single phase, 3-phase power?????

Discussion in 'Electronics & Electrics' started by corpseface, Sep 27, 2006.

  1. corpseface

    corpseface (Banned or Deleted)

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    Doing electricity in physics at school at the moment....mum walked over whilst I was doing some homework, and she said 'ooo electricity! We have 3-phase power in this house, most people don't have that!' but when I asked her what the difference was, she didn't actually know, she said she just knew it was better :lol: :rolleyes: All I can find in my text book is 'Most domestic installations use single-phase power'

    So what is the difference??
     
  2. maxy0987

    maxy0987 Member

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    3 phase is usually used if you are going to have a big load off one of the phases, usually an airconditioner would be the reason a house gets 3 phase (like my house), then they balance the other two accordingly.

    Google should have some good info on the subject if you want to know more.

    EDIT: here is a linky for you to get started(ignoring the fact that it is american), read about half way down...
    http://www.allaboutcircuits.com/vol_2/chpt_10/2.html

    EDIT 2: try wikipedia...
    http://en.wikipedia.org/wiki/Three-phase_electric_power
     
    Last edited: Sep 27, 2006
  3. ywn

    ywn Member

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    to start with you get 415v insted of 240v but it is 3 single phase conection on one socket 120 deg (i think it is 120 degrese) out of phase.
    and yes it is posable to use each phase seprete .

    note i will have to go and find my tafe books and read some more about it and i will get back with more info .
     
  4. Rezin

    Rezin Member

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    corpseface

    corpseface (Banned or Deleted)

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    Thanks very much, answered my question :)
    I suppose the reason our house has it is due to the large ducted cooling/heating system?

    I suppose it's also the reason why my entire computer(that is, 24inch LCD, computer itself, 2 printers, a playstation, and 2 amplifiers+speakers systems) can run off one powerpoint(with a 10-socket powerboard)? I've wondered for a while howcome people always say not to run too many things off one powerpoint, when it seems to work fine at my house...

    Also our TV has the TV, xbox, set-top box, amplifier and VCR all plugged into the one powerpoint, never had problems there either...Or is it normal for single phase to be able to do that as well, just it can be risky?

    I assume that is cos of 3-phase power??....cool :)

    Thanks for the help! :thumbup:
     
  6. Porky_123

    Porky_123 Member

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    corpseface you seemto have misinterpreted the information.
    the reason you can you say all you computer stuff, and say all your home theatre stuff off one powerpoint is becouse in comparison to other machinery they draw very little amperige, you can pull upto 10amps through a single phase plug. 3 phase plugs have 4 pins too. one for each phase and a earth.

    uses for 3 phase are generially for industrial uses, for example large welders and compressors. they are often drawing upto 40amps, or 40amps + if they're hardwired devices.
     
  7. Annihilator69

    Annihilator69 Member

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    Yeah, you'll notice the earth Pin on the power plugs are alot bigger then the usual 10A ones, and won't fit into a 10A socket.
     
  8. ywn

    ywn Member

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    3 phase is just 3x single plase conection in one (it is most likly that out of the 3 phases that are runing alont the power pole that the house nextto you will be on an diffrent phase to your house to even out the load) but sing 3 phase uses an higher amp rating cable that alows for high current to be used .
     
  9. Goth

    Goth Grumpy Member

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  10. dakiller

    dakiller (Oscillating & Impeding)

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    I don't really like the small section on the power distributions side of the wikipedia article; it doesn't emphasize some points in it enough

    Normally in a single phase circuit you have an active and a neutral line and it all works as to how you'd expect like that, current flows out the active and into the neutral (and back again at 50 Hz for AC)

    Now transmitting electricity a long distance costs lots of money and we want to be able to do it as efficiently as possible, with our single phase system we have two wires for this one circuit

    In the power station where the electricity is generated on the physical generator it rotates on a shaft and so on this shaft we physically add 2 more windings spaced at 120 around the shaft and with these three circuits we now are generating 3 phases of electricity with 120 electrically between the phases, and if you draw the sine waves over time they lag behind each other and looks something like this

    With these 3 phases you would think to send them a long distance you would now need 6 wires, an active and neutral for each. You can quite easily simplify that to 4 now so they all share the neutral and we've saved some cost on distribution there

    But if you draw these phases on a phasor diagram and sum the vectors you end up with 0, that means that there is no current flowing through the neutral wire here at all, we don't need that either, we just tie all the return wires to each other at either end for our neutral point and that is it, saving a total of 1/2 the cost of running cables compared to a single phase system and there is a picture here that shows how it is connected

    Hope that helps
     
  11. Butcher9_9

    Butcher9_9 Member

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    thats what i think it is too

    does the 3 phase power go to you house and then get convertered or is that done at the sub stations (i know they lower the voltage from +110000v to 24000 or 11000v)
     
  12. -KoMoD0-

    -KoMoD0- Member

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    Last edited: Sep 27, 2006
  13. mortal

    mortal Member

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  14. nux

    nux Member

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    I think usually houses alternate phases, so your neighbours would be on a different phase to you.
     
  15. ywn

    ywn Member

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    at the sub station nd then the big box things tha are on some power pols rase or lover the voltage depending on how far you ae from the sub sstation
     
  16. Critical_Impact

    Critical_Impact Member

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    Thats like the one at Strathpine Community Center, they run a powerbox off that which runs about 50 computers at once :D
     
  17. Kyl3

    Kyl3 Member

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    Oh my god...everyone is an electrical expert... :(

    Each house, that has single phase, is on a seperate phase to their neighbour. this is done to balance the load at the alternator.


    Power stations step up the voltage to avoid losses (other reasons also, not worth explaining..lol) along the grid, it is gradually stepped back down along the way, power through your streets is usually around 10kv or so. and it's stepped down from there to 240/415 before it enters your house.


    Well explained dakiller also :D
     
  18. EBOB

    EBOB Member

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    that socket is a 3phase socket and nutrel socket
    which means theres NO EARTH LINE

    which is why you more commonly see 5 pin sockets

    3 phases neutral + earth


    also running everything off 1 power socket can b dangerous espically off 1 power board as the power board can only provide 2400w or 10a anything close to that or above that and ull melt something usually powerboard

    and the reason why nothing has blown is nothing 2 do with 3 phase power

    it just usually means u own a warehouse or ur 2 lazy 2 open a window thus u have aircon

    also its not 10kv its 110kv that the power station steps it up to

    and then its stepped down by using a BIG iron core transformer thats why ur local disrobution box sounds like its HUMMMMING welcome to the 50hz hummm

    there is thousands and thousands of dollars worth of copper in ther if ur game 2 try and steal it...... someone does atleast 1 or twice a yr either try or do seal the copper out of 1 its usually the earth link bar but try and get the tranny as well make sure ur mate takes a pic of ur body being burnt into a bit of charcoal
     
    Last edited: Sep 28, 2006
  19. -KoMoD0-

    -KoMoD0- Member

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    crazy bastards wearing rubber gloves :)
     
  20. Kyl3

    Kyl3 Member

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    So youre telling me that it's only 'ever' stepped up to 10kv?
     

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