Technical article ■ Authors: M. Claus, D. Retzmann, D. Sörangr, K. Uecker Solutions for Smart and Super Grids with HVDC and FACTS Answers for energy. Content 0. Abstract 3 I. Introduction 3 II. HVDC and FACTS Technologies 3 A HVDC Developments 4 B FACTS Developments 5 III. Security and Sustainability of Power Supply with HVDC and FACTS 5 A Neptune HVDC Project – USA 5 B Basslink HVDC – Australia 6 C Prospects of HVDC in India 6 D Prospects of HVDC in China 7 E HVDC and FACTS in parallel Operation 8 F Prospects of VSC HVDC 9 IV. Conclusions 9 V. References 12 2 17th Conference of the Electric Power Supply Industry 27 - 31 October 2008 Solutions for Smart and Super Grids with HVDC and FACTS M. Claus, D. Retzmann1, D. Sörangr, K. Uecker Siemens AG Erlangen, Germany [email protected] Abstract— Deregulation and privatization are posing new grid of the future must be secure, cost-effective and challenges to high-voltage transmission systems. High-voltage environmentally compatible [2]. The combination of these power electronics, such as HVDC (High Voltage Direct Current) three tasks can be tackled with the help of ideas, intelligent and FACTS (Flexible AC Transmission Systems), provide the solutions as well as innovative technologies. The combination necessary features to avoid technical problems in heavily loaded of these three tasks can be solved with the help of ideas, power systems; they increase the transmission capacity and system stability very efficiently and assist in preventing intelligent solutions as well as innovative technologies. cascading disturbances. Environmental constraints, such as Innovative solutions with HVDC and FACTS have the energy saving, loss minimization and CO2 reduction, will also potential to cope with the new challenges. By means of Power play an increasingly more important role. The loading of existing Electronics, they provide features which are necessary to power systems will further increase which will lead to avoid technical problems in the power systems, they increase bottlenecks and reliability problems. Therefore, the strategies for the transmission capacity and system stability very efficiently the development of large power systems go clearly in the and help prevent cascading disturbances. direction of Smart Grids, consisting of AC/DC interconnections The vision and enhancement strategy for the future and point-to-point bulk power transmission “highways” (Super electricity networks are, for example, depicted in the program Grid Solutions). FACTS technology is also an important part of this strategy. These hybrid systems offer significant advantages for “SmartGrids”, which was developed within the European in terms of technology, economics and system security. They Technology Platform. Features of a future Smart Grid such as reduce transmission costs as well as help bypass heavily loaded this can be outlined as follows: flexible, accessible, reliable AC systems. and economic. Smart Grids will help achieve a sustainable development. Keywords-- HVDC, FACTS, Bulk Power Transmission, Security, II. HVDC AND FACTS TECHNOLOGIES Sustainability, Micro Grid, Smart Grid, Super Grid In the second half of the last century, high power HVDC I. INTRODUCTION transmission technology was introduced, offering new The electric power supply is essential for life of a society, dimensions for long distance transmission. This development like the blood in the body. Without power supply there are started with the transmission of power in a range of less than a devastating consequences for daily life. However, hundred MW and was continuously increased. deregulation and privatization are posing new challenges to Transmission ratings of 3 GW over large distances with the transmission systems. System elements are going to be only one bipolar DC line are state-of-the-art in many grids loaded up to their thermal limits, and wide-area power trading today. Now, there are ways of transmitting up to 6 GW and with fast varying load patterns will contribute to an increasing more over large distances with only one bipolar DC congestion [1, 2]. transmission system. The first project in the world at a DC In addition to this, the dramatic global climate voltage of +/- 800 kV is the Yunnan-Guang project in China developments call for changes in the way electricity is with a power transmission capacity of 5,000 MW. Further supplied. Environmental constraints, such as loss projects with similar or even higher ratings in China, India and other countries are going to follow. minimization and CO2 reduction, will play an increasingly important role. Consequently, we have to deal with an area of FACTS, based on power electronics, was developed to conflicts between reliability of supply, environmental improve the performance of weak AC Systems and to make sustainability as well as economic efficiency [3, 4]. The power long distance AC