November 11th to 15th 2007 - The 20TH World Energy Congress & Exhibition, Rome , Italy

Prospects of Smart Grid Technologies for a Sustainable and Secure Power Supply W. Breuer, D. Povh, D. Retzmann*, Ch. Urbanke, M. Weinhold Siemens, Germany

ABSTRACT Deregulation and privatization are posing new challenges on high voltage transmission and on distributions systems as well. System elements are loaded up to their thermal limits, and power trading with fast varying load patterns is contributing to an increasing congestion. In addition to this, the dramatic global climate developments demand for changes in the way electricity is supplied. Environmental sustainability and security of power supply are the goals for future grid developments. Estimated global investments required in the energy sector until 2030 are $16 trillion, according to IEA statistics. In Europe alone, some € 500 billion worth of investment will be needed to upgrade the electricity transmission and distribution infrastructure [1]. The electricity network of the future must be secure, cost-effective and environmentally compatible. KEY WORDS: Security and Environmental Sustainability of Supply; Smart Grid Technologies; Elimination of Bottlenecks in Transmission; Blackout Prevention; Increase in Transmission Capacity; Reduction in Transmission Losses; Enhanced Grid Access for Regenerative Energy Sources (RES)

1. INTRODUCTION The vision and enhancement strategy for the future electricity networks is depicted in the program for “SmartGrids”, which was developed within the European Technology Platform (ETP) of the EU in its preparation of 7th Frame Work Program.

*[email protected]

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Features of a future “SmartGrid” 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

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. Links will be strengthened across Europe and with other countries where different but complementary renewable resources are to be found. For the interconnections, innovative solutions to avoid congestion and to improve stability will be essential. HVDC (High Voltage Direct Current) 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 Backto-Back for grid power flow control (elimination of congestion and loop flows) or as a long-distance point-to-point transmission. 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 [1]. 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. GLOBAL TRENDS IN POWER MARKETS In the nearest future we will have to face two mega-trends. One of them is the demographic change. The population development in the world runs asymmetrically. On the one hand, a dramatic growth of population is to be seen in developing and emerging countries. On the other hand, the population in highly developed countries is stagnating. Despite these differences, the expectancy of life increases everywhere. This increase in population (the number of elderly people in particular) poses great challenges to the worldwide infrastructure. Water, power supply, health service, mobility – these are only some of the notions which cross one’s mind directly. The second mega-trend to be mentioned is the urbanization with its dramatic growth worldwide. In less than two years more people will be living in cities than in the country. Megacities keep on growing. Already today they are the driving force of the world’s economy: Tokyo e.g. is the largest city in the world, its population is 35 m people and it is responsible for over 40 % of the Japanese economic performance. Another example is Los Angeles with its 16 m citizens and a share of 11 % in the US-economy; or Paris with its 10 m citizens and 30 % of the French gross domestic product. Both of these mega-trends make the demand for worldwide infrastructure grow. Fig. 1 depicts the development of world population and power consumption up to 2020. The figure shows that particularly in developing and emerging countries the increase is lopsided. Fig. 2 highlights these phenomenal developments in China’s megacity Shanghai. This development goes hand in hand with a continuous reduction in non-renewable energy resources. The resources of conventional as well as non-conventional oil are gradually coming to an end. Other energy sources are also running short, ref. to Fig. 3. So, the challenge is as follows: for the needs of a dramatically growing world population with the simultaneous reduction in fossil power sources, a

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proper way must be found to provide reliable and clean power. This must be done in the most economical way, for a lot of economies, in the emerging regions in particular, cannot afford expensive environmentally compatible technologies. 7.5 Billion

World Population

27,000 TWh Power Consumption

6.1 Billion 4.4 Billion 45%

15,400 TWh

Developing and newly Industrialized Countries

29%

8,300 TWh 15%

71%

85% 1980

Industrialized Countries (OECD), CIS, Eastern Europe

55%

2020

2000

Sources: IEA, UN, Siemens PG GS4 - 2006

Fig. 1: Development of World Population and Power Consumption - 1980 to 2020 Financial District Pudong, Shanghai

1989

Today

Fig. 2: Development of Megacities – Example Shanghai, China Lifetime assuming static Consumption

Lifetime (proven Reserves)

Lifetime (Reserves + Resources)

Conventional Oil

45 years

70 years

Non-conventional Oil

20 y.

30-80 years

Conventional Gas

65 years

150 years

Non conventional Gas

0 years

600 years

Coal

200 years

1300 years

Uranium

100 years

>1000 years with recycling

Sources: IEA, UN, Siemens PG GS4 - 2006

Fig. 3: Decreasing Energy Resources 3/30

Consequently, we have to deal with an area of conflicts between reliability of supply, environmental sustainability as well as economic efficiency [10]. The combination of these three tasks can be solved with the help of ideas, intelligent solutions as well as innovative technologies, which is the today’s and tomorrow’s challenge for the planning engineers worldwide. This is exactly what Siemens has been doing over the last 160 years. In the field of power supply, the founder of the company, Werner von Siemens, launched the electrical engineering with his invention of the dynamo-electric principle in 1866. Since that time electric power supply has established itself on all the continents, however, with an unequal degree of distribution. Depending on the degree of development and power consumption, different regions have very different system requirements, ref. to Fig. 4.

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 (FACTS, HVDC) Introduction of higher Voltage Levels Isolated small Grids

Developing Countries

High Investments in Transmission Systems

Emerging Countries

Industrialized Countries

Fig. 4: Development of Power Consumption and System Requirements In developing countries, the main task is to provide local power supply, e.g. by means of developing small isolated networks. Emerging countries have a dramatic growth of power demand. Enormous amounts of power must be transmitted to large industrial regions, partly over long distances, that is, from large hydro power plants upcountry to coastal regions which involves high investments. The demand for power is growing as well. Higher voltage levels are needed, as well as long-distance transmission by means of FACTS and HVDC. During the transition, the newly industrialized countries need energy automation, life-time extension of the system components, such as transformers and substations. Higher investments in distribution systems are essential as well. Decentralized power supplies, e.g. wind farms, are coming up. Industrialized countries in their turn have to struggle against transmission bottlenecks, caused, among other factors, by increase in power trading. At the same time, the demand for a high reliability of power supply, high power quality and, last but not least, clean energy increase in these countries. In spite of all the different requirements one challenge remains the same for all: sustainability of power

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supply must be provided. Our resources on the Earth are limited, as shown in Fig.3, and the global climate is very sensitive to environmental influences. The global industrialization with its ongoing CO2 production is causing dramatic changes in the climate developments, ref. to Fig. 5.

