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Other than tripping over monkey business, report sheds little light on blackout Sunday
A fault in a “busbar”—a metallic strip or bar that conducts electricity and distributes it to electrical devices—at the Panadura grid substation (GSS) last Sunday triggered a system frequency drop and caused Sri Lanka’s entire power system to shut down, the Ceylon Electricity Board’s (CEB) preliminary report on last Sunday’s countrywide blackout has held, sources familiar with its contents said.
Monkey business
The 18-page document also contains a report by the CEB’s Operation & Maintenance Branch (Western South) which concludes that the “incident” at the Panadura GSS was caused by the electrocution of a monkey leading to “the multiple and cascaded tripping of the total transmission network”. But it calls for a detailed analysis of why the system “failed in total due to a localised incident” at the Panadura GSS, the sources said.
All power sector analysts and experts including officials interviewed by The Sunday Times concurred that a monkey might have created an electricity curtailment in a small area but should not have tripped the entire power system.
Meanwhile, despite the CEB presenting its preliminary findings to the Public Utilities Commission of Sri Lanka (PUCSL), as decreed by law, the regulator will conduct field visits tomorrow to the Panadura GSS, the CEB system control room and the Lakvijaya coal power plant in Norochcholai, the Sunday Times reliably learns.
The sources quoted the preliminary report as saying the busbar fault occurred at 11.13am on February 9, 2025, and “activated all five stages of under-frequency load shedding”. But frequency continued to fall and multiple power plants tripped in a cascade. These included all three units of Lakvijaya.
The five stages of under-frequency load shedding (UFLS) is a system where, as the power grid frequency drops progressively lower, five distinct levels of load are shed at predetermined frequency thresholds, with each stage shedding a progressively larger portion of the load to stabilise the system and prevent a complete blackout.
No mention of solar power issues in report
System restoration efforts brought electricity back to the Biyagama, Sapugaskanda and Kelaniya grid substations one hour and 10 minutes after the initial fault but failed again due to “unpredictable load variations”. Not long after, the Energy Ministry asked those with rooftop solar systems to disconnect them from the national grid until 4pm.
CEB engineers said this was to balance the grid and to facilitate power system restoration. It was a particularly sunny Sunday, they explained, and electricity demand was low as businesses and most industries were closed. Rooftop solar generation—estimated to be at around 1,400MW currently—is not visible to system control and this made it difficult for them to balance supply and demand, leading to tripping. But none of this is specifically mentioned in the CEB’s preliminary report. (It is also not known how many rooftop solar customers complied with the request).
Neither does the report allude to another theory that was floated tied to the inverter settings of rooftop solar units: it was argued that all of the solar power units connected to the Panadura GSS went offline after the “monkey incident” as their inverter settings are typically set at low tolerance levels and are prone to switching off even when there is a slight voltage drop. This purportedly caused a system imbalance and precipitated a countrywide blackout.
Anyhow, the second restoration attempt led to the power system being fully operational again by 3.45pm, four-and-a-half hours after the initial incident and in daylight hours, the sources said.
Protection system failures?
The incident report in the CEB’s preliminary findings, the sources said, speaks of a “loud explosion” at the grid substation and simultaneous tripping of the 33kV bus section and as well as the high and low voltage sides of the 132/33kV sides of the 132/33kV power transformer.
The report confirmed that the Control Room Operator was on duty at the time, the sources said, and that upon investigation two “surge arrestors” (devices that protect electrical systems from voltage spikes and surges) were found to have exploded. The charred remains of a monkey were found on the ground beneath the devices.
Among the various theories that were expounded, one—the most important one, some experts say—was markedly missing. Nadeera Wijesinghe, a chartered electrical engineer and power sector analyst experienced in power system modelling, simulation and protection system studies, insists that last Sunday’s and all other blackouts in the past decade (no less than six) are “due to incorrect configuration of the power system protection system”.
“The Sunday blackout originated from a monkey (phase-to-phase fault or a phase-to-earth fault) on the 33kV side,” he told the Sunday Times. If the protection systems worked correctly, it would have isolated the 33kV fault before that propagated to the 132kV & 220kV side,” Mr. Wijesinghe explained.
What happened is similar to having a full arm dissected near the shoulder) because a finger got infected, he said. “The fault was so small that if it had been isolated promptly, the transmission backbone would not even have seen it.”
Power system settings can easily be adjusted, Mr. Wijesinghed said: “You only need a knowledgeable engineer with a laptop and data cables. For most of the new substations, the CEB can do the changes sitting in Colombo.”
Gaps in the CEB report
Mr. Wijesinghe identified lapses in the CEB’s preliminary report which he, like our other sources, had seen. For instance, he said, it fails to give “the root cause analysis” of the blackout.
“The report attributes the fault to a monkey electrocution causing a 33kV busbar fault at the Pandura GSS,” he told the Sunday Times. “However, it does not provide a detailed technical analysis of how a localised fault led to a total system failure. The conclusion recommends further investigation which is not acceptable.”
Among other things, the report doesn’t explain why the cascading failure continued even after the fault was cleared. “There is no analysis of whether the protection systems (e.g., protection relays, circuit breakers) operated as intended or if there were delays or failures in their operation,” Mr. Wijesinghe continued. “It does not address whether the grid design or the protection settings—or the grid simulation model—led to the countrywide blackout.”
A software simulation that replicated the fault virtually using the transmission system software model and compared the results with the actual tripping events of the relays would have shed more light on whether or not the system performed as intended. This was not done in the report.
The report authors also “do not have a clue” as to why the power plants continued tripping and “also why the system frequency kept dropping, even after all five stages of under frequency load shedding was done”.
The total blackout was Sri Lanka’s fourth in five years. And as Susantha Perera, a senior electrical engineer with over 35 years of experience at the CEB, writes on page 3 of ST2, there has never been a serious follow-up by the utility, the ministry or successive governments despite each case being documented in detail. Nobody has been held accountable.
“There is no reason to believe things will be different this time, notwithstanding the massive publicity generated by the dead monkey found in the vicinity of the transmission substation at Panadura,” he predicts.
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