www.siemens.com/energy
Highly Efficient Solutions
for Smart and Bulk Power Transmission
of “Green Energy”
Presented at
21TH WORLD ENERGY CONGRESS,
Montreal, Canada
September 12–16, 2010
Authors:
W. Breuer, D. Retzmann, K. Uecker
Siemens AG, Energy Sector,
Power Transmission Division, Germany
Updated Version, July 2011
Answers for energy.
Table of Contents
2 |
Abstract 3
1. Introduction 4
2. Security and Sustainability due to Power Electronics 5
3. Benefits of Power Electronics for System Enhancement 8
4. Prospects of Power System Developments 10
5. Technologies for Smart and Super Grids 5.1 Smart Grid Solutions with VSC –
Modular Multilevel Converters 5.2 Super Grid Solutions with FACTS and HVDC –
“Classic” and Bulk 5.3 Super Grid Solutions with GIL –
Gas Insulated Lines 11
6. Conclusions and Outlook 20
7. References 22
11
15
20
Highly Efficient Solutions for Smart and Bulk Power
Transmission of “Green Energy”
W. Breuer, D. Retzmann*, K. Uecker
Siemens AG, Energy Sector
Erlangen, Germany
ABSTRACT
The electric power supply is essential for the survival of a society, like the blood in the body. Lack of
power brings about devastating consequences for daily life. However, deregulation and privatization
are posing new challenges to the 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 contribute to an
increasing congestion. In addition to this, the dramatic global climate developments call for changes
in the way electricity is supplied. Environmental constraints, such as loss minimization and CO2
reduction, will play an increasingly important role. Consequently, we have to deal with an area of
conflicts between reliability of supply, environmental sustainability as well as economic efficiency.
The power grid of the future must be secure, cost-effective and environmentally compatible. The
combination of these three tasks can be tackled with the help of ideas, intelligent solutions as well as
innovative technologies.
Innovative solutions with HVDC (High-Voltage DC) and FACTS (Flexible AC Transmission Systems)
have the potential to cope with the new challenges. By means of Power Electronics, they provide
features which are necessary to avoid technical problems in the power systems, they increase the
transmission capacity and system stability very efficiently and help prevent cascading disturbances.
KEY WORDS:
Smart and Super Grid Technologies; HVDC, FACTS; Sustainability and Security of Power Supply;
Increase in Transmission Capacity; Solutions for Bulk Power Transmission; Reduction in
Transmission Losses; Enhanced Grid Access for Regenerative Energy Sources (RES)
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*dietmar.retzmann@siemens.com
*dietmar.retzmann@siemens.com
Copyright © Siemens AG 2011. All rights reserved.
2
1. INTRODUCTION
The availability of electric power is the crucial prerequisite for the survivability of a modern society
and power grids are virtually its lifelines. Without power supply there are devastating consequences
for daily life. However, deregulation and privatization are posing new challenges to the 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 contribute to an increasing congestion.
In addition to this, the dramatic global climate developments call for changes in the way electricity is
supplied. Environmental constraints, such as loss minimization and CO2 reduction, will play an
increasingly important role.
Consequently, we have to deal with an area of conflicts between reliability of supply, environmental
sustainability as well as economic efficiency. The power grid of the future must be secure, costeffective and environmentally compatible. The combination of these three tasks can be tackled with
the help of ideas, intelligent solutions as well as innovative technologies. The combination of these
three tasks can be solved with the help of ideas, intelligent solutions as well as innovative
technologies. Innovative solutions with HVDC and FACTS have the potential to cope with the new
challenges. By means of Power Electronics, they provide features which are necessary to avoid
technical problems in the power systems, they increase the transmission capacity and system stability
very efficiently and help prevent cascading disturbances.
The vision and enhancement strategy for the future electricity networks are, for example, depicted in
the program for “SmartGrids”, which was developed within the European Technology Platform.
Features of a future Smart Grid such as this can be outlined as follows [1]:

Flexible: fulfilling customers’ needs whilst responding to the changes and challenges ahead

Accessible: granting connection access to all network users, particularly for RES and high
efficiency local generation with zero or low carbon emissions

Reliable: assuring and improving security and quality of supply

Economic: providing best value through innovation, efficient energy management and “level
playing field” competition and regulation
Smart Grids will help achieve a sustainable development. It is worthwhile mentioning that the Smart
Grid vision is in the same way applicable to the system developments in other regions of the world.
Smart Grids will help achieve a sustainable development.
An increasingly liberalized market will encourage trading opportunities to be identified and
developed. Smart Grids is a necessary response to the environmental, social and political demands
placed on energy supply.
Links will be strengthened across North and South America, East and West Europe, Africa and Asia,
interconnecting countries where different but complementary renewable resources are to be found. For
the interconnections, innovative solutions will be essential to avoid congestion and to improve
stability. HVDC provides the necessary features to avoid technical problems in the power systems. It
also increases the transmission capacity and system stability very efficiently and helps prevent
cascading disturbances. HVDC can also be applied as a hybrid AC-DC solution in synchronous AC
systems either as a Back-to-Back for grid power flow control (elimination of congestion and loop
flows) or as a long-distance point-to-point transmission.
FACTS technology encompasses systems for both parallel and series compensation. It rests upon the
principle of reactive power elements, controlled by means of power electronics, which can increase the
transmission capacity of long AC lines or stabilize the voltage of selected grid nodes. Due to a high
utilization degree of AC power grids, the application of FACTS technology will become an
increasingly more interesting issue also in the case of meshed power systems, e.g. in Europe.
