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Abstract—This work presents the main aspects and criteria adopted by the Brazilian independent system operator (ISO) for power system restoration due to total ...
IEEE TRANSACTIONS ON POWER SYSTEMS, VOL. 19, NO. 2, MAY 2004

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Guidelines for Power System Restoration in the Brazilian System Paulo Gomes, Antonio Carlos Siqueira de Lima, Member, IEEE, and Antonio de Pádua Guarini

Abstract—This work presents the main aspects and criteria adopted by the Brazilian independent system operator (ISO) for power system restoration due to total or partial collapses. Guidelines to avoid or minimize the occurrence of drawbacks during the restoring process are also outlined. It presents a summary of the recommendations and procedures. To exemplify the overall procedures, the restoration in the Rio de Janeiro area is presented including a possible alternative in case of a blackout in this area. Index Terms—Power system control, power system modeling, power system restoration.

I. INTRODUCTION

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ESTORATION processes deal with a broad range of phenomena involving from load flow to electromagnetic and electromechanical transients analysis. Therefore, a large variety of programs and models is needed and an extensive analysis is demanded to provide a set of viable solutions to restore the power after an outage [1], [2]. Although the probability of a global outage is rather small, a few occurred in Brazil (in 2002 and 1999) and in other countries, for instance, the West Coast in the U.S. (in 1996) [3] bringing severe consequences to the society, which has grown very dependable on electricity. Independent of how well planned, designed, or operated, any electrical system is prone to power outages; thus creating an interest in restoration procedures, tools, and models. In Brazil, the restoration procedures are intimately related to the evolution of the Electric Transmission System. The Southern part of the system, until the late 1970s, was dependent on the power supply from the Southeast through a weak 230-kV intertie. This configuration caused a large number of severe disturbances leading to the development of an underfrequency load shedding scheme to prevent system collapse. While the utilities in the South felt the need for decentralized restoration procedures aiming for a faster load pickup rate, other utilities in Brazil adopted an operation centers-based procedure being therefore centralized. Furnas (a transmission and generation utility responsible for most of the transmission system in the Southeast and Midwest regions of Brazil) was an exception. In 1982, it started adopting a decentralized procedure. In 1984 and 1985, there were three large disturbances in the Southeast area causing outages in several metropolitan regions with drastic economical and social impact [4]. One must remember that most industries Manuscript received April 29, 2003. P. Gomes and A. de Pádua Guarini are with the Operador Nacional do Sistema Elétrico, Rio de Janeiro, RJ 20091-000, Brazil (e-mail: [email protected]; [email protected]). A. C. S. de Lima is with the Federal University of Rio de Janeiro, Rio de Janeiro, RJ 21945-970, Brazil (e-mail: [email protected]). Digital Object Identifier 10.1109/TPWRS.2004.825862

in Brazil are located in the southeast. The total amount of interrupted load was above 10 000 MW. After these disturbances, some frequent problems were identified such as congestion of communication links, difficulties in identifying the postdisturbance configuration, halt in substation supervisions due to overflow alarms, high overvoltages limiting a complete restoration, loss of communications between operating centers of interconnected utilities, and a lack of a strategic plan for restoring the system as a whole. To solve or minimize these problems, a restoration task force was created in 1989 to establish guidelines and criteria for the restoration of the main grid which were later implemented in all of the utilities in the south/southeast/middle west. In 1996, a major blackout hit Southeast Brazil, leading to the creation of a new working group to review and update the restoration procedures. The last major blackouts occurred in 1999 and in 2002 and were initiated in the 440-kV system. The former began in the Bauru substation in São Paulo (southeast region) and caused the islanding of two power plants, Jupiá and Ilha Solteira, affecting all of the 440 kV of São Paulo and causing the switching off of the 765-kV (ac) and the 600-kV (HVDC) systems with an almost total collapse of the south/southeast and middle west regions and the latter also begun in the 440-kV system at the Araraquara substation, again almost all of the 440-kV system went down, causing the partial collapse of the 500-kV transmission system in the southeast. Some important areas in Brazil were subjected to a loss of supply for more than 4 h. In both cases, the amount of interrupted load was around 24 000 MW. These last blackouts have shown that in terms of system operation, the southeast presents a challenge where unexpected switchings may lead to voltage collapse. This is in part due to the topological structure of the Brazilian system where the 440-kV system supplies the largest loads in the southeast and is “surrounded” by a 500 kV with, usually, a lighter load. ANEEL (the Brazilian regulatory agency) urged the Brazilian ISO (ONS) to carry out a thorough review of all restoration procedures [5]. The priority procedure in the most affected areas in these last two blackouts (Rio de Janeiro, São Paulo, and Mato Grosso do Sul) was reassessed and alternatives restorations were proposed in case of unavailability in priority procedures. The restoration processes, be it partial or total, are defined nowadays by the grid code which states all of the responsibilities of operators, utilities operating centers, and the ISO regional and national operating centers. This document is updated constantly since any topology change, be it a connection of a new generating plant, transmission path, or any other procedure, implies in the change of restoration processes, partial or total.

