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

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

  1. grrrr

    grrrr Member

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    The most common high voltage lines are 10kV, 11kV, 14kV. They are indeed stepped down to 415 + neutral for your street, alternating houses are usually on different phases.

    EBOB you are incorrect.

    That pic of the socket has 4 pins which = 3 phase and earth. NO NEUTRAL.
    There are plenty of machines that run on 415VAC and do not require the neutral. The earth connection is required on all GPO sockets regardless of the number of phases.


    EBOB you are correct.

    There are more machines that use 415VAC and 240VAC (hence requiring the neutral) and thus use 5 pin connectors.
     
  2. Pyro

    Pyro Member

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    The large conductors you see on the big mofo powerlines (in NSW owned and operated by TransGrid) generally run on 330kV, 132kV, and more rarely, 500kV, and these feed directly to distributors such as EnergyAustralia, Country Energy, etc, as well as directly to industy, such as an aluminium smelter at Tomago. Just out of interest, Tomago aluminum smelter consumes around 10% of NSW's energy, and around 3% of Australia's energy goes straight to Tomago (around 850MW).

    3-phase power explains why on a big powerline like http://en.wikipedia.org/wiki/Image:Three_Phase_Electric_Power_Transmission.jpg these, you have 3 big conductors (plus the one or more likely two smaller earth wires at the very top, generally to guard against lightning). Some of these also have 6 conductors (plus the two earths) so as to carry two circuits.
     
  3. JET-RS

    JET-RS Member

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    lol, was speaking to a guy at a warehouse we keep our stock. Said when he was younger they'd break into telstra exchanges and fill up the boot of a car with the fat copper wire. Couple hundred kilo's in the boot would lower it asif towing a caravan or something.
     
  4. fo3

    fo3 (Taking a Break)

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    Yeah I have three phase power at my house. A lot of houses in perth do, mainly because a lot of people have/used to have bore pumps. Three phase is required for large motors, eg bore pumps and air cons or commercial/industrial stuff, because bore pumps were so popular here, nearly all the old suburbs of perth have three phase.
    Basically as said before, three phases run down most streets in case it's required, the standard hook up is to only single phase though. Anyone who needs it, gets it, otherwise the three phases are load shared, ie alternating over three houses.
    It came in handy a few weeks ago here, the main supply to our house dropped down to 70Vac, but the rear of the house was on a different phase so we could get everything back on line. The woman behind us was single phase, which happened to be on the 70Vac line. She wasn't happy when she realised us and our imeediate neighbours were uneffected. She had her own blackout and had everything stop working until the phase was restored.
     
  5. Symon

    Symon Castigat ridendo mores

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    That socket that was posted is three phase + earth, there is no neutral. You can't run computers (or any single phase load) off that unless you use a transformer of some kind.

    The standard voltage for Australia is 230/400 (single phase/three phase), note that this has been lowered from the previous standard of 240/415. For transmission voltages it's 3300, 6600, 11000, 22000, 33000, 66000, 132000, 275000, 330000, 500000 three-phase. Sure you can use others, but generally speaking it will cost you more. Underground mines use 1000 and 1100 volt systems, and it costs them a damn fortune for equipment. The Basslink project uses 400000V DC.

    3 phase supply is quite rare unless you have a big house or some other special requirement like pumps like fo3 mentioned. 2 phase supply is becoming more common since people are putting in big airconditioners these days.
     
  6. dazzawul

    dazzawul Member

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    Speaking of the 2400 watt limit on power sockets...

    I accidentally hung about 7-8 machines at a lan, including CRTs on All of them, off of the one powerboard, there was a bang, and all the machines cut off, there was a dumb idea..

    And three phase is good for industry cause they love motors running off of it (on single phase theres a surge of torque every half rotation which is a bitch on the axle, great for the lathes in the metalwork rooms :p )

    Cheers lads.
     
    Last edited: Sep 30, 2006
  7. G`Dave

    G`Dave Member

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    The humm you'll hear coming from a power pole transformer is 100Hz, twice the fundamental. The humm occurs when the flux throught he transformer core ramps up and changes the shape of the core, this happens when the flux ramps up in one direction, and again when it ramps up in the other direction, so twice per cycle. Hence 100Hz, not 50.
     
  8. OP
    OP
    corpseface

    corpseface (Banned or Deleted)

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    Wow, just read it all, very interesting :)

    Another question -
    We have a big box thing in a cupboard, which has the circuit breaker thingos in it. There's 3 of them and a big thing, and if one of them trips, it only cuts off some of the electricity in the house, some things will still work. e.g. once my brother soldered through the power cable of my soldering iron :rolleyes: and it tripped the thing, which turned off the microwave and computer but the oven and fridge were still turned on. Does this mean our phases are all split up?

