of two
SVC projects installed in South Africa. Same high reliability is also achieved for HVDC as
32 / 33
the technology applied uses the same components. Excellent on-site operating experience is
being reported, and the FACTS and HVDC technology became mature and reliable.
9. Conclusions
Deregulation and privatization is posing new challenges on high voltage transmission
systems. System elements are going to be loaded up to their thermal limits, and wide-area
power trading with fast varying load patterns will cause congestion. System enhancement will
be essential to keep the supply reliable and safe. Interconnection of power systems offers
many benefits for the operation of the grids. The performance of power systems, however,
decreases with size, loading and complexity of the networks. This is related to problems with
load flow, power oscillations and voltage quality. Such problems are even deepened by the
changing situations resulting from deregulation of the electrical power markets. The power
systems have not been designed for wide-area power trading with daily varying load patterns,
where power flows do no more follow the initial planning criteria of the existing network
configuration. Large blackouts in America and Europe confirmed clearly that the favorable
close electrical coupling might also include risk of uncontrollable cascading effects in large
and heavily loaded interconnected systems. FACTS and HVDC, however, provide the
necessary features to avoid technical problems in the power systems, and they increase the
transmission efficiency.
10. References
[1] U. W. Niehage, “Future Developments in Power Industry”, Key-Note Adress at
AESIEAP, 28-05 September 2005, New Delhi, India
[2] L. Kirschner, D. Retzmann, G. Thumm, “Benefits of FACTS for Power System
Enhancement”, 14-18 August, 2005, IEEE/PES T & D Conference, Dalian, China
[3] G. Beck, D. Povh, D. Retzmann, E. Teltsch, “Global Blackouts – Lessons Learned”,
Power-Gen Europe, 28-30 June 2005, Milan, Italy
[4] W. Breuer, D. Povh, D. Retzmann, V. Sitnikov, E. Teltsch, “Benefits of Power
Electronics for Transmission Enhancement”, 10-11 March 2004, Moscow, Russia
[5] W. Breuer, X. Lei, D. Povh, D. Retzmann, E. Teltsch, “Role of HVDC and FACTS in
future Power Systems”, 18-22 October 2004, 15th CEPSI, Shanghai, China
[6] W. Breuer, X. Lei, D. Povh, D. Retzmann, E. Teltsch, “Solutions for large Power System
Interconnections”, 18-22 October 2004, 15th CEPSI, Shanghai, China
[7] V. Gor, D. Povh, Y. Lu, E. Lerch, D. Retzmann, K. Sadek, G. Thumm, “SCCL – A new
Type of FACTS based Short-Circuit Limiter for Application in High Voltage Systems”,
CIGRÉ Report B4-209, Session 2004.
33 / 33