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This demands a continuous assessment and validation through a set of studies carried out by the ISO and the utilities. From these studies, new restoration procedures are implemented by the National Operating Center (owned by the Brazilian ISO).

II. RESTORATION CRITERIA The restoration studies take into account some main aspects: balance between load and generation with black start [2], definition of voltage limits, and availability of load blocks that can be picked up maintaining the system reliability. Moreover, in any restoration procedures an alternative solution should be taken into account in case of equipment unavailability so the overall process is not affected. The strategy must be such that the agents, who own the generating units, start the restoration, providing the operators with information regarding the amount of active power to be delivered to priority loads. The restoration strategy must keep the active power balance to avoid large frequency deviations and protection schemes misoperation. The main restoration criteria come from load-flow analysis, the results of the electromechanical and electromagnetic transients are applied only at a later stage defining whether the restoration sequence is viable. The load-flow analysis uses the concept of geoelectrical areas together with another index, the reliability degree, which defines the reliability of units capable of black-start. It gives qualitative information about the overall capability of using determined generation units during the restoration process. A. Geo-Electrical Areas The concept of the geo-electrical areas is not much different from the power restoration line used in Italy [6] where there is a predefined partitioning of the network. Therefore, geo-electrical areas are minimum grid configurations containing one or more generating units allowing the restoration of priority loads in the fastest and safest way. In other words, they represent the minimum of island configuration where the power supply is still attained within the normal limits. B. Reliability Degree This index is used to define a geo-electrical area, it gives qualitative information whether any specific units can be used for the restoration process. This degree can be classified in the following way: high reliability–units capable of black start independently of any external supply and can be started up from standstill; medium reliability—capable of supplying their auxiliary systems with terminal voltage in the generating units, must be kept rotating and excited after a disturbance occurs. Low Reliability–units that require an external supply from auxiliary systems. A geo-electrical area must contain at least one generating unit capable of black-start (i.e., at least a single high-reliability unit). Medium and low reliability units can participate in the first stages of the restoration as voltage and power support. The frequency control is carried out by the units with high reliability.

