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2 0 2 10 5 0 5 10 Lecture 3 Advanced FACTS Devices and Applications: Performance, Power Quality and Cost Considerations Paulo F. Ribeiro, BSEE, MBA, PHD, PE CALVIN COLLEGE Engineering Department Grand Rapids, MI 49546 http://engr.calvin.edu/PRibeiro_WEBPAGE/ [email protected] P. Ribeiro June, 2002 1 FACTS • • • • • • • • • • P. Ribeiro 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 Conditioners: SVC, STATCOM, TCSC, UPFC, SMES Specification, Cost Considerations and Technology Trends Impact of FACTS in interconnected networks Market Assessment, Deregulation and Predictions June, 2002 2 The Concept P. Ribeiro X V P P P P X V tg June, 2002 3 The Concept and Challenges 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. 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. P. Ribeiro June, 2002 4 The Concept 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). P. Ribeiro June, 2002 5 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 P. Ribeiro June, 2002 6 System Architectures and Limitations 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 P. Ribeiro June, 2002 7 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 P. Ribeiro June, 2002 8 Power Flow Control on AC Systems 50% Series Compensation 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 P. Ribeiro June, 2002 9 FACTS Applications and Implementations Transmission Transfer Capacity Enhancement Steady State Issues Voltage Limits Thermal Limits Angular Stability Limits Loop Flows Dynamic Issues Traditional Solutions Breaking Resistors Load Shedding Advanced Solutions FACTS Energy Storage Fixed Compensation Line Reconfiguration Transmission Link Better Protection FACTS Increased Inertia P. Ribeiro Devices June, 2002 Transient Stability Damping Power Swings Post-Contingency Voltage Control Voltage Stability Subsynchronous Res. Enhanced Power Transfer and Stability SVC STATCOM TCSC, SSSC UPFC 10 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) Energy Storage 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-Series P. Ribeiro June, 2002 Energy Storage 11 Power Electronics - Semiconductor Devices Diodes Transistors IGBT Thyristors SCR, GTO, MTO, ETO, GCT, IGCT, MCT 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) P. Ribeiro June, 2002 12 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) P. Ribeiro June, 2002 13 Power Electronics - Semiconductor Devices Decision-Making Matrix System VSI CSI Commutation Approach Natural Forced Switching Technology Synchronous PWM Transition Approach Hard Soft Circuit Topology Two-Level Multi-Level Device Type P. Ribeiro SCR June, 2002 GTO IGBT MCT MTO 14 AC Transmission Fundamentals (Series Compensation) E1 / 1 E2 / 2 P&Q I X 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. Vc Vx I P1 = E1 . E2 . sin () / (X - Xc) Vs Real Power Angle Curve 2 Vseff = Vs + Vc Vr Xeff = X - Xc Vx 2 Vc P1( x delta V1) Vxo 1 Vs Vseff 0 0 0 0 0.5 1 1.5 2 delta 2.5 3 Vr I 3.5 3.14 Phase Angle P. Ribeiro June, 2002 15 AC Transmission Fundamentals (Voltage-Series and Shunt Comp.) E1 / 1 P&Q E2 / 2 I X P Injected Voltage E1 E1 - E2 I E2 Integrated voltage series injection and bus voltage regulation (unified) will directly increase or decrease real and reactive power flow. P. Ribeiro June, 2002 16 AC Transmission Fundamentals (Stability Margin) Improvement of Transient Stability With FACTS Compensation Equal Area Criteria Q/V with VAR compensation (ideal midpoint) Amargin A2 no compensation A1 A1 = Acceleration Energy 1 2 3 A2 = Deceleration Energy Therefore, FACTS compensation can increase 1 - prior to fault crit power transfer without reducing the stability margin P. Ribeiro June, 2002 Phase Angle 2 - fault cleared 3 - equal area 3 >crit - loss of synchronism 17 Voltage Source Vs. Current Source Converters CSC Device Type Device Characteristic Symmetry Adv Dis Thyristor Self-Commutation Symmetrical Thyristor Self-Commutation Asymmetrical Adv Dis + Short-Circuit Current Lower + Higher Rate of Rise of Fault Current Losses Limited by DC Reactor + Fast Rise (Due to capacitor discharge) Higher - Lower + AC Capacitors DC Capacitors Required Not Required + + Not Required Required Valves dv/dt Lower (AC Capacitors) More Complex Depends on Current Flowing through Energy Storage + Higher Interface with AC System Reactive Power Generation Performance Harmonics P. Ribeiro VSC Less Complex Independent of Energy Storage + + June, 2002 18 Voltage Source Converters S hun