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  • mivey
    replied
    Originally posted by romex jockey View Post
    pretty good mivey...i'm wondering if the scada these days could do this?? ~RJ~
    IDK. Our SCADA does not do circuit modeling and analysis, just monitoring and control.

    Leave a comment:


  • mivey
    replied
    Originally posted by mbrooke View Post
    Thank you!

    Really like your method and choice of numbers.


    In what program did you model this? Just curious.
    WinIGS

    Leave a comment:


  • romex jockey
    replied
    pretty good mivey...i'm wondering if the scada these days could do this?? ~RJ~

    Leave a comment:


  • mbrooke
    replied
    Originally posted by mivey View Post
    You have to run the numbers.

    I ran a model for a 1 mile 115 kV transmission line with a 0.0001 ohm N-E connection to remote earth on the source end. Beyond that, I ran a 20 mile transmission line with a 0.0001 ohm N-E connection to remote earth at the source and load end. In the 20 mile section, I paralleled the earth with a giant conductor to short the earth resistance during a fault for case #1. For case #2 I then opened the parallel conductor to run fault current through earth only.

    If the earth is a perfect conductor, then we would expect most of the current to be in the earth instead of in the parallel path. But that is not the reality of how currents run through the transmission line and earth.

    The fault I created was a A-N fault at the end of the 21 miles. Clearly the earth path is resisting the current even though we have a negligible connection resistance to remote earth.



    With parallel path:

    In the 20 mile section:
    Phase A: 590 amps
    parallel path: 395 amps
    earth: 196 amps

    In the 1 mile section:
    Phase A: 590 amps
    earth: 590 amps



    Without parallel path:

    In the 20 mile section:
    Phase A: 430 amps
    earth: 430 amps

    In the 1 mile section:
    Phase A: 430 amps
    earth: 430 amps
    Thank you!

    Really like your method and choice of numbers.


    In what program did you model this? Just curious.

    Leave a comment:


  • mivey
    replied
    Originally posted by mivey View Post
    Not quite. If we could parallel enough dirt at no cost then we would have a perfect earth conductor. The real circuit does not behave that way. Nature tends to the lowest energy state and simply will not reach the whole earth for the transmission line. The current tends to maximize nearer the transmission line rather than going through China. This limits the parallel dirt and the net dirt resistivity becomes a significant factor.
    Not to say nothing runs in the China dirt but it might not even be measurable. i.e., The closer dirt gets much more current than the far dirt so soil resistivity is a significant factor.

    This is modeled using Carson's Equations.

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  • mivey
    replied
    Originally posted by mbrooke View Post
    By how much though?
    You have to run the numbers.

    I ran a model for a 1 mile 115 kV transmission line with a 0.0001 ohm N-E connection to remote earth on the source end. Beyond that, I ran a 20 mile transmission line with a 0.0001 ohm N-E connection to remote earth at the source and load end. In the 20 mile section, I paralleled the earth with a giant conductor to short the earth resistance during a fault for case #1. For case #2 I then opened the parallel conductor to run fault current through earth only.

    If the earth is a perfect conductor, then we would expect most of the current to be in the earth instead of in the parallel path. But that is not the reality of how currents run through the transmission line and earth.

    The fault I created was a A-N fault at the end of the 21 miles. Clearly the earth path is resisting the current even though we have a negligible connection resistance to remote earth.



    With parallel path:

    In the 20 mile section:
    Phase A: 590 amps
    parallel path: 395 amps
    earth: 196 amps

    In the 1 mile section:
    Phase A: 590 amps
    earth: 590 amps



    Without parallel path:

    In the 20 mile section:
    Phase A: 430 amps
    earth: 430 amps

    In the 1 mile section:
    Phase A: 430 amps
    earth: 430 amps

    Leave a comment:


  • mivey
    replied
    Originally posted by GoldDigger View Post
    The net resistance is indeed not zero, but most if not all of that resistance is the term associated with the earth electrode resistance rather than the distance to the uniground point. If the two electrodes are within each others' sphere of influence the overall resistance will be more complicated. That can lead to the appearance of the net resistance depending on the earth path length.


    Sent from my XT1585 using Tapatalk
    Not quite. If we could parallel enough dirt at no cost then we would have a perfect earth conductor. The real circuit does not behave that way. Nature tends to the lowest energy state and simply will not reach the whole earth for the transmission line. The current tends to maximize nearer the transmission line rather than going through China. This limits the parallel dirt and the net dirt resistivity becomes a significant factor.

    Leave a comment:


  • mbrooke
    replied
    Originally posted by mivey View Post
    They are not perfect conductors. Internal reactance influences the path.
    By how much though?

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  • mivey
    replied
    Originally posted by mbrooke View Post
    Probably not, but it would be low.


    Is it exceptionally high reactance that does it?
    They are not perfect conductors. Internal reactance influences the path.

    Leave a comment:


  • mbrooke
    replied
    Originally posted by romex jockey View Post
    so....i just gotta ask...am I looking at one huge poco MBJ?~RJ~
    Notice the wire from the bushing, into the CT, into some flexible conduit and down into the rock- same for the primary:


    https://youtu.be/bV2pMeKdkQM?t=142
    Last edited by mbrooke; 06-16-19, 08:09 PM.

    Leave a comment:


  • mbrooke
    replied
    I'll find you a better vid, but notice the wire from the 4th MV bushing going down into conduit which disappears into the soil:


    https://youtu.be/l53NrBvlorQ?t=180
    Last edited by mbrooke; 06-16-19, 08:07 PM.

    Leave a comment:


  • mbrooke
    replied
    Originally posted by mivey View Post
    #1:
    At the sub the N conductor is at the neutral point. A A-N fault drags A to the neutral point and the B-N and C-N arrestors see P/sqrt(3) volts (line-neutral).

    Far away the N conductor has a large impedance that allows it to float from the neutral point. An A-N fault drags N to A and the arrestors see B-A and C-A voltage (line-line).

    #2:
    The earth path has impedance.
    True.

    Though much less so for an MGN, right?

    Leave a comment:


  • mbrooke
    replied
    Originally posted by mivey View Post
    Dirt is matter and has electrical properties. Our currents travel in a limited amount of the earth's total matter.
    Why though? Does it not take all paths? I've heard people measuring 50 cycle power here in 60 over seas in earth driven electrodes.

    Leave a comment:


  • mbrooke
    replied
    Originally posted by mivey View Post
    mbrooke,

    Do you think if we had a copper wire as big as the earth we would get full benefit of all of that paralleled copper mass? We don't at a smaller scale do we?

    The fact is the currents travel in a peculiar manner in the wire and in the earth.
    Probably not, but it would be low.


    Is it exceptionally high reactance that does it?

    Leave a comment:


  • GoldDigger
    replied
    Originally posted by mivey View Post
    If you parallel enough dirt you can drive the net resistance to zero but the dirt has resistivity and the net impedance we see is not zero.
    The net resistance is indeed not zero, but most if not all of that resistance is the term associated with the earth electrode resistance rather than the distance to the uniground point. If the two electrodes are within each others' sphere of influence the overall resistance will be more complicated. That can lead to the appearance of the net resistance depending on the earth path length.


    Sent from my XT1585 using Tapatalk

    Leave a comment:

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