LEW HANES: What about the timing for purchasing power from outside sources?

BILL MELTON: Guidelines have us planning two hours, or longer, ahead.  For next hour purchases, the marketer has to have a confirmed transmission reservation in OASIS. The schedules should be submitted to the Interchange Coordinator not later than twenty minutes before the hour.

You inform the marketer that you need 300 megawatts for a specific hour, and he goes out and finds you 300 megawatts.  However, if you have miscalculated or lost generation unexpectedly and your need becomes 500 megawatts within that specified twenty minute time frame, the marketer cannot buy more power for the next hour. At that point you have to make that 200 megawatts up from your own resources.  So it can be costly if you miscalculate because you're going to be loading your higher cost resources at that time.

One other possibility is to shed load, but I would do that only as a last resort.  I would not do it unless I was pushed to the limit.  Of course, we have commercial and industrial customers that get special rates with the understanding that they are dropped first if we get into the alert process and we have exhausted our resources. These customers are considered interruptible load.

LEW HANES: Do you have a list of those customers?

BILL MELTON: Not individually, marketing has put them in blocks and each one of those blocks contains a certain amount of megawatts.  When we have a problem, we look at megawatts, not individual customers.  Therefore, when we get ready to shed these blocks, we rotate them to keep the outage time equitable among the blocks.  But since there are a different amount of megawatts in each block, you may go to a smaller block or a larger block, just according to how many megawatts you might need for the next hour to meet that load.

Another challenge we have to take into consideration is what we call our southwest quadrant.  The SWQ is a portion of Alabama, Florida and Mississippi that is limited in how many megawatts we can export out of that area due to stability problems.  If you have excess generation in that area and you reach your maximum quadrant export limit, you can no longer load the additional generation in that area. If it becomes necessary to shed the interruptible customers mentioned above, you cannot shed the interruptible customers inside the southwest quadrant if you are at the quadrant's maximum export limit. If you cut the load inside the quadrant, you increase the exports.
 

The problem is that the transmission system coming out of the southwest quadrant is not capable of handling all of the excess generation.  If you have certain outages in that area, you can cause the quadrant to actually separate from the rest of the system.  This could cause generator damage.

LEW HANES: What would you do if you've had a very mild day and no one has his air conditioner on?  Do you take some of the plants off-line, or reduce output?

BILL MELTON: Units can be removed from service if the mild weather is for an extended period of time but you must keep in mind the start-up and shut-down costs associated with the units involved. It may be in the best interest of the system, and more economical, to keep units on the line, or off the line as the case may be, if change in weather conditions is for a short period of time.