Government says that combination of 2 occurrences caused fall; the 1st of them, an overload on transmission lines in Ceará
The national blackout that left 25 states and the Federal District without power on Tuesday (15.Aug.2023) was caused by 2 problems, it seems. The Minister of Mines and Energy, Alexandre Silveira, said that the 1st reason was an overload on transmission lines in Ceará, but he did not detail what would have caused this. The other reason is still unknown. It is only known that it was also an intercurrence in the Northeast and North regions.
Experts heard by Power360 listed possible reasons that may have caused the breakdown. One of the main hypotheses is that an abrupt change in the flow of generation from wind and solar plants caused the system to crash by injecting more energy than the capacity of the transmission lines. The government has not ruled out the possibility, but there are other factors.
There is still no conclusion, but analysts and the government itself believe that it would hardly be a single problem. The ONS (National System Operator) will release a detailed report with the causes within 48 hours. The Federal Police and Abin (Brazilian Intelligence Agency) will also investigate whether there was any criminal action.
Find out what you know below:
COMBINATION OF FACTORS
Silveira classified the blackout as a rare event and a combination of at least 2 problems. He explained that the Brazilian electrical system works with the safety model “No–1”, with duplicity or redundancy in the operation. “For something to happen, there would have to be 2 events [falhas] concomitants”, he said.
In the minister’s own comparisons, this model works like 2 independent roads, but in the same direction. If one has problems and becomes clogged, there is another one that can replace it. This is necessary because transmission line problems can occur frequently.
OVERLOAD IN CEARÁ
The 1st cause identified was overload on transmission lines in Ceará. The numbers of ONS (National System Operator), responsible for the SIN (National Electric System), show that the load on the Northeast subsystem was at 11,848 MW at 8:30 am. There was a peak load soon after, reaching 17,648 MW at 8:31 am.
This overload caused the subsystem to crash automatically. The load in the region reached 6,542 MW at 8:40 am. It was only normalized around 14:42.
“There was a very large increase in generation in the North and Northeast subsystem. An energy load above capacity was injected into the transmission lines there, causing the system to trip, causing a load imbalance. And the other regions were affected by ONS intervention, disconnecting the generations so that this problem that occurred, which was serious, did not spread throughout the national interconnected system”explains Luciano Duque, electrical engineer and professor at Ceub (University Center of Brasília).
WIND AND SOLAR GENERATION
The flow of power generation in wind and solar plants in the Northeast of the country may be the cause of the overload. At the time of the occurrence, there was more energy from wind and solar power plants entering the Northeast grid than from thermal and hydroelectric plants. ONS figures show that the region concentrates most of its production in these sources, which account for 70% of the subsystem.
Adriano Pires, founding director of Cbie (Centro Brasileiro de Infraestrutura), says that as wind and solar sources are intermittent, they do not bring security of a continuous energy supply. Thus, these plants may not generate anything at times of low wind and lack of sun, but may have generation peaks at certain times of the day.
The current electrical system, however, does not support the jolts caused by this intermittence. Alexandre Silveira admitted that the system needs to be improved to adapt to these sources. “Clean and renewable energies are a reality. Wind is a reality, solar is a reality, and they are a one-way street. The system has to be more and more modernized so that stable energies can converge”said the minister.
According to Luciano Duque, this is one of the main possibilities for the breakdown. “When energy comes from hydroelectric or thermal, it produces continuously. In solar and wind, it is not continuous. Some of these sources, due to some problem or generation issue, injected a lot of load into the system. And the system understands this as an anomaly, because it is not prepared for it, and disarms”.
OTHER HYPOTHESES
Luciano Duque cites other possible causes that may have caused this energy spike in Ceará, such as an atmospheric discharge on the network or a short circuit in a generating source.
The 2nd cause, also due to a problem in the North and Northeast subsystems, may have been caused by failures in the protection and generation systems, or even human errors.
There is even the possibility of criminal action, such as, for example, sabotage in a transmission line, a hypothesis that has also been considered by the government.
MECHANISM CONTAINED MAJOR PROBLEM
The problem caused a domino effect that could have been even worse. That’s because the whole country is connected to the SIN, with the exception of Roraima. There are 4 subsystems, with more than 179,000 kilometers of transmission lines, which connect like a ring, taking and receiving energy from each other.
The ONS had to activate a mechanism, the Erac (regional load relief scheme) to disconnect the entire SIN and momentarily disconnect the North and Northeast from the rest of the national system so that the breakdown would not be generalized. As a result, there was an interruption of approximately 16,000 MW in the SIN load.
The incident occurred at 8:31 am, with an interruption of 18,900 MW (megawatts). 16,000 MW (megawatts) of load were interrupted in the North and Northeast. As a result of the activation of the mechanism, there was an intentional load cut of 2,900 MW in states in the Southeast, Midwest and South, preventing a larger blackout in these regions.
There was the opening of the North-Southeast interconnection and the bipoles 1 and 2 of Belo Monte, disconnecting these networks from the SIN and isolating the North and Northeast from the other regions. This action ensured faster recovery of loads.
“The problem could have been even bigger. The system is prepared for a certain generation capacity. 16,000 MW were interrupted in the Northeast. The load imbalance was large. And that could shut down the country’s entire system, which would make restoring power take much longer. It was a major problem, a serious system failure. If you don’t control this, the other side of this network would be more harmed and the damage would be greater because it would disarm the system here as well. Therefore, it is a controlled, intentional action”, says Professor Luciano Duque.
DELAYS TO REPLACE
Residents of the Northeast were left without electricity for more than 6 hours because of the blackout. The region concentrates the largest share of generation made by wind and solar plants in the country, which produce energy intermittently (not continuously) and take longer to produce again.
The States in the region were the last to have the supply normalized, around 2:30 pm. In the South, Southeast and Midwest, the distribution was normalized within 1 hour after the power outage, detected at 8:30 am. For analysts heard by the Power360the growing dependence on renewable sources brings uncertainty to the national electricity system.
Unlike hydroelectric and thermal energy, to be injected into the system, the production of wind and solar plants needs the transmission lines to be loaded. This is because these renewable energies produce direct current. To enter the system, they must be converted into alternating current, which requires more energy.
As the generation was turned off in the other sources to avoid a bigger problem, being resumed little by little, the solar and wind power plants took longer to be able to deliver energy to the system.
Around 2:00 pm on Tuesday (15.Aug), according to ONS records, hydroelectric generation in the Northeast was close to the maximum possible power. Wind and solar production was still around 20% of capacity.
“In the South and Southeast, we had Angra and gas and coal-fired thermal plants to quickly supply the lack of energy. In the Northeast there was no such possibility. Wind and solar energy is intermittent, when there is a drop, it takes a long time to come back. Not the thermal one, just press a button”said Adriano Pires.
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