Power outages in Sumatra serve as critical warning for national electricity system

Widespread power outages across Sumatra in the past month have sounded a critical alarm for Indonesia's national electricity system, according to the Institute for Essential Services Reform (IESR). The think tank emphasizes that the evaluations must extend beyond the system's ability to reliably supply electricity, to its resilience in the face of extreme events, including the increasingly frequent severe weather linked to the climate crisis.

IESR noted that PLN, Indonesia's state electricity company, explained the Sumatra outages were triggered by severe weather. Two 500 kV transmission circuits in the eastern corridor tripped, forcing a power transfer from the eastern to the western corridor (275 kV). This shift caused high voltage and frequency oscillations, ultimately compelling an isolation scheme that split Sumatra's electrical system into northern and southern sections to prevent wider disruption. The northern region faced a power deficit, while the south had a surplus. The southern system's defenses held, preventing blackouts there, but the northern region experienced a continuous drop in frequency, forcing power plant trips and leading to the outages.

A similar incident occurred on June 4, 2026, when damage to 12 PT PLN (Persero) transmission towers, some collapsing, others bending, disrupted power supply in several areas. The damage affected two main transmission lines: the 275 kV Galang–Simangkuk Extra High Voltage Air Line (SUTET) and the 150 kV Tebing Tinggi–Sei Rotan High Voltage Air Line (SUTT). Initial assessments suggest this incident was also linked to heavy rain and strong winds.

Deon Arinaldo, Director of Energy System Transformation at IESR, stated that these events demonstrate the need to test Indonesia's electrical system for both reliability and resilience. Reliability refers to the system's capacity to supply power stably under normal conditions, while resilience measures its ability to withstand, respond to, and recover from unexpected events like storms, floods, gales, extreme heat, or other climate-related disasters. "The power outages in Sumatra show that our electrical system needs a more thorough evaluation. The challenge is not only how to supply electricity reliably every day but also how the grid, power plants, and supporting infrastructure can endure extreme weather events that are becoming more frequent," Arinaldo asserted during a webinar on the vulnerability of electricity assets to climate change impacts.