what happens to the extra electricity?
RedfordHenry
| Posted in General Discussion on
This may sound like a stupid question, but when there is a major power outage due to downed transmission lines, such as the outage we are currently experiencing in NH from last weeks ice storms, what happens to the electricity that the power plants normally produce? Do they automatically know there is reduced demand and they just cut back production? Do they just slow down the turbines, maybe take one or two offline? It’s not like they can store the extra juice somewhere, right? I have a basic understanding of electrical theory but the “grid” really baffles me.
Replies
"due to downed transmission lines"
The power goes into the ground.
Just because they want to make it personal,
doesn't mean you have to take it personal.
Yes, you are correct. That is the sole purpose of the ground rod at your house and why all of those transformers on the utility poles are grounded to the earth.
I have a limited understanding of the utility company's transmission of electricity myself, my concern is at the point of service. In a house, that is the service panel, and a commercial building, that is usually at the transformer(s) on the premise.
What I do know, at least for my jurisdiction, is that the electrical utility's transimission starts at one 480V transformer, and I believe that is juiced hydroelectrically. Transformers are required every blank yards or miles to mantain the voltage and the transformers at the substations either step-up the voltage or drop it down. I know, I kind of thought that it would be more complicated than that too, but that was how it was explained to me, or at least how I remembered it.
how it was explained to me
You need to perform some fine tuning on your BS detection meter <G> - somebody who knew next to nothing really fed you a line.
OK. He is my teacher in my 3rd year electrical apprenticeship program. He has been doing electrical work since before you were an itch in your daddy's pants.
You need to fine tune your people skills.
Edited 12/20/2008 9:08 am ET by arcflash
That does not mean that is is not BS..
William the Geezer, the sequel to Billy the Kid - Shoe
OK. He is my teacher in my 3rd year electrical apprenticeship program. He has been doing electrical work since before you were an itch in your daddy's pants.
Just telling it like it is, no need to invite a ban. Is your 'teacher' over about 83 years old????
FWIW, my BSEE is from 1967. A few score peer reviewed published papers since then - e.g. IEEE and SAE publications.
Oh boy, here we go. The only thing that I see wrong with my post was the grounded transformer statement. I believe that the transformers are only grounded right before the point of service. The now grounded conductor becomes the neutral at the service and is grounded again thereby creating the grounding conductor. Utility lines are therefor ungrounded systems--for safety.
I do not understand the hostility. I think I made it clear in my post that I do not understand utility transmission all that well.......my schooling is about electrical theory, at the point of service. I am studying to be an electrician, not a lineman. I also thought that I made it clear that I may not be remembering correctly what was told to me. See above statement.
If I am in error with my previous statements, by all means, please enlighten me. In the meantime, tone it down abit with the negativity.
No, you have it totally wrong."Yes, you are correct. That is the sole purpose of the ground rod at your house and why all of those transformers on the utility poles are grounded to the earth."". I believe that the transformers are only grounded right before the point of service. The now grounded conductor becomes the neutral at the service and is grounded again thereby creating the grounding conductor. Utility lines are therefor ungrounded systems--for safety."Go out and look at some poles.You have have either 4 lines if the that part of the distribution system is 3 phase or 2 lines.The one line is the neutral or return. That line is continuous and grounded at each pole with a transformer. And I suspect every so many feet if there is no transformer. At the transformer you will typically see 4 terminals for common 120/240 service.One is the HV side and connect via a cutout (fuse) the HV supply line.2 are for the 2 legs of the 120/240 service.The 4 terminal is connected to the case of the transformer and on the inside the other end of the HV coil on the transformer and the center tap of the LV coil.And the outside that terminal connects to the HV neutral, to the house drop neutral and to a ground wire that runs down the pole.Often that wire run down the pole is just terminates with a spiral of wire under the pole butt.So the distribution system is GROUNDED and grounded at many places.There are two purpose for grounding the system. One is for a path for lightning strikes.The other purpose is to give a reference to the system. If the distribution system was ungrounded then even minute leakage currents or even capacitive coupling from the high voltage system could cause the LV side to rise to thousands of volts. Even to breakdown common insulation."What I do know, at least for my jurisdiction, is that the electrical utility's transimission starts at one 480V transformer, and I believe that is juiced hydroelectrically."I don't know what "juiced" means, but I am guess that it means that the power is generated by hydro plants. While that might be true I doubt if any system relies of just hydro. They will have combinations of types of plants that they either operate or buy power from.But it most certainly does not start out as 480 volts.Typically end distribution lines are in the range of 7 to 14 KV.And the feeds to the substations are in the 50-100 KV range.And the large feeder lines run in the hundreds of KV range."Transformers are required every blank yards or miles to mantain the voltage and the transformers at the substations either step-up the voltage or drop it down."The end transformer at the house has taps so that they can adjust for the nominal supply voltage.But in some cases they will have a bank of auto transformers to adjust for voltage drops in the distribution line. And some of them have tap changes that can dynamically adjust the voltage.You might also see banks of capacitors that are used for power factor correction.http://en.wikipedia.org/wiki/Electricity_distributionhttp://www.howstuffworks.com/power.htm.
