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Power Transmission

  1. Jun 7, 2010 #1
    I had a question about power generation that was confusing me for awhile, I hope someone can clear it up.

    A specific amount of power is generated by the power plant. If I am not using all the power that I can use, where does it go?

    is all the power always in use?

    if it is not in use, then how do they conserve it and "send it" when required.

    for example,

    1. I turn my light on, I am using power X

    2, I turn my light off I am using no power

    Is that power "X" still in use (ie. the electric distribution uses the non used power that it has)?
  2. jcsd
  3. Jun 7, 2010 #2


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    With just a light you are not going to see much load change on the generator. For large loads, like say power used in iron smelting, there will be a change in frequency when it is switched on and off. If you turn off a large load, the freq. will increase a little and when you engage a large load, the freq. will decrease a little. This is sometimes call rubber-banding. This is why loads on a system are monitored so that adjustments of the generators output can be made with automatic generation control software.
  4. Jun 7, 2010 #3
    The power company monitors usage & adjusts the fuel consumption accordingly. When the system is regulated at a specific load power, say 50 MW, the automatic voltage regulator keeps the nominal voltage constant & the frequency at 60 Hz (50 Hz elsewhere). When you add a load, the frequency slightly drops, as does the voltage. More fuel is burned in order to maintain constant voltage & frequency. When the extra load is removed, the voltage & freq slightly increase, so that the regulator reduces the fuel burned, restoring the niminal voltage & frequency.

    The generators in neighboring counties, cities, & states are tied together forming a grid. Their rotational kinetic energy is huge when combined. Your lamp is a tiny fraction of the total load. The rotational energy keeps the voltage & frequency steady for the short time needed for the fuel rate to be adjusted.

    Did that help?

  5. Jun 7, 2010 #4
    So in other words, the power generated is not constant. It keeps adjusting according to how much is in use?
  6. Jun 7, 2010 #5


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    So in other words, the power generated is not constant. It keeps adjusting according to how much is in use?

    That is right. The power station tries to generate a constant voltage. The power used from this voltage depends on the load.

    When the generators are lightly loaded (not supplying much current) they are easy to turn, so the accelerator pedal on the driving engine can be lifted to a position that uses less fuel.
  7. Jun 7, 2010 #6


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    When looking at the grid of a particular area (i.e a company operated area), you add up all the power going in to or out of the tie lines to other areas and (if you are not selling or buying where your generators are being ramped) the error between zero power flow and the actual flow (+ for in and - for out) is call the Area Control Area (ACE). It is usually required that this value crosses zero x number of times in a given hour. I can't remember what x is now. Anyway when determining how to control the generators to do this, frequency is also included in the calculation. It's a bias factor in the equation.
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