PLN Reveals Cause of Sumatra Power Outage: Power Swing Phenomenon

PT PLN (Persero) has disclosed the cause of the power outage in Sumatra on Friday, 22 May 2026, resulting from a disturbance in the 275-kV transmission line. Edwin Nugraha Putra, PLN’s Director of Transmission and System Planning, explained that Sumatra’s power system has major transmission lines carrying energy from the southern region to the north, including Jambi, North Sumatra, and Aceh. ‘There is a 500-kV corridor on the eastern side, and a 275-kV western line. On Friday, 22 May 2026, at precisely 18:44, a disturbance occurred on the 275-kV transmission line in Linggau-Lahat, South Sumatra,’ he stated during a press conference with the Indonesian National Police’s Criminal Investigation Agency (Bareskrim) on Monday, 25 May 2026. ‘This disturbance fed into the eastern 500-kV line, causing both circuits to trip. As a result, the 500-kV system was disrupted due to heavy rain and strong winds at the time.’ Edwin continued: ‘When the current flow normally moving eastward from south to north was interrupted, the current reversed direction, flowing south and shifting west towards Linggau-Lahat.’ ‘This current shift caused a phenomenon known as power swing, or oscillation, resulting in significant fluctuations in voltage and frequency as the current moved from the eastern to western lines,’ Edwin explained. ‘When the oscillation reached a certain threshold, the western 275-kV line had to isolate itself to prevent the power swing from causing wider disruptions,’ Edwin said. ‘Subsequently, a circuit on the Muara Bungo to Sungai Rumbai system also tripped. Once this happened, the Sumatra grid split. The southern region had excess generation, leading to high frequency, while the north had insufficient generation, resulting in low frequency. In the south, some generators tripped due to low frequency, but our defence schemes stabilised the southern system, though Lampung and most of South Sumatra still experienced outages,’ Edwin explained. However, in the northern region, the lack of generation caused low frequency. As a result, multiple generators tripped, triggering a domino effect. ‘One trip led to another, with frequencies dropping further until all generators in the northern system shut down, causing a complete blackout in Jambi, Riau, West Sumatra, North Sumatra, and Aceh,’ Edwin concluded.