For any interconnection (Western Grid, Eastern Grid, ERCOT Grid etc.) the frequency is global. That is to say the frequency is the same throughout each interconnection. In the Western Grid, for example, a control center in New Mexico will read the same frequency as a control center in Washington State. There are no low frequency areas or high frequency areas within an interconnection. If there is a system disturbance, like a sudden loss of load or generation, there will be what is called a frequency excursion. Rarely, if ever, will the excursion be severe enough to cause damage to the customer's equipment. The tripping and separation schemes in an interconnection won't allow it.
So I said all that to explain my observation that the frequency parameter in an EMS is mostly superfluous. The frequency will either be acceptable or it will be zero. The power is either there with an acceptable frequency or it's not there and you are in the dark. I realize this post doesn't answer any thing in the OP, but I wanted to throw it out there for the edification of our forum members.