Carbon Dioxide Variations in the Air 400 CO2 Concentration (ppmv)

The Industrial Revolution has caused a dramatic Rise in CO2

350

300

A crucial Global Issue: to achieve CO2 Reduction

250

200

Ice Age

Würm / Weichsel

0

100

Thousands of Years ago

Mindel / Elster

Riß / Saale

200

300

400

Sources: Wikipedia, Siemens PTD TI, 2006

Fig. 5: CO2 Increase due to Human Influence is much higher than Natural Fluctuation There is no ready-made solution to this problem. The situation in different countries and regions is too complex. An appropriate approach is, however, obvious: power generation, transmission, distribution and consumption must be organized efficiently. The approach of the EU’s “SmartGrid” vision is an important step in the direction of environmental sustainability of power supply, and new transmission technologies can effectively help reduce losses and CO2 emissions.

3. PROSPECTS OF POWER SYSTEM DEVELOPMENT The development of electric power supply began more than one hundred years ago. Residential areas and neighboring establishments were at first supplied with DC via short lines. At the end of the 19th century, AC transmission was introduced, using higher voltages to transmit power from remote power stations to the consumers. In Europe, 400 kV became the highest voltage level, in Far-East countries mostly 550 kV, and in America 550 kV and 765 kV. The 1150 kV voltage level was anticipated in some countries in the past, and some test lines have already been built. Fig. 6 and 7 depict these developments and prospects. Due to 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 size and complexity of power systems all over the world have grown. Power systems have been extended by applying interconnections to the neighboring systems in order to achieve technical and economical advantages. Large systems covering parts of or even whole continents, came into existence, to gain well known advantages, e.g. the possibility to use larger and more economical power plants, reduction of reserve capacity in the

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systems, utilization of the most efficient energy resources, as well as achieving an increase in system reliability. However, some Countries

1600 kV

will finally “go” ≥ 1 GV

1400

6

1200 1000

5

800 600 400

2

1

200

4

3

EHV: 800 kV as “realistic” Standard

The “Initial” Statement

0 1900

1910

1920 1 2 3 4 5 6

1930

1940

1950

1960

1970

1980

1990

2000 Year

2010

110 kV Lauchhammer – Riesa / Germany (1911) 220 kV Brauweiler – Hoheneck / Germany (1929) 287 kV Boulder Dam – Los Angeles / USA (1932) 380 kV Harspranget – Halsberg / Sweden (1952) 735 kV Montreal – Manicouagan / Canada (1965) 1200 kV Ekibastuz – Kokchetav / USSR (1985)

Fig. 6: Development of AC Transmission – Milestones and Prospects In the future of liberalized power markets, the following advantages will become even more important: pooling large power generation stations, sharing spinning reserve and using most economic energy resources, and considering ecological constraints, such as the use of large nuclear and hydro power stations at suitable locations, solar energy from desert areas and embedding big offshore wind farms. Examples of large AC interconnections are systems in North America, Brazil, China and India, as well as in Europe (UCTE - installed capacity 530 GW) and Russia (IPS/UPS - 315 GW), which are planned to be interconnected in the future.

ƒ

ƒ 1000 kV Line: SIL = 4 GW Transmission of 6-10 GW is feasible

ƒ

Voltage Levels of 735 kV to 765 kV AC were introduced in the following Countries: Canada, Brazil, Russia (USSR), South Africa, South Korea, U.S.A. and Venezuela UHV Transmission Lines (1,000 kV and above) were built in Russia and Japan ƒ Ekibastuz – Kokchetav (500 km) ƒ Kokchetav – Kustanay (400 km) ƒ Minami – Niigata / Nishi – Gunma (200 km) ƒ Kita – Tochigi / Minami – Iwaki (250 km) However, today these UHV Transmission Lines are operated at 500 kV

Fig. 7: Development of EHV and UHV AC Transmission

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UCTE Synchronous Interconnections: Δ f [mHz] 15

Frequency

5

Inter-Area Oscillations with Magnitudes up to 1000 MW



Damping Measures necessary

0

Spain

-100

Poland

-5

 P [MW]

Frequency & Power

-200

-15 -25

-300

-35

(border to France) Germany

-45

(border to France)

Active Power France-Germany

-400

(one 400-kV system)

-55 -65

-500

-75

-600 0

3

6

9

t [s]

15

12

Signals: simulated & measured by WAMS

… the 1st Step for System Extension The Interconnection CENTREL to UCPTE

a)

1st UCTE Synchronous Zone In synchronous Operation with 1st Zone

NORDEL

2nd UCTE Synchronous Zone In synchronous Operation with 2nd Zone

b)

Zone 1 & 2 “resynchronized” since 10-10-2004 …

… since then, the Risk of large Inter-Area Oscillations in UCTE has been increased *

IPS/UPS c)

UCTE - 1

* depending on the actual Load Flow Situation

UCTE - 2

Options for Grid Interconnection Turkey

AL MAGHREB

c) Fig. 8: UCTE – Steps a) & b) for Interconnection of Zones 1, 2 and further Options c) It is, however, a crucial issue that with an increasing size of the interconnected systems (ref. to Fig. 8), the advantages diminish. There are both technical and economical limitations in the interconnection if the energy has to be transmitted over extremely long distances through the interconnected synchronous AC systems. These limitations are related to problems with low frequency inter-area oscillations ([6], Fig. 8a), voltage quality and load flow. This is, for example, the case in the UCTE system, where the 400 kV voltage level is in fact too low for large cross-border and inter-area power

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exchange. Bottlenecks are already spotted (Fig. 9, NTC values) and, for an increase in power transfer, advanced solutions must be applied. Bottlenecks in the UCTE System

NTC Values for EastWest Power Transfer Source: UCTE - 5 / 2003

NTC = Net Transfer Capacity

Fig. 9: European Power Systems - Bottlenecks in UCTE In deregulated markets, the loading of existing power systems will further increase, leading to bottlenecks and reliability problems. System enhancement will be essential to balance the load flow and to get more power out of the existing grid. Large blackouts in America and Europe confirmed clearly that the favorable close electrical coupling of the neighboring systems might also include the risk of uncontrollable cascading effects in large and heavily loaded synchronous AC systems [9]. 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. 10: Large Power System Interconnections - Benefits of Hybrid Solutions 8/30

Therefore, the strategies for the development of large power systems go clearly in the direction of hybrid transmissions, consisting of DC and AC interconnections, including FACTS. Hybrid interconnected systems such as these offer significant advantages, in terms of technology, cost savings and reliability [9, 11, 12, 13, 19, 20]. Fig. 10 shows schematically a hybrid system with HVDC and FACTS. Power exchange in the neighboring areas of interconnected systems can be achieved by means of AC links, preferably with FACTS to increase transmission capacity and stability. The transmission of large power blocks over long distances should, however, be realized by means of HVDC links directly to the locations of power demand [12].

4. SECURITY OF SUPPLY – LESSONS LEARNED FROM THE BLACKOUTS In Fig. 11, a summary of the US-Canada Blackout on August 14, 2003 is shown. In Fig. 11 a) a view on the affected area is given and the satellite photos show the situation before and after the events. The figure indicates that the Québec’s system in Canada was not affected due to its DC interconnections to the US, whereas Ontario (synchronous interconnection) was fully “joining” the cascade. The reasons why Québec “survived” the Blackout are very clear: „

Québec´s major Interconnections to the affected Areas are DCLinks

„

These DC-Links are like a Firewall against Cascading Events

„

They split the System at the right Point on the right Time, whenever required

„

Therefore, Québec was “saved”

„

Furthermore, the DCs assisted the US-System Restoration by means of “Power Injection”

Fig. 11b) depicts the results of a study on the related transmission systems, published in May 2002. It can be seen that load flow in the system is not well matching the design criteria, ref. to the “hot lines”, shown in red color. In the upper right-hand corner of the figure, one of the later Blackout events with “giant” loop flows is attached which occurred just in the same area under investigation one year before. Fig. 12 shows that the probability of large Blackouts is much higher than calculated by mathematical modeling, particularly when the related amount of power outage is very large. The reasons for this result are indicated in the figure. This means that, when once the cascading sequence is started, it is mostly difficult or even impossible to stop it, unless the direct causes are eliminated by means of investments into the grid and by an enhanced training of the system operators for better handling of the emergency situations. For these reasons, further Blackouts occurred in the same year. The largest was the Italian Blackout, six weeks after the US-Canada events. It was initiated by a line trip in Switzerland. Reconnection of the line after the fault was not possible due to a very large phase angle difference (about 60 degrees, leading to blocking of the Synchro-Check device). 20 min later a second line tripped, followed by a fast trip-sequence of all interconnecting lines to Italy due to overload. During this sequence, the frequency in Italy ramped down for 47.5 Hz within 2.5 min, and the whole country blacked-out. Several reasons were reported: wrong actions of the operators in Italy (insufficient load rejection) and a very high power import from the neighboring countries in general. Indeed, during the night from Saturday to Sunday, the scheduled power import was 6.4 GW - this is 24 % of the total consumption at that time (27 GW; EURELECTRIC Task Force Final Report 06-2004). The real power import was

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even higher (6.7 GW; possibly due to the country-wide celebration of what is known as “White Night”), ref. to Fig. 13.

Blackout: a large Area is out of Supply

Québec´s HVDCs assist in Power Supply and System Restoration

However, some Islands still have local Supply

Before the Blackout

a)

Source: EPRI 2003

*

System Enhancement necessary ! Source: ITC 8/2003 – “Blackout”

Source: National Transmission Grid Study; U.S. DOE 5/2002 – “Preview”

b)

* PTDF

Problems only in the synchronous interconnected Systems

= Power Transfer Distribution Factor

Fig. 11: Blackouts 2003 - Example United States a) The Blackout Area - and a Satellite View b) Congestion and Loop Flows - Forecasting Studies and Cascading Events

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Fig. 12: Reasons for high Probability of Large Blackouts ... the Risk for a Spread of Disturbance to UCTE was high

“Scheduled” Power Transfer from the Neighbors to Italy: 6.4 GW out of 27 GW * Consumption: 24 % is too high !

From “White Night” to “Black Night”

Europe needs Enhancements, too

Due to Country-Wide Celebrations of the “White Night” in Italy, an increased Power Import of 6.7 GW was observed during Saturday Night, 9-27-2003

*Source: EURELECTRIC Task Force Final Report 06-2004

Fig. 13: Six Weeks after the US-Canada Blackout - a very large Blackout in Italy … In Table 1, a summary of the root causes for the Italian Blackout is given. It can be concluded, that the existing power systems from their topology are not designed for wide-area energy trading. The grids are close to their limits. Restructuring will be essential, and the grids must achieve “Smart” features, as stated before. This is also confirmed by the recent large blackout on 4.11.2006 which affected eight EU countries (Fig. 14). It has highlighted the fact that Continental Europe is already behaving in some respects 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. Identifying, planning and building this infrastructure in liberalized markets is an ongoing process that requires regular monitoring and coordination between market actors [1]. The electric power supply is essential for life of a society, like the blood in the body. Without power supply there are devastating consequences for daily life: breakdown of public transportation systems, traffic jams, computer outages as well as standstill in factories, shopping malls, hospitals etc.

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Lessons Learned: Power Systems have not been designed for “wide-Area” Energy Trading with daily varying load patterns

A Key-Issue in many Power Systems today: Source: UCTE Interim Report 10-27-2003 The Grids are “close to their

Limits”

Table 1: Summary of Root Causes for the Italian Blackout and Action Plan UCTE Interim Report 10-27-2003

Source:

Presented at CEPSI, 6-10 November, 2006, Mumbai - India

Fig. 14: European Power System Disturbance on 4th November 2006

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In Fig. 15, a conclusion on the today’s power system limitations is given and the solutions are outlined.