transmission feasible. Moreover, FACTS can help solve technical problems in the interconnected power 3 systems. FACTS are applicable both in a parallel connection which is highly important for the future is its integration into (SVC, Static VAR Compensator – STATCOM, Static the complex interconnected AC system (Fig. 1c). The reasons Synchronous Compensator), in a series connection (FSC, for these hybrid solutions are basically lower transmission Fixed Series Compensation - TCSC/TPSC, Thyristor costs as well as the possibility of bypassing heavily loaded AC Controlled/Protected Series Compensation - S³C, Solid-State systems. Series Compensator), or as a combination of both (UPFC, Typical configurations of HVDC are depicted in Fig. 2. Unified Power Flow Controller - CSC, Convertible Static HVDC VSC is the preferred technology for connecting Compensator) to control load flow and to improve dynamic islanded grids, such as offshore wind farms, to the power conditions. Rating of SVCs can go up to 800 MVAr; the system [1, 11-16]. This technology provides the “Black-Start” world’s biggest FACTS project with series compensation feature by means of self-commutated voltage-sourced (TCSC/FSC) is at Purnea and Gorakhpur in India at a total converters [8]. Voltage-sourced converters do not need any rating of 1.7 GVAr. “driving” system voltage; they can build up a 3-phase AC By means of these DC and AC Ultra High Power voltage via the DC voltage at the cable end, supplied from the transmission technologies, the “Smart Grid”, consisting of a converter at the main grid. number of highly flexible “Micro Grids” will turn into a Siemens uses an innovative Modular Multilevel Converter “Super Grid” with Bulk Power Energy Highways, fully (MMC) technology for HVDC VSC with low switching suitable for a secure and sustainable access to huge renewable frequencies, referred to as HVDC PLUS [14-16]. energy resources such as hydro, solar and wind [1]. A. HVDC Developments HVDC – High-Voltage DC Transmission: It makes P flow In general, for transmission distances above 600 km, DC z HVDC “Classic” with 500 kV – up to 4,000 MW transmission is more economical than AC transmission z HVDC “Bulk” with 800 kV – for 5,000 MW up to 7,200 MW (≥ 1000 MW). Power transmission of up to 600 - 800 MW z HVDC VSC (Voltage-Sourced Converter) over distances of about 300 km has already been achieved z HVDC can be combined with FACTS 800 kV for minimal Line with submarine cables, and cable transmission lengths of up to z V-Control included Transmission Losses approx. 1,000 km are at the planning stage. Due to these HVDC-LDT – Long-Distance Transmission developments, HVDC became a mature and reliable technology. B2B – The Short Link During the development of HVDC, different kinds of Back-to-Back Station Submarine Cable Transmission Long-Distance OHL Transmission applications were carried out. They are shown schematically AC AC AC AC AC AC in Fig. 1. DC Line DC Cable Can be Fig. 2: HVDC Configurations and Technologies connected to long AC Lines a) 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 b) links [10-13], ref. to Fig. 3. Fault-Current a) Back-to-Back Solution Blocking b) HVDC Long Distance Transmission V1 V2 c) c) Integration of HVDC into the AC System Hybrid Solution G ~ P G ~ I1 I2 Fig. 1: Options of HVDC Interconnections Slow Functions Q1 α and γ Q2 Slow Functions The first commercial applications were cable transmissions, “Classic” “Classic” for AC cable transmission over more than 80-120 km is onlyL and C L and C only technically not feasible due to reactive power limitations. Fast Functions Then, long distance HVDC transmissions with overhead lines Benefits of The Firewall HVDC in a were built as they are more economical than transmissions for Blackout with AC lines [5]. To interconnect systems operating at synchronous Power & Voltage Control Prevention different frequencies, Back-to-Back (B2B) schemes were AC System Fault-Current Blocking applied. B2B converters can also be connected to long AC lines (Fig. 1a). A further application of HVDC transmission Fig. 3: Benefits of HVDC - it makes Power flow 4 B. FACTS Developments In Fig. 5, the impact of series compensation on power Since the 1960s, Flexible AC Transmission Systems have transmission and system stability is explained and Fig. 6 been evolving to a mature technology with high power ratings depicts the increase in voltage quality by means of shunt [6, 7, 9]. The technology, proven in various applications, compensation with SVC (or STATCOM). became first-rate, highly reliable one. State-of-the-art SVC applications with containerized Fig. 4 shows the basic configurations of FACTS. solutions - including a new, very fast 48 hrs containerized SVC refurbishment technology - and advanced indoor FACTS – Flexible AC Transmission Systems: Support of Power Flow technologies provide additional benefits for the user.