sign in sign up
<<
Home , HVDC converter, Smart grid, Super grid

1

From to : Solutions with HVDC and FACTS for Grid Access of Sources

J.W. Feltes, Senior Member, IEEE, B.D. Gemmell, Member, IEEE, and D. Retzmann, Member, IEEE

HVDC and FACTS solutions provide the transmission or Abstract--Innovative solutions with HVDC (High incremental capacity, their dynamic benefits provide the Direct Current) and FACTS (Flexible AC Transmission Systems) ancillary benefits to address robust compliance. have the potential to cope with the system planning and Section II of this paper will discuss the planning challenges operational challenges of global climate developments and the for the integration of renewable energy sources. Section III call for changes in the way electricity is supplied. New power electronic technologies with self-commutated converters make will focus on the Smart Grid solutions with power , advanced technical features possible, such as independent control in the form of HVDC and FACTS, describing the fundamental of active and reactive power, and the capability to supply weak benefits, configurations and applications. In Section IV, a or passive networks. As part of the overall planning number of specific projects are described illustrating state-of- considerations, this paper presents the fundamental system the-art FACTS and HVDC technology solutions for Smart and planning, modeling and operational challenges of connecting Super Grid applications. large wind farms (both onshore and offshore) via long transmission systems, as well as the practical applications of II. INTEGRATION OF RENEWABLE ENERGY SOURCES – traditional and new power electronic technologies. A PLANNING CHALLENGE

Index Terms—FACTS, HVDC, UHV HVDC, Renewable The integration of large amounts of renewable energy Generation, Smart Grid, Super Grid, Onshore and Offshore sources poses several challenges to system planners. Wind Farms, Multiterminal HVDC, Long Distance However, the benefits of this generation, combined with Transmission. government incentives and mandates, demand that system planners embrace these developments and overcome these I. INTRODUCTION challenges. oday, more than ever before, electrical power is The major challenges related to the integration of large Tfundamental to modern society's existence. Global climate amounts of renewable energy sources are: developments and environmental constraints are playing • Conventional long range planning generally starts important roles in the security and sustainability of power with a reasonably well defined generation grids. The penetration of renewable energies, particularly development plan. Long range development of large wind farms, is forcing development of transmission renewable energy has a much larger degree of grids across the world. Significant challenges must be uncertainty in terms of amount, location, and addressed in order to interconnect these variable and remote technology. renewable energy sources in transmission • Large generating stations are generally sited with systems, challenges intensified by existing reliability, transmission access in mind. Renewable energy capacity, and congestion problems, as well as economic and sources are, of course, sited where their energy environmental concerns. The development and innovative supply is plentiful, for example the siting of wind application of Smart and Super Grids, integrating High farms in areas where there is strong and consistent Voltage Direct Current (HVDC) and Flexible AC wind. These areas tend to be distant from major load Transmission Systems (FACTS), and hybrid AC/DC centers and often are areas with weak transmission solutions, is proceeding at unprecedented levels due to the systems. superior advantages of these technologies. Power electronic • The electrical characteristics of conventional solutions provide the necessary features to address these generation technology have seen improvements in problems in the power grids of the future. Not only can materials and efficiency, but the basic characteristics have remained the same and are expected to be J.W. Feltes and B.D. Gemmell are with Energy, Inc., Power similar in the future. The electrical characteristics of Technologies International, Schenectady, NY 12305 USA (e-mails: renewable generation technologies are undergoing [email protected] and [email protected]). rapid development and will likely be significantly D. Retzmann is with Siemens AG, Power Transmission Solutions, 91058, Erlangen, (e-mail: [email protected]). different in the future. 978-1-4577-1002-5/11/$26.00 ©2011 IEEE 2

