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

Electrical distribution sysytem

  1. Apr 26, 2015 #1
    in 11kv /230 v delta /star connected distribution transformer neutral not connected to earh,then if we touch the one phase (ex:R phase)of secondery line, shall we get shock or not?
  2. jcsd
  3. Apr 26, 2015 #2

    jim hardy

    User Avatar
    Science Advisor
    Gold Member


    The circuit is completed by distributed capacitance of other two phases to earth.
    Current might amount to goodly fraction of an amp.
    Or it might be too little to feel.
  4. Apr 27, 2015 #3
    Thanks.i am new to this forum.
  5. Apr 27, 2015 #4
    If the ground is neutrely charged .
    And if The phase line is positively charged.
    The distribution Transformer neutrel not grounded. Then we touch the line
    From standing the ground what happens, will get full shock.
  6. Apr 27, 2015 #5

    jim hardy

    User Avatar
    Science Advisor
    Gold Member

    Full shock ? no.

    There is capacitance from all the wires and equipment in your distribution system to earth. How much depends on the size of the system.
    Currents flow through that capacitance from each phase to earth.

    When everything is balanced those three currents add to zero, of course .

    When you grab a phase you place yourself in parallel with one of those distributed capacitances.
    So voltage across that one drops and the others rise.
    How much current flows ? I'd say maximum would be 230V/Xc

    There might be a little contribution from interwinding capacitance in the 11kv/230v transformer.
    I've measured around 0.3 amp on a 480 system in a power plant.
    That'd be a good shock and might be lethal but it wouldn't cause an explosion.

    IEEE standard 241"The Green Book" recommends the neutral be earthed with a resistor approximately equal to Xc.
    A good industrial reference book will have formulas to estimate distributed capacitance.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook