TransCo president Alan T. Ortiz said the the system was "put back to normal at 6:11 p.m. (May 11)."
He said the earthquake did not cause toppling of any transmission tower, as initially reported. Upon verification, he said there was, in fact, no damage to any of TransCo’s facilities in the Visayas.
"All transmission lines, overhead or underground, as well as the submarine cables and associated facilities of TransCo did not suffer any damage during the earthquake," Ortiz noted.
The intensity 4.2 earthquake hit Tongonan, Leyte at around 10:02 a.m. yesterday causing all the geothermal plants in Leyte to trip off. These geothermal plants supply most of the power requirements of the Visayas grid.
As a result, generation loss was estimated at about 602 megawatts (MW).
This loss, in turn, caused the isolation of the Leyte-Luzon HVDC interconnection and activated the automatic load dropping (ALD) scheme.
The Leyte-Cebu transmission line also went into automatic load dropping due to the unstable system voltage. Hence, there was system failure in the whole Visayas grid.
Shortly after the earthquake, several power plants started running on houseload and restoration efforts were immediately undertaken.
By noon of May 10, power was partially restored in Leyte and Samar. Parts of Cebu being serviced by the Visayan Electric Co. (VECO) were synchronized to the grid later in the afternoon.