Prospects of Bulk Power EHV and UHV Transmission

Transcription

1 5th & 6th Feb, 2007 at India Trade Promotion Organisation - Pragati Maidan, New Delhi, India Prospects of Bulk Power EHV and UHV Transmission V. Ramaswami, D. Retzmann*, K. Uecker Siemens, ermany ABSTRACT Deregulation and privatization pose new challenges for high voltage transmission systems. System elements are loaded up to their thermal limits, and power trading with fast varying load patterns is contributing to an increasing congestion. In this respect, interconnection of separated power systems may offer important technical, economical and environmental advantages. For the interconnections, innovative solutions will be essential to avoid congestion and to improve system stability. HVDC (High Voltage Direct Current) and FACTS (Flexible AC Transmission Systems) provide the necessary features to avoid technical problems in the power systems, they increase the transmission capacity and system stability very efficiently and they help to prevent cascading disturbances. HVDC and FACTS will play an important role for the system developments, leading to Smart rids with better controllability of the power flows. For some countries, UHV transmission solutions with AC voltages of 1000 kv and DC systems with 800 kv are in the planning stage. This will increase the transmission capacity for AC links up to 10_W and for DC systems up to 5-6 W. UHV transmission will be applied in emerging countries like India and China, to serve their booming energy demands efficiently. In the paper, benefits of bulk power transmission solutions with HVDC and FACTS for system enhancement and grid interconnection are depicted and UHV technology issues for AC and DC are discussed. Prospects of high power electronics in future grid developments are presented. KEY WORDS: Power System Interconnection, System Stability, Blackout Prevention, Increase of Transmission Capacity, Prospects of UHV Solutions, Power-Flow Control, Short-Circuit Current Limitation, Parallel Operation of HVDC and FACTS *dietmar.retzmann@siemens.com 1/20

2 1. PERSPECTIVES OF POWER SYSTEM DEVELOPMENTS The development of power systems follows the need to transmit power from generation to the consumers. With an increased demand for energy and the construction of new generation plants, first built close and then at remote locations from the load centers, the size and complexity of power systems have grown. Examples of large interconnected systems are the Western and Eastern European systems UCTE (installed capacity 530 W) and IPS/UPS (315 W), which are planned to be interconnected in the future, ref. to Fig. 1. UCTE Synchronous Interconnections: Δ f [mhz] 15 5 Frequency -5 Frequency & Power Spain Poland P [MW] Inter-Area Oscillations with Magnitudes up to 1000 MW Damping Measures necessary Active Power France-ermany (one 400-kV system) ermany (border to France) (border to France) t [s] a) the 1 st Step for System Extension The Interconnection CENTREL to UCPTE Signals: simulated & measured by WAMS 1 st UCTE Synchronous Zone In synchronous Operation with 1 st Zone 2 nd UCTE Synchronous Zone In synchronous Operation with 2 nd Zone NORDEL b) Zone 1 & 2 resynchronized since since then,the Risk of large Inter-Area Oscillations in UCTE has been increased * * depending on the actual Load Flow Situation IPS/UPS UCTE - 1 c) Options for rid Interconnection UCTE - 2 Turkey AL MAHREB Fig. 1: UCTE Steps a) & b) for Interconnection of Zones 1, 2 and further Options c) c) 2/20

3 However, with an increasing size of the synchronous interconnected systems, the technical and economical advantages diminish. This is related to problems regarding load flow, inter-area power oscillations ([1], ref. Fig. 1a) and voltage quality. If power is to be transmitted through the interconnected system over longer distances, transmission needs to be supported. 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 exchange. Bottlenecks are already identified, and for an increase of power transfer, advanced solutions using HVDC and FACTS need to be applied. Large blackouts in America and Europe confirmed clearly, that the favorable close electrical coupling might also include risk of uncontrollable cascading effects in large and heavily loaded interconnected systems [3]. Such an enhancement scenario for power transmission systems is depicted in Fig. 2. Extensions of Interconnected Systems Increased Power Exchange among the Interconnected Systems Transmission of large Power Blocks over long Distances * (Hydro Resources, Solar Energy) Renewable Energy Resources at favorable Locations * * by by use use of of HVDC // FACTS for for remote Infeed Fig. 2: Enhancement of Transmission Systems Additional problems are expected when renewable energies, such as large wind farms, have to be integrated into the system, especially when the connecting AC links are weak and when there is no sufficient reserve capacity in the neighboring systems available [2]. Today: Tomorrow: Use of Dispersed eneration Load Flow will be fuzzy Fig. 3: Perspectives of Transmission and Distribution Network Developments 3/20

