Fumento "splains" it to you.
There are a lot of folks griping about the collapse of the power grid, and the predictable voices are blaming the President, as if he had something to do with the design and construction of the grid. First of all, the thing wasn't designed; it grew. Second, it's not a monolithic system with some control room out of Star Trek. It's grunches of smaller, local systems interconnected, co-operative but independent of each other. Third, the complaint that "Somebody ought to do something" is easy; determining what to actually do is the hard part.
To give you some idea of how hard that question is, I have to take you into the complexities of the power grid, give you a tour of how it operates, and why it is set up the way it is. My knowledge in this area is based on my Navy career as Nuclear Reactor Operator. I didn't deal directly with the power distribution system, but through extensive cross training, I am familiar with the principles and techniques involved. And if I make any mistakes, I'm sure Sparky will correct me.
A simple power grid has three components:
* A generator
* Transmission lines
* Distribution centers
The generator converts physical energy, ie movement, into electrical energy. The transmission lines carry this energy from the plant to the distribution center, where it is routed to the loads. If any of the three components fail, the grid goes down and the lights go out, and Auntie Eunice can't watch her stories.
Deciding that this was a bad thing, some fairly smart people decided that if you put two small generators instead of one big generator in the grid, if one failed, you could still handle most of the load with the one that was left, and Auntie wouldn't miss finding out if Jim and Suzy got married, even though Suzy was pregnant with Ralph's baby.
So that's what they did.
Now it gets interesting.
Two generators carrying the same load are said to be operating in parallel, like two horses pulling the same wagon. Now there has to be some way of controlling how much of the electrical load each generator is carrying, so that the system will be stable. Like our horse and wagon, if one horse is pulling harder than the other, not only is the off horse not doing his share of the work, but the wagon is also harder to steer. Unbalanced loads on parallel generators have a similar effect. Fortunately, it turns out that electricity is pretty cool, because it will automatically distribute the load based on the voltages the generators are putting out. The higher the voltage, the more load the generator will carry, reducing the load on the other generator. So we can control the output voltage of each generator to match the loads. Remember this bit, because it becomes very important later in the discussion.
So what we've done is increase the reliability of the system by building in backup generating plants, which adds both spare capacity, and redundancy. The problem is that building plants is expensive. There's a constant battle being fought over how much spare capacity the system needs, and how much redundancy is cost effective. Spare capacity costs money, but doesn't generate revenue, so plant owners want the minimum amount necessary to ensure reliability. Plant managers on the other hand, like to maximize spare capacity to be prepared for outages or overloads.
That's what a local system looks like. Now let's zoom out a little and look at the regional picture. We've got several local power grids, all working to supply power to their communities, all wrestling with the need to grow to meet demand, and to maintain enough spare capacity to handle outages. At some point, a couple of these systems got together, and realized that if they connected their power systems, they would increase their available spare capacity, and redundancy without having to build new plants. It was highly unlikely that a problem would strike both systems simultaneously, which meant that each system could rely on their own spare capacity, and the spare capacity of the other system to handle any outages.
The plant owners were happy with this arrangement, because now they could sell their spare capacity to another system, turning an overhead item into a revenue generating item. The plant managers were happy, because now they had enhanced redundancy, and massive spare capacity.
This is how the power grid came to exist. Discrete power systems interconnected to share both the load, and spare capacity.
"Now this all sounds great, but if the system is so stable, how come we still get massive blackouts?"
Well, there are two factors operating here. Many major cities do not generate anywhere near enough power to supply their loads. They depend on shared power from outside the city to meet their needs. The recent energy crisis in California was a perfect illustration of this. Due to outages, maintenance and other factors, the state could not generate enough electricity to meet its needs, and had to buy energy from other states. If a large city loses its access to that shared power, through a fault in the transmission or distribution system, it will not have enough power to sustain its load, and there will be a blackout. The second factor is that demand for electricity is outstripping supply. The grid has a fair amount of spare capacity under normal use conditions, but when power demand hits a peak, like it did this week due to the hot weather, spare capacity in the region is almost nil. Any outage at that point is extremely likely to cascade, spreading far beyond the initial blackout.
"That's the second time you've talked about a cascade. What do you mean?"
