I guess I don't understand how a grid frequency dropping too low can create major blackouts, is there an easy way to understand it? In my mind I just don't get why there wouldn't just be brownouts or loss of service in some places and not total blackouts.
This will be an extremely oversimplified response so don't take this as a complete technical description to use in the future.
Think of frequency (Hz) as gen/load balance. If there's too much generation, Hz goes up. If there's too little generation, Hz goes down.
Hz impacts all connected devices. Spinning motors & generators need to operate within set limits to control their power & torque angles as well as speed. Since N. America is a 60Hz system, a 2 pole generator is going to spin at 3600rpm. Once the small deadband is reached in the governors droop settings, additional torque is applied to the rotor to increase mw output. The actual speed of the rotor/generator doesn't change from 3600rpm, just additional torque applied to the rotor which then injects more mw to the system & forces the system Hz up. If there is a large enough disturbance to the system that Hz is forced down quickly, the spinning turbines inertia will physically slow down the Hz decay, then the governor will add torque to the rotor in an attempt to speed back up to its setpoint.
Large swings in Hz can & will damage turbines blading (especially the low pressure blading) as well as attached induction motors & other devices.
There are protective relays in place to shed load in predetermined steps to protect against this Hz decay & restore the gen/load balance. These schemes are part of an UFLS (under frequency load shed) or RAS (remedial action scheme). Most large load is offline by 59.3Hz with their internal protection devices. Additional load drops happening through the system operators schemes will happen in 3 stages prior to the 59.3Hz referenced earlier as well as a final step that's below 59.3 (usually at around 59.1Hz).
"Green" energy provides no spinning mass & usually no VAR support (for voltage support) during these excursions. If there's not enough spinning turbines on the system to absorb the initial shock & instantly respond, you'll end up with large cascading blackouts.
I've personally seen CAISO's system swing over 3,000mw in 5min due to PV cloud cover, let alone a disturbance event.
@rmenergy can correct me if I'm wrong but that is the way I am reading into it. Again though, I'm an idiot.