Increased Use of Distributed and Renewable Energy Resources

Need for more Energy

Capacity Increase and Bulk Tower Transmission over Long Distances

Urbanization Scarcity of Natural Resources

Distribution within congested Areas/Mega-Cities

Environmental Awareness

Goal: reliable, flexible, safe and secure Grids

Open Markets

Fig. 15: Challenges in Power Transmission and Distribution 5. USE OF SMART GRID TECHNOLOGIES FOR SYSTEM ENHANCEMENT AND GRID INTERCONNECTION In the second half of the last century, high power HVDC transmission technology was introduced, offering new dimensions for long distance transmission. This development started with the transmission of power in a range of a few hundred MW and was continuously increased. Transmission ratings of 3 GW over large distances with only one bipolar DC line are state-of-the-art in many grids today. World’s first 800 kV DC project in China has a transmission rating of 5 GW (ref. to section 6.) and further projects with 6 GW or even higher are at the planning stage. In general, for transmission distances above 700 km, DC transmission is more economical than AC transmission (≥ 1000 MW). Power transmission of up to 600 - 800 MW over distances of about 300 km has already been achieved with submarine cables, and cable transmission lengths of up to about 1,000 km are at the planning stage. Due to these developments, HVDC became a mature and reliable technology [3, 12, 13]. During the development of HVDC, different kinds of applications were carried out. They are shown schematically in Fig. 16. The first commercial applications were HVDC sea cable transmissions, because AC cable transmission over more than 80-120 km is technically not feasible due to reactive power limitations. Then, long distance HVDC transmissions with overhead lines were built as they are more economical than transmissions with AC lines. To interconnect systems operating at different frequencies, Back-to-Back (B2B) schemes were applied. B2B converters can also be connected to long AC lines (Fig. 16a). A further application of HVDC transmission which is very important for the future is its integration into the complex interconnected AC system (Fig. 16c). The reasons for these hybrid solutions are basically lower transmission costs as well as the possibility of bypassing heavily loaded AC systems [12]. Typical configurations of HVDC are depicted in Fig. 17. The major benefit of the HVDC, both B2B and LDT, is its incorporated ability of fault-current blocking which serves as an automatic firewall for Blackout prevention in case of cascading events, which is not possible with synchronous AC links.

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Can be connected to long AC Lines

a)

b)

a) Back-to-Back Solution b) HVDC Long Distance Transmission c) Integration of HVDC into the AC System Hybrid Solution

c)

Fig. 16: Types of HVDC Transmissions

HVDC - High Voltage DC Transmission: It makes P flow z HVDC “Classic” with LT Thyristors* (Line-commutated Converter) z HVDC “Bulk” with 800 kV – for 5,000 MW to > 7,000 MW z HVDC PLUS (Voltage-Sourced Converter – VSC) 800 kV for minimal Line Transmission Losses

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

AC

Submarine Cable Transmission

AC

AC

Long Distance OHL Transmission

AC

AC DC Line

DC Cable

* LTT = Light-Triggered Thyristor with integrated Break-over Protection

Fig. 17: HVDC Configurations and Technologies HVDC PLUS (Fig. 18) is the preferred technology for interconnection of islanded grids to the power system, such as off-shore wind farms. This technology provides the “Black-Start” feature by means of self-commutated voltage-sourced converters (VSC). Voltage-sourced converters do not need 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. Siemens uses an innovative Modular Multilevel Converter (MMC) technology for HVDC PLUS with low switching frequencies. Therefore only small or even nor filters are required at the AC side of the converter transformers. Fig. 18 summarizes the advantages in a comprehensive way. The specific features of MMC are explained in details in [21]. Since the 1960s, Flexible AC Transmission Systems have been developed to a mature technology with high power ratings [4, 5]. The technology, proven in various applications, became mature and highly reliable. FACTS, based on power electronics, have been developed to improve the performance of

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weak AC Systems and to make long distance AC transmission feasible [4]. FACTS can also help solve technical problems in the interconnected power systems. FACTS are applicable in parallel connection (SVC, Static VAR Compensator - STATCOM, Static Synchronous Compensator), in series connection (FSC, Fixed Series Compensation - TCSC/TPSC, Thyristor Controlled/Protected Series Compensation - S³C, Solid-State Series Compensator), or in combination of both (UPFC, Unified Power Flow Controller - CSC, Convertible Static Compensator) to control load flow and to improve dynamic conditions. Fig. 19 and 20 show the basic configurations of FACTS.

¾ Low Switching Frequency ¾ Reduction in Losses ¾ Less Stresses

In Comparison with 2 and 3-Level Converter Technologies … with Advanced VSC Technology = = =

= = =

~ ~ ~

~ ~ ~

= = =

= = =

Clean Energy to Platforms & Islands …

Fig. 18: DC with VSC – HVDC PLUS, the Power Link Universal System

FACTS - Flexible AC Transmission Systems: Support of Power Flow z SVC – Static Var Compensator* (The Standard of Shunt Compensation) z SVC PLUS (= STATCOM - Static Synchr. Compensator, with VSC) z FSC – Fixed Series Compensation and SCCL ** z TCSC – Thyristor Controlled Series Compensation* for Shortz TPSC – Thyristor Protected Series Compensation** Circuit Current z GPFC – Grid Power Flow Controller* (FACTS-B2B) Limitation z UPFC – Unified Power Flow Controller (with VSC)

AC

AC

* with LT Thyristors

GPFC/UPFC / UPFC

FSC

SVC / STATCOM AC

AC

/ TPSC TCSC/TPSC

Fig. 19: Transmission Solutions with FACTS 15/30

AC

AC

** with special High Power LT Thyristors

„ „ „ „

Voltage Control Reactive Power Control Power Oscillation Damping Unbalance Control (Option)

Benefits: o Improvement of Voltage Quality o Increased Stability

a)

Photo: 2 SVCs Pelham – SLD: 2 SVCs Harker – NGC, UK

~

~

TCSC/TPSC

α

FSC

Photo: TCSC & FSC, Kayenta, USA

b) Controlled Series Compensation:

Fixed Series Compensation: 

Increase in Transmission Capacity

Mostly, a Combination of both is used

  

Damping of Power Oscillations Load-Flow Control Mitigation of SSR

Fig. 20: Main FACTS Configurations (ref. to Text) a) SVC for Parallel Compensation b) TCSC/TPSC and FSC for Series Compensation 16/30

GPFC is a special DC back-to-back link, which is designed for fast power and voltage control at both terminals [14]. In this manner, GPFC is a “FACTS B2B”, which is less complex and less expensive than the UPFC. Rating of SVCs can go up to 800 MVAr, series FACTS devices are installed on 550 and 735 kV levels to increase the line transmission capacity up to several GW. Recent developments are the TPSC (Thyristor Protected Series Compensation) and the Short-Circuit Current Limiter (SCCL), both innovative solutions using special high power thyristor technology [14]. The world’s biggest FACTS project with Series Compensation (TCSC/FSC) is at Purnea and Gorakhpur in India with a total rating of 1.7 GVAr. Fig. 21 depicts the Siemens high power electronic applications worldwide. In the figure the number and the expansion in large HVDC long-distance transmission projects are also indicated. Lamar 2005 Virginia Smith 1988 Lugo 1985 3, 2 El Dorado 2006