III. STAGES IN RESTORATION PROCESS In the bulk Brazilian power system, the restoration processes have two stages: fluent and coordinated. In the former, there is no need for communication among the parts involved, while in the latter, several prior conditions must be reached. The National Operating Center is responsible for the coordination of the whole process. In other words, during fluent restoration, an operator need not communicate with any other substations. His or her function is to check whether the voltage conditions are met and if all of the reactors needed are connected and then switch on the transmission line. In the coordinated process, the operator has to contact an operating center of higher hierarchy and wait for instructions of what to maneuver. Moreover, in fluent restoration, it is assumed that the system is completely de-energised, except for any prescheduled islanding. The restoration procedure is started by high reliability hydropower units. The actual restoration process is started through the startup and synchronization of the generating units, energization of the transmission lines, and priority load pickup, with the least level of communication. For the restoration of the main grid of the Brazilian bulk power system, there are some recommendations and guidelines to establish the procedures for fluent restoration. • For each fluent restoration process, startup voltage level and the minimum amount of generators must be established. • The priority load pickup must be predefined keeping in mind the balance between generation and load and not exceed either the transmission paths and transformation available. • The maximum amount of power in each priority load pickup for each geo-electrical area must be predefined. • The load pickup is carried out in steps giving preference to reduced amounts; the apparent increase in restoration time is compensated for the increase in reliability and safety which is crucial in the fragile starting stage. • It should consider extreme load configurations such as maximum and minimum (heavy and light loads) to ensure that the restoration process can be carried out at any time. • If there are no restrictions, hydropower units should keep the highest number of units in operation during restoration. • Financial issues should not come into consideration during the restoration process. • Thermal power plants are usually considered last in the restoration procedure, although, if possible, they should be equipped with black start and islanding schemes to supply part of the system after a disturbance. • To avoid overvoltage during outages, capacitor banks are to be de-energized and transformer taps are operated in such a way as to minimize this risk. • Synchronous or static compensators are not to be involved in the general voltage control criteria unless the equipment usage is thoroughly defined in the operating procedure. In the case of a total collapse, the coordinated stage starts after some geo-electrical areas are restored. In the case of a partial collapse, there will not be a fluent but only a coordinated stage.

GOMES et al.: GUIDELINES FOR POWER SYSTEM RESTORATION IN THE BRAZILIAN SYSTEM

The national and regional operating centers coordinate the load shedding and closing of loops or parallelling of systems in distinct geo-electrical areas that were restored during the fluent restoration. The geo-electrical areas are first restored in a practically independent manner during the fluent phase. There are restoration procedures that involve, in the beginning, only fluent process and later on, start the coordinated one, while there can be a procedure where even the first steps in restoration are taken in a coordinated manner. The restoration can also be coordinated when there is any sort of impediment that requires the action of a group of distinct operating centers or a higher hierarchical entity. Hierarchy is defined in a way that the utilities operating centers are coordinated by the ISO regional operating center which, in turn, is controlled by the National Operating Center. The utilities are responsible for the load pickup within predefined parameters and this procedure can only begin after the following demands are met: nonexistence of equipment overload in the coordinated area; frequency stabilization; compatible voltage levels; connection of geo-electrical areas should only be done when the two areas involved present a stable configuration. IV. RESTORATION STUDIES Together with the index of generator reliability, the powerflow studies are done to assess the system conditions throughout all of the restoration stages, verifying equipment load, voltage profiles, and capabilities of the generating units prior, during, and after switchings. Therefore, those studies are responsible to check whether or not a certain restoration procedure meets all of the standards defined in the grid code. A. Initial Power Availability The first criteria is the availability of generating units equipped with black start (i.e., the amount of pickup load cannot exceed the initial active power capability for each region). The second criteria is the minimum amount of generating units that can be considered, taking into account maintenance and electrical parameters. If on the one hand, the number of generating units must be such that overload or self-excitation are avoided; on the other hand, the overall restoration time has to be less than the maximum operating time that any machine ) generating units or can operate unloaded. Therefore, for ( the minimum number of generating units available, equipped with blackstart, the initial power availability for a geo-electrical area is defined by (1) is the nominal where is the number of generating units, power actually available. If a geo-electrical area has more than one generation block equipped with black start and is participating in the fluent restoration process, the frequency control is carried out by only one of these generating blocks. B. Voltage Control in Geo-Electrical Areas During Fluent Restoration Shunt reactors are used together with the reactive power of the generating units to provide a reasonable voltage profile and

