The island-wide power failure of 17 October began with a sudden collapse of output at the first generating unit of the Lakvijaya coal power station, according to the preliminary investigation report issued by the National System Operator (NSO) — a finding that moves the focus away from the Upper Kotmale fault officials pointed to on the day.

The report was prepared at the request of the Public Utilities Commission of Sri Lanka (PUCSL) and submitted to the commission on 23 October, under the signature of NSO Acting Chief Executive Officer Eng. M.B.S. Samarasekara, Hiru News reported at 8.58 a.m. on Saturday.

What the report describes

The failure began at about 11.43 a.m. on 17 October. Lakvijaya Unit 1 was supplying 187 MW to the national grid when its output fell away within 450 milliseconds.

System frequency then dropped sharply, falling from 49.906 Hz to 48.75 Hz within two seconds. All five stages of the protection scheme that automatically disconnects demand at low frequency operated — and the collapse still could not be prevented. By 11.43:59 a.m., every generating unit connected to the national grid had stopped.

Total system demand at the moment of collapse was recorded at 1,135 MW, with 332.5 MW of additional generating capacity available for emergency use.

A supplementary report states that the under-frequency protection scheme was configured to shed 449.2 MW of demand — 39.6% of the generation on the system at that moment. Those two figures reconcile against the 1,135 MW demand reading.

The cause of the trigger is still open

The preliminary report does not reach a firm conclusion on why Lakvijaya Unit 1’s output fell in the first place. Because there is no record of the unit disconnecting automatically at that moment, the report raises the possibility that what was observed was the machine responding to the change in system frequency rather than causing it.

That distinction matters, and it is not settled. The report establishes the sequence; it does not establish the first cause.

This is a shift from the account given on the day

On 17 October, Energy Minister Anura Karunathilaka said investigators were examining whether a technical glitch reported the previous day at the Upper Kotmale power station had set off the collapse — the line this desk recorded at the time as a line of inquiry rather than a finding. The preliminary report’s sequence starts at Lakvijaya instead. Nothing published so far formally withdraws the Upper Kotmale line, and the report does not address it.

Restoration took five hours and fifteen minutes

Recovery work began immediately, built around the hydro stations — Kotmale, Victoria and New Laxapana. Kotmale’s first unit was reconnected to the national system at 12.11 p.m., and the main transmission system was restored by 4.58 p.m. — about five hours and fifteen minutes after the collapse, consistent with the stated start time.

Technical problems delayed the return of several plants, including a number of units at Lakvijaya itself.

Not reported

Hiru’s filing does not say why the report took until the end of the month to surface publicly, having been submitted on 23 October, nor whether PUCSL has responded to it. It gives no date for a final report. It does not state what residual output, if any, Lakvijaya Unit 1 held after the 450-millisecond drop — a figure rendered inconsistently in other accounts of the same document, and therefore not asserted here. The role of rooftop solar, raised by several parties after the outage, is not addressed in the portion of the report described.

Ada Derana carried the same report on Saturday, but its site has been returning CloudFront 403 errors to this desk for roughly seven weeks, so no publication date could be extracted and it is not cited here.