4 In the future, an increasing part of the installed capacity will, however, be connected to the distribution levels (dispersed generation), which poses additional challenges on planning and safe operation of the systems, see Fig. 3. In such cases, HVDC and FACTS can clearly strengthen the power systems and improve their performance. 2. SOLUTIONS FOR SYSTEM INTERCONNECTION The idea of embedding huge amounts of wind energy in the erman grid by using HVDC, FACTS and IL (as Insulated Lines) is depicted in Fig. 4. oal is a significant CO2 reduction through the replacement of conventional energy sources by renewable energies, mainly off-shore wind farms. Main problem of such large scale wind energy integration is its fluctuating availability, as shown in Fig. 5. It means, a significant amount of reserve capacity will be needed somewhere in the system, and - by using HVDC and FACTS - both load and generation reserve sharing will be enabled [6]. However, this scenario needs further investigations regarding the investment costs and UCTE system stability. Long-term: W AC or DC Cables platform incl. Baltic Sea & On-Shore platform IL in Tunnel to avoid Cables nearby the Coasts 4 x IL, 4 x SVC, 2 x HVDC Medium-term Planning Source: DENA Study Fig. 4: Integration of large Off-Shore Wind Farms by means of HVDC and FACTS Based on the global experience with large blackouts, strategies for the development of large power systems go clearly in the direction of hybrid transmissions, consisting of DC and AC interconnections, including FACTS [6]. Such hybrid interconnected systems offer significant advantages, both technically and in terms of reliability [5]. Fig. 6 shows schematically such a hybrid system using HVDC and FACTS. Power exchange in the neighboring areas of interconnected systems can be achieved by AC links, preferably including FACTS for increased transmission capacity and for stability reasons. The transmission of large power blocks over long distances should, however, be utilized by the HVDC transmissions directly to the locations of power demand [5]. HVDC can be implemented as direct coupler the Back-to-Back solution (B2B) - or as point-topoint long distance transmission via DC line. The HVDC links can strengthen the AC interconnections 4/20

5 at the same time, in order to avoid possible dynamic problems which exist in such huge interconnections. These options for HVDC application are depicted in Fig. 6. Additional Reserve Capacity is required This will be a strong Issue in the erman rid Development Problems with Wind Power eneration o Wind eneration varies strongly o It can not follow the Load Requirements Source: E.ON Fig. 5: Network Load and aggregated Wind Power eneration during a Week of maximum Load in the E.ON rid System System A System B System C System D System E System F Large Large System Interconnections, using using HVDC HVDC and FACTS HVDC - Long Distance DC Transmission HVDC B2B -viaac Lines High Voltage AC Transmission & FACTS DC thestability Booster and Firewall against Blackout Countermeasures against large Blackouts Fig. 6: Large Power System Interconnections - Benefits of Hybrid Solutions 5/20

6 3. DEVELOPMENTS IN THE FIELD OF HVDC In the second half of last century, high power HVDC transmission technology has been introduced, offering new dimensions for long distance transmission. This development started with the transmission of power in an order of magnitude of a few hundred MW and was continuously increased to transmission ratings up to 3 W over long distances by just one bipolar line. Transmission distances over 1,000 to 2,000 km or even more are possible with overhead lines. Transmission power of up to MW over distances of about 300 km has already been implemented using submarine cables, and cable transmission lengths of up to about 1,300 km are in the planning stage. By these developments, HVDC became a mature and reliable technology. During the development of HVDC, different kinds of applications were carried out. They are shown schematically in Fig. 7. The first commercial applications were HVDC sea cable transmissions, because AC cable transmission over more than km is technically not feasible due to reactive power limitations. Then, long distance HVDC transmissions with overhead lines were built because they are more economical than transmission 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. 7a). a) Can be connected to long AC Lines b) c) a) Back-to-Back Solution b) HVDC Long Distance Transmission c) Integration of HVDC into the AC System Hybrid Solution Fig. 7: Types of HVDC Transmissions A further and for the future very important application of HVDC transmission is its integration into the complex interconnected AC system. Fig. 7c depicts this idea for both B2B as rid Power Flow Controller (PFC) - and for long-distance point-to-point transmission. The reasons for these hybrid solutions are basically lower transmission costs as well as the possibility of bypassing heavily loaded AC systems. Typical configurations of HVDC are depicted in Fig. 8. In Fig. 9, an overview of both standard and extended operating ranges of HVDC is given. While using the full control range of HVDC up to 90 O, the B2B can feature FACTS functions, e.g. fast voltage control, in the same way as an SVC. As indicated in the figure, this new idea of PFC as a FACTS B2B has been successfully applied in a project at Lamar substation, USA [4, 7]. The major benefit of the HVDC (in comparison with FACTS), both B2B/PFC and LDT, is its incorporated ability for fault-current blocking, which serves as an automatic firewall for Blackout prevention in case of cascading events, which is not possible with FACTS. 6/20

