1. P. Ribeiro August, 2001 1 Mini-Curso Paulo F. Ribeiro, BSEE, MBA, PHD, PE CALVIN COLLEGE Engineering Department Grand Rapids, MI 49546 PRIBEIRO@CALVIN.EDU Power Transfer Phase Angle From EPRI An Overview on FACTS Controllers

2. P. Ribeiro August, 2001 2 Outline Introduction - The Concept History / Background - Origin of FACTS, Opportunities, Trends System Architectures and Limitations Power Flow Control on AC Systems Application Studies and Implementation Basic Switching Devices Systems Studies AC Transmission Fundamentals Voltage Source vs. Current Source Voltage Sources Static Var Compensator (SVC), STATCOM, TCSC, UPFC, SMES System Studies (by EMTP, ATP, Saber, EDSA, EMTDC) Systems Integration, Specification, Cost Considerations and Technology Trends Operation and Maintenance Impact of FACTS in interconnected networks Market Assessment, Deregulation and Predictions Conclusions - Final Words Questions and Open Discussions

3. P. Ribeiro August, 2001 3 The reason, therefore, that some intuitive minds are not mathematical is that they cannot at all turn their attention to the principles of mathematics. But the reason that mathematicians are not intuitive is that they do not see what is before them, and that, accustomed to the exact and plain principles of mathematics, and not reasoning till they have well inspected and arranged their principles, they are lost in matters of intuition where the principles do not allow of such arrangement. They are scarcely seen; they are felt rather than seen; there is the greatest difficulty in making them felt by those who do not of themselves perceive them. These principles are so fine and so numerous that a very delicate and very clear sense is needed to perceive them, and to judge rightly and justly when they are perceived, without for the most part being able to demonstrate them in order as in mathematics, because the principles are not known to us in the same way, and because it would be an endless matter to undertake it. We must see the matter at once, at one glance, and not by a process of reasoning, at least to a certain degree. 1660 PENSEES by Blaise Pascal

4. P. Ribeiro August, 2001 4 The Concept

5. P. Ribeiro August, 2001 5 A transmission system can carry power up to its thermal loading limits. But in practice the system has the following constraints: -Transmission stability limits -Voltage limits -Loop flows Transmission stability limits: limits of transmittable power with which a transmission system can ride through major faults in the system with its power transmission capability intact. Voltage limits: limits of power transmission where the system voltage can be kept within permitted deviations from nominal. Voltage is governed by reactive power (Q). Q in its turn depends of the physical length of the transmission circuit as well as from the flow of active power. The longer the line and/or the heavier the flow of active power, the stronger will be the flow of reactive power, as a consequence of which the voltage will drop, until, at some critical level, the voltage collapses altogether. Loop flows can be a problem as they are governed by the laws of nature which may not be coincident with the contracted path. This means that power which is to be sent from point ”A” to point ”B” in a grid will not necessarily take the shortest, direct route, but will go uncontrolled and fan out to take unwanted paths available in the grid. The Concept

6. P. Ribeiro August, 2001 6 FACTS devices FACTS are designed to remove such constraints and to meet planners´, investors´ and operators´ goals without their having to undertake major system additions. This offers ways of attaining an increase of power transmission capacity at optimum conditions, i.e. at maximum availability, minimum transmission losses, and minimum environmental impact. Plus, of course, at minimum investment cost and time expenditure. The term ”FACTS” covers several power electronics based systems used for AC power transmission. Given the nature of power electronics equipment, FACTS solutions will be particularly justifiable in applications requiring one or more of the following qualities: -Rapid dynamic response -Ability for frequent variations in output -Smoothly adjustable output. Important applications in power transmission involving FACTS and Power Quality devices: SVC (Static Var Compensators), Fixed * as well as Thyristor-Controlled Series Capacitors (TCSC) and Statcom. Still others are PST (Phase-shifting Transformers), IPC (Interphase Power Controllers), UPFC (Universal Power Flow Controllers), and DVR (Dynamic Voltage Restorers). The Concept

