WILLEMSTAD – A major change in wind generation started the chain of events that eventually led to Curaçao's island-wide blackout on August 27, 2025, but problems involving a generating unit's operating mode, control logic and voltage management ultimately played major roles in turning the disturbance into a complete power failure.
Those findings are contained in an independent ENGIE/Laborelec review commissioned by the Regulatory Authority of Curaçao, which examined the technical investigation conducted by DNV after the blackout.
According to the report, the initial event was a significant variation in wind generation. Generating units at Aqualectra's Dokweg power plant responded to the resulting frequency change by increasing their output.
One generating unit subsequently reached its temperature limits and automatically reduced its output, known technically as derating. This happened five times in succession.
The operator then changed the machine from “droop” operation to constant active-power mode. According to Laborelec, the intervention itself was understandable given the circumstances. However, changing the operating mode also changed the unit to constant power factor.
As a result, the generating unit stopped contributing to voltage support and began negatively affecting the system's reactive-power balance because of an inadequate MVar setting.
The review identifies the unclear procedure for changing operating modes and the internal control logic of the engines as major contributors to the blackout.
Aqualectra has since changed both.
During its site visit, Laborelec found that the procedure governing control-mode changes had been updated and was visibly available to operators at Dokweg. The logic used when switching operating modes was also modified.
Voltage management was another important issue. Following the blackout, the on-load tap changer transformers at the MAN plant were placed in manual mode. The review says several recommendations from the DNV investigation have already been implemented.
One of the report's most significant conclusions concerns Aqualectra's new battery system.
Laborelec states that had the Battery Energy Storage System been fully commissioned on August 27, 2025, the blackout would “very likely” have been avoided.
BESS is designed to respond rapidly to changes in frequency and can also assist with voltage regulation, making it particularly important for Curaçao as the island incorporates more variable wind and solar energy into its electricity system.
The investigators nevertheless warn against assuming that the battery alone solves the problem.
Further testing is recommended for the excitation systems of diesel generators, together with better coordination between limiters and protection systems. The report also recommends monitoring and logging their behavior to determine how generating units react during abnormal voltage conditions.
The RAC-commissioned review concludes that DNV used an appropriate methodology to investigate the 2025 blackout and that its recommendations are clear. It says following those recommendations would have prevented the August 2025 event.
At the same time, the blackout demonstrated that despite improvements made since the earlier outages, operator procedures, control logic and reactive-power management remain critical areas for Curaçao's electricity system.