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avoid high overvoltage due to Ferranti effects in the transmission paths. The reactive power supply provided by the generating units must comply with the machine capability curve. The amount of priority load to be picked up in any geo-electrical area is therefore defined from the total available active and reactive power delivery by the generating units. During all of the stages of the restoration process, the voltage control is such that the maximum allowed overvoltage is 110% of nominal voltage and the minimum is 90%. During normal operation, the range is narrower, 105% for the maximum and 95% for the minimum. C. Electromechanical Transients Electromechanical transients studies are carried out to analyze the behavior of frequency and voltage oscillations during load pickup and load rejection. In those studies, it is mandatory to represent the voltage and speed regulators of the units equipped with black start. In restoration studies, frequency deviations from 55 up to 65 Hz can be accepted as minimum and maximum limits, respectively. For thermal units, these limits are narrower, around 58 and 62 Hz, respectively. This limitation is a question of design, the units nowadays operating in Brazil are not capable of large frequency excursions. Besides the frequency oscillation, there is another issue related to the reactive power capability of thermal units. Typically, a thermal unit could energize around 150 to 200 km of a 500-kV transmission line. In Brazil, the main distance far exceeds this limit ranging from 600 up to 800 km. For dynamic voltage, the maximum and minimum acceptable are 85% and 125% (or 5% lower than the overvoltage protection limit). The electromechanical studies also help to evaluate the likeness of self-excitation in case a load rejection occurs during the early stages of the restoration process when the system is essentially unloaded. This phenomenon is a function of the electrical parameters of the machine, including speed and voltage regulators, and the total impedance of the network to be restored, considering also the load. Therefore, the electrical machines model must be as extensive as possible, including a possible protection scheme that might be used by the equipment. The priority loading during the fluent part of the restoration is carried out in steps, in which each represents an amount of load that does not compromise either voltage or frequency throughout the system. In an ideal scenario, the load pickup ought to be done in steps of 20%–50% of the available active power. The load pickup in the restoration process is not to be done in time intervals less than 1 min so the voltage and frequency oscillation due to the prior load can be stabilized with the action of voltage and speed regulators. For voltage levels prior to 230 kV whenever a loop or parallel is closed, the dynamic overvoltage must be evaluated as well as mechanical aspects of the machines in the process and the electromechanical stability of the system. Prior to the closing of any parallel or loop, the following limits are considered: maximum frequency deviation; maximum phase difference of 10 ; maximum overvoltage up to 10% of nominal voltage. It should also be noted that the voltage difference is not restrictive, the threshold is defined by the grid code. If for any reason it is not possible to achieve the phase angles within the

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Fig. 1.

IEEE TRANSACTIONS ON POWER SYSTEMS, VOL. 19, NO. 2, MAY 2004

Single-line diagram for the restoration in Rio de Janeiro area.

limits, the loop can be closed if either the voltage levels are below the recommended values or if there is an equipment overload. Whenever an outage occurs, the machines in the affected area must not participate in the automatic generation control. D. Electromagnetic Transients Electromagnetic transients studies define maximum voltage for equipment energization and if it is possible to energze the equipment without any risk considering transient overvoltages or system resonance. They are used to verify short-term conditions such as line, transformer energization, and load rejection. The priority loads are supplied after the transformer energization, which is done through the high voltage side and, therefore, more troublesome since there is a greater interaction between the capacitance of the transmission lines and the inductances of the transformer itself and the system. Furthermore, the losses in the high side of the system are smaller giving transients with lower damping. For the transmission lines, the studies contemplate the line energization with or without a fault at the receiving end of the transmission line. For the transformer, the results also provided the inrush current that can be useful for a protection system. As it is nowadays, these studies follow this strategy: obtain the load flow of the system; adjust the initial conditions of the transient case so the load-flow conditions are met. The load-flow results represent a prior to fault scenario for the transient case. A statistical case is done to obtain which is the worst case scenario. The load rejection studies define the levels of maximum load pickup during the restoration process as well as the minimum configuration of reactors for the system under study. There are two possible problems in terms of load rejection during restoration that can happen, either one being very harmful for the whole restoration procedure. The first one is related with undue operation of surge arresters because of load rejection overvoltages. The second one is related to misoperation of overvoltage protection schemes causing unwanted disconnection of already restored parts of the system. This leads to the repetition of prior steps demanding an interference from the operation center dealing with the process. Both problems lead to a delay and, in some cases, a reset of the whole restoration procedure. The aforementioned problems ought to be taken carefully

Fig. 2.