HVDC and FACTS applications will consequently play an important role in the future development of
power systems. This will result in efficient, low-loss AC/DC hybrid grids which will ensure better
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Copyright © Siemens AG 2011. All rights reserved.
3
controllability of the power flow and, in doing so, do their part in preventing “domino effects” in case
of disturbances and blackouts.
In what follows, the global trends in power markets and the prospects of system developments are
depicted, and the outlook for Smart Grid technologies for environmental sustainability and system
security is given.
2. SECURITY AND SUSTAINABILITY DUE TO POWER ELECTRONICS
From the point of view of the design concept, the AC grids are not configured as wide-area bulk
power transmission systems. By way of example, the Central European Power Grid (CE, former
UCTE) at a transmission voltage of 400 kV was originally based on the concept of a system which
provides power generation near the loads and has additional links to support the adjacent grids in the
case of disturbances or planned outages of individual generation units.
In the course of deregulation and privatization of European power markets the idea of an AllEuropean interconnected system came up, and in view of climate change, the issue of bulk power
transmission of environmentally compatible energy completed the picture. However, prior to
implementing this vision to the full extent, the grid concept must be adapted to these modified
conditions. Now, the question is how renewable energies, wind power in particular, influence the grid
in case of an outage.
At 21:38, both Circuits
of a 400 kV Line in the
Northern German Grid
were switched-off in
order to allow a large
Ship to pass the Ems
River
n-2 !
At around 22:10, the whole
Europe was affected and
UCTE split into 3 Islands
Source: UCTE – Final Report 2007-01-30
Fig. 1 - European Power System Disturbance on November 4, 2006
The prime example here is the massive outage experienced in the European grid on November 4,
2006. The events started in the evening around 9:30 pm, and were triggered by the deliberate
disconnection of two 400 kV lines over the Ems river in order to let a large vessel pass. Due to this, a
number of lines were overloaded which resulted in a domino effect typical of massive outages of this
kind and ended up in the splitting of the UCTE system (now CE, Central Europe) into three areas at
different frequencies. It was the over-frequency area which, in addition to the congestion provoked by
the failed lines, suffered from an excessive electric power infeed from wind farms, which was exactly
what an over-frequency area required the least at that time. This scenario is depicted in Figs. 1-3.
It has highlighted the fact that Continental Europe is already behaving to some extent as a single
power system, but with a network not designed accordingly. Europe's power system (including its
network infrastructure) has to be planned, built and operated for the consumers it will serve.
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Copyright © Siemens AG 2011. All rights reserved.
4
Identifying, planning and building this infrastructure in liberalized markets is an ongoing process that
requires regular monitoring and coordination between market actors.
Fig. 2 depicts separate parts of the CE grid in load-dependent colors; the red color marks a significant
overload – resulting in high phase-angle differences, and the green one reflects a situation in which
even more current can easily flow through.
b)
00
600
1200
1200
a)
Source: 5.
ELES Slovenia &
– Information Session, 28 Nov. 2007 Stuttgart, Germany
a) normal Condition & b) shortly before System Separation
Fig. 2 – Voltage Phase-Angle Difference
Fig. 3 – The Solution: Transmission of Windmill
Power by means of HVDC from
Area 2 to Area 1 and Area 3
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Copyright © Siemens AG 2011. All rights reserved.
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Should even far higher input from offshore wind farms into the northern German grid come into play
in the future, as Fig. 3 suggests, the HVDC technology could provide the best possibility to forward
the power surplus from the low-load North directly to the Southern load centres of Germany or to the
adjacent countries with higher power demand. This idea rests upon a well-known experience with
hybrid grids in other countries, according to which the DC point-to-point connection carries out an
easy power transfer over large distances and the adjacent AC grid is additionally supported by means
of FACTS.
The most devoted users of this hybrid concept are India and China, see Figs. 4 and 5. Further
examples of projects (from Siemens) with integrated AC/DC systems in a number of countries are
depicted in Fig. 4, right part.
Fully integrated
Adani HVDC – a private
Investor goes ahead
2011
960 km
2010-2011
2,500 MW
780 km
Ballia-Bhiwadi – Power Grid
Corporation of India Ltd
• Cahora Bassa, Mozambique-South Africa,
1977-79, 1920 MW, 533 kV, 1414 km
• Gezhouba-Shanghai, China, 1989, 1200 MW,
500 kV, 1040 km
2,500 MW
• Tianshengqiao-Guangzhou, China, 2000,
1800 MW, 500 kV, 960 km
• Guiguang I, China, 2004, 3000 MW, 500 kV,
940 km
• Guiguang II, China, 2007-2008, 3000 MW,
500 kV, 1225 km
1,450 km
• Western Alberta Transmission Link,
Canada, 2014, 1000 MW, 500 kV,
400 km
• East DC Link Project, Canada, 2014,
1000 MW, 500 kV, 500 km
• Jinping-Sunan, China, 2013,
7200 MW, 800 kV, 2095 km
2003
2007 2,500 MW
2,000 MW
• Yunnan-Guangdong, China, 2009-2010,
5000 MW, 800 kV, 1418 km
• Trans Bay Cable, HVDC PLUS, San Francisco,
2010, 400 MW, 200 kV, 88 km Cable
East-South Interconnector –
the DC Energy Bridge
• Hudson Transmission Project
Ridgefield (New Jersey), USA, B2B
Station 660 MW, 2013
• Xiluodo-Guangdong, China, 2013,
2 x 3200 MW, 2 x 500 kV, 1268 km
• Neptune, New York, 2007, 660 MW, 500 kV,
105 km Cable
Further Examples of
integrated HVDC Systems
• Xiangjiaba-Shanghai, China, 2010, 6400 MW,
800 kV, 2071 km
• INELFE, HVDC PLUS, France-Spain TEN
Interconnection, 2013, 2 x 1000 MW,
320 kV, 65 km Cable
• Nuozhadu-Guangdong, China, 2012-2013,
5000 MW, 800 kV, 1451 km
• Ningdong-Shandong, China, 2010-2011,
4000 MW, 660 kV, 1418 km
Fig. 4 – India: Three large HVDCs at 500 kV of which Adani and Ballia-Bhiwadi are fully
integrated into the AC Grid
Fig. 5 – Large HVDC Projects in Southern
China enable low-loss West-to-East
Transmission
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Copyright © Siemens AG 2011. All rights reserved.
