PLN reveals sequence of Sumatra blackout as 'power swing' triggers domino effect

JAKARTA — PT PLN (Persero) has revealed the sequence of events leading to a widespread blackout across parts of Sumatra on Friday, 22 May 2026, triggered by a power swing or oscillation in the transmission system.

Transmission Director Edwin Nugraha Putra stated that the disruption began at 6:44 pm WIB when a 275 kV transmission line from New Aur Duri to Sumsel 5 malfunctioned due to severe weather, including heavy rain and strong winds.

“The 275 kV line from New Aur Duri to Sumsel 5 experienced a fault. This is an input to the 500 kV line in the eastern section,” Edwin said during a press conference at the Bareskrim Police Headquarters in Jakarta on Monday, 25 May 2026.

When the fault occurred, two circuits on the eastern line tripped, causing the 500 kV line to disconnect from the system.

This caused the electricity flow, which was originally moving from south to north, to reverse direction and shift to the 275 kV western line.

The sudden current shift triggered a power swing, a phenomenon characterised by extreme voltage and frequency oscillations.

“The current shift caused what we term a power swing, commonly known as oscillation,” Edwin explained.

He added that when the oscillation reached technical thresholds, the 275 kV western line had to isolate itself to prevent wider disruptions.

In southern Sumatra, power generation exceeded demand, causing electricity frequency to rise, while northern regions faced a power shortage, leading to a sharp drop in frequency.

“Due to the low frequency, some power plants could not withstand the strain and tripped, triggering a domino effect,” Edwin said.

The failure of one plant caused frequency to drop further, leading to a chain reaction where other plants shut down sequentially.

This chain reaction resulted in blackouts across Jambi, Riau, West Sumatra, North Sumatra, and Aceh.