7 Back-to-Back - the short Link... Power & Voltage Control Fault Current Blocking Filters Filters a) Rating LDT: 130 kv kv MW 4000 f A = 50 Hz Example f B = 60 Hz B2B - Rating: 13,8 kv kv MW or with Cable/Line - the Long Distance Transmission up to km HVDC-LDT - Long Distance Transmission B2B -The Short Link Back-to-Back Station Submarine Cable Transmission Long Distance OHL Transmission AC AC AC AC AC AC 60 Hz 50 Hz DC Cable DC Line b) HVDC - High Voltage DC Transmission: It forces P to flow Standard with Thyristors (Line-Commutated Converter) AC/DC and DC/AC Conversion by Power Electronics HVDC PLUS (Voltage-Sourced Converter - VSC) HVDC can be combined with FACTS V-Control included c) Fault-Current Blocking ~ I1 V1 P V2 I2 ~ Benefits of HVDC in a synchronous AC System Slow Functions Fig. 8: HVDC Configurations a) Basic Scheme b) Technologies c) Control Features L and C Q1 α and γ Fast Functions Q2 Power & Voltage Control Fault-Current Blocking Slow Functions L and C The Firewall for Blackout Prevention 7/20

8 Fig. 9: HVDC Operating Ranges and the new PFC Solution as FACTS B2B Clean Energy from Platforms & Islands with VSC Technology Fig. 10: DC with VSC HVDC PLUS HVDC PLUS (Fig. 10) is the preferred technology for interconnection of islanded grids to the power system, such as off-shore wind farms. This technology provides the so-called Black-Start feature using self-commutated voltage-sourced converters (VSC). Voltage-sourced converters do not have the 8/20

9 need for 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. In Fig. 11, the benefits of using power electronics for system enhancement are summarized and a comparison of switching frequencies of line-commutated thyristor devices and self-commutated VSC are depicted. Conventional equipment (e.g. breakers, tap-changer transformers) offer very low losses, but the switching speed is very low. Power electronics can provide high switching frequencies up to several khz, however, with an increase in losses. From Fig. 11, it can be seen that due to less converter losses the preferred solution for Bulk Power Transmission is in fact the line-commutated thyristor technology. The today s losses of high power voltage-sourced converters with high switching frequencies are within the range of 4-5 %, which is too much for large bulk power DC transmission projects. More Dynamics for better Power Quality: Use of Power Electronic Circuits to control P, V & Q Parallel and/or Series Connection of Converters Fast AC/DC and DC/AC Conversion 4-5 % Transition from slow to fast Switching Frequency Thyristor 1-2 % 50/60 Hz TO < 500 Hz IBT / ICT > 1000 Hz Losses On-Off Transition ms The Solution for Bulk Power Transmission Fig. 11: Use of Power Electronics for FACTS & HVDC - Transient Performance and Losses 4. UHV TECHNOLOIES FOR BULK POWER TRANSMISSION 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 [4, 10, 11]. Ultra high DC voltage (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 [4, 8, 9]. AC long distance transmission, however, will be implemented in India by EHV levels of up to 800 kv, including FACTS. The road-map for India s hybrid bulk power grid developments are depicted in Fig. 12. India s energy growth is about 8-9 % per annum, with an installed generation capacity of 124 W in 2006 (92 W peak load demand), ref. to [8, 9]. The installed generation capacity is expected to increase to 333 W by 2017 [8]. Fig. 13 depicts how the ideas of hybrid bulk power interconnections are reflected in China's UHV grid developments. 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 W transmission capacity which shall be realized with both AC and DC transmission lines with ratings of 4-10 W each (at +/- 800 kv DC 9/20