Thus the planning process must be adjusted to plans. Plans that have flexibility and build up steadily have accommodate these uncertainties. advantages over those that require most of the investment early and hence are not as robust to potential changes in the assumptions inherent in the scenarios. Integration of A. Planning Process scenarios by identifying common features (i.e., transmission The basic objectives of the planning studies are: elements that show up in multiple plans) also gives the plan 1. To investigate potential generation developments flexibility to adapt to changes in assumptions about future 2. To identify technically and economically viable options, developments. including HVAC, HVDC or hybrid systems, for Cost estimates are then determined for the equipment interconnection of these generation projects to the required in each of the developed plans. Economic studies existing transmission grid, including reinforcements of the existing grid as needed, to deliver the renewable may also be performed to determine cost benefit ratios. Other energy to load centers reliably. factors such as environmental impacts, regulatory hurdles, and Of course, there are many trade-offs involved in financing impacts can be included in the comparison of determining a plan that best meets the delivery and reliability alternatives. objectives while also being economical and robust to potential B. System Studies future developments. The planning studies performed can be divided into the There are several approaches to developing long range following categories: expansion plans. Fig. 1 below illustrates one approach that • Power System Studies – load flow, short circuit and has been successfully applied. dynamic simulation to define the transmission requirements and options for the interconnection of Phase I Define Generation Siting the generation and potential operating issues and Scenarios strategies.

• FACTS (Flexible AC Transmission Systems)/HVDC (High Voltage Direct Current) Studies – Phase II determination of FACTS/HVDC technology, Develop Horizon Year Plans configuration and requirements, including high frequency analysis using EMTP based tools.

• Submarine Cable Study – for offshore or Phase III interconnections involving water crossings, a desktop Stage Plans marine survey would be required as part of the

selection of the cable technology and determination

Phase IV of technical considerations and cost of the submarine Qualify Projects for Implementation cable.

Cost Estimates for Selection of Options – typically a • present-value economic analysis based on equipment Least Cost Program costs and the cost of system losses.

Fig. 1. Planning Process • Economic Benefits – cost-benefit analysis and prioritizing of plan components. This process enables determining a long-term plan (horizon • Environmental, Financial, Commercial and of 15 to 30 years) that meets the global objectives and allows Regulatory Issues – assessment of the different the incorporation of major system changes such as use of a environmental impacts, financing requirements and higher AC voltage level or the incorporation of large HVDC regulatory issues associated with each alternative. lines. The process also accounts for the near-term (5 to 10 • Design Studies – the preferred alternative(s) would years) where load and generation developments are better be subjected to additional analysis to further refine known and ensures the compatibility of short-term and long- reactive compensation needs, system short circuit levels, protection concerns or special needs (e.g., term plans. special protection schemes), and impact on A key step is the selection of potential scenarios operational issues such as line energization, load incorporating potential generation development projects. This rejection, spinning reserves, response to extreme is not an easy task with the uncertainties involved with events, frequency and voltage control, and system renewable generation. An approach used by the Midwest ISO restoration. Use of series or is given in [1, 2]. FACTS/HVDC may also require subsynchronous Transmission plans are developed that accomplish the resonance analysis, harmonic studies, and control desired transfers and meet reliability criteria in the horizon interaction analysis. year. Power flow analysis, contingency studies and stability The final plan must be both flexible and robust. An analysis are performed to test the transmission plans. An expansion plan is comprised of distinct decisions. The most intermediate year or two are selected to test the staging of the critical decisions are those that have short lead times and 3 hence tend to lock the expansion into a particular plan. Less • Accessible: granting connection access to all network critical decisions are those that can be changed if needed, and users, particularly to renewable energy sources (RES) and are hence more accommodating of future uncertainty. highly efficient local generation with zero or low carbon Flexibility in a plan is its ability to adapt to uncertainty. For emissions example, transmission projects that are needed in a number of • Reliable: assuring and improving security and quality of scenarios provide more flexibility than projects that depend on supply particular futures, and projects which are not needed in the • Economic: providing best value through innovation, near-term allow the ability for changes in the plan if the future efficient energy management and “level playing field” develops significantly differently than the assumed scenarios. competition and [3, 4]. Robustness minimizes risk. The risk of a transmission plan The European SmartGrid vision is also applicable to includes both the risk that future transmission will be system developments in other regions of the world. Smart inadequate and unreliable and, oppositely, the risk that the Grids will help achieve sustainable development. A key to planned transmission will be underutilized. A robust plan achieve a good Smart Grid performance will be the use of determines with the most accuracy those projects that are . needed in the near-term, those that are needed in the most probable scenarios, and those that will fit into many futures. A. Based FACTS and HVDC Technologies Since the 1960s, FACTS have evolved and are now a mature technology with high power ratings. The core or the C. Additional Requirements Related to Renewable “workhorse” of line-commutated FACTS and HVDC Energy Resources installations are high-power , triggered optically by Most new renewable energy sources, in particular wind and means of laser technology, or electrically, depending on the solar plants, are intermittent. This adds additional application. uncertainties into the predicted generation patterns and power The fundamental shunt and series FACTS configurations transfers, and hence may result in a variety of impacts on the are listed in Table I. In shunt mode, a FACTS controller transmission system which need to be addressed. primarily influences the system voltage, and in series mode, a Since the technology involved in renewable generation FACTS controller influences transmission capacity by projects is evolving at a fast pace, renewable generation reducing the transmission angle and changing power flows. presents unique modeling requirements. In the last few years, significant efforts have gone into modeling different types of TABLE I -generators. Similar efforts are on-going with THE FUNDAMENTAL FACTS CONFIGURATIONS respect to large solar installations. However, based on the developments seen in the last few years, we can be sure that Abbreviation Full Name the equipment being installed in the future will be quite SVC Static Var Compensator STATCOM Static Synchronous Compensator different than that we are installing today. While it is hard to FSC Fixed Series Compensation predict exactly what those capabilities will be, we can assume TCSC Thyristor Controlled Series Compensation there will be improvements that remedy some of the problems UPFC Unified Power Flow Controller encountered today. Thus the long range plan can focus on big-picture issues, and local control issues (e.g., issues like In general, for power ratings greater than 1,000 MW and (LVRT) and transmission distances over 600 km, DC transmission is more requirements, presently a concern for wind units) need not be economical than AC transmission. The basic HVDC addressed in detail. configurations are listed in Table II. Power transmission of 5 However, the initial stages of the plan must clearly meet to 7 GW over distances of 2000 km has been achieved using national grid codes and comply with all of the designated HVDC. Power transmission of up to 600-800 MW over requirements for connection of renewable generation. distances of about 300 km has already been realized with submarine cables.