6
3. BENEFITS OF POWER ELECTRONICS FOR SYSTEM ENHANCEMENT
Power electronics is used in high-voltage systems for FACTS as well as for HVDC. HVDC helps
prevent bottlenecks and overloads in power grids by means of systematic power-flow control. The
function of the HVDC which is decisive for system security is that of an automatic firewall. This
firewall function can prevent the spread of a disturbance, which occurs in the system, at all times; as
soon as the disturbance has been cleared, power transmission can immediately be resumed. Moreover,
the HVDC technology allows for grid access of generation facilities on the basis of availabilitydependent regenerative energy sources, including large offshore wind farms, and, compared with the
conventional AC transmission, it boasts a significantly lower level of transmission losses on the way
to the loads [2 - 4].
FACTS technology was originally created to support weak AC grids and to stabilize AC transmission
over very long distances. FACTS technology encompasses systems for both parallel and series
compensation. It rests upon the principle of reactive power elements, controlled by means of power
electronics, which can reduce the transmission angle (increase in transmission capacity) of long AC
lines or stabilize the voltage of selected grid nodes to control load flow and to improve dynamic
conditions. Moreover, FACTS can help solve technical problems in the interconnected power systems.
Examples of FACTS controllers are:
 SVC - Static VAR Compensator
 STATCOM - Static Synchronous Compensator
 FSC - Fixed Series Compensation
 TCSC/TPSC - Thyristor Controlled/Protected Series Compensation
 S³C - Solid-State Series Compensator
 UPFC - Unified Power Flow Controller
 CSC - Convertible Static Compensator
Rating of SVCs can go up to 800 MVAr; the world’s biggest FACTS project with series compensation
(TCSC/FSC) is at Purnea and Gorakhpur in India at a total rating of 1.7 GVAr.
In Fig. 6, the basic applications of HVDC and FACTS to solve system problems are explained.
*
Fault-Current Limitation for connecting new Power Plants
SVC & HVDC for Voltage Collapse Prevention
Load Management by HVDC
The FACTS & HVDC “Application Guide”
Load Displacement by Series Compensation
* PTDF
= Power Transfer Distribution Factor
Fig. 6 – Elimination of Bottlenecks in Transmission – The Power Electronics Application
The figure depicts separate lines in load-dependent colors; the red color marks a significant overload,
and the green one reflects a situation in which even more current can easily flow through. For the sake
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Copyright © Siemens AG 2011. All rights reserved.
7
of a consistent load flow, the ideal solution would be to furnish the grid, which is entirely “open” for
power trading, with yellow lines, which helps do away with the less loaded grey ones. It is needless to
say that in the context of a complex, largely meshed grid without any additional measures to boost its
efficiency, an optimal load-flow control such as this is not possible. Due to a high utilization degree of
AC power grids, the application of FACTS technology will become an increasingly more interesting
issue also in the case of large meshed power systems, e.g. in Central Europe.
FACTS and HVDC applications will consequently play an important role in the future development of
power systems. This will result in efficient, low-loss AC/DC hybrid grids which will ensure better
controllability of the power flow and, in doing so, do their part in preventing “domino effects” in case
of disturbances and blackouts.
In Fig. 7, the configuration possibilities of HVDC are depicted and Fig. 8 shows a comparison of the
control features of HVDC and FACTS for interconnection of large systems.
Can be
connected
to long AC
Lines
a)
c)
DC supports AC in
Terms of Stability
b)
c)
a) Back-to-Back Solution
b) HVDC Long-Distance Transmission
c) Integration of HVDC into the AC System
The Firewall
for Blackout
Prevention
Fig. 7 – HVDC Configurations
G~
~
P
a)
~
Loads
FACTS “Classic”
G~
Loads

G~
b)
G~

Loads

+/- P
“Classic”
=
or VSC
=
G~

Loads
a) FACTS: Voltage / Load-Flow Control (one Direction only) & POD
b) HVDC Back-to-Back or Long-Distance Transmission:
Voltage / Bidirectional Power-Flow Control, f-Control & POD
POD: Power Oscillation Damping
FACTS VSC
Fig. 8 – System Interconnections: Control Features of FACTS and HVDC
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Copyright © Siemens AG 2011. All rights reserved.
8
4. PROSPECTS OF POWER SYSTEM DEVELOPMENTS
Based on the previous evaluations, Figs. 9 and 10 show the stepwise interconnection of a number of
grids by using AC lines, DC Back-to-Back systems, DC long distance transmissions and FACTS for
strengthening the AC lines.
