ONS identifies protection failures as the cause of the blackout

Last Friday (17), the ONS (National Electric System Operator) held the first meeting to prepare the RAP (Disturbance Analysis Report), which investigates the blackout that occurred last week.

The meeting, which brought together more than 250 professionals in an online format, was attended by representatives from the MME (Ministry of Mines and Energy) and the ANEEL (National Electric Energy Agency), in addition to the agents involved in the incident.

According to the ONS, preliminary analysis indicates that the incident began with a fire in a reactor on the 500 kV Ibiúna-Bateis C2 transmission line, owned by Eletrobras, considered event zero. After the protection system correctly tripped the affected circuit, a second trip, deemed incorrect, affected the C1 circuit on the same line.

Although these shutdowns, in isolation, did not pose a risk to the SIN (National Interconnected System), the outage extended to the busbar at Copel's Bateias Substation.

Blackout exposes vulnerability of national electricity system, says INEL

According to the ONS, the substation's protection system did not act as expected, causing a sequence of shutdowns in connected transmission lines, including the Londrina–Assis (500 kV) and Ivaiporã–Itaberá–Tijuco Preto (765 kV) LTs.

The Operator also reported that the outages resulted in the disconnection of the Southern region's electrical system from the rest of the country. "Since the Southern region exported approximately 5 GW to the rest of the SIN, there was an increase in frequency (excess generation) in the Southern subsystem and a reduction in frequency (generation less than the load) in the other subsystems," it explained.

"Underfrequency in the Southeast/Central-West, North, and Northeast regions of the SIN was controlled by the Regional Load Shedding Scheme (ERAC) through controlled load shedding, aiming to restore the balance between generation and system load. In the South region, overfrequency was controlled by shutting down generating units and by the regulators of the remaining plants," the Operator added.

The ONS also commented that, with the beginning of the disturbance at 00:31, the restoration of loads began at 00:35, having been completed at 02:15 in the South, North, Northeast and Southeast/Central-West subsystems.

The next RAP meeting is scheduled for October 28, when the ONS and the agents are expected to present a more detailed and conclusive report on the event. Once completed, the document will be forwarded to ANEEL, MME and to the agents involved, with the appropriate recommendations and measures.

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