10 and 1000 kv AC, ref. to the figure). Therefore, each corridor will have a set-up with 2-3 systems for redundancy reasons. With these ideas, China envisages a total amount of about 900 W installed generation capacity by For comparison, UCTE and IPS/UPS together sum up to 850 W today. HVDC SYSTEMS BY NR BHIWADI DADRI 2500 MW 1500 MW ARA RIHAND 500 MW BALIA 6000 MW 500 MW NER BISHWANATH CHARIYALI KOLHAPUR WR VINDHYACHAL CHANDRAPUR BHADRAVATI 1000 MW 1500MW PADHE 1000 MW 2000MW SASARAM ER TALCHER 2X500MW AZUWAKA LEEND HVDC BIPOLE Back-to-Back: 6 x (Σ 4,000 MW) DC Bipole : 6 x (Σ 13,500 MW) Main rid a) LAKSHADWEEP KOLAR SR HVDC BACK-TO-BACK ANDAMAN & NICOBAR Source: Brazil-India-China Summit Meeting on HVDC & Hybrid Systems Planning and Engineering Issues, July 2006, Rio de Janeiro, Brazil b) DEVELOPMENT OF CHICKEN NECK AREA 50 W Hybrid: 10 W AC 40 W DC EXISTIN CHICKEN NECK AREA Up to 10 W AC 6-7 x 6 W DC 800 kv DC 800 kv DC FUTURE 800 kv DC 800 kv DC Fig. 12: rid Developments in India [8, 9] a) System Overview including the Chicken Neck Area b) Hybrid Solutions in the Chicken Neck including UHV DC 10/20

11 The benefits of the large hybrid power system interconnections in India and China are clear: Increase of transmission distance and reduction of losses - using UHV and EHV 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 sources, including large wind farms and solar fields can much more easily be integrated However, using the 1000 kv AC lines, there will be in fact stability concerns: if for example such an AC line - with up to 10 W transmission capacity - is lost during faults, large inter-area oscillations might occur. For this reason, additional large FACTS controllers on the UHV AC lines for stability support are in discussion in China. Transmission Capacity of each Corridor will be 20 W in 2020 Solutions: 800 kv DC & 1000 kv AC DC: 4-6 W n x AC: 6-10 W North Corridor 3 x 20 W the installed eneration Capacity will be 900 W Sources: Central Corridor South Corridor Fig. 13: Perspectives of rid Developments in China - AC & DC Bulk Power Transmission from West to East via three main Corridors [12] Specific issues for the necessary UHV technology developments are depicted in the following, as seen from the Siemens perspective [4, 12]. It is obvious that the UHV insulation requirements will lead to a huge increase of the mechanical dimensions of all equipment, including PTs, CTs, breakers, disconnectors, busbars, transformers and reactive power equipment. Some main equipment does not require detailed investigations since existing technology basically enables to extrapolate from lower voltage applications. An example for this type of equipment is the DC thyristor valve which is based on a modular design. Additional thyristor levels to be connected in series are well feasible and do not require any conceptual changes. However, for other equipment it has to be verified to which extent existing technology and know-how are adequate for design and manufacturing process. This includes the following equipment: AC grid transformers and DC converter transformers including bushings AC and DC wall bushings 11/20

