THE GRID operator issued a yellow alert warning lasting a few hours over the Luzon power grid Wednesday afternoon, after five power plants with a total capacity of 1,230 megawatts (MW) went on forced outage.

In an announcement on Viber, National Grid Corp. of the Philippines (NGCP) said the grid was under yellow alert beginning noon until 3:45 p.m.

Yellow alerts, signifying thinning reserves, become red alerts if the supply-demand balance worsens to the extent of requiring rotating brownouts.

The NGCP said the plants undergoing unplanned outages are Unit 2 of the Sual plant, Unit 1 of GN Power, Unit 1 of SLTEC, Unit 2 of SLPGC and Unit 3 of Limay.

Meanwhile, two power plants ran on de-rated capacities of 315 MW.

The operating requirement of the Luzon grid was 10,514 MW, while available capacity was 10,935 MW.

At 3:45 p.m., NGCP lifted the yellow alert, citing “receding system demand.”

During yellow alerts, distribution utility Manila Electric Co. (Meralco) asks participants of its interruptible loading program (ILP) to prepare for possible de-loading.

The ILP calls on large power users with generating facilities to hold off from drawing power from the grid when supply is tight.

“When NGCP places the Luzon Grid on Yellow Alert, Meralco will automatically advise all ILP participants to prepare for possible activation or de-loading. Part of the advisory to ILP participants is a request to inform Meralco if the participant can de-load or not during the period of the alert,” Meralco Vice-President and Head of Utility Economics Lawrence S. Fernandez told BusinessWorld on Viber.

When the yellow alert was lifted, Meralco informed ILP participants that the grid was “on white condition.”

The Luzon grid previously underwent a spate of yellow and red alerts at various times between May 31 and June 2, due to forced plant outages, higher demand and thinning reserves. — Angelica Y. Yang