OK here’s the best I can do. The maps are a little old.
This Mindanews report says the following lines tripped:
- Agus 2-Kibawe lines 1 and 2
- Abaga-Agus 2 lines 1 and 2
- Abaga-Agus 6 lines 1 and 2
- Abaga-Tagoloan
- Abaga-Aurora
- Abaga-Lugait-Tagoloan
This first graphic is a zoomed in portion of a 2003 Napocor Grid Map showing the central Mindanao area.
Now, the Agus 2 – Kibawe line is an infamous line. Back in March of this year:
“Tower Number 19 along the Agus 2-Kibawe 138KV line was bombed and toppled around 11:30 in the evening on Tuesday March 13, 2007 at Barangay Sugod, Marawi City with the use of improvised high-powered explosives”
Back in December 2004, Napocor President Ortiz was dispatched to Mindanao after a massive blackout occurred one day after the deadly public market bombing in General Santos. Napocor reported to the press that it was not terrorist related but:
“there was however a sudden “transient high restive line fault” along the Abaga-Agus 2 to Agus-Kibawe that resulted to the tripping and overloading of other lines”
I’m sure people were antsy about the Dec ‘04 being terrorist related because back in April of 2003 towers were damaged along the Agus-Kibawe 138 kV circuit.
Here is a slide from the 2004 Transmission Development Plan showing that terrorist activities on the Agus-Kibawe line caused Napocor to plan a new alternative transmission line between Abaga and Kibawe to the east. 
Now, looking at the grid map, it’s clear that my post earlier today was wrong when I said: “Nine 138 kV circuits is essentially the whole transmission system.” Clearly, nine circuits is a minority of the transmission lines in Mindanao. But they are key and at the heart of the system.
[Updates in comments below]
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Any thoughts on what caused this incident?
Bambi Capulong of Transco says it was a “technical glitch” occurring at 1:04 pm on a Sunday afternoon that caused caused 90% of the whole Transco/Napocor Mindanao power grid to collapse. But if it was indeed a “glitch” – and they could certainly tell if it was a glitch or not because it is standard operating procedure to have in each and every Transco substation a “glitch detector” that “measures any false or spurious electronic signal that may be caused by a brief, unwanted surge of electric power” and turns on a red light on the panel. So all they have to do is see if that red light is on or not – if it was indeed a glitch then there were other things going on at time that compounded the immediate impact of the glitch. The system is designed to withstand a single contingency – if a relay fails due to a glitch, then the system should remain stable even if a single circuit is tripped. But if other conditions are also not normal, then the failure can cascade – that is probably what happened. But Transco is not disclosing what the other conditions were that contributed to the cascade.
Or it could be disgruntled employees. Or it could be that the Palawano tuko has migrated.
Mindanews reports that Emmanuel Abellanosa, Transco Assistant Vice President for Mindanao, says the cause of the problem was a conductor “flashover” (somehow related to an insulator, it seems) in the switchyard of Agus 6 Hydroelectric Power Plant in Iligan City.
A flashover is not a glitch.
The fact that a “flashover” occurred is one thing – it’s a matter for the Transco engineers and maintenance crews to address. But the fact that a “flashover” took down 90% of the Mindanao grid is a matter of public concern (we’re paying, afterall, for every peso Transco spends and invests). It may be that a “cure” for that situation is hugely expensive and we all might just agree that we take the risk of recurrence. But the conversation isn’t engaged. We have no knowledge. We have no venue for input. That’s the type of environment that a “public utility” should think about changing.