2 Bellaire & Crosby 2008 Inez 1998 Spring Valley 1986 2 Dominion 2003 2 Marcy 2001-2003

Devers 2006

••

Nine Mile 2005 Dayton 2006

• • • • • • • • •••••• • • •• • ••• •• • • •• •• • •

Porter 2006 Paul Sweet 1998 2 Adelanto 1995 2 Midway 2004 3 Vincent 2000 Clapham 1995, Refurbishment Military Highway 2000

2 Tecali 2002

Eddy County 1992 La Pila 1999

•

Nopala 2007 Cerro Gordo 1999 3 Juile 2002

.

Imperatriz 1999 Sinop 2007 Serra de Mesa 1999

… and over 115 Industry SVCs all over the World Status: 06-2007

In total: over 170 SVCs

•

• • • • •• • • • • • • • •

•• •

Fortaleza 1986 Milagres 1988

•

K.I. North 2004

Campina Grande 2000

Maputo 2003

Funil 2001 P. Dutra 1997

• •••

Illovo Athene Impala

Muldersvlei 1997

Load Flow

2 Hechi 2003 2, 2 Tian Guang 2003 3 Puti 2005 2 Gooty 2003 2 Cuddapah 2003

•

2 Sabah 2006

• •

Kapal 1994

•

•

1994-1995

Limpio 2003

2 Yangcheng 2000

Jember 1994

Barberton 2003

••

Parallel

.

Baish 2005 • Samitah 2006 Iringa 2006 Shinyanga 2006

Bom Jesus da Lapa 2002

Series

2006

2 Fengjie 2006

• • • ••

• ••

•

Buzwagi 2007

Ibiuna 2002

•

2 Lucknow 2006

Ahafo 2006

Sao Luiz 2007

2, 2 Gorakhpur 2, 2 Purnea

Kanjin (Korea) 2002

2 Zem Zem 1983

•

1997

2 x 1.7 GVAr !

•• •• •

•

Laredo 2000 2 Benejama & Seguin 1998 Saladas 2006 Kayenta 1992

5 North-South III, Lot B 2007

Acaray 1981

.

.•

Sullivan 1995 Dürnrohr 1983 Jacinto 2000 2 Hoya Morena & Jijona 2004 Welsh 1995

Cano Limón 1997

Atacama 1999

Moyle MSC 2003

Brushy Hill 1988 Willington 1997 3 Montagnais 1993 Châteauguay 1984

Chinú 1998

Samambaia 2002

2 Pelham, 2 Harker & 2 Central, 1991-1994

Ghusais, Hamria, Mankhool, Satwa

Etzenricht 1993 Wien Südost 1993

Radsted 2006 Siems 2004

Rejsby Hede 1997

9 Powerlink 2007, Refurbishment Nebo 2007, Strathmore 2007 Refurbishment 2 Kemps Creek 1989 2 Greenbank & Southpine 2008

FSC

SVC

B2B/GPFC

NGH

MSC/R

UPFC

TPSC

STATCOM

CSC

Plus 21 Projects for HVDC Long Distance Transmission …

TCSC

Flicker STATCOM

11 x VSC

8 alone between 2000 & 2005 in 4 Continents

Fig. 21: FACTS & HVDC worldwide – Example Siemens (ref. to Text) Bulk Power UHV AC and DC transmission schemes over distances of more than 2000 km are currently under planning for the connection of various large hydropower stations in China [17, 18]. Ultra high DC (up to 800 kV) and ultra high AC (1000 kV) are the preferred voltage levels for these applications to keep the transmission losses as low as possible. In India, there are similar prospects for UHV DC as in China due to the large extension of the grid [15, 16]. The road-map for India’s hybrid bulk power grid developments is depicted in Fig._22. India’s energy growth is about 8-9 % per annum, with an installed generation capacity of 124 GW in 2006 (92 GW peak load demand). The installed generation capacity is expected to increase to 333 GW by 2017 [20]. Fig. 23 depicts how the ideas of hybrid bulk power interconnections are reflected in China's UHV grid developments [19]. The focus is on interconnection of 7 large inter-provincial grids of the Northern, Central and Southern systems via three bulk power corridors which will built up a redundant “backbone” for the whole grid. Each corridor is planned for about 20 GW transmission capacity which shall be implemented with both AC and DC transmission lines with ratings of 4 - 10 GW each (at +/800_kV DC and 1000 kV AC, ref. to the figure). Therefore, each corridor will have a set-up with 2 - 3

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systems for redundancy reasons. With these ideas, China envisages a total amount of about 900 GW installed generation capacity by 2020. For comparison, UCTE and IPS/UPS together sum up to 850 GW today.

HVDC SYSTEMS BY 2011-12

NR BHIWADI

DADRI

2500 MW 60 00 M W

1500 MW

RIHAND AGRA

500 MW

NER

BALIA

50 0

BISHWANATH CHARIYALI

MW SASARAM

ER

VINDHYACHAL

WR

CHANDRAPUR BHADRAVATI

1000 MW

• Back-to-Back: 6 x

TALCHER

(Σ 4,000 MW)

1500 MW 2X500MW GAZUWAKA

PADGHE

0M

W

20 KOLAR

Main Grid

HVDC BIPOLE HVDC BACK-TO-BACK

Source: “Brazil-India-China Summit Meeting on HVDC & Hybrid Systems – Planning and Engineering Issues”, July 2006, Rio de Janeiro, Brazil

SH

N& ANDAMA R NICOBA

SR

K LA WE AD EP

a)

• Bipole : 6 x (Σ 13,500 MW)

LEGEND

MW

1 00

00

KOLHAPUR

DC

b) DEVELOPMENT OF CHICKEN NECK AREA

50 GW Hybrid:

EN CHICK

NECK

AREA

≈ 10 GW AC ≈ 40 GW DC EX

IS

10 Up t o

G TIN

C GW A

6 -7 x VD 800 k

C

VD 800 k

RE

DC

C

VD 800 k

F UT U

6 GW

800 k

C

V DC

Fig. 22: Grid Developments in India [8, 9] a) System Overview – including the “Chicken Neck Area” b) Hybrid Solutions in the Chicken Neck – including UHV DC

