Power interruption hit parts of Luzon on 12 September after the grid was placed on "red alert" due to unplanned power plant outages, transmission line tripping, and reduced electricity generation of some power facilities, said an advisory from the National Grid Corporation of the Philippines.

The NGCP issued a "red alert" originally from 1 p.m to 4 p.m. but was extended until 8 p.m., which meant affected areas may experience rotational brownouts.

The power transmission operator said the red alert was lifted by 5 p.m., a few hours ahead of schedule.

NGCP reported at least seven electric generating plants were simultaneously forced outages leading to a loss of more than 3,400 megawatts in the power system.

The generating facilities on unscheduled shutdowns included the Unit 1 of GNPower Dinginin plant, Calaca-2 plant, Masinloc 2 and 3, Sual 1 and 2 plants, and Quezon Power plant.

The outages were also caused by the reduced capacity of the other power plants, which resulted in 226MW additional capacity lost in the Luzon grid.

Power distributor Meralco said interruptible load program participants are ready to switch on their generating units to ease the capacity in the main grid anytime.

On 11 September, the thin power supply in the grid led to brownout, following the tripping of the 500-kilovolt Nagsaag-Bolo lines 1 and 2 of NGCP.

In a separate statement on 12 September, Energy Sec. Popo Lotilla said there are no fuel supply constraints despite thin power reserves: "We assure the public that the DoE is verifying the cause of the forced outages… as there appear to be no fuel supply constraints. A team from the DOE will conduct actual physical spot checks and validate the condition of the transmission lines and the affected power plants."