ITB Expert Cites Weather as Suspected Cause of Sumatra Blackout

A widespread power outage (blackout) in Sumatra is likely caused by mechanical stress from strong winds on transmission lines, particularly at cable connection points or mid-span joints. Dr Ir Djoko Darwanto, an electricity system expert from the Bandung Institute of Technology (ITB), believes weather factors played a major role in the incident.

This is evident from the fault characteristics pointing to mechanical stress at transmission conductor connection points. ‘If we look at the reported fault pattern and the damage occurring at cable joints, weather factors are very likely to have contributed to this incident,’ he stated in a report on Friday, 29 May 2026.

Previous preliminary investigations by the National Police Criminal Investigation Agency (Bareskrim), the Forensic Laboratory Centre (Puslabfor), and PLN identified three possible causes for the transmission cable failure: thermal stress due to weather, connection point issues, and mechanical stress from load and wind.

According to Djoko, the public often assesses weather conditions based on ground-level observations. However, at transmission conductor heights, wind speeds can be significantly higher, causing continuous cable oscillation.

‘Conditions below may seem mild, but at conductor level, winds can be strong enough to cause cables to move and pull against each other, creating repeated stress on the cables,’ he said.

He explained that repeated movement from wind exposure increases stress on cable connection points, especially when the system is under high load.

Moreover, the break occurred at a mid-span joint — where two conductors are joined using specific methods and protective measures. This area is where the cable spans are connected.

He noted that connection points are among the most critical areas in transmission systems as they experience a combination of vibrations, temperature changes, and pressure distribution when cables move due to wind.

‘The pressure distribution at connection points differs from that of intact cable sections, making these areas a key focus in transmission systems,’ he added.