7. P. Ribeiro August, 2001 7 Introduction: History, Concepts, Background, and Issues Origin of FACTS -Oil Embargo of 1974 and 1979 -Environmental Movement -Magnetic Field Concerns -Permit to build new transmission lines -HVDC and SVCs -EPRI FACTS Initiative (1988) -Increase AC Power Transfer (GE and DOE Papers) -The Need for Power semiconductors Why we need transmission interconnection -Pool power plants and load centers to minimize generation cost -Important in a deregulated environment Opportunities for FACTS Increase power transfer capacity SVC (Nebraska GE 1974, Minnesota Westinghouse 1975, Brazil Siemens 1985) TCSC, UPFC AEP 1999 Trends -Generation is not being built -Power sales/purchases are being

8. P. Ribeiro August, 2001 8 System Architecture Radial, interconnected areas, complex network Power Flow in an AC System Power Flow in Parallel and Meshed Paths Transmission Limitations Steady-State (angular stability, thermal limits, voltage limits) Stability Issues (transient, dynamic, voltage and SSR) System Issues (Post contingency conditions, loop flows, short-circuit levels) Power Flow and Dynamic Stability Considerations Controllable Parameters Basic FACTS Devices - Impact of Energy Storage System Architectures and Limitations

9. P. Ribeiro August, 2001 9 The relative importance of transmission interconnection Interconnections in a European type system are not very important because the system is built by providing generation close to the loads and therefore, transmission is mainly for emergency conditions. In the US,very large power plants far from the load centers were built to bring "coal or water by wire". Large plants provided the best solution - economy of scale. Also, seasonal power exchanges have been used to the economic advantage of the consumers. Newer generation technologies favor smaller plants which can be located close to the loads and therefore, reduces the need for transmission. Also, if distributed generation takes off, then generation will be much closer to the loads which would lessen the need for transmission even further. However, for major market players, once the plant is built, the transmission system is the only way to bring power to the consumer that is willing to pay the most for the power. That is, without transmission, we will not get a well functioning competitive market for power. System Architectures and Limitations

10. P. Ribeiro August, 2001 10 Power Flow Control on AC Systems Radial Parallel Meshed Power Flow in Parallel Paths Power Flow in a Meshed Systems What limits the loading capability? Power Flow and Dynamic Considerations

11. P. Ribeiro August, 2001 11 Power Flow Control on AC Systems Relative Importance of Controllable Parameters Control of X can provide current control When angle is large X can provide power control Injecting voltage in series and perpendicular to the current flow, can increase or decrease 50% Series Compensation

12. P. Ribeiro August, 2001 12 Transmission Transfer Capacity Enhancement Advanced Solutions Transmission Link Enhanced Power Transfer and Stability Line Reconfiguration Fixed Compensation FACTS Energy Storage Better Protection Increased Inertia Breaking Resistors Load Shedding FACTS Devices Traditional Solutions SVC STATCOM TCSC, SSSC UPFC Steady State Issues Voltage Limits Thermal Limits Angular Stability Limits Loop Flows Dynamic Issues Transient Stability Damping Power Swings Post-Contingency Voltage Control Voltage Stability Subsynchronous Res. FACTS Applications and Implementations

13. P. Ribeiro August, 2001 13 FACTS Devices Shunt Connected Static VAR Compensator (SVC) Static Synchronous Compensator (STATCOM) Static Synchronous Generator - SSG Battery Energy Storage System (BESS) Superconducting Magnetic Energy Storage (SMES) Combined Series and Series-Shunt Connected Static Synchronous Series Controllers (SSSC) Thyristor Controlled Phase-Shifting Transformer or Phase Angle Regulator (PAR) Interline Power Flow Controller (IPFC) Thyristor Controlled Series Capacitor (TCSC) Unified Power Flow Controller (UPFC) Relative Importance of Different Types of Controllers Shunt, Shunt-Serie Energy Storage

14. P. Ribeiro August, 2001 14 Devices Diode (pn Junction) Silicon Controlled Rectifier (SCR) Gate Turn-Off Thyristor (GTO) GE MOS Turn-Off Thyristor (MTO) SPCO Emitter Turn-Off Thyristor (ETO) Virginia Tech Integrated Gate-Commutated Thyristor (IGCT) Mitsubishi, ABB MOS-Controlled Thyristor (MCT) Victor Temple Insulated Gate Bipolar Transistor (IGBT) Power Electronics - Semiconductor Devices Diodes Transistors IGBT Thyristors SCR, GTO, MTO, ETO, GCT, IGCT, MCT