William the Geezer, the sequel to Billy the Kid - Shoe
Thank you Bill, you came through. Its nice to get an answer void of sarcasm.
I'm sure that my locale has several means with which to supply the transformers, I don't know for sure. Transformers do not only get tapped to the center. Corner tapped delta, center tapped wye, are just a few examples. Now bear with me because I've only studied little stick drawings, and not seen the actual theory applied in real time in the field.
I do remember my instructor telling me that our utilities all begin with one transformer. You've got to remember that you can "create" any type of voltage with the right amount and proper transformers. In other words, I could get 15 kV out of 120V with the right transformer configuration.
"Corner tapped delta, "That is not a transformer. But rather a bank of transformers and the "tap" not inside the transformer, but the connection between transformers."I do remember my instructor telling me that our utilities all begin with one transformer."That is really not true. Only in the most simplistic way of looking at it. In general the system is more like a spider web. There will multiple generators at most locations feeding multiple transformers feeding multiple lines. And then there will be multiple generating plants and/or feeds from other suppliers.And most sub-station will have several different feeds coming into them.Even the loop around my development (about 300 houses) can be feed from 2 different directions, but all of the same sub-station.You've got to remember that you can "create" any type of voltage with the right amount and proper transformers. In other words, I could get 15 kV out of 120V with the right transformer configuration.Yes, I think that is about the voltage of neon sign transformers..
William the Geezer, the sequel to Billy the Kid - Shoe
Edited 12/20/2008 9:01 pm by BillHartmann
Let's see if I understand this all right .....
The power comes in the hot wire ... goes back to the transformer on the neutral wire ... and is sent back ovwer the hot? So I've been getting the same electricity over and over? And they keep charging me for the SAME elctricity?
It just don't seem right,.
Actually, you are getting charged for the same electrons moving thru your house over and over again.
What the $$ charge really is for though is the 'guy' with the whip (burning coal, falling water, nuke heat, etc) who has to push those lazy electrons to even stroll around and around thru the transformer and thru your house all day long.
If they are really whipped up and the meter is spinning like mad, one of those electrons is making good average forward speed, nearly 1 foot per hour. If not pushed to hard, they are real lazy, preferring to more or less just mill around frantically in one spot but barely moving forward to get to your house. They is gossipy little rascals though, tell a big crowd of them one thing at the transformer and the gossip travels to the electrons in the house almost at the speed of light.
Actually, three transformers. All major distribution is done with 3-phase and that requires three transformers.But yes, you can use a transformer to convert up or down. In fact, most transformers don't "care" which way they're being used.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
ya gotta quit throwing out those facetious one-liners, some people will beleive you <G>
He he he
Just because they want to make it personal,
doesn't mean you have to take it personal.
Hey, did you see the thread about corded impact screwdrivers,in the tool thread ?
Just because they want to make it personal,
doesn't mean you have to take it personal.
thread about corded impact screwdrivers,in the tool thread
Yep, found it, left a response.
Interesting question, The only "battery" that I am aware of is the ludington Pumped Storage System that is a huge man made pond in which water is pumped into from Lake Michigan during low demand times (at night, I think) and then released through turbines to generate electricity during peak demand times
the power is on a grid, a bunch of lines going everywhere. the power plant keeps the grid at a certain voltage, so if a line goes down, the power just jumps onto another line, and the power plant adjust to maintain that voltage on the grid. But a power plant by your house might not be the one that generation the power at your house. It could be hundred of miles away. depending on price of fuel in the area. So the power plant by your house might just be bumping up the voltage. they do monitor the grid constant, at all times. So they can tell if they have a problem
The rotational inertia of the drive or built up steam pressure or flowing water driving a big generator is the only problem, otherwise the load on the generator just is reduced.