tC om p en sa toi n S e r ies C om p en sa toi n V S ys etm bu s V S ys etm bu s V C oup lni g T ran s of m r er C oup lni g T ran s of m r er I X I T ran s of m r e r el a kage ni du c at n ce X Vo Vo DC A -C Sw itch ni g C on ve r te r DC A -C Sw itch ni g C on ve r te r Cs P. Ribeiro T ran s of m r e r el a kage ni du c at n ce Cs + + V dc V dc June, 2002 19 Voltage Source Converters Basic 6-Pulse, 2-level, Voltage-Source Converter di c ea eb ec ai Ta 1 D a 1 Tb 1 D b1 T c1 bi D c1 V dc + Cs V dc ci 2 H y po the tci a l n eu tra lp o ni t V dc Ta 2 D a 2 Tb 2 D b2 T c2 D c2 2 ea Vdc eb Vdc ec Vdc eab [a ] ebc eca P. Ribeiro ia ib ic D Ta1 a1 Ta2 D a2 D b1 Tb1 D Tb2 D c1 b2 June, 2002 Tc 2 20 [b ] Voltage Source Converters 2, 3, 5-level, VSC Waveforms vd c 2 vd c 2 + e ou t vd c 2 v dc + vd c 2 v dc + 2 v dc v dc N eu tra l m ( di -) po ni t vd c e ou t + 1 v dc + 2 + v dc N e u tra l m ( di -) p o ni t e ou t vd c P. Ribeiro + - v dc v dc June, 2002 + 21 Voltage Source Converters Output voltage control of a two-level VSC v =V 0 it v= V s n io v o= V o ( ) t * t = * v o ( ) v o ( ) v oF ( )= V (+ ) s n i t t (v+ v )d c v d c nom ni a l (v - v )d c t C idc v d c= 1 i d c d t C i d c = f v oF ( )= V (+ ) s n it P. Ribeiro vdc June, 2002 22 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. P. Ribeiro June, 2002 23 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 MW HVDC 2 Terminals FACTS 2000 MW 500 MW 1000 MW 2000 MW $ 40-50 M $ 75-100M $120-170M $200-300M $ 5-10 M $ 10-20M $ 20-30M $ 30-50M (*)Hingorani/Gyugyi P. Ribeiro June, 2002 24 FACTS and HVDC: Complimentary Solutions HVDC Projects: Applications Submarine cable Long distance overhead transmission Underground Transmission Connecting AC systems of different or incompatible frequencies 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 P. Ribeiro June, 2002 25 FACTS Attributes for Different Controllers FACTS Controller Static Synchronous Compensator (STATCOM without storage) Static Synchronous Compensator (STATCOM with storage, BESS, SMES, large dc capacitor) Static VAR Compensator (SVC, TCR, TCS, TRS Thyristor-Controlled Braking Resistor (TCBR) Static Synchronous Series Compensator (SSSC without storage) Static Synchronous Series Compensator (SSSC with storage) Thrystor-Controlled Series Capacitor (TCSC, TSSC) Thyristor-Controlled Series Reactor (TCSR, TSSR) Thyristor-Controlled Phase-Shifting Transformer (TCPST or TCPR) Unified Power Flow Controller (UPFC) Thyristor-Controlled Voltage Limiter (TCVL) Thyristor-Controlled Voltage Regulator (TCVR) Interline Power Flow Controller (IPFC) P. Ribeiro Control Attributes Voltage control, VAR compensation, damping oscillations, voltage stability Voltage control, VAR compensation, damping oscillations, transient and dynamic stability, voltage stability, AGC Voltage control, VAR compensation, damping oscillations, transient and dynamic stability, voltage stability Damping oscillations, transient and dynamic stability Current control, damping oscillations, transient and dynamic stability, voltage stability, fault current limiting Current control, damping oscillations, transient and dynamic stability, voltage stability Current control, damping oscillations, transient and dynamic stability, voltage stability, fault current limiting Current control, damping oscillations, transient and dynamic stability, voltage stability, fault current limiting Active power control, damping oscillations, transient and dynamic stability, voltage stability Active and reactive power control, voltage control, VAR compensation, damping oscillations, transient and dynamic stability, voltage stability, fault current limiting Transient and dynamic voltage limit Reactive power control, voltage control, damping oscillations, transient and dynamic stability, voltage stability Reactive power control, voltage control, damping oscillations, transient and dynamic stability, voltage stability June, 2002 26 FACTS Implementation - STATCOM P&Q E1 / 1 I E2 / 2 X Regulating Bus Voltage Can Affect Power Flow Indirectly / Dynamically P1 = E1 (E2 . sin ())/X P. Ribeiro June, 2002 27 FACTS Implementation - TCSC E1 / 1 P&Q E2 / 2 X Line Impedance Compensation Can Control Power Flow Continuously P1 = E1 (E2 . sin ()) / Xeff 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 ... P. Ribeiro June, 2002 28 FACTS Implementation - SSSC E1 / 1 P&Q E2 / 2 I X P1 = E1 (E2 . sin ()) / Xeff Xeff = X - Vinj/I P. Ribeiro June, 2002 29 FACTS Implementation - UPFC