The Dominican Republic"s National Interconnected Electricity System (SENI) collapsed on Monday morning after the abrupt loss of generation at strategic thermal power plants.
According to official records from the grid operator, system frequency fell to 56 Hz following a sharp drop in power injected into the grid, resulting in a nationwide blackout.
Preliminary reports linked the event to a failure in the synchronisation system at the Punta Catalina power station, one of the country"s largest coal-fired plants.
Technical sources confirmed that the plant"s synchronisation equipment malfunctioned.
A manual intervention was attempted but failed to stabilise operations, leading to the unit"s disconnection.
The outage of this large thermal block was not contained.
Its disconnection triggered the simultaneous trip of the Quisqueya 1 and Quisqueya 2 units, operated by EGE Haina, causing a sudden and significant reduction in available generation capacity.
Within seconds, the balance between supply and demand was disrupted beyond the system"s automatic response capability.
In islanded systems such as the Dominican Republic"s which lacks international interconnection to buffer disturbances the sudden loss of large thermal units can trigger a total system collapse if spinning reserve fails to compensate immediately.
The frequency drop to 56 Hz activated automatic protection schemes, further disconnecting loads and generating units.
Once frequency deviates so severely from the nominal 60 Hz standard, cascading outages become increasingly difficult to contain.
The Dominican Electricity Transmission Company (ETED) confirmed that technical teams are investigating the root cause and working to restore service as quickly as possible.
The most severe collapse since 2015The latest blackout comes only months after the most severe power system collapse recorded since 2015, which occurred in November 2025.
During that event, the SENI went from serving approximately 3,000 MW of demand to operating with just 41 MW available, reflecting a near-total loss of generation.
At the time:
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Thermal and solar PV generation fell virtually to zero.
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Hydropower operated at minimum technical levels.
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Only a limited number of wind power plants remained connected.
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The Automatic Load Shedding Scheme was activated but failed to prevent a system-wide collapse.
That incident had already exposed structural limitations related to frequency support, protection coordination and operational resilience in the face of large-scale disturbances.
Reliability implications for the SENIThe 56 Hz frequency recorded on Monday represents a severe deviation from operational standards.
At that level, generators, transformers and protection systems operate outside nominal parameters, increasing technical risk and requiring a staged system restoration process.
Restoring a collapsed grid typically involves:
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Stabilising frequency using black-start capable units.
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Gradually reconnecting large thermal blocks.
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Carefully synchronising generation to avoid new oscillations.
A disorderly reconnection process can trigger further instability and prolong outages.
Beyond the specific synchronisation failure, the event renews debate over the structural robustness of the Dominican electricity system.
The concentration of generation capacity in high-capacity thermal units means that failures in control or protection systems can have immediate systemic consequences.
The recurrence of large-scale blackouts within a relatively short period underscores the need to strengthen operational resilience.
This may include modernising protection schemes, enhancing dynamic frequency response, expanding fast-response reserves and evaluating energy storage solutions capable of improving grid stability.
The ongoing technical investigation will determine the root cause of the incident.
However, the latest collapse confirms that the Dominican power system continues to operate with narrow margins when faced with the abrupt disconnection of large generation units a critical issue for energy security, grid reliability and future investment in renewables and grid integration.