12 DC smoothing reactors AC reactive power equipment, including FACTS AC breakers and disconnectors DC bypass switches and DC disconnectors AC and DC measurements Regarding shunt-connected FACTS controllers, there are no specific additional efforts necessary for the medium voltage equipment at the secondary side of the grid transformers. For series connected FACTS, if applied, efforts will be needed for a robust construction of the platforms matching the required seismic performance. Converter transformers are one of the very important components for UHV DC application. It is well understood that the existing technology and know-how of converter transformers can manage higher DC voltages. Yet, there are critical areas which need careful consideration and further development in order to keep the electrical stresses at a safe level. Above all the windings and the transformer internal part of bushings on the valve side of the converter transformers with the barrier systems and cleats and leads require very careful attention. In the following, design aspects for key UHV DC equipment are outlined. From Figs it can be seen that for transformers the bushings will be a major issue with regard to mechanical dimensions, including transportation to site. Existing Technology and Know- How can well manage higher DC Voltage Stresses Transformers for 800 kv HVDC System are within existing Manufacturing Capabilities Transportation Limits and Converter Configuration will determine Type and Size R&D in Progress in specific Fields Works for 800 kv DC Transformer Fig. 14: Transformer for UHV DC In the State of Development An example of the complete HVDC station layout is given in Fig. 16. Main idea of this concept is to use two 12-pulse converters with 400 kv DC operating voltage each and then to connect them in series in order to achieve the desired 800 kv arrangement. A major benefit of this solution will be a smaller size of the converter transformers, if transportation restrictions exist. Furthermore, it increases the redundancy of the transmission: each of the 4 converters of plus and minus pole can be bypassed and the assigned DC line will be operated at 400_kV reduced voltage level. Due to this, the single line diagram of +/- 800kV UHV DC converter station will be mostly the same as a +/- 500kV HVDC converter station. A configuration of two 12 pulse-groups per pole has also a long term operation experience worldwide. It means there is no basic new concept to be developed. The arrangement of the valve-units in two 400 kv valve halls per pole is outlined in Fig /20

13 800 kv DC Bushing in Test Field Fig. 15: UHV DC Bushing at Test Lab TU raz Austria Main benefit will be the use of proven modular technologies by just expanding them to the new application. This is also valid for the AC and DC control and protection schemes. However, the measurements will need to be adapted to the higher voltage level. The 800 kv DC concept can be summarized as follows: UHV DC Valves using proven modular Design based on existing Technology and Know-How for DC Voltage 800 kv Valve Tower Configuration: Double or Quadruple Valve Proven existing LTT Technology Based on the above discussions and descriptions, the following conclusions can be made for the design of UHV AC and DC bulk power transmission systems: Regarding the main equipment, UHV DC systems of up to 800 kv and UHV AC systems of up to 1000 kv are technically feasible In general, UHV equipment can be designed and manufactured on the basis of existing technologies For most of the station equipment only some or even no R&D is anticipated UHV DC applications are also in discussion for bulk power long distance transmission projects in other regions of the world, e.g. South America and South Africa [12]. 13/20

14 Transformer Bushings 400 kv DC 800 kv DC Each Pole can be operated with 400 kv DC DC Neutral 400 kv-valve roup 800 kv-valve roup N-1 Criteria: Redundancy through Bypass-Breakers DC Line Fig. 16: Fully redundant HVDC Scheme with two 400 kv 12-Pulse Converters per Pole DC Neutral 400 kv Valve Hall 400 kv DC 400 kv DC 800 kv Valve Hall to 800 kv DC Line Ready for Transmission Fig. 17: Valve Hall Configuration for 800 kv HVDC 14/20

15 5. PROJECTS FOR SYSTEM ENHANCEMENT WITH HVDC 5.1. ui-uang HVDC Project China The 3000 MW +/-500kV bipolar ui-uang HVDC system (Fig. 18) 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. In addition to that, Fixed Series Compensation (FSC) and Thyristor Controlled Series Compensation have been 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 essentially contributes to reliable operation of the system [4, 12] View of the Thyristor-Module Rating: Voltage: 3000 MW ± 500 kv Contract: Nov. 1, 2001 Project completed terminated 6 Months ahead of Schedule by Sept Thyristor: 5" LTT with integrated Overvoltage Protection Fig. 18: eographic Location and Main Data of ui-uang HVDC Project - China 5.2. HVDC Project Neptune - USA After the 2003 blackout in the United States, new projects are smoothly coming up in order to enhance the system security. One example is the Neptune HVDC project. Siemens PTD has been 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. Because new overhead lines can not be built in this high density populated area, power should directly be brought to Long Island by HVDC cable transmission, by-passing the AC sub-transmission network. 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. 15/20

