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I Does current flow back to the power plant through ground?

  1. Apr 10, 2017 #1
    Hi.

    I fear I might not have understood some fundamental concepts about electric power transmission. So we have "neutral" which is brought to earth potential. Does this mean the electrical circuit from the power plant over highly conductive aluminium cables to my home closes back to the power plant through ground? I'd assume (dry) soil should have huge electrical resistance, is this wrong?

    I also read that the first transatlantic telegraph cable from 1858 was just a single electrical wire and the circuit was closed through ground across the ocean, which I find equally hard to believe.

    Am I missing something here? Is Earth a much better conductor than I thought? Or doesn't there have to be a physical current if ground at my home is at the same potential as it is at the power plant?
     
  2. jcsd
  3. Apr 10, 2017 #2
    'Earth' is by definition a grounded state for some parts of an electronic device.
    The device works by shoving electrons around in an 'above ground' state.
    The Earth as a whole is so massive compared to say some computer, that the conduction of electrons within the ground is of no significance.
     
  4. Apr 10, 2017 #3

    russ_watters

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    It's wrong, but not for the reason you think.

    First of all, alternating current alternates. It means even the "hot" wire has electricity traveling in both directions.

    Next, power plants use 3-phase power, which doesn't have a neutral, and the electricity oscillates in and out on the three wires.

    And last, the actual earth isn't (usually...) used as a return path, it is just used as a common reference for 0 voltage and an emergency dump if there is a problem. The actual return path is through the neutral....except insofar as the neutral and "ground" wire are connected.

    But in terms of your house to the transformer supplying it, yes, the "neutral" and "ground" are connected and are the "return" path of the electricity.
     
  5. Apr 11, 2017 #4
    I have worked on a number of fairly large standby gensets, and they were always 3 phase Y-connected with a grounded center point.
     
  6. Apr 12, 2017 #5
    What do you mean by "of no significance"? In the transatlantic telegraph cable, is there an electron flow through the ground from one continent to the other, or is it more like electrons get dumped into the ground at one end and drawn from the ground at the other with no real current equalizing this imbalance?
     
  7. Apr 13, 2017 #6

    davenn

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    this is incorrect, you misunderstand the process

    you are forgetting that in an AC ( mains power or any other AC circuit -- audio/RF) circuit the electrons don't really go anywhere, they just oscillate about a point in the cable. So there is NO loss of electrons at one end of the link and build up at the other end of the link


    Dave
     
  8. Apr 13, 2017 #7
    True. But could I (theoretically) find a path in the ground between the continents along which the electrons oscillate in phase with the cable, so the circuit is closed like a usual AC circuit?

    Also, with no capacitance or inductance present, the AC resistance in a circuit is the same as DC resistance. And I can still only imagine that the resistance of the ground between two continents must be enormous.
     
  9. Apr 13, 2017 #8

    davenn

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    have a read of this article for practical SWER power transmission

    http://stonepower.se/Images/SWER.pdf
     
  10. Apr 13, 2017 #9
    I see lightning frequently. I am fairly confident charged particles are moving about. The charges will balance eventually. Lightning shoots both ways. Electrical forces are much stronger than gravity. I can recall several instances when I tried to throw away a thin sheet. Instead of dropping into the waste bin it flew sideways and stuck to a stack of plastic totes. A large charge build up could pull (or repel) clouds and/or exchange ions with space.

    Ground wires in a house usually connect to the plumbing which connects to the water table. The water table is also a conductive path to the sub-station near you. I am not sure about areas outside of USA. Running the ground wire into dry dirt would not be up to code here.

    AC electricity is more like waves in a pond and not like water delivered your faucet. The electrons in the wire are moving back and forth. Direct currents can move up or down a wire that is also carrying AC current.
     
  11. Apr 14, 2017 #10

    Svein

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    It used to be that way. But modern plumbing uses plastic, not copper...
     
  12. Apr 14, 2017 #11

    CWatters

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    Current flow in a balanced three phase circuit...

    https://en.m.wikipedia.org/wiki/File:3-phase_flow.gif
     
  13. Apr 14, 2017 #12

    CWatters

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  14. Apr 15, 2017 #13

    vela

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    Soil may have a high resistivity, but resistance depends also on the length and cross-sectional area. Earth is so big, the effective cross-sectional area is so large, the resulting resistance is low. Another way of thinking about it is you effectively have a bunch of high resistances in parallel, which results in a low resistance.
     
  15. Apr 15, 2017 #14
    I would like you to clear up this statement "But in terms of your house to the transformer supplying it, yes, the "neutral" and "ground" are connected and are the "return" path of the electricity."
    As far as I know the return path is not through the earth.
    If any current flows through the earth this is detected as a fault and safety circuits cut off the supply.
    Do you mean that the earth (ground) and neutral are connected at the transformer/ supply station??
     
  16. Apr 15, 2017 #15

    rcgldr

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    To follow up on Dr. D's post:

    This "centers" the 3 phase voltage about ground.

    In my area of the USA, the final step down transformer (6900 volts down to 220 volts) has one input terminal connected to a stepped down voltage (via other step down transformers) from one of the three phase sources and the other input terminal connected to earth ground. The output side of the transformer outputs 220 volts center tapped to earth ground. This results in both "halves" of the 110 volt supply using one output terminal and ground, or 220 volts using both outputs. At the house, the circuit breaker box has an earth ground used for the "neutral" on either 110 volt supply, and an additional grounded wire used for the third connector for the in house wall sockets. There should be no current flow in that third socket ground wire, while the "neutral" in my home shows about 2 to 5 volts AC depending on usage.
     
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