Rosa María Pastrán
A fault that originated in the transmission lines of the Acajutla substation, in Sonsonate, and whose cause is still under investigation, caused this Wednesday a power outage that affected 10% of the Central American region, informed the Regional Operator Entity (EOR).
Central America has a Regional Electric System (SER) in which Guatemala, El Salvador, Honduras, Nicaragua and Costa Rica participate through the interconnection of lines that cross their borders. The EOR is the institution in charge of coordinating the operation of all these interconnections.
The failure started at around 6:46 pm in the transmission lines that connect the Acajutla substation of the company Transmisora de El Salvador (ETESAL), informed the Transactions Unit (UT), the entity that operates and manages the wholesale electricity market in El Salvador. A version was requested from ETESAL, but at the closing of this note there was no response.
"There was a disconnection of the transmission lines, when they were disconnected what happened is that generation began to be lost. So that our system could be protected, the protection scheme began to operate to maintain the load-generation balance", commented Marcela María Molina, manager of Regulatory Affairs of the UT.
This balance means that at all times the energy generation must be equal to the demand, which allows maintaining the security of the system.
The indicator to maintain this balance is the frequency. For the power system to remain stable, the frequency must be 60 hertz, which is supervised "at all times" by the UT in order to avoid any misalignment and take action in case this occurs, said Molina.
"What happened in the event is precisely this, that when generation was disconnected the frequency began to drop. Then protection schemes that we have in our system began to operate, so that the system is maintained and there is no collapse," Molina added.
"This caused the loss of the energy flow that was being produced by EDP (Energía del Pacífico) with 231 megawatts; Termopuerto, with 67 megawatts; and Acajutla (ETESAL), with 127 megawatts. In total, there was an instantaneous loss of 425 megawatts," said René González, executive director of the EOR.
This loss represented approximately 40% of the generation that at that time was meeting El Salvador's demand, said González.
Due to this event, and as a protection mechanism, El Salvador isolated itself from the rest of the Central American countries. The EOR explained that the SER was divided into four islands: Guatemala, El Salvador, Honduras, and Nicaragua-Costa Rica-Panama (these three countries forming a single island).
"If these interconnections were not opened by means of control schemes, which were installed by the EOR together with the national operators to protect the electrical systems, during this situation, we would have had a total loss of 2,000 megawatts, which would have been a more catastrophic effect in Nicaragua, Honduras, El Salvador and even Guatemala", said Gonzalez.
Initially, the OER estimated that the disconnection following this disturbance caused a loss of approximately 800 megawatts (MW) between Guatemala, Honduras and El Salvador. Yesterday, the entity's latest report indicated a loss of 1,081 MW: 429 MW in El Salvador, 389 MW in Guatemala and 287 MW in Honduras.
"At that time we had a demand of approximately 8,400 megawatts in Central America. We could easily have had about 25% of the Central American region shut down (if the emergency plan had not been activated). However, the effect was reduced to practically 10%. The total losses were 10% of the demand at that time," said the EOR's executive director.
"These are protections that act automatically and are activated when there is a frequency imbalance," said Molina about the SER's safety mechanisms.
The recovery occurred in just over an hour, which is considered "relatively fast", since times are always conditioned by a series of "exogenous elements", said González. "Within an hour, all the interconnections were closed in the countries, we were closing with Mexico and the interconnections that were opened by the control schemes."
According to the EOR, Nicaragua, Costa Rica and Panama did not face losses but only an affectation just at the moment when there was an overgeneration of energy because these tried "inertially" to back up the fault that was in the north of the Central American region because that is how the system is organized.
"The generators when they are connected to the power grid and find that there is a deficit out there that needs to be taken care of, inertially all their power flows are marked in that direction," said González. The Central American electricity market is also connected to the southern part of Mexico in points such as Tapachula and Chiapas where there is hydroelectric and natural gas generation, as well as other sources.
When "the partial blackout" occurred, it gives an interaction of the six electrical systems together with the Mexican system.
gives interaction of the six electrical systems together with the Mexican system.
"When these energies are added, the line they bring is heated... the low voltage is produced with the connection with Mexico, that line goes out and generates an even greater deficit coordinated between Guatemala and El Salvador; this combined deficit produces that some energy comes from the south from Panama and Costa Rica, crosses Nicaragua, Honduras, and reaches El Salvador and Guatemala and Honduras", said Gonzalez about what happened last Wednesday.
Until yesterday, the causes of this disturbance were unknown. "We only know that the fault originated in the double circuit lines that go from Acajutla to Sonsonate. The first circuit was built by ETESAL, the second circuit was built by the company EDP (Energías del Pacífico). They are the ones who could specify. When there are failures in the transmission lines, there is a patrol that is done to identify if it was an accident that could have occurred, or any other cause", said Gonzalez.
Both the UT and the EOR held meetings to inquire about the event.
"If these interconnections were not opened by means of control schemes, we would have had a total loss of 2,000 megawatts".
"There was a disconnection of the transmission lines, when they were disconnected what happened is that generation began to be lost."