Description of the Disturbance

The blackout which occurred on November 10th, at 10:13 PM, under adverse meteorological conditions, was caused by atmospheric discharges and/or the reduction of effectiveness of isolators submitted to these severe conditions and was an unusual event, with very low probability to occur.

Itaipu powerplant, located in Parana, has an installed capacity of 14,000 MW and is responsible for about 20% of the energy consumed in Brazil and 87% of the energy consumed in Paraguay. The transmission system, which is owned by Furnas Centrais Eletricas, is formed by five lines, each about 900 kilometers long. Two of which run in DC, from Foz do Iguacu to Ibiuna, in Sao Paulo; the other three lines, in alternate current of 765 kV, extend to Tijuco Preto (SP). Particularly in the case of Itaipu, the 765 kV system was operating according to an even more rigorous safety criterion, above the standard usually adopted (simple contingency), foreseeing the possibility of losing up to two lines, i.e., in N-2 ( double contingency).

According to oscillographic data, a short circuit was registered, at 10:13 PM, in the stretch between Ivaipora (PR) and Itabera (SP), close to this substation. The short circuit has reached the three transmission lines of 765 kV of Itaipu transmission system in about 10 hundredths of a second, verified since the incident occurred on the first line until the complete elimination of the event, in the third. The contingency was totally atypical, with three nearly simultaneous single phased short circuits, which progressed to three-phased short circuits due to the proximity to the substation.

The Special Protection Systems deployed by ONS acted correctly and immediately. The three transmission lines were turned off automatically to prevent damage to equipment. The opening of the three circuits interrupted the amount of energy supplied to the Southeast region and triggered a condition of oscillation amongst the several areas of the BIPS, which, consequently, caused the cascading opening of dozens of transmission circuits, disrupting power supply in different regions. For a better understanding of the severity of the impact, it is noteworthy that, between the opening of the three 765 kV lines and the collapse in the states of Sao Paulo, Rio de Janeiro, Espirito Santo and Mato Grosso do Sul, the process took less than five seconds.

Consequences of the Disturbance and System Restoration

The blackout of November 10th hit the regions in different ways and it was more significant in the Southeast/Midwest, where there was an interruption of 23, 335 MW (62% of the area’s load). The islanding schemes functioned satisfactorily and prevented the spread of the problem, reducing the impact of the disturbances in the South, North and Northeast. The South, Northeast and North were little affected by the blackout, with 1%, 8% and 7% of its load interrupted, respectively, the latter two by the performance of the Regional Load Relief Scheme (ERAC). In the BIPS, the total interrupted load was 24,436 MW, or 40% of the total.

From a diagnosis of the situation, the process of restoration began immediately and was gradually and coordinately developed, as indicated in ONS Grid Procedures. The power failure had an average duration of 222 minutes in Espirito Santo, Mato Grosso do Sul, Rio de Janeiro and Sao Paulo. Other 14 states had interruptions of less than 40 minutes: Minas Gerais, Mato Grosso, Goias, Rio Grande do Sul, Santa Catarina, Parana, Acre, Rondonia, Bahia, Sergipe, Paraiba, Alagoas, Pernambuco and Rio Grande do Norte.

Analysis of the Disturbance and Proposed Measures

The detailed study of the event is consolidated in the Disturbance Analysis Report - RAP, which was referred to the CMSE and ANEEL on December 17th, 2009. The RAP presents a list of 53 actions with deadlines and responsibilities that are consistent with the three fundamental goals pursued by ONS: the first is to work proactively, improving, whenever possible and feasible, the safety of the system, the second is, once the problem occurred, to minimize the domino effect, and the third is to reduce the restoration time.

Various actions proposed in the RAP are already being implemented, and some have been completed. Aiming at preserving the reliability of the electric network, pending the completion of actions related to Itabera substation (installation of booster sheds and improved shielding), ONS, based on determination of CMSE, has increased the safety level in the 765 kV system, between Foz do Iguaçu and Tijuco Preto substations, deploying limits that support the loss of three circuits in this interconnection (operational criterion N-3), even if, to meet this guideline, the additional thermal generation dispatch becomes necessary.

Since the amount of thermal generation required is directly associated with the load behavior, these values are being defined by ONS in the daily programming, with the objective of meeting the safety requirements at the lowest cost.

Finally, aiming at improving the safety of the BIPS, below, some of the actions that will receive priority approach are highlighted:

• Re-evaluation, in a joint work with EPE, of the safety criteria currently used for the expansion planning and the operation, especially for strategic points of the transmission systems, as major load centers and relevant transmission interconnections.
• Elaboration of proposal of criteria for selecting a set of strategic installations of the BIPS, establishing additional procedures to those currently in place for access, operations planning, protection and control, real time operation and maintenance, as well as specific criteria in order to subsidize the fiscalization processes by ANEEL.
• Re-evaluation of the system restoration procedures and transmission corridors, analyzing the feasibility of using thermal power plants, nuclear plants Angra 1 and Angra 2, and other resources, as well as the installation of self-restoration devices in more plants.
• Re-evaluation of existing schemes in the main transmission lines and generating plants of the BIPS and the continuity of the islanding process by sub-frequency in small and medium hydropower plants, with local load.
• Evaluation of the protection philosophy of transmission lines and equipment of the main trunks, which may affect the performance of the BIPS as a whole.