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Transmission Capacity of DC: 4-6 GW each Corridor will be 20 GW Solutions: 800 kV DC & nx in 2020 …

North Corridor

1000 kV AC

AC: 6-10 GW

3 x 20 GW … the installed Generation Capacity will be 900 GW Central Corridor Sources:

South Corridor

Fig. 23: Perspectives of Grid Developments in China - AC & DC Bulk Power Transmission from West to East via three main Corridors The benefits of hybrid power system interconnections as large as these are clear: • • • • •

Increase in transmission distance and reduction in losses - with UHV HVDC serves as stability booster and firewall against large blackouts Use of the most economical energy resources - far from load centers Sharing of loads and reserve capacity Renewable energy resources, e.g. large wind farms and solar fields can be integrated much more easily

However, with the 1000 kV AC lines there are also some stability constraints: if for example such an AC line of this kind with up to 10 GW transmission capacity is lost during faults, large inter-area oscillations might occur. For this reason, additional FACTS controllers for power oscillation damping and stability support are in discussion. The idea of embedding huge amounts of wind energy in the German grid by using HVDC, FACTS and GIL (Gas Insulated Lines) is depicted in Fig. 24. The goal is a significant CO2 reduction through the replacement of conventional energy sources by renewable energies, mainly offshore wind farms [2]. Power output of wind generation can vary fast in a wide range, depending on the weather conditions. Therefore, a sufficiently large amount of controlling power from the network is required to substitute the positive or negative deviation of actual wind power infeed to the scheduled wind power amount. Fig. 25 shows a typical example of the conditions, as measured in 2003. Wind power infeed and the regional network load during a week of maximum load in the E.ON control area are plotted. The relation between consumption and supply in this control area is illustrated in the figure. In the northern areas of the German grid, the transmission capacity is already at its limits, especially during times with low load and high wind power generation [7]. An efficient alternative for the connection of offshore wind farms is the integration of HVDC long distance transmission links into the synchronous AC system as schematically shown in Fig. 26 [13].

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AC or DC Cables

Long-term: 30 - 50 GW platform

incl. Baltic Sea & On-Shore

platform

Medium-term Planning

GIL in Tunnel to avoid 40-50 Cables nearby the Coasts

2020 4 x GIL, 4 x SVC, 2 x HVDC

Source: DENA Study 02-24-2005

Fig. 24: Integration of large Offshore Wind Farms by means of GIL, FACTS and HVDC - A Smart Grid Solution This will be a strong Issue in the German Grid Development

„ Additional Reserve Capacity is required

Problems with Wind Power Generation: o Wind Generation varies strongly o It can not follow the Load Requirements

Source: E.ON - 2003

Fig. 25: Network Load and aggregated Wind Power Generation during a Week of maximum Load in the E.ON Grid 20/30

Long-term: 30 - 50 GW Share in installed wind energy of 12,223 MW

Share in installed Wind Energy of

E. ON Netz: E. ON Netz: 48 % Vattenfall Europe Transmission: Vattenfall Europe Transmission: 37 % RWE Net: 14 % RWE Transportnetz Strom: EnBW Transportnetze: 1% EnBW Transportnetze:

Vattenfall Europe Transmission

Source: E.ON -

12,223 MW

48 % 37 % 14 % 1%

2003

Benefits of such a Solution: o Load Sharing o Generation Reserve Sharing

Installed Generation Capacity: 120 GW (2006) Fig. 26: Use of HVDC Long Distance Transmission for Wind Farm Grid Access 6. PROJECTS WITH HVDC AND FACTS – FOR ENVIRONMENTAL SUSTAINABILITY AND SECURITY OF SUPPLY 6.1. Bulk Power DC Transmission in China The 3000 MW +/-500kV bipolar Gui-Guang HVDC system (Fig. 27) with a transmission distance of 980 km was build to increase the transmission capacity from west to east [12]. It is integrated into the large AC interconnected system. In the same system there is also an already existing HVDC scheme in operation. Both DC systems operate in parallel with AC transmission in this grid.

2004

View of the Thyristor-Module Rating: Voltage:

3000 MW ± 500 kV

Contract: Nov. 1, 2001 terminated 66 Months Months Project completed ahead of Schedule by Sept. 2004

Fig. 27: Highlights of the GuiGuang HVDC Transmission Project

Thyristor: 5" LTT with integrated Overvoltage Protection

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In addition to this, Fixed Series Compensation (FSC) and Thyristor Controlled Series Compensation were used in the system. Due to long transmission distances, the system experiences severe power oscillations after faults, close to the stability limits. With its ability to damp power oscillations, HVDC plays an important role for reliable operation of the system [13]. In June 2007, Siemens received the order from China Southern Power Grid Company, Guangzhou, to construct a high-voltage DC transmission (HVDC) system between the province of Yunnan in the southwest of China and the province of Guangdong on the south coast of the country together with the Chinese partners. The system will be the first in the world to transmit electricity at a DC voltage of +/800 kV. At the same time, this project with a power transmission capacity of 5000 MW will be the long-distance HVDC link with the world’s highest power capacity which has ever been achieved. The additional electric power from Yunnan is intended to supply the rapidly growing industrial region of the Pearl River delta in the province of Guangdong and the megacities of Guangzhou and Shenzhen. In the future, the electricity generated by several hydro-electric power plants will be transported from Yunnan via 1,400 km to Guangzhou over this long-distance HVDC link. This HVDC link will save the CO2 emissions of more than 30 million tons a year. This corresponds to the amount of harmful gas which would be produced otherwise, for example through the construction of additional conventional fossil power plants in the province of Guangdong to serve the regional grid. Fig. 28 gives an overview of this world’s biggest HVDC project.

