Brazilian Defense Plan Against Extreme Contingencies X.Vieira Filho L.A.S. Pilottto N. Martins A.R.C. Carvalho A. Bianco Senior Member Senior Member Fellow Member Member CEPEL - Centro de Pesquisas de Energia Elétrica Caixa Postal 68007 CEP:21944-970 Rio de Janeiro, Brazil Abstract: This paper presents some of the short-term measures developed from the studies following the blackout in the Brazilian South/Southeast/Center-West power system in March 11 th 1999. The concept of Security Zones and Network Security Matrix is introduced. A new PLC-based SPS was designed to create controllability zones. This new scheme was named Security Control and is triggered by network topological changes. The Security Control is fast acting, with clearing times around 200 ms. A typical Security Controller logic is presented, showing its benefits for the Brazilian interconnected power system. Keywords: Extreme Contingencies, Special Protection Schemes, Network Security Control, Programmable Logic Controller, Security Zone, Angle Stability Control, Voltage Collapse INTRODUCTION The March 11 th blackout caused the loss of 25 GW of load and was the most severe of the Brazilian electric system history. The Minister for Energy, concerned with the security of the Brazilian power system, instructed ELETROBRÁS, the holding company of the Brazilian Federal utilities, to coordinate studies and define actions to reduce the probability and severity of large disturbances and associated blackouts. ELETROBRÁS rapidly formed seven task forces, involving engineers from the various utilities, to define measures for the improvement of the reliability and security of the Brazilian South/Southeast/Center-West power system. Among the short-term measures, it is worth highlighting the commissioning of various new special protection schemes, involving mainly generator tripping, in order to minimize the impact of bus faults (or line faults with breaker failure) in critical substations. The medium and long-term measures comprise several improvements in the system to effectively enlarge the operational margins, which have been critical due to the unanticipated load growth in recent years. Reinforcements in both generation and transmission assets are proposed. Other actions are also foreseen, such as the addition and modernization of equipment, accompanied by the installation of a network of dynamic system monitors. This paper describes the work carried out by the Joint Working Group responsible for improving the security of the Brazilian Interconnected Power System. The concepts of Network Security Matrix and Security Zones are introduced. A PLC-based SPS triggered by network topological changes is presented. The concepts involved in the design of SPSs are described together with one typical SPS application. THE BRAZILIAN POWER SYSTEM The Brazilian electric power system presents some unique characteristics. It has a predominantly hydro generation (around 94%) with large amounts of energy being transferred from remote sites to the load centers, through long distance power corridors operated in EHV. The total installed capacity is 65 GW and the Itaipu power plant itself is responsible for more than 18% of the total energy production in the country. There are frequent operating conditions that involve heavy energy transfers, even during light load, due to hydroelectric coordination for optimal water usage. System planning is currently based on the (n-1) criterion where a temporary fault in a single generation or transmission element should not cause supply interruption or violations in system operating limits. The Brazilian system has been continuously experiencing a high load growth, around 5% per year. This fact, coupled with recent economic constraints, caused the system to operate closer to stability limits, thus increasing the probability of system-wide effects following major disturbances. THE BLACKOUT OF MARCH 11 th 1999 The initiating event of the March 11 th 1999 blackout was a phase-to-ground fault at the Bauru 440 kV bus, which caused the opening of five incoming 440 kV lines. The power system survived the first event, but then collapsed because of a shortcoming of backup relaying. The subsequent outages of several power plants in the São Paulo area, followed by the loss of both the HVDC and the 750 kV AC links from Itaipu, resulted in a complete system break up and a load loss of 24,731 MW. This disturbance affected as much as 75 million people, for as long as four hours. Several natural islands remained in operation, totaling 10,000 MW. In the South region, the total load restoration was performed in 49 minutes. In the federal states of Minas Gerais, Goiás, Federal District, Mato Grosso and Tocantins restoration took 30 minutes. There was a complete blackout in the federal states of São Paulo, Rio de Janeiro, Espírito Santo and Mato Grosso do Sul. The restoration process was much slower (up to 4 hours) in these four states, due to unforeseen difficulties and some equipment damage. THE ACTIVITIES OF THE BLACKOUT JOINT WORKING GROUP The March 11 th 1999 blackout was the most severe disturbance experienced by the Brazilian power industry. ELETROBRÁS, under the instruction of the Ministry of Energy, convened a Joint Working Group involving CEPEL (the Brazilian Electric Power Research Center), ONS (the Brazilian ISO), and most of the utilities, to study the event and propose measures to improve the overall system security. The recommendations of the study include short, medium and long-term measures to reduce the probability of system-wide breakups following multiple contingencies.