BALO-I, Lanao del Norte -- Unidentified armed men bombed another power transmission tower belonging to the National Grid Corporation of the Philippines (NGCP) early Wednesday morning.

Emmanuel Abellanosa, NGCP vice president for operation and management, said the armed men used four improvised explosive devices in toppling the tower, which is located just 500 meters away from a police detachment in Sitio Taburo, Barangay Nangka in this town.

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There have been seven NGCP towers bombed in the last two months, two of which were completely toppled. A toppled power pylon costs at least P5 million to repair.

Max Trinidad, NGCP security division head in Mindanao, said: "We are facing blank wall on there were series of pylon bombings. The NGCP did not even receive any extortion letter."

The toppled towers included Tower 24 in Bara-ason, Kauswagan town; the latest was in Baloi town.

Police and military authorities are investigating the bombings.

The destruction of these transmission towers are without consequence.

NGCP said rotating brownouts "of short durations throughout Mindanao" will be implemented following Wednesday’s bombing.

"Electric cooperatives and private power utilities are asked by the National Grid Corporation of the Philippines to voluntarily shed load effective Wednesday,” the power firm said in a statement.

Abellanosa said the load curtailment scheme is resorted to maintain the integrity of the Mindanao power grid following the isolation of Agus 1 (40 megawatts) and Agus 2 (100 megawatts) hydroelectric power plants at 12:45 a.m. Wednesday.

He said the load curtailment is a temporary scheme to keep a manageable supply and demand condition in the grid while it is under some constraints.

"NGCP, as the grid operator, is especially looking at the generation reserve level, which should not be less than the on-line plant with the biggest load. The load curtailment scheme affords this crucial flexibility. The NGCP hopes for the utmost cooperation of its power customers on the load shedding scheme," the firm said.

It said it has mobilized manpower and materials to immediately install an "Emergency Restoration System (ERS) to temporarily energize the damaged lines and restore power flow from the Agus plants." (Richel V. Umel)