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Power Electronics Help to Control Electrical Grids
An anonymous reader writes: "IEEE Spectrum magazine has a timely article about how power electronics are proving necessary for the widespread connection of wind turbines to the electric power grid. It explains many issues that currently make it difficult to utilize wind power. Older articles discuss other issues affecting the nation's power grid."
Better warning systems... Wanna fill out forms telling the government exactly when you plan on turning on your lights?
The power company doesn't get an early warning for how much power people are going to use. They can guess based on weather conditions and history, but that's not accurate enough a number for them to work with.
Remember back to physics class... (or read this on How Stuff Works if you can't...). Voltage equals current times resistance. And anything that you plug in to use power is a resistor. What this means in simple terms is that whenever you turn on anything, you've changed the resistance value on your local power network, so either you've just changed the voltage on the power network, or some power generator somewhere is going to have to step up to the plate and provide more current.
If you've ever read APC marketing material, you know that you want your computer, and for that matter everything else you plug in, to get a nice steady dose of 120 Volt power. There's a little room for tolerance, but not much.
So, whenever a city's power draw changes, the electicial system's gotta react pretty quickly. Too little voltage is a clear problem, it's a brownout. Too much voltage is also a problem, it's a power surge. The large power grids come into play as a way for a network that has too much power and a network that has too little to solve each others problems by joining together and letting physics do its thing.
So, when something goes horribly wrong, it takes nine seconds for a ordinary day to become a bad one. Nobody had any warning because the power grid has to react instantly to unexpected situations, and usually does just fine. It was the one time it didn't react properly that we all noticed.
For those unaware of what's going on, here is a quick excerpt of President Bush denying money for a secure grid... (Source)
On top of this it was announced that grids would be targeted by terrorists.
(source)Here is a link to a mirrored doc of the Electronic Power Risk Assessment, there is going to be a huge amount of finger pointing, and political partisan bs behind this entire incident, but read it for yourself in plain english how your (P)Resident will not fund plan for a more secure system.
Off topic? I think not
MoFscker
While it's true that most wind turbines use induction generators, they do so for several reasons, including:
All the turbines I have worked with have either had modest capacitor banks to correct for reactive power, or used insanely cool AC/AC back-to-back inverters to produce line quality AC.
I'm also concerned about the article's allegations of power intermittence. Wind turbine rotors have a fair amount of rotational inertia, so they're not capable of passing every flutter of the wind to the generator. It seems that this part of the article is a sales pitch for a new product that the vast majority of installations won't need.
I was also amused at the requirement of wind turbines to "ride through" grid frequency variations. This is basically a nice way of spinning the fact that wind turbine controllers are often far more picky about the frequency they'll accept or put out, than the rather poor regulation that applies to our power grids.
An finally, that picture. Where on earth did they get it? Apart from the fact that it's a contravention of every safety code to climb the tower of a running turbine, the climber must be a human sloth. To get that kind of motion blur on wind turbine blades, you'd have to have several minutes' exposure. Thus our perfectly sharp climber (and their horse) must be moving incredibly slowly ...
Unfortunately DC power distribution is highly inefficient. When transmitting power down a long lenght of wire DC creates a much higher voltage drop (power loss) across the line than AC.
I do not remember the figures, but this is the reason why AC was chosen for power distribution, even though there were various factions hyping the danger of using AC (electrocution and such).
Also this is why AC is transmitted at such high voltages for the large runs... for the same amount of power, a higher voltage means less current, less current means less voltage drop across the line, therefore less loss of power...
GE manufactures a turbine rated for 3.6MW output. Ge is currently an industry leader in these types of turbines though, they are desiged primarily for offshore use. Smaller MW ratings between 1.5 and 2.8 are more common. Unfortunately, even with wind turbines producing @ 3MW it would require approximately 1.26 Million of them to meet the U.S.'s current power demands. Currently Coal plants are responsible for the majority of our power capacity in the U.S.
While the *idea* of wind power is certainly a nice one, and the notion of helping the environmement is well intentioned, the reality is that wind is insufficient as a power source and as a result - it's ability to displace the most polluting source, coal, will be ineffective. Other solutions will be required to truly solve the pollution/capacity problem that we face.
A potentially viable start to "solving" some fo these problems would be to distribute residential power generation, especially in dense urban areas. Technologies such as fuel cells, and compact turbines could be used for this. An added benefit of this strategy would be zero emissions and heat reclemation in the case of fuel cells, and better regulatory control over the emissions of compact gas fired turbines.
My two cents.
Actually GE's patent on variable speed turbines is widely considered to be a bogus patent with an immense amount of prior art before it. There were several companies building variable speed turbines before GE did, Bergey being the best best known, they just did not patent the principle of electronic conversion in wind turbines because electronic converters have been used since at least the sixties in a variety of applications. GE's patent has been overturned in Europe by a patent dispute board. The GE patent, acquired when GE bought Enron Wind, is currently only in force in North America and it is being challenged there.
This is one area that electric cars may be able to provide a valuable service in what's known as vehicle to grid. A small company in california has been doing a lot of research on the topic and it looks promising. Theoretically, if you get enough electric cars that are plugged into the grid whenever they're not in use, they can provide near-realtime load balancing by remote dispatching from the power company. Say the power surge that took out the grid happened, but this time with a few hundred thousand electric cars plugged into it. The company could send a broadcast to the cars to absorb the extra load within a few seconds, and stop the cascading failure. Conversely, if there's a sudden demand spike, the cars could be ordered to temporarily supply it until the spike subsided. Obviously there's many technical hurdles but the general idea is very cool.
It's safer and simpler to pump water uphill into reservoirs to be extracted hydroelectrically later. That's what they do currently. earth-fill gravity dams are much cheaper and more reliable than massive electrolysis plants.
If a job's not worth doing, it's not worth doing right.
In the UK we have at least one pump storage station for evening out loads - but not for months at time. Its basically two large lakes one above the other, excess power pumps water up, then when there is a surge in demand it goes back down through a generator.