    I think dad said once we had one phase for the ducted heating/air conditioning, one for the pool chlorinator thingo + whitegoods, then one for lights and general powerpoints etc.

    I could be totally wrong though, it's a vague memory. I'll ask him again when he's home.
     
  9. grrrr

    grrrr Member

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    The one of two things that tripped. A circuit breaker or a RCD. Most houses are wired with single phase, but with multiple circuit breakers. Each circuit breaker will be rated at 10A (ish)* and supply various rooms etc.

    RCDs are generally just used to (semi)** protect general purpose outlets. Which basically means it doesnt protect the lighting, water heater, or air con circuits.

    * the water heating system or the air con may have larger breakers 15A or something.

    ** RCDs trip when they detect 30mA (standard for houses) of current leeking to earth instead of going from active to neutral. They may stop you from dieing if you touch something live and the electricity travels through you to ground somewhere. They will do nothing to stop you from dieing if you touch the active and the electricty travels through you back to the neutral. Ironically 30mA @240VAC is plenty enough to kill you anyway.
     
  10. rickbishop

    rickbishop Member

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    Just to add to Symons advice, it is only 415v appliances that use the 4 pin 3phase socket. Large industrial motors, heaters, and refrigeration (the kinds of stuff that would NEVER be in a house).

    Much more common in commercial applications is the 5 pin 3phase. It has 3 phases, earth, and a common neutral. The phase to phase voltage is 415v, but the phase to neutral voltage is 230v, so with the appropriate breakout board, you can use it to power 230v appliances.

    Some houses these days have a 3phase supply, primarily due to the increased use of chunking great hot water systems and air conditioners. Whilst relatively rare, it is becoming more common for the hot water system to have it's own phase, the A/C to have it's own phase, and the rest of the house on the third phase.
     
  11. banshee

    banshee Member

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    And just to throw something else into the subject. As you increase frequency, the mass of the core required for efficiency reduces. As a result, all aircraft A/C systems run on 115V 400Hz, since this is the best compromise between less weight in txfrs vs increasing expense with frequency.

    Oh, and from when I did my elec eng assoc. dip., the power generated at power stations is more likely to be 12 phase whuck is the split into 4 sets of 3 phase for transmission. High voltages are used for long distance transmission due to ohms law. Higher voltage -> less current -> less resistance loss.
     
  12. Caracal

    Caracal Member

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    Alternate transmission line voltages

    And just to throw more information into the fire.....

    There are also 11000, 12700, 19000 and 33000 volt distribution systems that use a single wire with earth return (SWER) It is usually used for very long distance line where there is not much load e.g. 700km long lines into outback Queensland. At each farm there is a transformer that steps this down to 240 volts or perhaps two 240 volt supplies which are out of phase by 180 degrees giving 480 volts between the two phases.

    This is by far the cheapest distribution system as only one high voltage wire is run.

    There are also Hybrid 3 phase SWER systems just to confuse matters further.

    In Australia our high voltages are generally run as three phases without the neutral. By contrast in the US I have seen three phases with neutral on the high voltage.

    3 Phase is not rare in Australian homes.

    Cheers

    Caracal
     
  13. brokenback

    brokenback Member

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    Nearly... High voltage Txmission lines are used as there is less Power lost (during transmission). P (lost)= Is^2 (squared) x R where Is^2 is the secondary Txmission current and R is the line resistance. The relationship between Primary and secondary voltages and current is: Vp/Vs= Is/Ip (where Vp is volts primary and Is is current secondary...you get the jig).

    Thus Is = Vp/Vs x Ip, increasing Vs reduces Is, which in turn reduces power Txmission losses as they were a product of P=Is^2 x R.

    Thus the transmission lines can be smaller (read less costly and weight) as they carry less current and lose less power over them.
     
  14. banshee

    banshee Member

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    That is a more detailed version of what I said. Although I didn't specify that the resistance loss was power... Any resistance causes power dissipation due to I^2 * R.

    So to simplify, higher voltage gives less current. Less current through cable resistance means less power lost during transmission due to the cable resistance in line with the equations above. Then you just have the alternate problem of arcing and leakage, eventually, if the voltage is too high. Hence those huge insulator stacks that the HV cables hang from and how far apart they are hung.
     
