[dynoman]

The AP article references FERC. Here's a few graphs from FERC that show current frequency variations; They already drop much lower 59.99 Hz. I've never seen less than 59.93 or more than 60.02 where I work, we are in MISO (https://www.midwestiso.org/Pages/Home.aspx) the upper midwest.

[dynoman]

Here’s a .pdf that might outline what is proposed, I haven’t read through it yet but will;

http://www.nerc.com/docs/standards/dt/Project_2007-12_Draft_1_Comment_Report_2011_05_05.pdf

[meyer]

The graphs are correct - it isn't unusual to briefly drop below 59.95 HZ, and occasionally, we hit above 60.05 HZ as well. The two biggest drivers of frequency excursions outside of the 0.05 HZ bandwidth are loss of large generating units on the interconnection and major changes in transaction schedules between different utilities.

I remember a few years ago when a utility had 2 1200+ megawatt generators trip off line at the same time. Frequency dipped to 59.87 HZ. One of my industrial customers actually experienced an automatic transfer to his backup generator due to operation of an underfrequency relay.