Well, let's go back and look at our parallel generators. Remember that voltage controls the load sharing. When we take a plant off-line intentionally, we slowly lower the voltage, allowing the remaining plant to pick up the load gradually. When a plant trips off-line on an overload, the load is transferred immediately. When this happens, the increased load causes two things to happen to the remaining plant. Electrical current flow goes way up, which drives voltage way down. This condition can cause the generator to overheat and burn up. Literally burn up, with sparks, and flames and whatnot. Since this was something that everybody wanted to avoid, being messy and very expensive, safety systems were designed to shut the generator down on low voltage conditions.
So, if one portion of the grid goes off-line suddenly, the generators adjacent to it on the grid will see a sharp rise in current demand, resulting in a voltage drop. If there is enough spare capacity, the remaining generators will absorb the load, and return voltage to the normal level. If not, the voltage drop will be more severe, and the adjacent generators will trip on a low voltage.
So, the parallel operation is a double edged sword. It greatly minimizes the chances of an overload causing a power failure, but if there is a power failure, there is an increased risk of the overload to spread throughout the grid.
Now, there was another factor at work during this blackout as well. Nuke plants must have a stable source of local power to stay online. While the plants can be run in a self sustaining mode, federal law requires them to shut down if they lose local power. When the blackout hit, 9 nuke plants lost local power, and were forced to shut down, resulting in additional strain on the remaining grid.
"But my power goes out during thunderstorms all the time. How come it doesn't take down the entire grid?"
The answer to that question lies with in the power distribution centers. Electrical substations take power from the system, and route it into a smaller area. Each substation is protected with voltage and current limiters, which trip the substation in the event of a problem, like a lightning strike, or Elroy Barnes ramming into a power pole at 85 mph. These limiters are very similar to the circuit breakers in your house. When something goes wrong, they trip, isolating power until the problem is fixed. These breakers take that section of the load off of the system, keeping it from affecting the rest of the grid. These substations are small enough that they can be reset without a major impact on the system.
"So why not install the same things on the grid?"
We do, but the problem is that the grid is so interconnected, that tripping an overload protection in one place may result in another overload down the line because grid level trips cut off generators as well as loads. Also, the magnitude of the loads means that, unlike the local substation, you can't just flip a switch to bring the load back on. If you did, you would cause more undervoltage trips.
"But my power is usually back on in a few minutes, why is it going to take hours/days to recover from this blackout?"
Two reasons. First, the magnitude of the outage. There are literally thousands of switches and breakers to reset in order to bring everything back online. Second, the process of bringing loads back onto the grid is a little more involved than resetting a breaker in your house. In order to bring large sections of the grid back online, first you have to isolate a down section, connect it one piece at a time to a bank of generators, also isolated from the grid, then match voltage between those generators, place them in parallel for load sharing, then match the parallel group to the grid, then connect the bank to the grid. Once the load is shared, you can transfer load to the grid, isolate the generators you need for the next group, and start all over again.
It takes time, and is a pain in the ass, particularly for the folks without power, but the alternative is an overload that turns all the power station in the northeast into a smoking pile of slag.
OK, so now you know a little bit more about how the light turns on when you flip a switch, so let's get back to the issue of "Somebody has to do something!
The obvious answer is "Build more power stations!"
We are, but there are questions:
Coal, gas, hybrid, biomass, nuclear, solar, or hydroelectric?
And where? NIMBY nuts have ruled out building anything as nasty as a power plant anywhere near where they live, so real estate is very limited.
How are we going to pay for it? Utility price hikes? Federal tax money? State tax money?
These are questions that are fought over every day when utilities decide to build new plants. Lawsuits, protests, changing building codes, environmental impact statements, establishing infrastructure, etc all slow the process.
Another idea is to dismantle the grid. That would certainly keep blackouts from spreading, but at a tremendous cost. Local blackouts would become far more common; utility prices would skyrocket as utilities would be forced to build more plants to maintain a safe margin; cities would collapse as there simply isn't the room available to build the power plants needed to sustain them. All in all, it isn't a viable option.
That's really it. Most proposals boil down into one of the two categories above. Until we come up with a truly distributed power system, the grid will remain vulnerable to this kind of widespread blackout. I'm sure that we'll add a few more engineering controls to try and minimize the spread of future overloads, and I'm fairly certain that they won't do a bit of good.
What can be done, particularly in the cities, is to ensure that emergency backups are widely available. Hospitals, emergency services, communications services should all be required to have back up generators with enough fuel to last for 3 days. This is an area where fuel cells may really fit the bill.
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