Self-excitation at Marimbondo during restoration.

during the fluent part of restoration, since, in this stage, the black start units are still separated in geo-electrical areas with rather different characteristics and sometimes without sufficient generation, prone to higher overvoltages due to load rejections. V. RESTORATION IN THE RIO DE JANEIRO AREA The main operative procedure for a power restoration in the Rio de Janeiro Area is done through the Marimbondo power plant with a local generation support from a 138-kV system in the main Rio de Janeiro Area which is used to increase the system stability during the restoration. This local generation is owned by Light (local distribution company in Rio de Janeiro while the Marimbondo and the associated transmission system belong to Furnas). Fig. 1 shows the geo-electrical area for the restoration configuration and the associated voltages in per unit. At the Grajau substation, there is also a synchronous compensator connected through a step-up (13,8 kV:500-kV) transformer. The synchronous compensator is used only after the main load is restored. The total capability of the Marimbondo power plant is 1488 MW (eight units of 186 MW). The minimum quantity of units at the Marimbondo power plant was defined by electromechanical studies considering the minimum amount that would avoid self-excitation after a load rejection. To further illustrate these tests, Fig. 2 shows the voltage at the 500-kV bus (Marimbondo Substation) during a restoration process where load rejection occurs at each step during the process. From the aforementioned figure, one can see that with one machine at Marimbondo, it is impossible

GOMES et al.: GUIDELINES FOR POWER SYSTEM RESTORATION IN THE BRAZILIAN SYSTEM

Fig. 4.

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Restoration of the Rio de Janeiro area with the south system.

A. Alternative Restoration in Rio de Janeiro Area

Fig. 3. Voltage at Tijuco Preto 765 kV after the transformer energization without the south system.

to even reach the next substation (Araraquara 500 kV) without risking self excitation. To reach the Poços de Caldas 500-kV substation, three machines are needed at Marimbondo; therefore, to reach the substations of Grajaú, Adrianópolis, and São José, totaling 740 km of 500-kV transmission lines without risking self excitation, the Marimbondo power plant must be operated with five machines. The initial amount of power available during the restoration in the case of five machines in Marimbondo is of . The startup voltage at the 13.8-kV bus at Marimbondo is equal to the lower limit of the automatic voltage regulator (AVR) 90%, the stepup transformer has a fixed tap at 100%, even though in normal operation, it is equipped with a load tap changer (OLTC). For this system, the voltage at Grajaú, Adrianópolis, and São José must be below 110%. Prior to adjusting the amount of load to be supplied, one must define the minimum reactor configuration to make sure that during the entire process, there is not any equipment with a steady-state voltage higher than 110%. For the system in Fig. 1, four line reactors are used: two 73-Mvar reactors at Marimbondo– Adrianópolis and at Araquara–Poços de Caldas, and two 136-Mvar reactors at Poços de Caldas– Cachoeira Paulista and Cachoeira Paulista–Adrianópolis. Another 136-Mvar reactor at Cachoeira Paulista 500 kV is also needed. To maintain the voltage control at Poços de Caldas 345 kV, to avoid high voltage during the energization of the 500-kV Cachoeira Paulista–Adrianópolis transmission line, and to detune the system resonance frequency so the load transformers can be energized, another reactor is used at the tertiary of the 500/345/13.8-kV transformer at Poços de Caldas. The maximum load was defined through electromagnetic studies so there is no equipment risk during load rejection, it reaches 420 MW (360 MW for the Light Company and 60 MW for CERJ (distribution company of Great Rio de Janeiro). In this restoration process, one point is clearly seen, even though one has almost 600-MW generation, it can only supply 60% of that amount due to the circuit limitations.