“Micro Grid” (autonomous)
“Smart Grid”
“Super Grid”
L
C
L
C
L
C
C
C
C
L
C
L
L
CA
CA
C
L
C
C
CA
C
C
C
C
CA
C
C
C
L
C
C
L
C
C
C
L
C
L
L
CA
G
+
Storage
S
+
L
C
Generation
Smart, controlled Loads
C
L
CA
C
C
C
C
C
CA
C
C
C
C
L
C
C
G
C
C
C
L
C
C
C
= Cell Agent
=
G
C
L
C
C
L
C
C
C
C
C
C
C
L
C
C
C
C
C
C
C
S
G
G
C
C
L
Cell
G
L
AC
S
G
Bulk Power AC/DC
Power Transmission
Division
Energy
Highway
DC
06-2010
1
Virtual
Power
Plant
Fig. 9: Prospects of Grid Developments
System
G
System
A
System
B
System
C
System
D
System
E
System
F
The Result: Large
Interconnections,
LargeSystem
SystemInterconnections
Interconnections,with
withHVDC…
HVDC…and FACTS
Step 3
Step 2
Step 1
HVDC – Long-Distance DC Transmission
HVDC B2B – via AC Lines
High-Voltage AC Transmission & FACTS
DC is a Stability Booster and
“Firewall” against “Blackout”
A “Super Grid” – “Smart” & Strong
“Countermeasures”
against large
Blackouts
Fig. 10: Hybrid System Interconnections – “Supergrid” with HVDC and FACTS
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Copyright © Siemens AG 2011. All rights reserved.
9
These integrated hybrid AC/DC systems provide significant advantages in terms of technology,
economics as well as system security. They reduce transmission costs and help bypass heavily loaded
AC systems. With these DC and AC Ultra High Power transmission technologies, the “Smart Grid”,
consisting of a number of highly flexible “Micro Grids” will turn into a “Super Grid” with Bulk Power
Energy Highways, fully suitable for a secure and sustainable access to huge renewable energy
resources such as hydro, solar and wind, as indicated in Fig. 9. This approach is an important step in
the direction of environmental sustainability of power supply: transmission technologies with HVDC
and FACTS can effectively help reduce transmission losses and CO2 emissions.
The state-of-the-art AC and DC technologies and solutions for Smart and Super Grids are depicted in
the following sections.
5. TECHNOLOGIES FOR SMART AND SUPER GRIDS
The core or the “workhorse” of line-commutated HVDC and FACTS installations are high-power
thyristors, triggered optically by means of laser technology or electrically depending on application.
Thyristors can only switch on the current. The switching-off is carried out by the next current zero
crossing itself. This is the reason why a thyristor converter is referred to as a line-commutated system.
Should no line voltage be available on one side of an HVDC system or in a FACTS application, the
system would no longer be functioning. An advantage of thyristor converters is their high loading
capacity both during nominal and overload operation as well as in the event of contingency.
Consequently, bulk-power systems at high transmission capacities of 5 to over 7 GW can be
implemented with thyristors only. A further benefit consists in comparatively low station losses. The
TPSC technology mentioned before uses special-purpose thyristors capable of withstanding transient
over-loading of up to approximately 110 kA.
The “strength”, i.e. short-circuit power of the grid, is an important design criterion for the application
of line-commutated HVDC systems. If the grid is too weak, a thyristor-based HVDC system must
reduce its power or, under certain conditions, shut down completely in order to avoid system collapse
resulting from repetitive commutation failures. In the case of weak grids, remedy is provided by
FACTS for grid support, i.e. a combination of the HVDC and FACTS as in the example of the SVC
Siems for the HVDC project Baltic Cable [3].
Additionally, the problem can be tackled by means of “self-commutated” converters. Self-commutated
converters make use of elements which can be switched off, mostly modular or press-pack high-power
transistors, all of which, in their turn, consist of a number of separate elements, connected in parallel.
In this way, a converter turns into an electronic generator. Self-commutated converters are normally
furnished with a voltage-sourced DC circuit. With its help a separate capacitor or a number of them
keep the voltage constant (VSC: Voltage-Sourced Converter), whereas a conventional thyristor-based
HVDC system keeps the source current constant (CSC: Current-Sourced Converter) by means of
reactors.
A detailed description of different VSC solutions is given in [2], for example. A general advantage of
the VSC-based HVDC systems consists in the fact that one of the power grids subject to coupling can
be completely voltage-free or passive, for, with the help of the intact grid, the other one can be started
again similar to a power plant. This black-start capability is particularly interesting for connecting
large offshore wind farms off the coast of Germany.
5.1 Smart Grid Solutions with VSC - Modular Multilevel Converters
An innovative development known as the MMC (Modular Multilevel Converter) technology is
described in item [2], which is applied by Siemens as an “HVDC PLUS” for the HVDC projects and
as an “SVC PLUS” for FACTS. This technology stands out due to its compact modular design and a
new multilevel converter, which allows to generate an AC system of a virtually ideal sinus waveform
from DC voltage in the voltage source by means of a great number of fine steps without any additional
filters. The reactive power elements and filters of normally 50% of the active power, required in
HVDC “Classic” applications, can be done completely away with in this case, which helps reduce the
footprint of an HVDC station by approx. 40 %. VSC technology is the preferred solution for Smart
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Copyright © Siemens AG 2011. All rights reserved.
10
Grid applications, whereas the “Classic” and Bulk Thyristor technology is the solution for Super
Grids.
An overview of the first MMC HVDC project with a 200 kV XLPE DC sea cable transmission is
given in Fig. 11. The goal of this project was to eliminate bottlenecks in the overloaded Californian
grid: new power plants cannot be constructed in this densely populated area and there is no right-ofway for new lines or land cables. This is the reason why a DC cable is laid through the bay, and the
power flows through it by means of the HVDC PLUS technology in an environmentally compatible
way.