III. SMART GRID SOLUTIONS WITH POWER ELECTRONICS TABLE II CONVENTIONAL HVDC CONFIGURATIONS

One vision and enhancement strategy for future electricity Long Distance Transmission HVDC networks is depicted in the “SmartGrids” program, which was • Overhead Line (>1,000 km) developed within the European Technology Platform (ETP) of • Submarine Cable (>100 km) the EU in its preparation of the 7th Framework Program. Back-to-Back HVDC Features of a future “SmartGrid” of this kind can be It is, however, necessary to mention that conventional line- outlined as follows: commutated converters have some technical restrictions. Of • Flexible: fulfilling system needs while responding to the particular note is the fact that the commutation within the changes and challenges ahead converter is driven by the AC , and therefore requires 4 proper conditions of the connected AC system, such as a minimum short-circuit power. B. Voltage-Sourced Converter (VSC) Based FACTS and HVDC Technologies Voltage-sourced converters do not require any “driving” system voltage; they can build up a 3-phase AC voltage via the DC voltage. This kind of converter uses power with turn-off capability such as IGBTs (Insulated Gate Bipolar ) [5]. Today, the majority of long distance offshore wind farms employing DC connections rely on voltage-sourced converter (VSC) technology, which uses self-commutated technology with that have turn-on and turn-off capabilities. This turn-on and turn-off capability provides the benefit of blackstart capability, which is necessary at an Fig. 2. Siems SVC, Germany – Supporting Baltic HVDC Link offshore wind farm point of connection to start up the wind farm. A second benefit for offshore application of the VSC B. Remote Hydro Power in India technology is the compact converter design (largely due to the reduced need for filters for damping harmonics), allowing In order to facilitate clean and low cost hydroelectric power economic DC wind farm connections to be built on offshore from Bhutan in India to satisfy the increasing power demands platforms. of the New Delhi megacity, the existing long distance transmission system was upgraded with the world’s largest Another benefit of the VSC HVDC is the use of modern FACTS project with series compensation. The Tala TCSC extruded cables as the voltage polarity in the cable remains the Project included two series compensation installations of 1.7 same regardless of the direction of power. Also, the Gvar each, at the Purnea and Gorakhpur Substations, with a implementation of multiterminal systems is relatively simple, combination of fixed series compensation (FSC) and thyristor and it is possible to configure complete DC networks with branches and ring structures. controlled series compensation (TCSC) [7] in two 400 kV AC transmission lines with a length of 475 km, as shown in Fig. 3. These VSC converters can also be used as STATCOMs to The TCSC is used when fast control of the line impedance is provide the necessary voltage control, even in unbalanced required, for load-flow control and for power oscillation networks (for example, in the presence of large single-phase damping. The FSC is an economic way to reduce transmission loads). Symmetry of the three-phase system can, to some extent, be restored by using load balancing control. In angle over the line and to increase the transmission capacity. addition, the VSC converters can be configured as active AC or DC filters, which offer benefits over passive filters.

