The National Grid Corp. of the Philippines has explained the cause of the Visayas-wide blackout last April 25 that cut power supply to Cebu, Negros, and Panay for more than 10 hours.
The power outage was initially caused by the tripping of the 230KV Transmission Line 2 between the Energy Development Corp. – Leyte Marshalling Station and Tabango substation at 9:38 a.m., NGCP said in a statement.
It occurred while the transmission line was on shutdown as requested by EDC for the maintenance and calibration of their metering equipment, affecting all power plants located in Brgy. Tongonan, Kananga, Leyte.
These two 230 KV power lines are being used to transmit power from the marshalling station to Tabango, Leyte then to Cebu using the submarine power cables.
The cause of the tripping was brought about by several factors involving not only operations and maintenance of the line but also the generation aspect, the NGCP said.
When the Marshalling Station –Tabango Line 2 tripped, it has a load of 340 megawatts, much higher than usual because Line 1 was de-energized. The total load of Visayas Grid at the time was at 901.8 MW, with Leyte-Samar-Bohol at 530.7 MW and Cebu-Negros-Panay at 371.1 MW.
NGCP explained that power outages usually occur when a tree limb or foreign object touches two wires at the same time causing a short circuit. The circuit breaker will instantly trip and all customers served on the circuit will lose power.
However, power outage can be avoided if there is an available standby power, which can be readily used in case there is tripping.
The NGCP said there have been many tripping incidents in the past but power outage did not happen because there was enough power supply to cover for those lines that tripped, but the present situation is completely different.
Hours after the April 25 blackout, the Marshalling Station-Tabango Line 1 that supplies power to Cebu-Negros-Panay Grid was energized at 2:36 p.m.
This was followed by the Tabango to Talisay, Daanbantayan submarine power cable at 2:44 p.m., resuming link or interconnection to Cebu and paving the way to gradually restore power to normal in the Visayas grid, the NGCP added.*