Commercial Operation: ¾ 2009 – Pole 1 1,418 Km

5,000 MW

¾ 2010 – Pole 2

+/- 800 kV DC

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. 28: World’s first 800 kV HVDC – in China Southern Power Grid 6.2. Security of Supply for the Mega-Cities: Example HVDC Project Neptune – USA After the 2003 blackout in the United States, new projects are gradually coming up in order to enhance the system security. One example is the Neptune HVDC project. Siemens PTD was awarded a contract by Neptune Regional Transmission System LLC (RTS) in Fairfield, Connecticut, to construct an HVDC transmission link between Sayreville, New Jersey and Long Island, New York. As new overhead lines can not be built in this densely populated area, power should be brought directly to Long Island by HVDC cable transmission, by-passing the AC sub-transmission network. For various reasons, environmental protection in particular, it was decided not to build a new power plant on Long Island

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near the city in order to cover the power demand of Long Island with its districts Queens and Brooklyn which is particularly high in summer. The Neptune HVDC interconnection is an environmentally compatible, cost-effective solution which will help meet these future needs. The low-loss power transmission provides access to various energy resources, including renewables. The interconnection is carried out via a combination of submarine and subterranean cable directly to the network of Nassau County which borders on the city area of 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 one single source, Siemens is providing seamless coverage of 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 were developing 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.

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”

Safe and reliable Power Supply for the Mega Cities – “Blackout Prevention”

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. 29: Highlights of Neptune HVDC Project - USA In Fig. 29, highlights of this innovative project that are typical for future integration of HVDC into a complex synchronous AC system are depicted. During trial operation, 2 weeks ahead of schedule, Neptune HVDC proved its Blackout prevention capability in a very impressive way. On June 27, 2007, a Blackout occurred in New York City. Over 380,000 people were without electricity in Manhattan and Bronx for up to one hour, subway came to standstill and traffic lights were out of operation. In this situation, Neptune HVDC successfully supported the power supply of Long Island and due to this, 700,000 households could be saved there.

6.3. Green Power with Basslink HVDC – Australia Fig. 30 gives an overview of the Basslink project in Australia, which transmits electric power from wind- and hydro sources very cost-efficiently from George Town in Tasmania to Loy Yang in Victoria and the same way back.

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2005

Benefits of HVDC

Clean & Low Cost Energy over Long Distance – suitable for Peak-Load Demand Improvement of Power Quality Improvement of local Infrastructures

Hydro Plants for: ¾ Base Load and ¾ Energy Storage

“flexible”

Plus Wind Power

Benefits of HVDC: ¾ Clean Energy ¾ CO2 Reduction ¾ Cost Reduction

“fuzzy”

Covering Base and Peak-Load Demands Fig. 30: Basslink HVDC – Sustainability of a “Smart” and flexible Grid This happens by means of HVDC via a combination of submarine cable (with 295 km the longest submarine cable in the world up to now), subterranean cables (8 km for reasons of landscape protection) and overhead lines over a total transmission distance of 370 km. The nominal power is 500_MW at a DC Voltage of 400 kV and a current of 1250 A. The overload capacity of the transmission system is 600 MW during 10 hours per day.

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Both Victoria and Tasmania profit from the interconnection of their networks: During times of peak load Tasmania delivers “green energy” from its hydro power stations to Victoria, while Tasmania can cover its base load demands out of the grid of Victoria during dry seasons when the hydro-reservoirs are not sufficiently filled. Furthermore, the island of Tasmania receives access to the power market of the Australian continent. Tasmania intends to install additional wind farms to increase its share in regenerative energy production. The figure shows that hydro power is perfectly suitable to be supplemented with the rather “fuzzy” wind energy – in terms of base load as well as through its ability to store energy for peak load demands. So far, the DC link can do much more to reduce CO2 through the combined use of regenerative energies.

6.4. HVDC Transmissions East-South Interconnector and Ballia-Bhiwadi - India The HVDC East-South interconnection (commercial operation in 2003) uses both advantages, the avoidance of transmission of additional power through the AC system and the interconnection of power areas which can not be operated synchronously. Fig. 31 shows the geographical location of the DC Interconnector and its main data. A view of the HVDC northern terminal in the state of Orissa is given in Fig. 32.

Talcher

Kolar

2003 Fig. 31: Geographic Map and Main Data of Indian East-South Interconnector In April 2006, Siemens was awarded an order by Powergrid Corporation of India to increase the transmission capacity of the East-South DC transmission from 2000 MW to 2500 MW. As the upgrade is now completed, it is possible to make maximum use of the system’s overload capacity. To increase the capacity of the link, the Siemens experts have developed a solution known as Relative Aging Indication and Load Factor Limitation (RAI & LFL). By these means, it is possible to utilize the overload capacity of the system more effectively without having to install additional thyristors. Furthermore, in March 2007, Siemens and consortium partner Bharat Heavy Electricals Ltd (BHEL) have been awarded an order by the Power Grid Corporation of India Ltd, New Delhi, to construct a new HVDC transmission. The purpose of the new HVDC transmission system is to strengthen the

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power supply to the growing region around New Delhi. The system is scheduled to go into service in November 2009. This is the fourth long-distance HVDC transmission link in India.

2500 MW RAI & LFL: full Use of Overload Capacity – without additional Thyristors

2007 2003

2000 MW

DC Station Talcher – State of Orissa

Fig. 32: Site View of Indian East-South Interconnector – DC Station Talcher The power transmission system is to transport electrical energy with low loss from Ballia in the east of Uttar Pradesh province to Bhiwadi, ca. 800 km away in the province of Rajasthan near New Delhi. In comparison with a conventional 400 kV AC transmission line, this HVDC transmission link improves transmission efficiency so that 688.000 tons of CO2 will be saved. As head of the consortium, Siemens has overall responsibility for the project, including the design of the HVDC transmission system, and will deliver the bulk of the core components. The company will also undertake the transport functions, construction work, installation and start-up. Partner BHEL is supplying transformers for one of the two converter stations as well as switchgear components. The new long-distance HVDC transmission link is the second system that Siemens is building in India.

6.5. Getting more Power out of the Grid: SVC Siems - Germany In Figs. 33-34, an innovative FACTS application with SVC in combination with HVDC for transmission enhancement in Germany is shown [8, 14]. It’s a matter of fact that this project is the first high voltage FACTS controller in the German network. The 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, only a limited power transfer (450 MW) with the DC link was possible since its commissioning in 1994, in order to avoid repetitive HVDC commutation

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failures and voltage problems in the grid. In an initial step towards grid access improvement, an additional transformer for connecting the 400 kV HVDC AC bus to the 110 kV bus was installed.

HVDC and FACTS in parallel Operation

HVDC: Power Increase – from 450 MW to 600 MW Reduction

in CO2:

634,000 tons p.a.

