A nationwide power outage that plunged the country into darkness for several hours on Tuesday, November 11, has been traced back to a critical operational error.
The root cause of the general blackout was the manual disconnection of an energized line at the 138 kV San Pedro de Macorís I substation, according to a technical report released Wednesday, 26 November 2025 by the Coordinating Body of the National Interconnected Electric System (OC-SENI).
The report details how this action triggered a catastrophic sequence of failures across the grid:
High-intensity short circuit: The manual disconnection immediately generated a high-intensity short circuit, which activated the system’s protection mechanisms.
The ‘cascade reaction’: As part of a protective cascade reaction, several nearby transmission lines automatically disconnected to isolate the fault.
Generation loss and imbalance: This isolation caused a massive 575 MW of Eastern generation capacity to separate from the rest of the system. This abrupt separation created a severe imbalance between power supply (offer) and power usage (demand).
Automatic shutdowns: Large power plants, adhering to their safety protocols, automatically tripped off-line to protect themselves and the overall system.
System collapse
The analysis further explains that although the SENI managed to stabilize the grid’s frequency within the first 89 seconds, the system remained vulnerable. The combination of insufficient synchronized cold reserve and the incomplete restoration of certain circuits (EDAC) left the grid weak.
“This weakness ultimately led to an abrupt drop in frequency, which caused the total loss of the system,” the document stated.
Corrective action and oversight
The OC-SENI emphasized that the investigation was completed promptly—within the same month as the incident—by a specialized, multi-sector technical team.
The coordinating body highlighted that the report includes a series of recommendations and corrective actions designed to fortify the national electric system’s operation, including:
Continuing the installation of protection systems at double-bus substations nationwide.
Making operational adjustments to leverage new technologies in thermal and renewable generators.
Integrating battery storage systems for auxiliary and autonomous start-up services.
Reviewing and adjusting the activation times for protection mechanisms and automatic disconnection schemes.
Verifying high-frequency and auxiliary services criteria at various generation plants.
The OC-SENI announced it is currently in permanent session, working closely with sector companies to oversee the implementation of these measures and ensure the continuous improvement, technical efficiency, and operational security of the SENI.
Read more in Spanish:
Listin Diario
El Dia
27 November 2025