E1 / 1 P&Q E2 / 2 I X Regulating Bus Voltage and Injecting Voltage In Series With the Line Can Control Power Flow P1 = E1 (E2 . sin ()) / Xeff Xeff = X - Vinj / I Q1 = E1(E2 - E2 . cos ()) / X P. Ribeiro June, 2002 30 FACTS Implementation - UPFC Series Transformer Shunt Inverter Series Inverter Shunt Transforme r Unified Power Flow Controller P. Ribeiro June, 2002 31 FACTS Implementation - STATCOM + Energy Storage E1 / 1 I P&Q E2 / 2 X Regulating Bus Voltage Plus Energy Storage Can Affect Power Flow Directly / Dynamically Plus Energy Storage P. Ribeiro June, 2002 32 FACTS Implementation - SSSC + Energy Storage E1 / 1 P&Q E2 / 2 I X Voltage Injection in Series Plus Energy Storage Can Affect Power Flow Directly / Dynamically and sustain operation under fault conditions Plus Energy Storage P. Ribeiro June, 2002 33 FACTS Implementation - UPFC + Energy Storage E2 / 2 P&Q E1 / 1 I X Plus Energy Storage P. Ribeiro Regulating Bus Voltage + Injected Voltage + Energy Storage Can Control Power Flow Continuously, and Support Operation Under Severe Fault Conditions (enhanced performance) June, 2002 34 FACTS Implementation - UPFC + Energy Storage Series Inverter Shunt Inverter 1000μ F 1000μ F 1000μ F 1000μ F SMES Chopper and Coil Unified Power Flow Controller - SMES Interface P. Ribeiro June, 2002 35 FACTS Implementation - UPFC + Energy Storage MOV UPFC Grounding SMES Chopper and Coil - Overvoltage Protection P. Ribeiro June, 2002 36 FACTS Implementation - TCSC + STACOM + Energy Storage $ Regulating Bus Voltage + Energy Storage + Line Impedance Compensation Can Control Power Flow Continuously, and Support Operation Under Severe Fault Conditions (enhanced performance) P. Ribeiro June, 2002 37 FACTS Implementation - IPFC E3 / 3 E1 / 1 E2 / 2 P12 = E1 (E2 . sin (1- 2)) / X P13 = E1 (E2 . sin (1- 3)) / X P. Ribeiro June, 2002 38 FACTS Implementation - IPFC Series Transformer, Line 1 Series Transformer, Line 2 Series Inverter #1 Series Inverter #2 Interline Power Flow Controller P. Ribeiro June, 2002 39 Enhanced Power Transfer and Stability: Technologies’ Perspective Compensation Devices FACTS Devices Energy Storage Fast SMES Real Power Injection and Absorption P P TSSC SSSC UPFC Electric Grid Q STATCOM Q 2 Acceleration Area 1.5 STATCOM Fast Reactive Power Injection and Absorption June, 2002 Increased Power Transfer Additio nal Stabilit y Margin Electric Grid Fast Reactive Power Injection and Absorption P. Ribeiro P Power Transfer TSSC SSSC UPFC Deceleration Area Stability Margin 1 0.5 0 0 0.5 1 1.5 2 2.5 3 Phase Angle 40 FACTS + Energy Storage Q The Role of Energy Storage: real power compensation can increase operating control and reduce capital costs STATCOM Reactive Power Only Operates in the vertical axis only P MVA Reduction 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. P. Ribeiro P - Active Power Q - Reactive Power STATCOM + SMES Real and Reactive Power Operates anywhere within the PQ Plane / Circle (4-Quadrant) June, 2002 41 FACTS + Energy Storage - Location Sensitivity Additional Power Transfer(MW) Closer to generation Closer to load centers SMES Power (MW) P. Ribeiro June, 2002 42 Enhanced Power Transfer and Stability: Location and Configuration Type Sensitivity No Compensation 60. 8 59. 2 time (sec) 2 STATCOMs 1 STATCOM + SMES 60. 8 60. 8 59. 2 59. 2 time (sec) time (sec) Enhanced Voltage and Stability Control Voltage and Stability Control (2 x 80 MVA Inverters) P. Ribeiro ( 80 MVA Inverter + 100Mjs SMES) June, 2002 43 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 · Planners, 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. · Functional 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. P. Ribeiro June, 2002 44 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 P. Ribeiro June, 2002 45 Cost Considerations Technology Reconductor lines Fixed or Switched Shunt Reactors Fixed or Switched Shunt Capacitors Fixed or Switched Series Capacitors Static VAR Compensators Thyristor Controlled Series Compensation (TCSC) STATCOM STATCOM w/SMES Transmission Line Transfer Enhancement Increase thermal capacity Voltage reduction – Light Load Management Voltage support and stability Power flow control, Voltage support and Stability Voltage support and stability Power flow control, Voltage support and stability Voltage support and stability Voltage support and stability Cost Range $50K to $200K per mile $8-$12 kVAR $8-$10 kVAR $12-$16 kVAR $20-$45 kVAR $25-$50 kVAR $80-$100 kVAR $150-$300 kW Unified Power