In case of any problem during the restoration of the main path, there is one alternative whether there are at least three machines at Marimbondo: restoration through the geo-electrical area formed by Marimbondo and Itaipu, therefore using the 765 kV and south systems, as shown in Fig. 4. In this configuration, the restoration of the Rio de Janeiro area could be carried out a priori through the parallelling of 500-kV corridors Marimbondo–Cachoeira Paulista and the 765-kV system. However, this is not feasible since dangerous overvoltages would appear in case of a load rejection and the machines in Itaipu would be subjected to self-excitation. To maintain the voltage control, one must use some “ballast” loads in Campinas 138 kV, Cachoeira Paulista 138 kV, and Terminal Leste 345 kV to keep the voltage profile. That is the reason why the parallel of Campinas and Tijuco Preto through the 345-kV system must be executed prior to the parallelling of the 500-kV and the 765-kV system at Tijuco Preto. These loads are normally restored by different geo-electrical areas; therefore, this alternative also interferes with other restoration procedures. One alternative to using the extra loads is to install another 136 Mvar at Cachoeira Paulista 500-kV substation, however, this would demand a new substation layout to allow the equipment to be installed. From Itaipu to Tijuco Preto, the total length of the 765-kV system to be energized is of 892 km. This configuration has a high Ferranti effect even though there is a 50% shunt compensation in the lines, the total amount of shunt compensation required during the restoration of the 765-kV system is 3270 Mvar. This configuration is so critical that, for instance, without a 180-Mvar tertiary reactor at 765/550/69 kV, 1650-MVA transformer at Ivaiporã 765-kV substation one cannot energize the last part of the 765-kV circuit between Itaberá and Tijuco Preto. In normal operation, to avoid the excessive high transient and steady-state voltages due to this energization, the last part of the 765 kV is energized through Tijuco Preto 765-kV bus. To further illustrate this situation, Fig. 3 shows the energization of the 1500 MVA, 765/345/20 kV at Tijuco Preto through the high voltage side, the energization leads to an overvoltage above the transformer limits, shown in the figure as straight lines. Without the south system voltage support, one cannot energize this transformer accordingly to the operational limits. The extra generation provided by Itaipu reaches 1800 MW (minimum three units) and the extra load pickup adds only up to 470 MW. Despite an apparent gain in generation, the peculiarities imposed by circuit configuration in Brazil lead to the conclusion that this alternative represents no gain for the restoration

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in the Rio de Janeiro area since the amount of load pickup is essentially the same. Fig. 4 shows the one-line diagram for this alternative restoration procedure. Another possible restoration alternative for the Rio de Janeiro area deals with using three distinct geo-electrical areas: one from Marimbondo until Poços de Caldas, the 765-kV system, and the area that supplies the capital of Minas Gerais, Belo Horizonte, and Great São Paulo. This scenario presents the longest restoration duration time and affects the load pick up of other large load centers. The total load supplied to the Rio de Janeiro Area is 360 MW if there is a local reactive compensation at the 138-kV bus and 270 MW otherwise. This alternative also presents no gain to the main procedure and is to be used only when there is a problem in the main procedure. VI. CONCLUSION The restoration process in Brazil is a technical challenge, the generation is located far from the consumer load, as shown in the paper, for the Rio de Janeiro Area, this distance may range from 740 km (in the main procedure using five units at Marimbondo) up to almost 2000 km (in the case of the alternative using the 765–kV system). This situation puts high stress at the reactive power compensation throughout the whole process, it must help in the prevention of self-excitation and prevent excessively high steady-state voltages. The absence of a single-line reactor may invalidate a corridor demanding cooperation between different geo-electrical areas to attend the load. The concept of geo-electrical area helps the definition of which power plant must supply a specific load center. Only hydro units are considered since the line charging for the geo-electrical areas far exceeds the capability of any existing thermal unit in Brazil. In most of the restoration studies, only steady-state and stability cases are considered, nonetheless all of the restorations in Brazil have shown the necessity of incorporating electromagnetic transients studies; otherwise, unrealistic results may occur leading to an inefficient and risky restoration process as is the case of the Rio de Janeiro Area presented here. It seems valid to conclude that for a system where the transmission distance is high, over 400 km, there must be a careful analysis of the performance concerning not only steady-state and stability but also electromagnetic transient studies. The load shedding was defined as a function of safety of the voltage and the level of reactive compensation in the LIGHT area. An alternative restoration process can only be chosen if it presents a minimum interference with the other processes. The load pickup capability in Rio de Janeiro area does not increase with a higher amount of generation nor does this imply a faster restoration procedure for this area. The fastest restoration procedure is the one carried out only by the Marimbondo power