2010
=
~
=
Transmission
Constraints before TBC
Transmission
Constraints after TBC
Elimination of Transmission Bottlenecks
Energy Exchange
by Sea Cable
No Increase in
Short-Circuit Power
=
~
=
P = 400 MW
Q = +/- 170-300 MVAr
Dynamic Voltage Support
Fig. 11 – The “Trans Bay Cable“ Project in the U.S., World’s first VSC HVDC
with MMC Technology and +/- 200 kV XLPE Cable
2014
VDC = +/- 320 kV
864 MW
SylWin1
2013
800 MW
VDC = +/- 300 kV BorWin2
HelWin1 VDC = +/- 250 kV
576 MW
2013
=
~
=
~
==
~
=
=
864 MW
Fig. 12 – HVDC PLUS and WIPOS: Three Projects, Germany – Offshore VSC HVDC with 866
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11
Siemens’ second HVDC PLUS project is the world’s largest DC Offshore installation BorWin 2 with
a power transfer of 800 MW for Grid Access of wind energy (Fig. 12).
The entire PLUS system has a modular structure and can be flexibly configured, what simplifies its
standardization, see Fig. 13. The converter modules are connected on the secondary side of a highvoltage coupling transformer (for simplification not shown in the figure) to build the HVDC or the
SVC. Due to the MMC configuration, there is almost no – or, in the worst case, very small - need for
AC voltage filtering to achieve a clean voltage. The system configuration is very compact and
normally occupies 50 % less space than a “classic” HVDC or SVC systems.
Examples of projects with SVC PLUS and the configuration possibilities are shown in Fig. 14.
Converter Arm
Power Module
with DC Capacitor
PM 1
PM 1
PM 1
PM 2
PM 2
PM 2
PM n
PM n
PM n
v
Vd
v
ud
PM 1
PM 1
PM 1
PM 2
PM 2
PM 2
PM n
PM n
PM n
Phase Unit
Controlled Voltage Sources
Controlled Voltage Sources
Fig. 13 – VSC Technology with MMC: SVC PLUS and HVDC PLUS (ref. to Text)
Configuration of Multilevel Voltage Sources for SVC (left Side) and HVDC (right Side)
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Copyright © Siemens AG 2011. All rights reserved.
12
SVC PLUS:
 3 x PLUS L in parallel
 132 kV / 13.9 kV
a)
SVC PLUS:
 4 x PLUS L in parallel
 150 kV / 13.9 kV
2010
2011
… and London Array
World’s largest Offshore Wind Farm
630 MW & Upgrade up to 1 GW
b)
SVC PLUS:
 2 x PLUS M in parallel
 220 kV / 11 kV
2010
 Dynamic Voltage Support
during and after AC Line Faults
(Voltage Dip Compensation)
c)
Containerized Solutions:
SVC PLUS S: +/- 25 MVAr
SVC PLUS M: +/- 35 MVAr
SVC PLUS L: +/- 50 MVAr
SVC PLUS Hybrid (Option):
MSR (Mechanically Switched Reactors)
MSC (Mechanically Switched Capacitors)
Open Rack Solution (Building):
SVC PLUS C: +/-100 MVAr
Up to 4 parallel L-Units: +/- 200 MVAr
Fig. 14 – A wide Range of Application Possibilities:
a) Grid Access of Green Energy with SVC PLUS - Greater Gabbard and London Array, UK
b) Power Quality in AC Systems – Kikiwa Project, South Island, New Zealand
c) From Containerized to Open Rack and Hybrid Solutions
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Copyright © Siemens AG 2011. All rights reserved.
13
The state-of-the-art highly flexible MMC technology for HVDC PLUS and SVC PLUS makes it
possible to easily comply with all the known voltage quality requirements (Grid Codes) for grid access
of wind farms as well as for transmission systems. In addition to this, the MMC PLUS technology is
used for traction supply with Static Frequency Converters (SFC) and for industrial applications. The
field of synergies and applications is therefore boundless.
5.2 Super Grid Solutions with FACTS and HVDC - “Classic” and Bulk
The progressive worldwide urbanization, as well as the trend towards megacities with more than
10 million inhabitants, poses new challenges on the power transmission systems. In every country of
the world the economic pulses coming from cities provide more than half of the gross domestic
product of the respective country, according to UN-statistics. One of the most important factors for the
economic dynamics of megacities is an effective infrastructure. It goes without saying that the basis
for this infrastructure is constituted by a reliable and efficient power supply.
An important development in the power supply of megacities is the outsourcing of power generation
to close or more distant surrounding regions. That is, transmission networks and distribution systems
are forced to interconnect increasingly longer distances. Furthermore, efficiency and reliability of
supply play an important role in every planning, particularly in the face of increasing energy prices
and almost incalculable safety risks during power blackouts.
Such an example is shown in Fig. 15. In India, for the increasing power demands of the area of the
Megacity New Delhi, the world’s biggest FACTS project with series compensation (TCSC/FSC) was
installed at Purnea and Gorakhpur with a total rating of 2 x 1.7 GVAr, ref. to the figure. This project
provides clean and cheap hydro power from Bhutan over long distances. The systems at Purnea and
Gorakhpur Substations use a combination of FSC and TCSC. TCSC is used if fast control of the line
impedance is required, for load-flow control and for damping of power oscillations and FSC is an
economic way to reduce the transmission angle over the line and to increase the transmission capacity.
