The National System Operator (NSO) has submitted a preliminary investigation report to the Public Utilities Commission of Sri Lanka (PUCSL) regarding the island-wide power outage that occurred on October 17.
According to the report, at around 11:43 a.m. on that day, 187 megawatts of electricity generated by the first unit of the Norochcholai Lakvijaya Power Plant were disconnected from the system within 450 milliseconds.
As a result, the system frequency dropped rapidly to 48.75 hertz, leading to the complete collapse of the national power system within 4.1 seconds of the incident, the report states.
The National System Operator further noted that all five stages of the Under Frequency Load Shedding (UFLS) mechanism, which is designed to protect the stability of the power system when the frequency drops, were activated during the incident.
Accordingly, a total of 449.2 megawatts of electricity supply was disconnected. This represented 39.6% of the total power generation of 1,135 megawatts recorded immediately before the outage, the report noted.
However, despite the activation of these protection mechanisms, the complete collapse of the power system could not be prevented, according to the report.
Power Plants Deactivated Following Activation of Protection Systems
Meanwhile, in addition to the generating units at the Norochcholai Power Plant, generating units at several hydropower stations, including Victoria, Kotmale, Randenigala, Samanalawewa and Laxapana, were also deactivated following the activation of their protection systems.
Following the system failure, the National System Operator immediately commenced restoration operations. The restoration of the entire transmission system took five hours and 15 minutes, the report stated.
Accordingly, electricity supplies were restored through four main systems: the Mahaweli system, using the Kotmale and Victoria power plants; the Laxapana system, using the New Laxapana and Wimalasurendra hydropower plants; the Samanalawewa/Southern system, using the Samanalawewa and Kukuleganga power plants; and the Colombo system, using the Kelanitissa power plant.
The report further stated that all main substations had been successfully restored by 4.58 p.m., with the entire national transmission system taking five hours and 15 minutes to restore.
Technical Issues Encountered During Power System Restoration
The National System Operator also reported that technical issues and operational delays occurred in certain generating units during the restoration process.
In particular, a delay was encountered when restarting a generating unit at the Yugadanavi Power Plant due to a technical issue in an auxiliary system.
However, the preliminary report has not yet established the specific root cause of the sudden disconnection of the first generating unit at the Norochcholai Power Plant.
The National System Operator has stated that a detailed report on the matter is scheduled to be submitted to the Public Utilities Commission at a later date.
