I've been reading the Dick Mills article posted in another thread.

Something in the article triggered a memory of a discussion I had with my local distribution electricity provider. The fellow whom I talked with is the CIO of the company.

The Mills article states that it would be a smart thing for all spare generation capacity to be on-line at the critical time (during the roll-over and presumably for some time afterwards). The CIO whom I talked with also mentioned that all spare generation would be on-line at the critical time(s).

Now having read the discussions for awhile it appears the consensus is that this idea of having every available generator on-line is a good one. I also understand the idea of capacity .vs. demand.

However, I do not see an explanation of *why* this is a good idea. And frankly, I disagree that it indeed *is* a good idea.

Here's why :

Assume that the reaction time of human-in-the-loop decision making is long compared to computer-only control loops.

Assume that the control systems have been switched to manual for a *network*. (Gen./ Trans./ Dist.) Feedback regarding internal and external system parameters are available, but control loop feedback is performed manually.

If an incorrect response is made to some control loop decision branch, the recovery time available before catastrophic failure is shortened.

I'll give a simple example :

There is a battery at some voltage with a short circuit current capacity of 1 A. This 1 A. is not enough to melt the wire. An accidental short is placed across the battery with this wire. The wire is intact, but perhaps damaged.

Now, the person with the battery thinks that there may be some problem in the future with the battery. He puts a few more in parallel with it just in case.... Oooops, there's that pesky short, and this time the short circuit lasted longer!

Anyone care to discuss the pros/cons of this sceneario, and perhaps discuss the tradeoffs?

Thanks, Bob.

-- Anonymous, March 22, 1999

Answers

Bob, Having more generation on-line sounds like a good idea, but I always get a tad nervous when we start doing things differently - change brings increased risk of something unexpected happening. An example of this is power plant power level changes, typically more risky than steady state operation. An analogy is your car on ice - everything is fine, until you start or stop...;)

I do expect a number of nukes to be at a reduced power level to be better prepared for a runback though...

Regards, FactFinder

-- Anonymous, March 25, 1999

Bob,

Like Factfinder, I agree that all generation on-line sounds good! But this can bring its own set of problems. In some areas, the demand cycle can be extraordinarily steep. Particularly in the winter months. In the south, demand can vary significantly from low load periods to peak periods and while the most efficient units do stay on-line, less efficient units are cycled off during low load periods. This is not only for economic reasons but for practical reasons as well. Put simply you must have sufficient demand to sustain stable capacity. Just as each unit has a maximum capacity, it attempts to maintain a minimum capacity as well.

There are three types of instabilities units can be susceptible to at low loads. Electrical instability; thermodynamic instability and control instabilities. Though I cant back this up here, I would suspect that coal units are the most susceptible to low load instabilities due to the nature of their fuel supply and burner control systems. These units can often require expensive alternate fuels for flame stabilization if demand drops below its minimum capacity.

Well, why dont they just sell power off system? If everyone is running everything they have, who are you going to sell it to?

Alternatively, I would think that placing units in hot standby may be more practical here in the south.

-- Anonymous, March 26, 1999