I think you need this: overvoltage, undervoltage, overcurrent and residual, frecuency low and high, Why? the answer is power quality, Is this the most important for your facility or not? if yes, you must put it all, if not, don´t worry be happy...
If there was no electricity there would be no internet. Good point, don´t you?
Under frequency load shedding is generally coordinated at a regional level. Load should never be tripped for over frequency. The may be a need for auto restore on over frequency if too much load was dropped. But in all cases coordination over a larger area.
Also, I've never before seen reference to 81H or 81L, the standard usage is 81O and 81U.
For a load feeder, normally I'd say no. As davidbeach said, usually utilities will coordinate such protection throughout their service area.
Do you have unusual loads that could be damaged by over/under frequency? That might be an argument in favor of such protection.
Do you already have the protection hardware installed and its just a question of enabling the functions? Then I'd say maybe.
You might want to talk to your utility and see what their settings are and get their input. Your setpoints could be set outside of theirs as backup protection. And it will give them a heads up to anticipate possible problems if you do drop load during some system anomaly.