15. P. Ribeiro August, 2001 15 Power Electronics - Semiconductor Devices Principal Characteristics Voltage and Current Losses and Speed of Switching Speed of Switching Switching Losses Gate-driver power and energy requirements Parameter Trade-off Power requirements for the gate di/dt and dv/dt capability turn-on and turn-off time Uniformity Quality of silicon wafers IGBT has pushed out the conventional GTO as IGBTs ratings go up. IGBTs - Low-switching losses, fast switching, current-limiting capability GTOs - large gate-drive requirements, slow-switching, high-switching losses IGBTs (higher forward voltage drop)

16. P. Ribeiro August, 2001 16 Power Electronics - Semiconductor Devices Decision-Making Matrix

17. P. Ribeiro August, 2001 17 Planing Studies Evaluate the technical and economic benefits of a range of FACTS alternative solutions which may allow enhancement of power transfer across weak transmission links. Part I of this effort should concentrate on preliminary feasibility studies to assess the technical merits of alternative solutions to correct real and reactive power transfer ratings, system voltage profiles, operational effects on the network, equipment configurations, etc. A - Load flow studies will be performed to establish steady-state ratings, and identify the appropriate locations for connection of alternative compensation devices. Load flow studies will be used to address the following: System Criteria (maximum steady-state power transfers, short-term operating limits, etc.) Controller Enhancements (controller types, ratings, sensitivities, etc.) Controller Losses (based on operating points and duration) System Losses (system losses base on controller operating point and duration) Overvoltsages ((steady-state and short-term voltage insulation requirements) Compare technical and economic benefits of alternatives Identify interconnection points Identify critical system contingencies Establish power transfer capability of the transmission system Confirm that reliability criteria can be met Identify the cost of capital of equipment and losses Identify steady-state and dynamic characteristics of FACTS controllers Stability Studies IEEE

18. P. Ribeiro August, 2001 18 System Studies IEEE

19. P. Ribeiro August, 2001 19 System Studies System data and configuration Outages and load transfer Load Flow (P,Q, V,  ) Transient Stability (P,Q, V, , time) Dynamic Stability (P,Q, V, , , time) Generato r data Voltage Reg. Data (AVR) Governor data Relay data System operat. limits Induction motor data Fault data System changes Load Shedding Identify Transmission Systems - Provide System data and Configuration Outages and load transfer Perform Load Flow (P,Q, V,  ) System operat. limits Identify and Size Transfer Enhancement Solutions Devices Perform Economic Analysis IEEE

20. P. Ribeiro August, 2001 20 System Studies IEEE

21. P. Ribeiro August, 2001 21 E2 /  2 X E1 /  1 I P&Q E1 E2 E1. sin (  ) E2. cos(  ) (E1 - E2. cos(  ) E2. sin(  ) I (E2 - E1. cos(  ) Iq1 = (E1 - E2. cos(  ) / X E1. Cos (  ) Ip1 = E2 sin(  ) / X E1 - E2 P1 = E1. Ip1 AC Transmission Fundamentals

22. P. Ribeiro August, 2001 22 Active component of the current flow at E1 Ip1 = (E2. sin (  )) / X Reactive component of the current flow at E1 Iq1 = (E1 - E2. cos (  ))/X Active Power at the E1 end P1 = E1 (E2. sin (  ))/X Reactive Power at the E1 end Q1 = E1(E1 - E2. cos (  )) / X AC Transmission Fundamentals

23. P. Ribeiro August, 2001 23 E2 /  2 P1 = E1 (E2. sin (  ))/X I X E1 E2 E1 - E2 Regulating end bus voltage mostly change reactive power - Compensating at an intermediate point between buses can significantly impact power flow E1 /  1 I P&Q Q / V P1 = k1.E1 (E2. sin (  /k2))/X AC Transmission Fundamentals (Voltage - Shunt Control)

24. P. Ribeiro August, 2001 24 E1 E2 I X E1 - E2 Injected Voltage Injecting Voltage in series with the line mostly change real power E1 /  1 E2 /  2 I P&Q Vinj P1 = E1. E2. sin (  ) / (X - Vinj / I) AC Transmission Fundamentals (Voltage-Series Injection)

