Luzon residents were left wondering what exactly hit them last 12 September when suddenly the National Grid Corp. of the Philippines raised the power alert level to red, which meant the high probability of a brownout that most Filipinos thought they have already been spared from.

Most breathed a sigh of relief toward the afternoon as the alert was eased to yellow.

Even the Department of Energy was left wondering, reading between the lines of the statement of DoE Secretary Raphael "Popo" Lotilla, who said there is no constraint on fuel supply.

Lotilla's reaction was to mention the state of fuel availability, since seven major power plants simultaneously went off-grid, depriving the Luzon network of more than three gigawatts of electricity.

Power plants that suffered an unplanned outage were the 300-megawatt Calaca plant; 668-MW Dinginin; 460-MW Quezon Power; 647-MW Sual 1; 647-MW Sual 2; 344-MW Masinloc 2 and 335-MW Masinloc 3.

Rotating brownouts were experienced on Monday, meaning that the NGCP and power distributors in the Luzon grid had to ration the available supply.

NGCP's report to the Energy Regulatory Commission indicated the Luzon grid was on yellow alert between 10 a.m. and 1 p.m. and from 5 to 9 p.m. Red alert was raised from 1 to 6 p.m.

Lotilla said the sudden electricity shortfall is under investigation, in which a team from the DoE conducted actual physical spot checks to validate the condition of the transmission lines.

NGCP, likewise, reported three generating units with a total of 226 MW were subjected to "deration."

For the sudden drop in power supply to happen in a relatively cool season when demand is not that high, along with the fact that most were "unplanned," raised intriguing questions.

Another coincidence in the outage was that most of those that conked out are owned by SMC Global Power, which has a pending rate adjustment plea for its Ilijan and Sual plants.