IV. SPECIFIC SMART AND SUPER GRID SOLUTIONS A number of projects are described below which illustrate state-of-the-art FACTS and HVDC technology solutions for Smart and Super Grid applications.

A. FACTS and HVDC in Parallel Operation− Baltic HVDC Undersea Link Since commissioning in 1994, the Baltic Cable HVDC Link between Germany and had transfer limits of less than or equal to 450 MW imposed by voltage constraints in the German network, which also avoided repetitive HVDC commutation failures and voltage problems on the grid. The innovative application of shunt FACTS technology in 2005 Fig. 3. Tala TCSC/FSC – World’s Largest Series Compensation Project facilitated the needed transmission enhancements to allow an C. Offshore Wind Farm in Europe increased transfer of renewable energy. A new -100/+200 BorWin2 is an offshore consortium which will connect two Mvar SVC (as shown in Fig. 2) connected at the Siems 400 North Sea offshore wind farms to the German grid, as kV Substation provided the necessary fast acting coordinated depicted in Fig. 4. The Veja Mate and Global Tech 1 offshore voltage control, allowing the HVDC link to operate at its wind farms are located 125 km offshore (northwest of the design rating of 600 MW. [6] island of Borkum, where sea depths are approximately 40 m), and will have a combined power generation capacity of 800 5

MW. Given the distance offshore, the submarine cable connection to the mainland grid would require HVDC, There are several benefits when using UHV HVDC. At a combined with the blackstart and compact design benefits of voltage of ±800 kV, the line losses drop by approximately VSC based HVDC technology. The selected DC transmission 60% compared with ±500 kV for the same power transfer. voltage was ±300 kV. The offshore floating, self-lifting When comparing transmission losses of AC and DC, the latter platform was designed to accommodate all the requisite typically has 30-40% less losses. electrical equipment for the HVDC converter station, In , a total of 35 “bulk power” HVDC projects are including the converter itself, two , four AC cable planned for 2010 to 2020, with a combined transmission compensation reactors and high-voltage gas-insulated capacity of 217 GW. A great number of these projects are for (GIS). The transmission link is scheduled to enter power transmission from hydro power plants situated in the commercial service in 2013 [8]. middle of the country to the distant load centers [9]. in China is growing quickly; installed wind power capacity was 10 GW in 2008, and is predicted to be 270 GW by 2030. Most wind power resources in China are far from load centers, and large-scale, high voltage and long distance transmission using FACTS and HVDC solutions will likely be required to deliver this power [10].