25. P. Ribeiro August, 2001 25 X E1 /  1 E2 /  2 I P&Q Real Power Angle Curve Changes in X will increase or decrease real power flow for a fixed angle or change angle for a fixed power flow. Alternatively, the reactive power flow will change with the change of X. Adjustments on the bus voltage have little impact on the real power flow. Vx I Vxo Vs I Xeff = X - Xc Vx Vr Vc Vseff = Vs + Vc Vr Vc Vseff P1 = E1. E2. sin (  ) / (X - Xc) Vs Phase Angle Power Transfer AC Transmission Fundamentals (Series Compensation)

26. P. Ribeiro August, 2001 26 X E1 /  1 E2 /  2 I P&Q P E1 E2 I E1 - E2 Injected Voltage Integrated voltage series injection and bus voltage regulation (unified) will directly increase or decrease real and reactive power flow. AC Transmission Fundamentals (Voltage-Series and Shunt Comp.)

27. P. Ribeiro August, 2001 27  1 - prior to fault  2 - fault cleared  3 - equal area  3 >  crit - loss of synchronism Improvement of Transient Stability With FACTS Compensation Equal Area Criteria 11 22 33  crit A1 A2 Amargin Maximum Power Transfer Phase Angle no compensation with VAR compensation (ideal midpoint) A1 = Acceleration Energy A2 = Deceleration Energy Therefore, FACTS compensation can increase power transfer without reducing the stability margin Q / V AC Transmission Fundamentals (Stability Margin)

28. P. Ribeiro August, 2001 28 Voltage Source Vs. Current Source Converters

29. P. Ribeiro August, 2001 29 Voltage Source Converters

30. P. Ribeiro August, 2001 30 Basic 6-Pulse, 2-level, Voltage-Source Converter Voltage Source Converters

31. P. Ribeiro August, 2001 31 2, 3, 5-level, VSC Waveforms Voltage Source Converters

32. P. Ribeiro August, 2001 32 Voltage-Source Converter Bridges Voltage Source Converters

33. P. Ribeiro August, 2001 33 Output voltage control of a two-level VSC Voltage Source Converters

34. P. Ribeiro August, 2001 34 Output voltage control of a three-level VSC Voltage Source Converters

35. P. Ribeiro August, 2001 35 Multi-pulse VSC with wave-forming magnetic circuits Voltage Source Converters

36. P. Ribeiro August, 2001 36 FACTS Technology - Possible Benefits Control of power flow as ordered. Increase the loading capability of lines to their thermal capabilities, including short term and seasonal. Increase the system security through raising the transient stability limit, limiting short-circuit currents and overloads, managing cascading blackouts and damping electromechanical oscillations of power systems and machines. Provide secure tie lines connections to neighboring utilities and regions thereby decreasing overall generation reserve requirements on both sides. Provide greater flexibility in siting new generation. Reduce reactive power flows, thus allowing the lines to carry more active power. Reduce loop flows. Increase utilization of lowest cost generation.

37. P. Ribeiro August, 2001 37 FACTS and HVDC: Complimentary Solutions HVDC Independent frequency and control Lower line costs Power control, voltage control, stability control FACTS Power control, voltage control, stability control Installed Costs (millions of dollars) Throughput MWHVDC 2 TerminalsFACTS 2000 MW$ 40-50 M$ 5-10 M 500 MW$ 75-100M$ 10-20M 1000 MW$120-170M$ 20-30M 2000 MW$200-300M$ 30-50M (*)Hingorani/Gyugyi

38. P. Ribeiro August, 2001 38 FACTS and HVDC: Complimentary Solutions Large market potential for FACTS is within the ac system on a value-added basis, where: The existing steady-state phase angle between bus nodes is reasonable The cost of a FACTS device solution is lower than HVDC or other alternatives The required FACTS controller capacity is less than 100% of the transmission throughput rating HVDC Projects: Applications Submarine cable Long distance overhead transmission Underground Transmission Connecting AC systems of different or incompatible frequencies

39. P. Ribeiro August, 2001 39 FACTS Attributes for Different Controllers

40. P. Ribeiro August, 2001 40 X Regulating Bus Voltage Can Affect Power Flow Indirectly / Dynamically E1 /  1 E2 /  2 I P&Q P1 = E1 (E2. sin (  ))/X FACTS Implementation - STATCOM

41. P. Ribeiro August, 2001 41 Line Impedance Compensation Can Control Power Flow Continuously E1 /  1 E2 /  2 P&Q P1 = E1 (E2. sin (  )) / Xeff X FACTS Implementation - TCSC Xeff = X- Xc The alternative solutions need to be distributed; often series compensation has to be installed in several places along a line but many of the other alternatives would put both voltage support and power flow control in the same location. This may not be useful. For instance, if voltage support were needed at the midpoint of a line, an IPFC would not be very useful at that spot. TCSC for damping oscillations...