16 Siemens and Neptune RTS developed the project over three years to prepare it for implementation. In addition to providing technological expertise, studies, and engineering services, Siemens also supported its customer in the project s approval process. In Fig. 19, highlights of this innovative project that are typical for future integration of HVDC into a complex synchronous AC system are depicted Ed Stern, President of Neptune RTS: High-Voltage Direct-Current Transmission will play an increasingly important Role, especially as it becomes necessary to tap Energy Reserves whose Sources are far away from the Point of Consumption Customer: End User: Location: Project Development: Supplier: Transmission: Power Rating: Transmission Dist.: Neptune RTS Long Island Power Authority (LIPA) New Jersey: Sayreville Long Island: Duffy Avenue NTP-Date: 07/2005 PAC: 07/2007 Consortium Siemens / Prysmian Sea Cable 600/660 MW monopolar 82 km DC Sea Cable 23 km Land Cable Fig. 19: eographical Location and Main Data of Neptune HVDC - USA 5.3. East-South Interconnector - India The grid in India has been developed to regional power systems which were operating asynchronously [6]. Later interconnections between regional systems have been made by AC and Back-to-Back HVDC. The first HVDC long distance transmission was Rihand-Delhi which is integrated into the 400_kV AC system. 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. 20 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. 21. In April 2006, Siemens has been 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. After the upgrade is completed, it will be 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 will be possible to utilize the overload capacity of the system more effectively without having to install additional thyristors. 16/20

17 Talcher Kolar 2003 Fig. 20: eographic Map and Main Data of Indian East-South Interconnector MW MW RAI & LFL: full Use of Overload Capacity without additional Thyristors DC Station Talcher State of Orissa Fig. 21: Site View of Indian East-South Interconnector DC Station Talcher 17/20

18 5.4. Basslink HVDC - Australia 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: Base Load and Energy Storage flexible Plus Wind Power fuzzy Covering Base and Peak-Load Demands Benefits of HVDC: Clean Energy CO2 Reduction Cost Reduction Fig. 22: Basslink HVDC for a Smart and flexible rid Fig. 22 gives an overview of the Basslink project in Australia, which transmits electric power from wind- and hydro sources very cost-efficiently from eorge Town in Tasmania to Loy Yang in Victoria and the same way back. This happens by means of HVDC via a combination of submarine cable (with 18/20

19 295 km the longest submarine cable in the world up to now), land 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. 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. Insofar, the DC link can contribute still more to the reduction of CO2 through the combined use of regenerative energy sources. 6. CONCLUSIONS Deregulation and privatization pose new challenges on high voltage transmission systems. System elements are loaded up to their thermal limits, and wide-area power trading with fast varying load patterns will contribute to an increasing congestion. Power System Expansion with Advanced Transmission Solutions HVDC PLUS Fig. 23: From Congestion, Bottlenecks and Blackout towards a Smart rid Environmental constraints will also play an important role. The loading of existing power systems will further increase, leading to bottlenecks and reliability problems. As a consequence of lessons 19/20

20 learned from the large blackouts in 2003, HVDC and FACTS will play an important role for the system developments, leading to Smart rids (see Fig. 23) with better controllability of the power flows. UHV bulk power DC long distance transmission will be the preferred solution for emerging countries like India and China to serve their booming energy demands efficiently. 7. REFERENCES [1] H. Breulmann, E. rebe, 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 , CIRE Session 2000, Paris [2] M. Luther, U. Radtke, Betrieb und Planung von Netzen mit hoher Windenergieeinspeisung ET Kongress, October 23-24, 2001, Nuremberg, ermany [3]. Beck, D. Povh, D. Retzmann, E. Teltsch: lobal Blackouts Lessons Learned ; Power-en Europe, June 28-30, 2005, Milan, Italy [4] 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 [5] D. Povh, D. Retzmann, E. Teltsch, U. Kerin, R. Mihalic: Advantages of Large AC/DC System Interconnections ; Report B4-304, CIRE Session 2006, Paris [6] W. Breuer, D. Povh, D. Retzmann, E. Teltsch: Trends for future HVDC Applications ; 16th CEPSI, November 6-10, 2006, Mumbai, India [7]. Beck, W. Breuer, D. Povh, D. Retzmann: Use of FACTS for System Performance Improvement ; 16th CEPSI, November 6-10, 2006, Mumbai, India [8] 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 [9] 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 [10] 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 [11] Y. Zeng, Chinese CS 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 [12] W. Breuer, M. Lemes, D. Retzmann, Perspectives of HVDC and FACTS for System Interconnection and rid Enhancement ; Part 1 DC and AC Technology Issues for Bulk Power EHV and UHV Transmission; Part 2 Power System Expansion with Advanced Technologies Solutions for a Smart rid Brazil-China-India Summit Meeting on HVDC and Hybrid Systems Planning and Engineering Issues, July 16-18, 2006, Rio de Janeiro, Brazil 20/20