[Pontiac]

due to a low frequency throughout the national territory, caused by outlets of power plants.

I am going to guess that they mean Plant Outages.

[Fellow Traveler]

Probably the grid frequency started to go significantly below 60Hz. To much load on the system for the power available. Most generators will trip on low frequency. I’ve seen charts tracking system frequency before. When Comanche peak in Texas would trip the system frequency would get as low as 58.5, half way to tripping my customers generators.