The National System Operator (NSO) has submitted a preliminary investigation report to the Public Utilities Commission of Sri Lanka (PUCSL) on the islandwide power outage that occurred on October 17.

According to the report, several hydropower plants were also disconnected from the national grid after their protection systems were activated following the initial power failure.

At around 11.43 a.m. on the day of the incident, 187 megawatts of electricity generated by Unit 1 of the Lakvijaya Power Plant in Norochcholai were lost from the national grid within just 450 milliseconds.

Following this, the frequency of the electricity system rapidly dropped to 48.75 hertz, resulting in the complete collapse of the national power system within 4.1 seconds of the initial incident, the report revealed.

All five stages of the automatic load-shedding mechanism, which is designed to maintain power system stability when frequency levels fall, were activated during the incident.

As a result, 449.2 megawatts of electricity were automatically disconnected from the grid. This accounted for 39.6% of the total electricity generation of 1,135 megawatts recorded before the outage.

However, the report noted that these automatic measures failed to prevent the complete collapse of the electricity system.

In addition to the generating units at the Norochcholai power plant, units at several hydropower stations, including Victoria, Kotmale, Randenigala, Samanalawewa and Laxapana, were also shut down following the activation of their protection systems.

The National System Operator immediately commenced restoration operations following the system failure.

According to the preliminary investigation report, it took five hours and 15 minutes to restore the entire transmission system.

The restoration process was carried out using four main power systems: the Mahaweli system, the Laxapana system, the Samanalawewa South system and the Colombo system.

Under the Mahaweli system, the Kotmale and Victoria power plants were used to restore electricity supply.

The New Laxapana and Wimalasurendra hydropower plants were brought into operation under the Laxapana system, while the Samanalawewa and Kukule Ganga power plants were utilised under the Samanalawewa South system.

Meanwhile, the Kelanitissa power complex was used under the Colombo system as part of the efforts to restore electricity supply across the country.