Medium Term Analysis

In January 2009, ONS released the Annual Grid Operation Planning Study 2009 / 2010 PEL, which presents the evaluations of the electrical performance of the transmission grid of the BIPS in the period between January 2009 and April 2010, in accordance with the criteria and standards established in the Grid Procedures.

The PEL Study has been developed, mainly in order to evaluate: 1) the performance of regional interconnections, 2) the need for thermal generation due to transmission constraints, and 3) the power supply to areas of the BIPS.

From these assessments, the main results of 2009/2010 PEL were:

• Proposals to adapt the schedule of the transmission grid expansion work (transmission lines, transformers, etc.) to the needs of the BIPS. In this regard, management actions for the immediate implementation of projects already granted by ANEEL and the proposal for speeding up ANEEL’s authorization to a set of priority structural facilities which bring direct benefits to the performance of regional interconnections and / or to the power supply to specific areas should be emphasized.
• Indication of operational solutions such as the deployment of Special Protection Systems - SEP and the changing in the grid’s topology, such as, for example, opening of busbars. These interim solutions are justified as operational resources until the structural reinforcements and new system expansions identified in planning studies are implemented.
• Operational strategies that will be used in the BIPS operation in this horizon, to be detailed and updated in the quarterly and monthly studies, as well as in medium term energy management studies, as they apply.

ONS has been developing various actions, together with the associate agents, focused on the BIPS reliability analysis and operational electrical safety. The goal is to diagnose the main needs for improvement of the BIPS and to indicate the steps to be taken in order to revitalize existing facilities, adapting them to the safety standards prescribed in the Grid Procedures. These studies are consolidated in the System Installations Modernization Plan - PMIS, which is routed to ANEEL.

Short Term Analysis

Throughout 2009, ONS developed studies and implemented measures which enabled the operation of the electric grid in accordance with the criteria of supply continuity, reliability and quality of supply established in the Grid Procedures. Amongst these studies and measures, it is important to mention:

• The on-site implementation of adjustments resulting from the optimization of control systems of Salto Osorio and Samuel hydroelectric generating units and Termonorte II thermoelectric plant, which contributed to the damping of electromechanical oscillations;
• The design and implementation of new Special Protection and Control Systems (SEPs) as well as the revision of existing ones, reaching a total of 279 such systems installed in the BIPS.

The deployment of an SEP, which controls the shutdown of generating units at Tucurui plant after the shutdown of three or more 60 Hz units of Itaipu by the Emergency Control Scheme associated with the 765 kV Link, should also be highlighted in 2009. This particularly innovative system, in which the shutdown signal travels 3,500 km, increases the interchange to the Southeast region by 700 MWmed, ensuring the integrity of the BIPS and avoiding more serious consequences to the grid’s safety.

Studies to optimize the control systems of generators, in order to ensure adequate damping of electromechanical oscillations, thus minimizing the consequences of disturbances have been developed. In these works, both the entry into operation of new plants and the topological changes of the transmission grid with the addition of new components were covered, such as the transmission line at 230 kV Jauru-Vilhena, C1 and C2, which integrates Acre / Rondonia System to the BIPS.

Also in 2009, ONS participated in working groups together with the agents and ANEEL, in a joint work with the State Departments of Energy, in order to speed up the implementation of works necessary to guarantee the power supply to specific areas in the system such as Rio Grande do Sul, Sao Paulo and Maranhao.

The BIPS is designed according to the safety criterion known as N-1, which means that, even with the unavailability of any element (single contingency), the system should be able to remain operating without interruption of power supply, loss of system stability, violation of patterns of electrical measures (frequency, voltage, harmonics, etc.) and without reaching the limits of equipment and facilities overload. In 2009, there were over 500 such contingencies involving the BIPS transmission grid. The appropriate action of the SEPs, and the good performance of control systems, including additional signal stabilizers, ensured the operational safety of the BIPS. However, the operation of any system is subject to multiple contingencies, such as the one occurred 11/10/2009.

Improvements were made in the system restoration processes, such as new corridors for fluent load restoration, aiming at accelerating the normalization of supply after disturbances.