Power generation

Discussion in 'General Electronics Chat' started by markdem, Dec 3, 2013.

  1. markdem

    Thread Starter Member

    Jul 31, 2013
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    Hi All,

    I am looking for some information about power generation. (Conventional power plant type, not HHO some other crap).

    I would like to know some details like;
    -How does the power generator ramp up\down output depending on load?
    -How does the generator know\sense the load?
    -If I plug in a xkW motor into a power point, will the power plant burn an extra y amount of coal?
    -What happens if output if much greater then demand (think earth hour)?
    -What stops someone, or something, injecting power into the grid that is out of phase, over voltage and\or wrong frequency?

    I have looked on the web, but I get simple answers like "steam drives turbine - make electricity - you use it". I also don't want to know or care about "The Smart Grid". I would like to know what happens now.

    Anyone know of any websites or books on this subject.

    Thanks
     
  2. crutschow

    Expert

    Mar 14, 2008
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    The power to the turbine (steam or gas) driving the generator is throttled up\down.
    The grid voltage is used to determine the load. If the voltage is slightly low then the generator is throttled up, if the voltage is slightly high the generator is throttled back.
    Yes.
    Then the generator is throttled back.
    If the injected power is not the correct voltage, phase, or frequency, then the grid will look like a short circuit to the injecting source and the injecting source will look like a short circuit to the grid. This will blow a fuse and/or burn the source out. For example, when a generator at the power plant is brought online, its frequency and phase is carefully matched to the grid using a synchroscope before the switch is closed to connect it to the grid. Otherwise the resulting large transient currents would likely seriously damage the generator along with some splendid fireworks. :eek:
     
  3. WBahn

    Moderator

    Mar 31, 2012
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    You can take it pretty much as a given that if you fight the grid, the grid will win.

    In the 1970's ('75?) a power plant in Utah made a mistake in setting up their synchronizing circuits (something that couldn't happen today but things where much more manual back then) and they were actually out of phase when they brought in the contactors to put the generator on the grid. Things when wrong real fast, including throwing very large pieces of the generators through the roof of the power plant building. Amazingly, no one was killed, though I believe there were some rather serious injuries.
     
  4. JDT

    Well-Known Member

    Feb 12, 2009
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    Its interesting to note that the power grid cannot store power. All the power generated has to be used immediately. If you switch on something electrical in you house some power station somewhere has to immediately start generating more power.

    Luckily, the rotating turbines at the power station have inertia. So this is a form of power storage and can smooth out the very short-term fluctuations.

    With renewables like solar or wind, the grid-tie inverter automatically handles the synchronization to the grid.
     
  5. TheComet

    Member

    Mar 11, 2013
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    So this brings in an interesting question: What happens if everyone in the country were to simultaneously turn off every electronic device in their house, wait a minute, and then simultaneously turn everything back on again?

    An awesome way to troll the power stations.
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    A split second after turn-on, trips would probably operate at the power plants and shut down the grid :D.
     
  7. wayneh

    Expert

    Sep 9, 2010
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    Reminds me of taco night in the dorm. An hour after dinner, there was no water pressure in the building, due to everyone flushing at once. :eek:
     
    GopherT likes this.
  8. markdem

    Thread Starter Member

    Jul 31, 2013
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    Thanks for the reply guys. But still, the thirst for more knowledge is still there.
    As the TheComet suggested, what would happen if there was a large short term difference in load? I guess a good example would be a new factory powering on something that has a high inrush current? A aluminium smelter would be a good example. What about the other way, when the smelter shuts down? I think the problem I have with understanding this is that I know it takes time for a fire to heat water to make steam. It is not a instant change. Do they "store" the steam in some form of "capacitor" ready for use? Is there some form of other capacitance in the system that helps store power?

    I would love to visit a power station one day and talk to some engineers, but I guess that would not be allowed as they would think I am some kind of terrorist. Seems to be the way everyone thinks these days :(
     
  9. WBahn

    Moderator

    Mar 31, 2012
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    The high pressure steam itself stores a lot of energy, both in the form of heat and in the form of pressure -- that IS the energy that is converted to power by the generator, via the turbine. That energy is readily accessible very fast and as a heavy load comes onto the generator the governors open the values more to access more of that energy quickly. Similarly, when a heavy load comes off, the governors close the valves some so as to not access as much energy so that they minimize the overspin of the generators. At the same time, other systems are compensating the fuel flow to the boilers (or whatever the comparable action is for that type of power plant) so as to more closely match the longer term average requirements. For transients that are either small enough or fast enough, the steam has the capacity to absorb it and the fuel flow to the boiler is effected only minimally and possibly not for some time.
     
  10. crutschow

    Expert

    Mar 14, 2008
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    Generally users of large amounts of power don't shut down or start up rapidly. They start up in stages to avoid large sudden changes in power usage. Also the grid is typically fed by several large power plants that are better able to balance the load and adjust to large changes in power.

    As far as steam "storage" the hot water in the boiler acts like a large sink and can instantly generate more steam for a short period to take up sudden changes, time enough for increased fuel to the fire to catch up with the increased steam load.
     
  11. Tesla23

    Active Member

    May 10, 2009
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  12. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Or in the case of the 15 Hydro stations we have, just open another sluice gate.;)
    Max.
     
  13. tinkerman

    Member

    Jul 22, 2012
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    Steel smelters create large swings in power as the electodes penetrate into the molten metal. Mines have similar swings with their elevators. At one time they used synchronous motors to help control the voltage so other customers weren't distrubed so much be the swings in power. Today they use static var controllers which are almost instantaneous in response. But that still doesn't completely remove the effects. Or the utility might limit useage or times of the day. We have a steel mill in this locality and if you watch carefully during the wee hours of the day you will notice a flicker with incandescent bulbs, especially it it's operated through brightness control. That's probably because the steel mill is hitting it hard while everyone is sleeping. Naturally the size of the grid has a great impact too. Lots of generators and many lines buffer the effects.
     
  14. crutschow

    Expert

    Mar 14, 2008
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    Are you talking about over-excited synchronous motors being used to help correct the power factor? That could eliminate perhaps about 10-15% of the total motor load current as compared to an induction motor, not a large amount but somewhat helpful in reducing voltage drop from the load.
     
  15. RichardO

    Well-Known Member

    May 4, 2013
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    A coworker told about when he worked in a lumber mill in northwestern US. The trees they cut up were huge -- something like one tree per truck load.

    They would warn the power company when they were about turn on the motor to start cutting so an extra generator on line just for them!
     
  16. WBahn

    Moderator

    Mar 31, 2012
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    Many large power users actually build their own powerplant for reasons like this (among others). Coors (whose main brewery is within walking distance of campus here) has their own power plant. It let's them to make allowance for these kinds of foreseeable transients. It also makes it so that the penalty for non-unity power factor correction isn't as big since the line losses are predominantly very local. Last I heard, which was nearly twenty-five years ago, they didn't produce enough total power for all their needs, but they tried to run their generators near their peak efficiency full time and sold back power during their off-peak usage periods.
     
  17. markdem

    Thread Starter Member

    Jul 31, 2013
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    Thanks for all the reply's guys, clears a few things up for me.

    Thanks
     
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