Manila, Sept. 17 -- A two-hour yellow alert has been raised over the Visayas grid on Thursday due to low power supply, according to the National Grid Corp. of the Philippines (NGCP).

The alert is in effect from 5 p.m. to 7 p.m., NGCP said.

A yellow alert is issued when the grid's operating margin falls below the required contingency reserve.

As of 8 a.m. Thursday, available capacity in the Visayas grid was about 2,505 megawatts (MW), against peak demand of about 2,290 MW, NGCP said.

The grid's capacity was affected by the continued unavailability of Unit 1 of Therma Visayas Inc. and Unit 3 of Panay Energy Development Corp.

NGCP said 12 power plants are currently unavailable in September. Another 21 plants have been unavailable for fi...