station with five machines without interference from any other geo-electrical area. REFERENCES [1] M. Adibi, Ed., Power System Restoration – Methodologies and Implementation Strategies. Piscataway, NJ: IEEE Press, 2000. [2] B. Delfino, G. Denegri, E. Bonini, R. Marconato, and P. Scarpellini, “Black start and restoration of a part of the Italian HV network: Modeling and simulation of a field test,” IEEE Trans. Power Syst., vol. 11, pp. 1371–1379, Aug. 1996. [3] D. Kosterev, C. Taylor, and W. Mittelstadt, “Model validation for the August 10, 1996 wscc system outage,” IEEE Trans. Power Syst., vol. 14, pp. 967–979, Aug. 1999. [4] “GCOI, “Restoration Philosophy for the South-Southeast and Midwest”,” (in Portuguese), ELETROBRAS, Rio de Janeiro, Brazil, 01/97, 1997. [5] “ONS, “Reevaluation of Restoration Procedures in the North and Northeast Region”,” (in Portuguese), ONS, Rio de Janeiro, Brazil, Tech. Rep. ons-3 073/2001, 2001. [6] E. Mariani, F. Mastroianni, and V. Romano, “Field experiences in reenergization of electrical networks from thermal power plant,” IEEE Trans. Power App. Syst., vol. PAS-103, pp. 1707–1713, July 1984.

Paulo Gomes was born in Rio de Janeiro, Brazil, on August 25, 1948. He graduated from the Rio de Janeiro State University, Rio de Janeiro, Brazil, in 1973, and received the Master of Science and Doctor of Science degrees from Itajubá Federal University, Itajubá, Brazil, in 1976 and 2000, respectively. He received the MBA degree from Fundação Getúlio Vargas, Rio de Janeiro, in 1995. Currently, he is in charge of the ONS Special Studies, Protection and Control Area with the Operador Nacional do Sistema Elétrico, Rio de Janeiro, where he has been since 1999. He was also with ELETROBRÁS, Rio de Janeiro, from 1976 to 1996, and Power Security and Quality Company, Rio de Janeiro. He has been teaching power system dynamics at the Rio de Janeiro State University, Rio de Janeiro, since 1979.

Antonio Carlos Siqueira de Lima (S’95–M’00) was born in Rio de Janeiro, Brazil in 1971. He received the B.Sc., M.Sc., and Ph.D. degrees in electrical engineering from the Federal University of Rio de Janeiro (UFRJ) in 1995, 1997, and 1999, respectively. Currently, he is an Associate Professor with the Electrical Engineering Department of the UFRJ where he has been since 2002. In 1998, he was a Visiting Scholar with the Department of Electrical and Computer Engineering at the University of British Columbia, Vancouver, BC, Canada. From 2000 to 2002, he was with the Brazilian Independent System Operator, ONS, Rio de Janeiro, Brazil, dealing with electromagnetic transient studies for the Brazilian National Grid.

Antonio de Pádua Guarini was born in Monte Sião, Brazil, in 1951. He received the B.S.E.E. degree in 1974 from the Federal University of Itajubá, Itajubá, Brazil, and the M.S.E.E. degree from the Federal University of Rio de Janeiro, Rio de Janeiro, Brazil, in 1981. Currently, he is with the Brazilian Independent System Operator, ONS, Rio de Janeiro, Brazil, dealing with power system restoration and protection special system studies for the Brazilian National Grid. He was with CEPEL from 1974 to 1996, first acting in the area of transmission line projects and since 1976 in the HVDC and static compensator systems (SVC), transients, and power quality areas. His main interests are HVDC/SVC specification and studies, especially ac/dc harmonics filters/capacitor banks in regards to reactive power compensation.