IEDs: What do they monitor?

[wightywest]

I have limited to no experience working with IEDs except what I learned in school. What are some things that they monitor?

[clipboardwarrior]

I have limited to no experience working with IEDs except what I learned in school. What are some things that they monitor?

I'm late to this question, but protective relays are an example of an Intelligent Electronic Device (IED). https://en.wikipedia.org/wiki/Intelligent_electronic_device These monitor, among other things, current, voltage, and frequency.