42. P. Ribeiro August, 2001 42 X Breaker Slatt TCSC TCSC module #1 MOV TCSC #2 TCSC #5 TCSC #3 TCSC #6 TCSC #4 FACTS Implementation - TCSC

43. P. Ribeiro August, 2001 43 XX Damping Circuit Breaker Kayenta TCSC TCSC 15 to 60 Ω MOV Breaker MOV 40 Ω55 Ω FACTS Implementation - TCSC

44. P. Ribeiro August, 2001 44 X E1 /  1 E2 /  2 I P&Q FACTS Implementation - SSSC P1 = E1 (E2. sin (  )) / Xeff Xeff = X - Vinj/I

45. P. Ribeiro August, 2001 45 X E1 /  1 E2 /  2 I P&Q Regulating Bus Voltage and Injecting Voltage In Series With the Line Can Control Power Flow P1 = E1 (E2. sin (  )) / Xeff Xeff = X - Vinj / I FACTS Implementation - UPFC Q1 = E1(E2 - E2. cos (  )) / X

46. P. Ribeiro August, 2001 46 Shunt InverterSeries Inverter Unified Power Flow Controller Series Transformer Shunt Transforme r FACTS Implementation - UPFC

47. P. Ribeiro August, 2001 47 X Regulating Bus Voltage Plus Energy Storage Can Affect Power Flow Directly / Dynamically E1 /  1 E2 /  2 I P&Q Plus Energy Storage FACTS Implementation - STATCOM + Energy Storage

48. P. Ribeiro August, 2001 48 X E1 /  1 E2 /  2 I P&Q FACTS Implementation - SSSC + Energy Storage Plus Energy Storage Voltage Injection in Series Plus Energy Storage Can Affect Power Flow Directly / Dynamically and sustain operation under fault conditions

49. P. Ribeiro August, 2001 49 X E1 /  1 E2 /  2 I P&Q Plus Energy Storage Regulating Bus Voltage + Injected Voltage + Energy Storage Can Control Power Flow Continuously, and Support Operation Under Severe Fault Conditions (enhanced performance) FACTS Implementation - UPFC + Energy Storage

50. P. Ribeiro August, 2001 50 Shunt Inverter Series Inverter Unified Power Flow Controller - SMES Interface SMES Chopper and Coil 1000μ F FACTS Implementation - UPFC + Energy Storage

51. P. Ribeiro August, 2001 51 SMES Chopper and Coil - Overvoltage Protection UPFC Grounding MOV FACTS Implementation - UPFC + Energy Storage

52. P. Ribeiro August, 2001 52 $ Regulating Bus Voltage + Energy Storage + Line Impedance Compensation Can Control Power Flow Continuously, and Support Operation Under Severe Fault Conditions (enhanced performance) FACTS Implementation - TCSC + STACOM + Energy Storage

53. P. Ribeiro August, 2001 53 E1 /  1 E3 /  3 FACTS Implementation - IPFC P12 = E1 (E2. sin (  1-  2)) / X E2 /  2 P13 = E1 (E2. sin (  1-  3)) / X

54. P. Ribeiro August, 2001 54 Series Inverter #1Series Inverter #2 Interline Power Flow Controller Series Transformer, Line 2 Series Transformer, Line 1 FACTS Implementation - IPFC

55. P. Ribeiro August, 2001 55 Increased Power Transfer Enhanced Power Transfer and Stability: Technologies’ Perspective Fast Real Power Injection and Absorption Fast Reactive Power Injection and Absorption Fast Reactive Power Injection and Absorption Compensation Devices FACTS Devices Energy Storage Electric Grid P QQ P Additi onal Stabilit y Margin P TSSC SSSC UPFC SMES Acceleration Area Deceleration Area Stability Margin STATCOM TSSC SSSC UPFC