Fig. 15 – Tala TCSC Project: Bulk Hydro Power from Bhutan to Delhi Area
World’s largest FACTS for Series Compensation
The most devoted user of the Bulk Power DC transmission concept is China. The UHV HVDC
systems at 800 kV require the most state-of-the-art converter technology. The separate components of
this kind of installations boast impressive design and dimensions owing to the required insulation
clearance distances. China requires this HVDC technology to construct a number of high-power DC
energy highways, superimposed to the AC grid, in order to transmit electric power from huge hydro
power plants in the center of the country to the load centers located as far as 2,000 to 3,000 km away
with as little losses as possible. Fig. 16 depicts an example of the 3,000 MW HVDC project GuiGuang I in Southern China.
| 15
Copyright © Siemens AG 2011. All rights reserved.
14
.
2004
Fig. 16 – HVDC projects in Southern China enable low-Loss West-to-East Transmission of Hydropower-based electrical Energy produced in the Country‘s Interior to coastal Load Centers
(Example of Long-Distance Transmission Gui-Guang I)
The “next generation” HVDC project is the UHV DC Yunnan-Guangdong at a transfer capacity of
5 GW (see Figs.17 - 18). Siemens and the utility China Southern Power Grid succeeded to put pole 1
of this world’s first 800 kV HVDC into operation in December 2009 and pole 2 in June 2010.
Commercial Operation:
1,418 km
5,000 MW
 2009 – Pole 1
 2010 – Pole 2
+/- 800 kV DC
Siemens – the Leader in Bulk Power UHV DC Transmission Technology
Yunnan-Guangdong
Reduction in CO2
versus local Power Supply with Energy-Mix
32.9 m tons p.a. – by using Hydro Energy and HVDC for Transmission
Fig. 17 – Yunnan-Guangdong: World’s first 800 kV UHV DC in China Southern Power Grid
The Yunnan-Guangdong project helps save around 33 m tons CO2 in comparison with local power
generation, which, in view of the current energy mix in China, would be connected with a relatively
high carbon amount, ref. to Fig. 17. Figs. 18-19 give views of the huge dimensions of the HVDC
stations and the equipment.
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Copyright © Siemens AG 2011. All rights reserved.
15
Fig. 18 – Yunnan-Guangdong: Example of Sending Station Chuxiong; from ‘3D Model’ to Reality
Fig. 20 shows pictures of the system inauguration of Pole 1 of this big project, which in fact is a kickoff for the DC Super Grid Developments, worldwide. There are many benefits when using UHV DC:
at a voltage of +/- 800 kV, the line losses drop by approx. 60 % compared with the present standard of
500 kV DC at the same power – for 660 kV, the loss reduction is 43 %. When comparing transmission
losses of AC and DC, it becomes apparent that the latter typically has 30 to 40 % less losses. The
converter losses (i.e. those of both converter stations, incl. transformers, valve cooling and other
equipment) amount to 1.3 to 1.5 % of the rated power only (depending on design).
The second 800 kV HVDC project Xiangjiaba-Shanghai of State Grid Corporation of China (ref. to
Fig. 21a), which also involves Siemens as well as ABB and Chinese partners, boasts significantly high
yearly CO2 savings of over 40 m tons thanks to very high hydro power transmission capacity of
6.4 GW. This currently world’s biggest UHV DC started bipolar operation in June 2010. Siemens and
its Chinese partners delivered all HVDC transformers and thyristor valves with new 6-inch thyristors
for the sending station Fulong, one year ahead of schedule. These are the biggest HVDC transformers
and power converters ever built.
Further UHV DC projects at a transmission capacity of up to 9 GW are being planned in China, see
Fig. 21b). A total number of 35 “Bulk Power” HVDC projects are planned for the time period 2010 to
2020, and the total transmission capacity will amount to 217 GW (as currently planned). A great
number of these UHV DC projects in China is meant for power transmission from hydro power plants
situated in the middle of the country to the distant load centers.
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Copyright © Siemens AG 2011. All rights reserved.
16
800 kV DC
800 kV DC
2 x 400 kV DC
800 kV DC
Fig. 19 – 800 kV UHV DC Yunnan-Guangdong:
View of the Bipolar Valve Halls – Two 400 kV Systems in series to build 800 kV (upper Part)
Inside the 800 kV Valve Hall – the Converter System (Middle Part)
Bipolar DC Line - uniting the single +/- Lines coming out of the Station (Lower Part)
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Copyright © Siemens AG 2011. All rights reserved.
17
2,500 MW
2,500 MW
Fig. 20 – Yunnan-Guangdong UHV DC Inauguration on Dec. 28, 2009: Celebration of Pole 1
successful Commissioning and Start of full Bipolar Operation in June 2010
a)
Fulong – World’s biggest HVDC Converter
Station in Operation: Transformers &
Thyristor Valves with new 6-inch Thyristors
from Siemens Leshan
Xiangjiaba-Shanghai
Shanghai
Sichuan Power Grid
Chongqing
Xiangjiaba
Xiluodu left
Nanhui
Wuhan
Xiangjiaba
Zhexi
Changsha
Xiluodu-Zhu
zhou
Xiluodu
left
Xiluodu right
Xiluodu rightXiluodu-Zhex
i
970km
Zhuzhou
km
1728
2,071 km
Commercial Operation:
6,400 MW
 July 2010 – both Poles
+/- 800 kV DC
Guangdong
Reduction in CO2
versus local Power Supply with Energy Mix
41 m tons p.a. – by using Hydro Power and HVDC for Transmission
b)
1.
Yunnan – Guangdong
800 kV, 5000 MW, 2009/10
2.
Xiangjiaba – Shanghai
800 kV, 6400 MW, 2010
3.
Qinghai – Tibet
500 kV, 1200 MW, 2011
4.
Mongolia – Tianjin
660 kV, 4000 MW, 2012
5.
Russia – Liaoning
660 kV, 4000 MW, 2012
6.
Nuozhadu – Guangdong
800 kV, 5000 MW, 2012
7.
