Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Modeling E and B field of power lines

  1. Nov 1, 2016 #1
    I’m confused:

    Long distance electric power lines are modelled with distributed impedance and are therefore modelled as transmission lines.

    Long distance electric power lines are considered to be a two wire line (for a single phase of the electric power line anyway). What other types of transmission line could it be? (see page 5 of the following pdf for an example of the two wire line and other types of transmission line: http://www.sonoma.edu/users/f/farah...onLines/TransLine/TransmissionLinesPart_I.pdf)

    Two wire transmission lines have TEM mode where electric and magnetic fields are orthogonal to each other and both are orthogonal to the direction of propagation

    Long distance electric power lines have a B field which circles the power line (as per ampere’s law) and the E field is parallel to the axis of the transmission line.

    So I am confused: If long distance power lines are really two wire transmission lines with TEM mode, then the E field can’t be axial and the B field can’t circle the power line. On the other hand the B field does circle the power line as per ampere’s law and the E field is axial.

    (sorry for the cross post, meant to post this here)
  2. jcsd
  3. Nov 1, 2016 #2


    User Avatar
    Gold Member

    The E-field links the two conductors together and so it is at right angles to the conductors. The B field of each wire is of opposite rotation, so it looks like a figure of eight, with a strong field between the wires.
  4. Nov 1, 2016 #3


    User Avatar
    Science Advisor

    Welcome to PF.
    Long distance lines are three phase. Because the directional sum of currents in the three wires is zero, and the average voltage is zero, the external EM fields away from the line all tend to cancel. The three phases make a "single line" that is modelled as a simple transmission line, quite independent of conductor count.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted