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Thread: high voltage power distribution question

  1. #1
    DIY Junior Member kevincw01's Avatar
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    Default high voltage power distribution question

    My neighborhood has a power substation attached too it and there are some very large poles that carry the power to/from from the substation. Each pole has 3 physically separated wires (like this http://imgur.com/uIuUv.jpg )

    The other day we had a storm that knocked down a bunch of these metal poles leading away from the substation. I noticed that as a temporary solution the power company installed jumper cables connecting the 3 wires (top to mid and mid to btm). When they did this our power was restored (15hrs later). This confused me because I had always thought that the 3 wires were similar to residential wiring amd represented hot, neutral and ground. But this solution appears to show that they are 3 seperate "hot" sources. Can anyone enlighten me, Im a curious guy...
    Last edited by kevincw01; 06-02-2012 at 04:21 PM.

  2. #2
    Plumber jimbo's Avatar
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    High voltage transmission is 3 phase... 3 hots, no neutral, no ground.

  3. #3
    DIY Junior Member kevincw01's Avatar
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    I thought the purpose of 3 phase was to consilidate 3 power sources on one conductor(each out of phase). Why are the separate for transmission? Im also wondering why they joined them as a temp fix?

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    Licensed Electrical Contractor Speedy Petey's Avatar
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    This is an extremely deep subject.
    Three phase is three hots. Single phase is two (or even one) hots.

    Utilities use the earth as a reference, NOT as any kind of safety return or backup.

    The VERY high primary voltages are used to transmit the power over very long distances. The three primary lines are then stepped down to usable levels with transformers.

  5. #5

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    Yes each of the 3 conductors is out of phase by 120 degrees. Added together you get 360 degrees which is one rotation of the source generator. It is a single power source producing power on 3 conductors. These conductors cannot be bridged together as it would short circuit the generator so I'm not sure what you are seeing.

    Your house is wired to only one of the three phases. That voltage has been stepped down to 240V so you can use it. The transformer outside your house also has a center tap on the 240v single phase power going to your home. This is what you think of as the neutral. Any device connected between the center tap and either one of the other two conductors gives you 120V. This is called single split phase power.

    Your grounding conductor in your electrical outlets is just a second neutral. Its purpose in life is to provide a second low resistance path for electricity to follow. In the event of a device failure we hope that the power will default to follow the grounding conductor back to the panel and trip the breaker. The ground wiring never leaves your house.

    -rick

  6. #6
    DIY Junior Member kevincw01's Avatar
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    Ok so I did some research on 3 phase distribution and understand the 3 conductors but I still cant understand why they connected all phases together to temporarily restore power while they repaired the poles.

  7. #7
    DIY Junior Member kevincw01's Avatar
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    Oops,didnt see your post rick. nevermind, and thanks everyone.

  8. #8
    Licensed Electrical Contractor Speedy Petey's Avatar
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    Quote Originally Posted by kevincw01 View Post
    Ok so I did some research on 3 phase distribution and understand the 3 conductors but I still cant understand why they connected all phases together to temporarily restore power while they repaired the poles.
    They probably did that and also grounded them while they work on them dead. This way any uncalled for re-power would trip a breaker.

  9. #9
    Plumber jimbo's Avatar
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    In about an hour, you went from this """ I thought the purpose of 3 phase was to consilidate 3 power sources on one conductor(each out of phase). Why are the separate for transmission? Im also wondering why they joined them as a temp fix? """"


    to this:
    Quote Originally Posted by kevincw01 View Post
    Ok so I did some research on 3 phase distribution and understand the 3 conductors but I still cant understand why they connected all phases together to temporarily restore power while they repaired the poles.
    With all due respect, may I suggest you stick to plumbing, volley ball, ANYTHING but electricity!

  10. #10
    Jack of all trades DonL's Avatar
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    Quote Originally Posted by Speedy Petey View Post
    They probably did that and also grounded them while they work on them dead. This way any uncalled for re-power would trip a breaker.
    That is the correct answer, It is for Safety.

    You should win a Prize.
    Theory only works perfect in a vacuum.

    Cyber Security Protection for Windows C:\ > WWW.WinForce.Net

  11. #11
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by kevincw01 View Post
    I thought the purpose of 3 phase was to consilidate 3 power sources on one conductor(each out of phase). Why are the separate for transmission? Im also wondering why they joined them as a temp fix?
    One conductor is one phase. There can't be three phases on one conductor

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