The struggle for the optimal electric power generation system from Edison to now
Open Access Article Originally Published: November 01, 2003
To Part One
A Short Primer on "Load-frequency Control"
If you ever wanted to know how to operate a central station turbine generator, but were afraid to ask, now's your chance.
Here's your first question. How do you supply the right amount of electric energy from a generator when it is to serve a varying load as people, located far from the central station and out of sight are turning their electric switches on and off?
The answer: you can do it by regulating the flow of steam energy. Just open or close a valve between a steam boiler drum and a steam turbine that permits steam flow into the central station turbine generator.
Turning a water valve regulating flow of water energy from a penstock into a hydroelectric turbine generator will do the same thing.
But how do you know how much steam from a boiler or water from a reservoir, to feed into the turbine generator? Easy. Watch a frequency meter.
The turbine is quite a massive piece of machinery connected to the generator rotor that is also a pretty heavy thing, connected by a steel shaft perhaps six inches to a foot thick. It acts as the "flywheel" of the system. It stores kinetic energy just as the flywheel of an un-interruptible power system ("UPS") stores energy to maintain power for your computer during an unexpected power outage or the flywheel of your car stores energy it gives up as needed between power strokes from the cylinders or when you start up hill before you step on the gas. (It only has so much so you better push in on the clutch as the engine slows down too much or it will stall.) If the steam energy or water energy going into the turbine is less than the electrical energy needs of the load, or if one of your turbine generators breaks down, the turbine generators still on line will give up some of the rotational energy stored in their flywheels to make up the difference and fall below 60 cycles per second. The turbines and generators rotating on the same shaft, or directly coupled, will slow down and frequency will fall. If customers turn off their switches your turbine generators will receive too much steam energy – more than the customers are using -- the surplus goes to the stored energy and the frequency goes up above 60 cycles per second or 60 Hz. When frequency is right on 60 Hz, no corrective action is needed.
If you have a scientific bent, the amount of energy stored is equal to the mass of the flywheel, in this case the mass of the turbine, generator, and connecting shaft, times the square of its rotational velocity or MV squared. As it gives up its stored energy it will slow down. The mass is unchanged so frequency drops. (Better shed some of your load before it slows down too much or it won't be able to come back up again. Those customers will be annoyed if you shed them for a few minutes but they'll really be irate if the system goes down completely; you have many generators, and it will take hours to rebuild your system carefully keeping everything in balance all the while. What a hard decision for a poor working stiff! Wrong decision and it's off with his head. )
You can shed load from your control center where you have remote control over circuit breakers at distribution substations. Maybe a plan of automatic load shedding keyed to low frequency will help as it frees the system dispatcher from responsibility for the decision.
Frequency is available all over interconnected electric systems no matter how large the interconnection – even when it extends from the Rockies to the Atlantic -- so it is a handy signal on which to base the control of system operation. In these days of large scale interconnection it doesn't vary very much since it is determined by the sum total of energy stored in all the generators operating in parallel if the system stays together. That's a pretty big mass for all the generators from the Atlantic Ocean to the Rocky Mountains that are now operating normally in parallel. Plug a frequency meter into your wall socket and you will see it vary, usually only from 59.97 to 60.03. If a big unit trips off line somewhere, it might go down to 59.94 for a few minutes. If it goes down much below that, the trip of lines may have put you in an island of generation and transmission lines, separated from the remainder of the interconnection, with not enough generation to supply the load and not enough stored energy to give your system operator much time to react.
GO TO NEXT PAGE >>
|
| Times Article Viewed: 4278 |
|
|
|
Reader Comments
A valid email address and confirmation is required before your comment can be posted. Comments not confirmed within
24 hours are automatically deleted.
2 comments so far...
05-Nov-2003
1142
| |
Interesting article with a plausible description of 'Spinning reserves', but I fail to see why Nikola Tesla is referred to as eccentric. He has in excess of 1000 patents to his name and developed some of the most important devices of the last century and this. The flourescent light is one, along with AC motors, AC generators, AC power distribution system etc. It seems to me that he was more prescient than eccentric. And the negative press and actions of Edison in the early years and Westinghouse in latter years have done much to discredit an otherwise brillaint engineer. By comparison Faraday, who is considered the father of electricity, was a mere tinkerer on the sidelines and yet Tesla is still derided. Fortunately there are people out there who recognize the contribution that Tesla made and continue to redress this gross misconduct by correcting such misguided perceptions.
Posted by: Tony Thomson
|
|
05-Nov-2003
1144
| |
So electricity generation has been a matter of national security for all this time. No wonder so few people are not willing to go off grid. They are quite possibly scared to death. Scared that they would be breaking a law and those proverbial guys in the black suits would come knocking on their door. Its all so very conveinient; someone invents a thing, an wealthy business man see's an oportunity and invests, this catches on and spreads, the U.S. government steps in (after all what are govern-ments for?)and takes the reigns, I could go on and on with this but I will spare you. The point is, or at least should be, that its not against the law to live off grid. A responsible people, like most Americans citizens are, should be encouraged to make the move off grid and produce their own electric power for their own consumption. This should be done with non polluting renewable energies of course. It is my firm belief that all of the energy a single family dwelling should every need, can and should be produced at the dwelling. This includes homemade Hydrogen gas for the home and the automobile as well. Sometimes I wonder if the reason this has not happened is because there are those that would have us believe that it would be a threat to our nation. Not for an individual, to not be dependent on large corporations but for millions to not be depenent on those corporations. Kind of like how King George of Great Brittain must have felt when the American colonist decided to be independent. Am I wrong to assume that a very large part of the American spirit is our desire for independence, for individual freedoms? But yet in order to have that independence we all must depend on the corporations that do so much for us in our daily lives, so much! except liberate us from a dependence on the coporations.
Posted by: Thomas Schmidt
|
|