Flow Controller (UPFC) Operating principle Increases thermal limit for line Procurement Availability Competitive Compensates for capacitive varload Compensates for inductive varload Reduces inductive line impedance Competitive Compensates for inductive and/or capacitive var-load Reduces or increases inductive line impedance Competitive Compensates for inductive and capacitive var-load Compensates for inductive and/or capacitive var-load plus energy storage for active power SVC and TCSC functions plus phase angle control Limited competition Limited Competitive Competitive Limited competition Power flow control, $150-$200 kW Sole source Voltage support, and Stability Unified Power Flow Power flow control $250-$350 kW SVC and TCSC functions plus Sole source Controller (UPFC) w/SMES Voltage support and voltage regulator, phase angle Stability, controller and energy storage Shaded area indicates technologies that are either permanently connected or switched on or off with mechanical switches. (i.e. these are not continuously controllable) P. Ribeiro June, 2002 46 Cost Considerations Hardware Eng & Project Mgmt. Installation Civil Works Commissioning Insurance 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 P. Ribeiro June, 2002 47 Technology & Cost Trends $ I $$$ $ I additional cost savings possible P. Ribeiro June, 2002 48 Concerns About FACTS Cost Losses Reliability P. Ribeiro June, 2002 49 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 100% Power Electronics Delta-P4 Delta-P2 Delta-P3 Delta-P1 100% Conventional Cost of System P. Ribeiro Stig Nilson’s paper June, 2002 50 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 P. Ribeiro June, 2002 51 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. P. Ribeiro Joint World Bank / ABB Power Systems Paper Improving the efficiency and quality of AC transmission systems June, 2002 52 Power Quality Issues 1 – Background 2 – The Need For An Integrated Perspective of PQ 3 – Harmonics 4 – Imbalance 5 – Voltage Fluctuations 6 – Voltage Sags 7 – Standards, Limits, Diagnostics, and Recommendations Flexibility, Compatibility, Probabilistic Nature, Alternative Indices 8 – Combined effects 9 – Power Quality Economics 10 – Measurement Protocols 11 – Probabilistic Approach 12 – Modeling & Simulation 13 – Advanced Techniques (Wavelet, Fuzzy Logic, Neural Net, Genetic Algorithms) 14 – Power Quality Programs P. Ribeiro June, 2002 53 Compatibility: The Key Approach P. Ribeiro June, 2002 54 Relative Trespass Level (RTL) U k Uref k RTL k max 0, Uref k Uk - measured or calculated harmonic voltage Uref - harmonic voltage limit (standard or particular equipment) k - harmonic order 8 8 8 6 6 RT Lk RT Lk 4 0 0 2 2 P. Ribeiro 4 2 2 0 8 4 6 8 k 10 12 14 13 June, 2002 0 0 0.05 0.1 0 Uk .1 55 Harmonic Distortion Diagnostic Index Applying Fuzzy Logic Comparisons Alternative Approach Individual Harmonics (Vh) Equipment Malfunction Fuzzy - Color Code Criteria No Problem b c Below NormalOver Below Normal Heating Normal a Caution Possible Problems Very Hot d Imminent Problems e 1 Normal Levels 0 P. Ribeiro A B Caution Possible Severe Dangerous Problems Distortions Levels C June, 2002 D E F G RTL 56 How To Interpret This? P. Ribeiro June, 2002 57 How To Interpret This? P. Ribeiro June, 2002 58 The Total Quality Environment Power System Value Chain Environmental Maintainability Availability Safety Efficiency Reliability Performance Price Power Quality Energy INPUTS Generation Delivery Conversion Power Processing Communication OUTPUTS Light / Motion Central Station T&D AC-AC Supplies Motion SMES Batteries FACTS SMES PQ Parks UPS Appliances Power Electronics Systems and Components User Utility P. Ribeiro June, 2002 59 Conclusions • • • • • • • • P. Ribeiro 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 June, 2002 60 Conclusions A Balanced and Cautious Application The acceptance of the new tools and technologies will take time, due to the computational requirements and educational barriers. The flexibility and adaptability of these new techniques indicate that they will become part of the tools for solving power quality problems in this increasingly complex electrical environment. The implementation and use of these advanced techniques needs to be done with much care and sensitivity. They should not replace the engineering understanding of the electromagnetic nature of the problems that need to be solved. P. Ribeiro June, 2002 61 Questions and Open Discussions P. Ribeiro June, 2002 62