A few questions about disconnecting from the power grid:

1) Is disconnecting a physical process, a software procedure, or a combination of the two?

2) Who would make that decision?

3) Would that person (or business entity) making the decision be required to first gain approval from an outside person (or entity) before disconnecting?

4) If that person (or business entity) making the decision does not need outside approval, are they at least required to notify present "interconnectees" of an intention to withdraw services?

Thanks

-- Anonymous, December 15, 1998

Answers

Critt, although this doesn't specifically answer your questions, it does give some reference to disconnecting from the grid. The recent 10Q of the Carolina Power & Light Co. had this statement in its Contingency Plan section:

"In order to mitigate the risk of cascading regional electric failures, the Company can, as a last resort, isolate its transmission system either automatically or manually."

There are a couple of other utility 10Q's which made reference to being able to isolate themselves from the grid, but each time it was stated that it would only be done as an emergency measure of last resort. This would imply that the answers to your questions #3 and #4 would be "no", but I can't prove a no answer is correct.

-- Anonymous, December 16, 1998

It will happen manually at the direction of the Regional Security Coordinator(people decision) or automatically by the under frequency relays(equipment decision) as the system frequency sags. These relays operate in cycles so this is a pretty fast process. The relays control zones that shed a pre-determined percentage of the load per zone. More serious sags will trigger more zones to trip.

In reference to the San Francisco outage....relaying is somewhat of a black art with many many factors impacting the as-designed operation of the device. As a system grows and loading conditions change these settings have to be updated. It's definately not plug-and-play.

Jim

-- Anonymous, December 16, 1998

Thanks, Bonnie and Jim. You've provided enough information for me to go forward.

-- Anonymous, December 17, 1998