E. Onshore Wind in , US The state of Texas is moving forward the Competitive Renewable Energy Zone (CREZ) transmission projects to increase in-state wind generation to greater than 18GW; delivering wind power from West Texas and the Panhandle to the load centers of the highly populated areas (i.e. Austin, Houston, San Antonio and Dallas/Fort Worth). When complete, significant new bulk transmission will provide the necessary upgrades to deliver the wind power generated. Given the distances (i.e. 600 to 800 km), the multiple transmission owners, the multiple parallel Fig. 4. BorWin2 Germany – World’s First 800 MW VSC HVDC transmission paths and the need for grid code compliance with the Electricity Reliability Corporation of Texas (ERCOT), a D. Remote Hydropower and Wind Power in China number of large shunt and series FACTS solutions are being integrated as part of the coordinated CREZ transmission China has constructed a number of high-power DC energy build-out [11]. highways, superimposed on the AC grid, in order to efficiently (i.e. minimizing losses) transmit from huge hydropower plants in Central China to the load F. Offshore Wind in US Mid-Atlantic States centers located as far away as 2,000 to 3,000 km. These ultra The application of multiterminal offshore HVDC is in the high voltage (UHV) HVDC systems at 800 kV require state- planning phase to develop backbone transmission off the coast of-the-art line-commutated converter technology. The world’s of the Mid-Atlantic States. The Atlantic Wind project aims to first 5 GW ±800 kV 1,418 km HVDC system entered service connect 6,000 MW of offshore wind – multiple wind farms, in 2009, which helps save around 33 million tons of CO2 all in relatively shallow water – via an HVDC transmission annually when compared to local power generation (see Fig. backbone (driven by the distances offshore along with the 5). associated benefits of HVDC). In addition, the HVDC project will provide grid congestion relief benefits to the existing land based transmission [12].