56. P. Ribeiro August, 2001 56 STATCOM Reactive Power Only Operates in the vertical axis only STATCOM + SMES Real and Reactive Power Operates anywhere within the PQ Plane / Circle (4-Quadrant) P Q The Combination or Real and Reactive Power will typically reduce the Rating of the Power Electronics front end interface. Real Power takes care of power oscillation, whereas reactive power controls voltage. The Role of Energy Storage: real power compensation can increase operating control and reduce capital costs P - Active Power Q - Reactive Power MVA Reduction FACTS + Energy Storage

57. P. Ribeiro August, 2001 57 SMES Power (MW) Additional Power Transfer(MW) Closer to generation Closer to load centers FACTS + Energy Storage - Location Sensitivity

58. P. Ribeiro August, 2001 58 2 STATCOMs 1 STATCOM + SMES Voltage and Stability Control Enhanced Voltage and Stability Control System Frequency (Hz) 60. 8 59. 2 time (sec) (2 x 80 MVA Inverters) ( 80 MVA Inverter + 100Mjs SMES) System Frequency (Hz) 60. 8 59. 2 System Frequency (Hz) 60. 8 59. 2 time (sec) No Compensation Enhanced Power Transfer and Stability: Location and Configuration Type Sensitivity

59. P. Ribeiro August, 2001 59 FACTS For Optimizing Grid Investments FACTS Devices Can Delay Transmission Lines Construction By considering series compensation from the very beginning, power transmission between regions can be planned with a minimum of transmission circuits, thus minimizing costs as well as environmental impact from the start. The Way to Proceed · P lanners, investors and financiers should issue functional specifications for the transmission system to qualified contractors, as opposed to the practice of issuing technical specifications, which are often inflexible, and many times include older technologies and techniques) while inviting bids for a transmission system. · F unctional specifications could lay down the power capacity, distance, availability and reliability requirements; and last but not least, the environmental conditions. · Manufacturers should be allowed to bid either a FACTS solution or a solution involving the building of (a) new line(s) and/or generation; and the best option chosen.

60. P. Ribeiro August, 2001 60 Specifications (Functional rather than Technical ) Transformer Connections Higher-Pulse Operation Higher-Level Operation PWM Converter Pay Attention to Interface Issues and Controls Converter Increase Pulse Number Higher Level Double the Number of Phase-Legs and Connect them in Parallel Connect Converter Groups in Parallel Use A Combination of several options listed to achieve required rating and performance

61. P. Ribeiro August, 2001 61 Cost Considerations

62. P. Ribeiro August, 2001 62 Cost Considerations Cost structure The cost of a FACTS installation depends on many factors, such as power rating, type of device, system voltage, system requirements, environmental conditions, regulatory requirements etc. On top of this, the variety of options available for optimum design renders it impossible to give a cost figure for a FACTS installation. It is strongly recommended that contact is taken with a manufacturer in order to get a first idea of costs and alternatives. The manufacturers should be able to give a budgetary price based on a brief description of the transmission system along with the problem(s) needing to be solved and the improvement(s) needing to be attained. (*) Joint World Bank / ABB Power Systems Paper Improving the efficiency and quality of AC transmission systems

63. P. Ribeiro August, 2001 63 Technology & Cost Trends I $$$ $ I additional cost savings possible $

64. P. Ribeiro August, 2001 64 Concerns About FACTS Cost Losses Reliability

65. P. Ribeiro August, 2001 65 Economics of Power Electronics Sometimes a mix of conventional and FACTS systems has the lowest cost Losses will increase with higher loading and FACTS equipment more lossy than conventional ones Reliability and security issues - when system loaded beyond the limits of experience Demonstration projects required Cost of System 100% Power Electronics 100% Conventional Delta-P 1 Delta-P 2 Delta-P 3 Delta-P 4 Stig Nilson’s paper