Here is an example: The John Day dam on the columbia river drives a big DC high voltage link to SoCal. If that big line drops out, there is "lots of extra electricity" that needs to go someplace while the gates on the hydraulic turbines close (if load simply removed, the generator just speeds way up and destroys itself). That dam has a big field of transmission towers strung with stainless steel wire (high resistance) that the generator output is switched onto while the turbine gates are closing.
For that case, the 'extra electricity' goes into heating lots of steel wire for a few seconds..
Hope that helps your understanding.
>DC high voltage<
DC? For real? why DC?
Edison's still planning his comupance.
Family.....They're always there when they need you.
lots to read at http://en.wikipedia.org/wiki/Power_grid and the related links at the bottom.
Yes, direct current.
Lots of reasons, efficiency, fewer partial dischage effects, etc.
Big thyristor rectifiers and inverters now 'easy' to build compared to 50 years ago.
lots of easy google hits for more info.
http://en.wikipedia.org/wiki/Pacific_DC_Intertie
EDIT PS: see you already deceided to 'google'
Edited 12/19/2008 10:15 pm ET by junkhound
> Why DC?Several reasons, one big one being that frequency and phase does not need to be matched on a DC network, allowing it to serve to tie together widely separated AC networks.There is also a major reduction in inductive and capacitive losses on a DC transmission line vs AC. Not a big deal for a short haul of a couple of hundred miles, but significant for the extremely long transmission lines out west.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
"(if load simply removed, the generator just speeds way up and destroys itself)"I think you're forgetting that, from the earliest days, power generation turbines have had regulators built in to keep rpm constant irrespective of load in order to keep the generator producing at 60 Hertz.BruceT
Like Mike said, you can regulate the speed of a steam turbine or diesel engine pretty closely because you can close a steam valve or the injectors on a diesel pretty fast.
Cannot close the gates on a big hydro turbine that fast in case of a large load dump, hence the need for somewhere to dump the energy for a few seconds.
The grid itself varies off 60Hz slightly over short periods, but the average over time is controlled to exactly 60 Hz, (or 50Hz)
You ever wonder why a common electric clock uses 5W, when the kW-hr meter on your service entrance uses < 2W, even very old-old meters? ***
When electric clocks were first proposed for widespread usage just after WWI, the electric clock inventor needed to convince PoCOs to regulate frequency to better than 55-65Hz. PoCos needed to bill the 5W load on millions of electric clocks to give an incentive to control the average frequency to exactly 60Hz over a day, otherwise your power would be 55Hz to 65Hz depending on time of day and load. Thus, telechron made all their clock motors inefficient 5 W motors!
** my own house has mostly battery operated clocks, at a savings of approximately $5 per clock per year in electricity costs -- unplug all those laptop and cell phone chargers when not charging also, savings will buy a few beers<G>
These machines are synchronous generators. This means that if they are connected to the grid they are at 60 hz (1800 rpm for a nuke , 3600 rpm for fossil). If you don't supply enough steam or liquid water for hydro they motorize (tail waggin' the dog). Generally the controls manage to prevent that.>
When I was in school in the 60's one of the profs told this story. I think that we where discussing this right after the 65 blackouts in the NE.LG&E (Louisville) had 2 main tielines. One north to Indianapolis and one south to TVA.Lightning hit the Indy line and took out the northern part of it. There was a small town on that line on the LG&E side of the break.LG&E decided to get the extra power from TVA to supply that town. The protectors on the TVA line had been miss set. So that line dropped out.Instead of just dropping the city and then restoring power after a few minutes after the lines got reset they tried to be "good guys" and keep them on line.But they could not generate enough power. They where afraid that if they dropped voltage that there would be too many motors burning out.So they decide to drop frequency.Well that made them the odd duck.TVA ended up having to break all of their other ties, drop down in frequency so that they could resync to LG&E.Then bring them backup and resync all of their other ties..
William the Geezer, the sequel to Billy the Kid - Shoe
Years ago Purdue U had there own power plant. Later, as the campus expanded some of it was on public power.The story that I heard was that the power plant had two clocks, one connected to their power and the other to public power.Each Saturday night they would speed up or slow down their generators to get the clocks back in sync..