G. European Countries Developing Offshore Super Grid Europe is embarking on ambitious plans to develop the infrastructure and market conditions to ensure that vast offshore renewable energy resources can be harnessed and supplied to where they are most needed. The North Seas Countries’ Offshore Grid Initiative Memorandum of Understanding [13] was recently signed to create a Super Grid; a vast undersea grid of HVDC interconnections, Fig. 5. World’s First ±800 kV UHV HVDC Project 6 combined with onshore grid upgrades. Current projections are Guangdon,” Sixth International Conference of Power Transmission for over 150 GW of operating in the and Distribution Technology, Guangzhou 2007, China. [10] J. Zhang, X. Xu, J. Feltes, “Development and Planning of Wind Power North Sea by 2050. in China,” In Proc. IEEE Power and Energy Society General Meeting, 2010. V. SUMMARY [11] Commission of Texas, Competitive Renewable Energy Zone,Project Information [Online]. Available: In this paper, the planning challenges encountered in http://www.texascrezprojects.com addressing the addition of large amounts of renewable energy [12] Atlantic Wind Connection [Online]. Available: http://atlanticwindconnection.com sources, including solar and both onshore and offshore wind, [13] The North Seas Countries’ Offshore Grid Initiative Memorandum of were described. Renewable energy often must be transmitted Understanding [Online] Available: over long distances, while ensuring appropriate reliability and https://www.entsoe.eu/fileadmin/user_upload/_library/news/MoU_No rth_Seas_Grid/101203_MoU_of_the_North_Seas_Countries__Offsho grid code compliance, resulting in the need for bulk re_Grid_Initiative.pdf transmission and innovative technologies. This paper has presented the benefits of the use of smart power electronic technologies, in the form of HVDC and FACTS, which VII. BIOGRAPHIES provide utilities and transmission developers the advanced features and functionality to overcome these challenges. James W. Feltes (M’79, SM’94) received his Examples are given which show the successful application of BSEE degree with honors from Iowa State these technologies in Northern Europe, China, India and the University in 1979 and his MSEE degree from Union College in 1990. He joined PTI, now , and plans for the creation of Super Grids based Siemens PTI, in 1979 and is currently a Senior on HVDC and FACTS are described. Manager in the Consulting Department. At PTI, he Innovative solutions with HVDC and FACTS have the has participated in many studies involving planning, analysis and design of transmission and distribution potential to cope with the system planning and operational systems. He is an instructor for several of the challenges of global climate developments and the call for courses taught by PTI. He is a member of several changes in the way electricity is supplied. The ongoing IEEE committees, working groups, and task forces dealing with power system stability and control. He is a Senior Member of the changes occurring in the production of electricity and the IEEE and is a registered professional engineer in the state of New York. associated demands on the transmission system will require innovative solutions. Solutions such as HVDC and FACTS Brian D. Gemmell (M’00) received his MEng and employing power electronics are presently playing a critical PhD in Electrical and Electronic Engineering from the University of Strathclyde, UK in 1990 in 1995 role in enabling grid access for renewable energy and will respectively. During 1992, he spent 6 months as a continue to do so in the foreseeable future. Visiting Engineer at the Institute of Technology. He worked for ScottishPower (1994- 2000) in Substation Engineering and Transmission VI. REFERENCES Planning. He spent 7 years working in FACTS & HVDC Business Development in North America [1] L. Fan, D. Osborn, J. Miland, and Z. Miao, “Regional Transmission and is currently General Manager of Siemens PTI, Planning for Large-Scale Wind Power,” in Proc. 2010 IEEE Power based in Schenectady, NY. and Energy Society General Meeting, 2009. [2] D. Tewari, Y. Mishra, J. Furnish, and D. Manjure, “Effective Planning Dietmar Retzmann was born in Pfalzfeld, Germany, Approach to Interconnect Bulk Quantities of Wind Generation” in on November 4, 1947. He graduated in Electrical Proc. 2010 IEEE Power and Energy Society General Meeting, 2010. Engineering (Dipl.-Ing.) at the Technische [3] “European Technology Platform SmartGrids – Vision and Strategy for Hochschule Darmstadt, Germany in 1974 and he Europe’s Electricity Networks of the Future,” 2006, Luxembourg, received Dr.-Ing. degree from the University of Belgium. Erlangen-Nuremberg, Germany in 1983. [4] W. Breuer, D. Povh, D. Retzmann, Ch. Urbanke, M. Weinhold, Dr. Retzmann is with Siemens Erlangen, “Prospects of Smart Grid Technologies for a Sustainable and Secure Germany since 1982. Currently, he is director for Power Supply,” The 20TH World Energy Congress, November 11-15, Technical Marketing & Innovations HVDC/FACTS 2007, Rome, Italy. in High Voltage Division, Power Transmission [5] B. Gemmell, J. Dorn, D. Retzmann, D. Soerangr, “Prospects of Solutions. Multilevel VSC Technologies for Power Transmission,” IEEE His area of expertise covers project development, simulation and testing of Transmission & Distribution Conference & Exposition 2008, Chicago, HVDC, FACTS, System Protection and Custom Power as well as system Illinois, USA. studies, innovations and R&D activities. [6] M. Claus, D. Retzman, D. Sorangr and K. Uecker, "Solutions for Dr. Retzmann is active in Cigré, IEEE, ZVEI and VDE. He is author and Smart and Super Grids with HVDC and FACTS,” 17th Conference of co-author of over 160 technical publications in international journals and the Electric Power Supply Industry, 27-31 October 2008, Macau. conferences. In 1998, he was appointed guest-professor at Tsinghua [7] “HVDC and FACTS Go Global,” Dietmar Retzmann, Siemens University, Beijing, and in 2002 at Zhejiang University, Hangzhou, China. Energy, Electric Light and Power [Online]. Available: Since 2004, he is lecturer on Power Electronics at the University of Karlsruhe, http://www.elp.com/index/display/article- Germany. Since 2004, he gives lectures on HVDC/FACTS at the University display/331126/articles/utility--engineering-td/volume- of Karlsruhe, Germany. In 2006, he was nominated “Siemens TOP 13/issue-6/features/hvdc-and-facts-go-global.html Innovator.” [8] Siemens AG [Online]. Available: http://www.siemens.com/press/en/pressrelease/?press=/en/pressrelease /2010/power_transmission/EPT201006085.htm [9] S. Balbierer, M. Haeusler, V. Ramaswami, R. Hong, Sh. Chun, Sh. Tao, "Basic Design Aspects of the 800 kV UHVDC Project Yunnan-