Source:

Fig. 33: SVC Siems, Germany - Support of HVDC Baltic Cable

SVC - Essential for enhanced Grid Access of the HVDC

The Solution

The Problem – no Right of Way for 400 kV AC Grid Access of Baltic Cable HVDC

2004

Fig. 34: The Solution – the first HV SVC in the German Grid at Siems Substation

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Finally, in 2004, 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. The enhanced grid access of the HVDC can save an amount of 634,000 tons of CO2 emissions p.a. through the import of more hydro power from Nordel to Germany. Prior to commissioning, intensive studies were carried out; first with the computer program NETOMAC and then with the RTDS real-time simulator by using the physical SVC controls and simplified models of the HVDC [14]. In Fig. 34, a view of the Siems SVC in Germany is depicted.

7. CONCLUSIONS Deregulation and privatization are 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 lead to an increasing congestion.

Power System Expansion … … with Advanced Transmission Solutions

HVDC PLUS

Fig. 35: From Congestion, Bottlenecks and Blackout towards a “Smart Grid”

Environmental constraints, such as energy saving, loss minimization and CO2 reduction, will play an increasingly important role [1, 10]. The loading of existing power systems will further increase, leading to bottlenecks and reliability problems. As a consequence of “lessons learned” from the large blackouts in 2003, advanced transmission technologies will be essential for the system developments, leading to Smart Grids (see Fig. 35) with better controllability of the power flows.

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HVDC and FACTS provide the necessary features to avoid technical problems in the power systems; they increase the transmission capacity and system stability very efficiently, and they assist in prevention of cascading disturbances. They effectively support the grid access of renewable energy resources and reduce the transmission losses by optimization of the power flows. Bulk power UHV AC and DC transmission will be applied in emerging countries such as India and China to serve their booming energy demands in an efficient way.

8. REFERENCES [1] European Technology Platform SmartGrids – Vision and Strategy for Europe’s Electricity Networks of the Future; 2006, Luxembourg, Belgium [2] DENA Study Part 1: „Energiewirtschaftliche Planung für die Netzintegration von Windenergie in Deutschland an Land und Offshore bis zum Jahr 2020“; February 24, 2005, Cologne, Germany [3] Economic Assessment of HVDC Links; CIGRE Brochure Nr.186 (Final Report of WG 14-20) [4] N.G. Hingorani: “Flexible AC Transmission”; IEEE Spectrum, pp. 40-45, April 1993 [5] FACTS Overview; IEEE and Cigré, Catalog Nr. 95 TP 108 [6] H. Breulmann, E. Grebe, M. Lösing, W. Winter, R. Witzmann, P. Dupuis, P. Houry, T. Pargotin, J. Zerenyi, J. Dudzik, L. Martin, J. M. Rodriguez: “Analysis and Damping of Inter-Area Oscillations in the UCTE/CENTREL Power System”; Report 38-113, CIGRE Session 2000, Paris [7] M. Luther, U. Radtke: “Betrieb und Planung von Netzen mit hoher Windenergieeinspeisung”; ETG Kongress, October 23-24, 2001, Nuremberg, Germany [8] H. Waldhauer: “Grid Reinforcement and SVC for full Power Operation of Baltic Cable HVDC Link”; The 38th Meeting and Colloquium of Cigré Study Committee B4 “HVDC and Power Electronics”, Technical Colloquium, September 25, 2003, Nuremberg, Germany [9] G. Beck, D. Povh, D. Retzmann, E. Teltsch: “Global Blackouts – Lessons Learned”; Power-Gen Europe, June 28-30, 2005, Milan, Italy [10] U.W. Niehage: “Future Developments in Power Industry”; Key-Note Address at AESIEAP, 28-05 September 2005, New Delhi, India [11] U. Armonies, M. Häusler, D. Retzmann: “Technology Issues for Bulk Power EHV and UHV Transmission”; HVDC 2006 Congress – Meeting the Power Challenges of the Future using HVDC Technology Solutions, July 12-14, 2006, Durban, Republic of South Africa [12] D. Povh, D. Retzmann, E. Teltsch, U. Kerin, R. Mihalic: “Advantages of Large AC/DC System Interconnections”; Report B4-304, CIGRE Session 2006, Paris [13] W. Breuer, D. Povh, D. Retzmann, E. Teltsch: “Trends for future HVDC Applications”; 16th CEPSI, November 6-10, 2006, Mumbai, India [14] G. Beck, W. Breuer, D. Povh, D. Retzmann: “Use of FACTS for System Performance Improvement”; 16th CEPSI, November 6-10, 2006, Mumbai, India [15] R.P. Singh: “New Projects on HVDC in India”; Brazil-China-India Summit Meeting on HVDC and Hybrid Systems – Planning and Engineering Issues, July 16-18, 2006, Rio de Janeiro, Brazil [16] R.P. Sasmal: “Planning Issues on HVDC Systems in India”; Brazil-China-India Summit Meeting on HVDC and Hybrid Systems – Planning and Engineering Issues, July 16-18, 2006, Rio de Janeiro, Brazil

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[17] W. Ma: “Main Aspects of UHVDC System Planning and Design”; Brazil-China-India Summit Meeting on HVDC and Hybrid Systems – Planning and Engineering Issues, July 16-18, 2006, Rio de Janeiro, Brazil [18] Y. Zeng: “Chinese CSG Experience on HVDC Transmission”; Brazil-China-India Summit Meeting on HVDC and Hybrid Systems – Planning and Engineering Issues, July 16-18, 2006, Rio de Janeiro, Brazil [19] W. Breuer, M. Lemes, D. Retzmann, “Perspectives of HVDC and FACTS for System Interconnection and Grid Enhancement”; Brazil-China-India Summit Meeting on HVDC and Hybrid Systems – Planning and Engineering Issues, July 16-18, 2006, Rio de Janeiro, Brazil [20] V. Ramaswami, D. Retzmann, K. Ücker: “Prospects of Bulk Power EHV and UHV Transmission”; GRIDTECH 2007 – New Technologies in Transmission, Distribution, Load Dispatch & Communication, February 5-6, New Dehli, India [21] J. M. Pérez de Andrés, J. Dorn, D. Retzmann, D. Soerangr, A. Zenkner: “Prospects of VSC Converters for Transmission System Enhancement”; POWERGRID EUROPE 2007, June 26-28, Madrid, Spain

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