The National Grid Corporation of the Philippines (NGCP) said it is investigating possible sabotage behind one of the transmission line disturbances that contributed to widespread red and yellow alerts across Luzon and Visayas earlier this month.

During a joint House hearing on May 26, NGCP President and CEO AnthonyL. Almeda said the company has not ruled out foul play in the May 13 outage involving the 500-kilovolt Ilihan-Tayabas transmission line.

“NGCP is still investigating the root cause of the transmission disturbance and sabotage has not been ruled out and we have already requested the PNP for assistance,” Almeda said.

According to NGCP, the outage began after the Dasmariñas-Ilihan 500-kV line tripped at 4:46 a.m., followed nearly two hours later by the tripping of the Ilihan-Tayabas 500-kV line at 6:30 a.m.

NGCP officials said investigators later discovered that one of the conductors on the Ilihan-Tayabas line had been cut.

Lawmakers during the hearing questioned whether the damage appeared deliberate after photos of the affected conductor were presented during the proceedings.

NGCP said the simultaneous loss of the two transmission lines isolated the Ilijan and EERI natural gas facilities from the grid, removing around 1,319 megawatts of supply from the system.

The company maintained, however, that the prolonged red and yellow alerts were not caused solely by the transmission disturbances, but also by additional generation outages and rising electricity demand.

According to NGCP, 31 power plants were already on forced outage or operating at reduced capacity before the incident occurred.

“96.7% or 235 of 243 red alerts are attributable to generation supply issues,” Almeda said during the hearing.

NGCP also reiterated its call for additional non-intermittent baseload power supply, warning that red alerts may continue if supply vulnerabilities remain unresolved.

“The incoming solar capacity is a welcome addition to our pool of energy sources,” Almeda said. “But as the sun begins to set and the solar power harvest starts whining, the system again loses much needed capacity.”

The hearing also revealed disagreements between NGCP, the Department of Energy (DOE), and lawmakers regarding the timeliness and completeness of incident reports submitted after the outages.

DOE officials said they initially received only limited incident notices, while more detailed reports were submitted several days later.

The Energy Regulatory Commission (ERC) also told lawmakers that some submissions were not made within prescribed reporting timelines.

NGCP, however, maintained that restoration efforts were prioritized during the incident, with both affected transmission lines restored within the same day.

As power demand continues rising and grid operations become increasingly complex, how should the Philippines strengthen both the physical security and resilience of its energy infrastructure?

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