high voltage power distribution question

Discussion in 'Electrical Forum discussion & Blog' started by kevincw01, Jun 2, 2012.

  1. kevincw01

    kevincw01 New Member

    Messages:
    20
    Location:
    san diego, ca
    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: Jun 2, 2012
  2. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    High voltage transmission is 3 phase... 3 hots, no neutral, no ground.
  3. kevincw01

    kevincw01 New Member

    Messages:
    20
    Location:
    san diego, ca
    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?
  4. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    988
    Location:
    NY State, USA
    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. drick

    drick In the Trades

    Messages:
    392
    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. kevincw01

    kevincw01 New Member

    Messages:
    20
    Location:
    san diego, ca
    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. kevincw01

    kevincw01 New Member

    Messages:
    20
    Location:
    san diego, ca
    Oops,didnt see your post rick. nevermind, and thanks everyone.
  8. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    988
    Location:
    NY State, USA
    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. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    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:
    With all due respect, may I suggest you stick to plumbing, volley ball, ANYTHING but electricity!
  10. DonL

    DonL Jack of all trades

    Messages:
    3,812
    Location:
    Houston, TX
    That is the correct answer, It is for Safety.

    You should win a Prize.
  11. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,529
    Location:
    North Carolina
    One conductor is one phase. There can't be three phases on one conductor
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