8.
9.
Jingping – Sunan
800 kV, 7200 MW, 2012
Xiluodu – Guangdong
500 kV, 2 x 3200 MW, 2013
Humeng – Tangshan
660 kV, 4000 MW, 2013
10. Ningdong – Zhejiang
800 kV, 7200 MW, 2013
11. Xiluodu – Zhejiang
800 kV, 7200 MW, 2013
12. Sichuan – Hunan
660 kV, 4000 MW, 2014
1 x B2B
3 x 500 kV
7 x 660 kV
19 x 800 kV
5 x 1000 kV
21. Baoqing – Liaoning
660 kV, 4000 MW, 2017
Heilongjiang
5
30
17
Xinjiang
34
Inrfar Mongolia
Gansu
35
15. Hami – Henan
800 kV, 7200 MW, 2014
22
16
20
15
Ningxia
Qinghai
Xizang
31
3
23
14
Beijing
25
Hebei
28
19 Shanxi
Shaanxi
10
33
Anhuj
Shanghai
1
8
11
27
4
6
24
Hainan
Bangkok
Jiangsu
Hubai
3
Zheijang
Jiangxi
Hunan
Guizhou 13
Yunnan
Liaoning
Tianjin
26
12
32
7
23. Tibet – Chongqing
800 kV, 7200 MW, 2017
24. Jinghong – Thailand
500 kV, 3000 MW, 2018
25. Ximeng – Wuxi
800 kV, 7200 MW, 2018
Shandong
Henan
18
2
Sichuan &
Chongqing
21
9
4
13. Xiluodu – Hunan
660 kV, 4000 MW, 2014
14. Humeng – Shandong
800 kV, 7200 MW, 2014
Jilin
29
22. Hami – Shandong
800 kV, 7200 MW, 2017
Fujian
Guangdong Taiwan
26. Baihetan – Hubei
800 kV, 7200 MW, 2018
27. Wudongde – Fujian
1000 kV, 9000 MW, 2018
28. Northwest – North
B2B, 1500 MW, 2018
29. Mongolia – Jing-Jin-Tang
800 kV, 7200 MW, 2019
30. Russia – Liaoning
800 kV, 7200 MW, 2019
31. Zhundong – Jiangxi
1000 kV, 9000 MW, 2019
32. Tibet – Zhejiang
1000 kV, 9000 MW, 2019
33. Baihetan – Hunan
800 kV, 7200 MW, 2020
34. Yili – Sichuan
1000 kV, 9000 MW, 2020
35. Kazakhstan – Chengdu
1000 kV, 9000 MW, 2020
Fig. 21 – a) World’s biggest and longest 800 kV DC Transmission Project: Xiangjiaba-Shanghai
b) Over 217 GW of additional HVDC Transmission Capacity are expected in China
between 2010 and 2020
Copyright © Siemens AG 2011. All rights reserved.
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18
5.3 Super Grid Solutions with GIL – Gas Insulated Lines
GIL initially was developed in 1974 and 1975. At that time, the cost level compared to an overhead
line was in the range of 30 times more expensive. Later, in 1998 and 1999, a second generation of GIL
was developed where the power transmission capability was increased from 2,500 A to 4,000 A and at
the same time the cost factor went significantly down in comparison with overhead lines and cables.
Fig. 22 gives examples of a new directly buried Bulk Power GIL installation in Germany, near the
International Airport of the City of Frankfurt.
Site View: Status June 2009
Site View: Status October 2009
Laying Process:
 Pushing the
GIL Element
by Element
and
 Phase by
Phase
2010




Customer: Amprion
Location: Airport Frankfurt
Award of Contract: July 2008
Installation: first directly buried GIL
GIL vs. Cable
2 Systems 4 Systems
Same Costs
 Transmission Capacity: 2 x 1,800 MVA
 Length of GIL: appr. 1 km
 Gas for Insulation: 80% N2, 20% SF6
Fig. 22 – Bulk Power Corridor with GIL: 400 kV Installation at Kelsterbach, Germany
6. CONCLUSIONS AND OUTLOOK
The security of power supply in terms of reliability and blackout prevention has the utmost priority
when planning and extending power grids. The availability of electric power is the crucial prerequisite
for the survivability of a modern society and power grids are virtually its lifelines. The aspect of
sustainability is gradually gaining in importance in view of such challenges as the global climate
protection and economical use of power resources running short. It is, however, not a means to an end
to do without electric power in order to reduce CO2 emissions. A more appropriate way is to integrate
renewable energy resources to a greater extent in the future (energy mix) and, in addition to this, to
increase the efficiency of conventional power generation as well as power transmission and
distribution without loss of system security.
The future power grids will have to withstand increasingly more stresses caused by large-scale energy
trading and a growing share of fluctuating regenerative energy sources, such as wind and solar power.
In order to keep generation, transmission and consumption in balance, the grids must become more
flexible, i.e. they must be controlled in a better way. State-of-the-art power electronics with HVDC
and FACTS technologies provides a wide range of applications with different solutions, which can be
adapted to the respective grid in the best possible manner. DC current transmission constitutes the best
solution when it comes to loss reduction when transmitting power over long distances. The HVDC
technology also helps control the load flow in an optimal way. This is the reason why, along with
system interconnections, the HVDC systems become part of synchronous grids increasingly more
often – either in form of a B2B for load-flow control and grid support, or as a DC energy highway to
relieve heavily-loaded grids.
FACTS technology was originally developed to support systems with long AC transmission lines.
FACTS installations are increasingly more often used in meshed grids to eliminate congestion and
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Copyright © Siemens AG 2011. All rights reserved.
19
bottlenecks. FACTS will play its role for strengthening long distance AC transmission and meshed
grids as well.
In conclusion of the previous sections and based on studies and practical experience, the features of
the different solutions can be summarized as follows (Fig. 23):
Solutions with Overhead Lines
Note: Power AC @ 1 System 3 , Power DC @ Bipole +/-
 High-Voltage DC Transmission:
 HVDC “Classic” with 500 kV (HV) / 660 kV (EHV) – 3 to 4 GW
 HVDC “Bulk” with 800 kV (UHV) – 5 GW to 7.5 GW
Option UHV DC 1,100 kV: 10 GW
The Winner
is HVDC !
For Comparison: HVDC PLUS (VSC) ≤ 1,100 MVA
 AC Transmission:
 400 kV (HV) / 500 kV AC (EHV) – 1.5 / 2 GVA
 800 kV AC (EHV) – 3 GVA
 1,000 kV AC (UHV) – 6 to 8 GVA
Solutions with DC Cables *
* Distances over 80 km: AC Cables too complex
 500 / 600 kV DC – per Cable, Mass Impregnated: 1 GW to 2 GW (actual - prospective)
Solutions with GIL – Gas Insulated Lines
** Reference: Bowmanville, Canada, 1985 - Siemens
*** Reference: Huanghe Laxiwa Hydropower Station,
China, 2009 - CGIT (USA)
 400 kV AC (HV) – 1.8 GVA / 2.3 GVA (directly buried / Tunnel or Outdoor)
 500 kV AC (EHV) – 2.3 GVA / 2.9 GVA (directly buried / Tunnel or Outdoor)
 550 kV AC (EHV) – Substation: Standard 3.8 GVA / Special 7.6 GVA **
 800 kV AC (EHV) – Tunnel: 5.6 GVA ***
Fig. 23 – Comparison of AC and DC Bulk Power Transmission Solutions
Fig. 23 includes an option for a 1,000 kV UHV DC application, which is currently under discussion in
China. This option offers the lowest losses and highest transmission capacity, however, it is obvious
that the extended insulation requirements for 1,000 kV will lead to an increase of the already huge
mechanical dimensions of all equipment, including PTs, CTs, breakers, disconnectors, busbars,
transformers and reactive power equipment.
HVDC – High-Voltage DC Transmission: It makes P flow
 Three HVDC Options available: PLUS (VSC), “Classic” and Bulk
 With DC, Overhead Line Losses are typically 30-40 % less than with AC
 For Cable Transmission (over 80 km), HVDC is the only Solution
 HVDC can be integrated into the AC Systems
 HVDC supports AC in Terms of Stability
 System Interconnection with HVDC:
 DC is a “Firewall” against Cascading Disturbances
 Bidirectional Control of Power Flow – quite easy
 Frequency, Voltage and POD Control available
 Staging of the Links – with DC quite easy
 No Increase in Short-Circuit Power
 DC is a Stability Booster
Fig. 24 – Summary: Features and Benefits of HVDC
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Copyright © Siemens AG 2011. All rights reserved.
20
Regarding long distance Bulk Power transmission, HVDC is the best solution, offering minimal
losses. The features and benefits of HVDC are summarized in Fig. 24. It goes without saying that a
combination of FACTS and classic line-commutated HVDC technology is feasible as well. In the case
of state-of-the-art VSC-based HVDC technologies, the FACTS function of reactive power control is
already integrated that is, additional FACTS controllers are superfluous. However, “Bulk Power”
transmission up to the GW range remains reserved to classic, line-commutated thyristor-based HVDC
systems.
For Bulk Power Transmission over short distances, GIL is a very attractive solution due to its high
transmission capacity and small right-of-way requirements, in comparison with cables and overhead
lines. This includes Bulk Power solutions for supply of both megacities and load centers. GIL can also
be used in long tunnels and on bridges – there are no security and no EMI issues with this technology.
The vision of a European Super Grid is gaining impetus since the foundation of the DESERTEC
Industrial Initiative in 2009. The basic idea is the combination of different kinds of renewable energies
across Europe – a very promising scenario, which has to be developed step-by-step, ref. to Fig. 25.
Source: DESERTEC Foundation
An Initiative of the Club of Rome
Siemens has a commitment in the Desertec Industrial
Initiative (DII). The objective of this initiative is to
develop over the mid-term a technical and economic
concept for solar power from Africa. Work will also
focus on the clarification of legal and political issues.
Fig. 25 – Super Grid in Europe: The DESERTEC Concept
7. REFERENCES
[1] European Technology Platform SmartGrids – Vision and Strategy for Europe’s Electricity
Networks of the Future; 2006, Luxembourg, Belgium
[2] D. Retzmann, “Modular Multilevel Converter – Technology & Principles” and “HVDC / FACTS
using VSC – Applications & Prospects”, Cigré-Brazil B4 “Tutorial on VSC in Transmission
Systems – HVDC & FACTS”, October 6-7, 2009, Rio de Janeiro, Brazil
[3] W. Breuer, D. Povh, D. Retzmann, C. Urbanke, M. Weinhold, “Prospects of Smart Grid
Technologies for a Sustainable and Secure Power Supply”; The 20TH World Energy
Congress, November 11-15, 2007, Rome, Italy
[4] M. Claus; D. Retzmann, D. Sörangr, K. Uecker, “Solutions for Smart and Super Grids
with HVDC and FACTS”, 17th Conference on Electric Power Supply Industry CEPSI
2008, October 27-31, Macau, SAR of China
22 |
Copyright © Siemens AG 2011. All rights reserved.
21
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22
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