66. P. Ribeiro August, 2001 66 Operation and Maintenance Operation of FACTS in power systems is coordinated with operation of other items in the same system, for smooth and optimum function of the system. This is achieved in a natural way through the Central Power System Control, with which the FACTS device(s) is (are) communicating via system SCADA. This means that each FACTS device in the system can be operated from a central control point in the grid, where the operator will have skilled human resources available for the task. The FACTS device itself is normally unmanned, and there is normally no need for local presence in conjunction with FACTS operation, although the device itself may be located far out in the grid. Maintenance is usually done in conjunction with regular system maintenance, i.e. normally once a year. It will require a planned standstill of typically a couple of days. Tasks normally to be done are cleaning of structures and porcelains, exchanging of mechanical seals in pump motors, checking through of capacitors, checking of control and protective settings, and similar. It can normally be done by a crew of 2-3 people with engineer´s skill. Joint World Bank / ABB Power Systems Paper Improving the efficiency and quality of AC transmission systems

67. P. Ribeiro August, 2001 67 Impact of FACTS in interconnected networks The benefits of power system interconnection are well established. It enables the participating parties to share the benefits of large power systems, such as optimization of power generation, utilization of differences in load profiles and pooling of reserve capacity. From this follows not only technical and economical benefits, but also environmental, when for example surplus of clean hydro resources from one region can help to replace polluting fossil-fuelled generation in another. For interconnections to serve their purpose, however, available transmission links must be powerful enough to safely transmit the amounts of power intended. If this is not the case, from a purely technical point of view it can always be remedied by building additional lines in parallel with the existing, or by uprating the existing system(s) to a higher voltage. This, however, is expensive, time-consuming, and calls for elaborate procedures for gaining the necessary permits. Also, in many cases, environmental considerations, popular opinion or other impediments will render the building of new lines as well as uprating to ultrahigh system voltages impossible in practice. This is where FACTS comes in. Examples of successful implementation of FACTS for power system interconnection can be found among others between the Nordic Countries, and between Canada and the United States. In such cases, FACTS helps to enable mutually beneficial trade of electric energy between the countries. Other regions in the world where FACTS is emerging as a means for AC bulk power interchange between regions can be found in South Asia as well as in Africa and Latin America. In fact, AC power corridors equipped with SVC and/or SC transmitting bulk power over distances of more than 1.000 km are a reality today. Joint World Bank / ABB Power Systems Paper Improving the efficiency and quality of AC transmission systems

68. P. Ribeiro August, 2001 68 Conclusions Future systems can be expected to operate at higher stress levels FACTS could provide means to control and alleviate stress Reliability of the existing systems minimize risks (but not risk-free) Interaction between FACTS devices needs to be studied Existing Projects - Met Expectations More Demonstrations Needed R&D needed on avoiding security problems (with and w/o FACTS) Energy storage can significantly enhance FACTS controllers performance

69. P. Ribeiro August, 2001 69 Final Words Power supply industry is undergoing dramatic change as a result of deregulation and political and economical maneuvers. This new market environment puts demands for flexibility and power quality into focus. Also, trade between companies and countries of electric power is gaining momentum, to the benefit of all involved. This calls for the right solutions as far as power transmission facilities between countries as well as between regions within countries are concerned. FACTS Benefits included: -An increase of synchronous stability of the grid; -An increased voltage stability in the grid; -Decreased power wheeling between different power systems; -Improved load sharing between parallel circuits; -Decreased overall system transmission losses; -Improved power quality in grids. The choice of FACTS device is simple and needs to be made the subject of detailed system studies, taking all relevant requirements and prerequisites of the system into consideration, so as to arrive at the optimum technical and economical solution. In fact, the best solution may often be lying in a combination of devices.

70. P. Ribeiro August, 2001 70 From an economical point of view, more power can be transmitted over existing or new transmission grids with unimpeded availability at an investment cost and time expenditure lower, or in cases even far lower than it would cost to achieve the same with more extensive grids. Also, in many cases, money can be saved on a decrease of power transmission losses. From an environmental point of view, FACTS enables the transmission of power over vast distances with less or much less right-of-way impact than would otherwise be possible. Furthermore, the saving in transmission losses may well bring a corresponding decrease in need for generation, with so much less toll on the environment. All these things help to enable active, useful power to reach out in growing quantities to growing populations under safe and favorable conditions all over the world. Also, individual countries´ own border lines no longer constitute any limit to power industry. With FACTS, power trade to the benefit of many can be established to a growing extent across borders, by making more efficient use of interconnections between countries, new as well as existing. Final Words

71. P. Ribeiro August, 2001 71 Questions and Open Discussions

72. P. Ribeiro August, 2001 72 Appendix