The Most Difficult Hurdle in Restoring Sumatra's Power System Following a Mass Blackout

Darmawan Prasodjo, the President Director of PT PLN (Persero), said the synchronisation of coal-fired steam power plants (PLTU) is the most difficult stage in restoring Sumatra’s electricity system after a mass outage on Friday night, 22 May 2026, affected several areas on Sumatra. The disruption originated from the 275 kV Muara Bungo–Sungai Rumbai transmission line in Jambi on 22 May 2026 at 18:44 WIB. The outage, suspected to be caused by bad weather, triggered a domino effect on the Sumatra interconnection system, affecting Jambi, West Sumatra, Riau, North Sumatra and Aceh. “For the PLTU system, coal-fired steam power plants, the process takes quite a long time because we have to heat water to become steam,” Darmawan said in a virtual press conference on Saturday, 23 May 2026. He explained the Sumatra electricity system briefly experienced imbalance due to the transmission disturbance. In some areas there was an oversupply causing the frequency and voltage to rise, which led to some plants tripping out of the system. In other areas, deficits occurred as plants disconnected from the grid. This condition caused the frequency and voltage to fall, allowing the disturbance to spread across various parts of Sumatra. “And we note that this condition apparently followed a domino effect. So there was a disturbance of the electricity system from Jambi, Riau, North Sumatra to Aceh,” he said.