William the Geezer, the sequel to Billy the Kid - Shoe
It would seem to me that the electric grid is interconnected nationwide. If power isn't being used in one region it is diverted to other areas. Because as you said once it is generated it needs to be used and cannot be stored (in theory)
One thing I have posted in another thread is a website for an upstart company. Essentially uses electric car batteries as a storage container for generated electricity.
http://www.betterplace.com/
I'll agree with your presumption that the "grid" is probably interconnected nationwide. Assuming that is correct, I wonder how power plant A distinguish its product from power plant B. Is it one giant pool of electricity that just zips around looking for a need? Can you tell it's a cold, snowy night in NH?
The grid isn't just nationwide, it's North American wide. But if I recall correctly, it's broken up into regional chunks, which are usually connected by HVDC interconnects. This means that the 60Hz cycles don't have to be synchronized from region to region.
Rare on this forum is a question I can answer professionally (power engineer).
The output current drops in the power plant generator stator. The steam turbine responds by throttling down on steam flow by shutting its control valves. Less steam is demanded from the boiler or reactor. Less fuel is burned.
It's really not different than hitting a downhill on cruise control in your car.
So turn off those lights when you don't need them.
( As I write this I'm looking out the window at my Christmas lights; keeping turbines rolling and steam flowing. Oh well! )
To all a good night.
My recollection, relative to power loss/downed power lines, that there are in-line circuit breakers in the transmission lines that can/will trip under such circumstances - correct?
Jeff
Yes. That's for a fault. For example: if a tree falls across a power line the system reacts to it by tripping the nearest circuit breaker on an overcurrent trip. That keeps the rest of the grid on line and isolates the fault. Kind of explains why you see your power go off and then return quickly in a thunderstorm. The system is reacting to isolate the fault yet impact the least number of customers.The question asked earlier was about the response to a rapid drop in demand; like every cook turning their electric oven to off at the same time on Thanksgiving day. You could actually see a difference in steam flow from 2PM to 8 PM.More interesting to watch the fat guys loosen their belts and resume snoring following a good feed.
Edited 12/19/2008 10:41 pm ET by mike585
Thanks for shedding "light" on this Mike. I'm starting to get it now, I think.
When a load goes offline suddenly it can indeed cause problems for nearby generating facilities. Generators are controlled by a set of governors (at one time electro-mechanical but now all computerized) that automatically adjust steam/water/whatever input to respond to changing load. But they can't adjust rapidly enough to compensate for an extremely sudden major transmission cable outage, and so the generators may end up blowing a breaker of sorts and going offline. This can cause a cascading power outage.
It just depends on how sudden and how major the outage is, what other transmission lines can absorb, etc.
The details are a bit messy, as generators have to be synchronized in frequency and phase with others nearby, in addition to voltage.
Think about your gas powered generator.
The load on the engine from the generator is high when you have stuff running and the engine uses more fuel due to the bigger demand. When there is not as much demand, the generator spins free-er as there is less restriction (I guess the induction or the pull on the windings or something but if I ever learned it, I dont remember it)
The plants just keep on running but not as much pull. Depending on what the plant is, I recon they can cut back on stuff too. I do know in Philly, there are several natural gas and coal plants that run during high demand periods to add more power to the grid and are kept idling when there is not the demand and a friend was telling me these are expensive generators so that is why the utility companies like to balance out the peaks.
The production plants are shut down automatically. This is computor operated, with human backup>G<
Look at it this way ....
First, get on an exercise bicycle. Start pedalling. Keeping the same rate, start increasing the resistance; most bikes have an adjustment for this. To maintain the same rate, you have to peddle harder, in essence, burn more fuel.
The PoCo generator is like that. The more demand there is for power, the harder it is for the generator to turn. So, they add fuel, and turn on additional generators. If the load drops, so does their fuel consumption.
"Downed" power lines are eventually turned off. That is, either a safety device disconnects them, or a lineman does. This, oddly enough, is where your household wind / solar / back up generator / battery bank can create a danger for the lineman. He can't kill the power.
The idea behind having a "grid" is that each area is powered from more than one line. So, if one source goes down, the other can continue to supply power. Various devices are used by the PoCo to limit the 'out' area to a small area near the problem. This often means, btw, that several line crews will be working at different places, orchestrated by the main office, connecting and disconnecting things as ordered.