  15. BrightSpark

    BrightSpark Member

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    Misinformation abounds

    Hi all, I won't pick on individuals but a lot of the above info is misleading or just plain incorrect. I teach Electrical Apprentices in a TAFE College for a living. Been doing it, teaching that is, for more than 20 years and before that worked in most states of Australia as a licensed electrician. Power is generated at power stations in Australia as 3 phase at 20,000Volts. It is then stepped up through a transformer to 275,000Volts or 500,000Volts depending on the state and power station. Yes the power loss is relate to I squared R loss, in power lines and as an example if you double the voltage the power loss drops to one quarter.

    3 phase is more efficient than single phase where large loads are required e.g. industrial and commercial motors and large domestic airconditioners. A 3 phase motor is lighter, cheaper and more efficient than the same physical size of single phase motor. If three phases are connected to a house the large load eg aircon, is connected across the three phases for the compressor motor. The other motors for the indoor and outdoor fan can be single or three phase, depending on the size and make of the aircon.

    The rest of the electrical circuits of the house are connected individually across a phase and neutral. For example the hot water may be on the first or A phase, the power circuits, minimum of 2 for a house, across say B and C phases to neutral, lights across A phase again and hotplates across C phase and the oven on B phase.

    Putting the record straight, curently (pun intended) Australia still uses 415Volts between phases ands 240Volts from each phase to neutral. The move to 400/230 volts is the NEW recommended levels and if we follow the UK example will only be introduced in brand new suburbs initially untill most of us have replaced our current crop of appliances designed for 240Volts and then the Supply Authorities will drop the voltages in existing suburbs. All new appliances are now manufactured to operate correctly on 230 Volts.

    If they dropped the voltage now, most compressor type appliances would have a much shorter life span, fridges freezers aircons, trying to start up against the pressure of the compressor on what would be considered to be very close (within 2 volts) of current the minimum voltage. Because we import so much of our electrical goods, and just about every other type of goods, from counties where 210, 220 and 230 Volts are the standards, we as a very small player in the wold market are coming into line with overseas standards.

    Sorry if this is long winded and pedantic but wrong info can lead people to make mistakes.

    One last point, all current power boards MUST be fitted with a miniature circuit breaker set to trip if the total load exceeds 10 Amps. However some imported boards I have seen are made in such a way I suspected they may melt down before the 10Amp limit is reached. All boards are "type tested" to our Australian Standards before they can be sold.

    If you have any questions I would happy to help if I can.

    Regards, Brightspark.
     
  16. Sam_706

    Sam_706 Member

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    I've been reading through all this info and have a question:

    Why do some houses have 2 lots of wires coming in from the street. That is; 2 of the double wires. While others houses just have 1 double wire.

    Does that have some relation to the 3 phase wiring?

    My house has 2 double wires coming from the street but it appears that 3 wires only enter the house.

    Hope this makes some kind of sense.
    Cheers
     
  17. Symon

    Symon Castigat ridendo mores

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    These 'NEW' standards have been in place for at least 5 years if my memory serves me correctly. What you say is true for the domestic market, people will get a bit upset if their old fridge burns out due to the lower voltage, but people will probably get even more upset if their new fridge burns out from overvoltage.

    The tolerance for the old 240V system was 5%, so you could get voltages as high as 252V out of a power point, which is 9% over the 230V standard - depending on how good your motor is it might be able to handle it, but some won't. From what I understand the initial stage of lowering will only be to 235V to keep a happy medium, and then some years later 230V.

    However in the commercial/industrial scene moves have been made to lower voltages much more quickly. The reason for this is cost, 400V motors are cheaper than 415V ones since they are mass produced overseas, and it is only a simple matter of changing tap settings to lower the voltage of existing systems. I know of several major projects at the moment that have all specified 400V machines.

    There wasn't anything 'misleading' in my post, I just didn't elaborate on the information, and for the record, I am a qualified electrician who has worked in 3 states, and am also a practicing electrical engineer.
     
    Last edited: Oct 12, 2006
  18. Pyro

    Pyro Member

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    Don't forget 330,000V! :)

    Ok, but why? And i'm not being a bastard, I'm just yet to hear an explanation that I can say ' Ok, sounds great' :)
     
  19. MUTMAN

    MUTMAN Member

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    hey pyro, 3 phase is only more efficent to make and distribute.
    its not more energy efficient at running stuff.
    if my faded and jaded memory serves me right...
    1 phase is 45% eff. eg 1 phase going at 50Hz in a typical sine wave has 45 % of the amount of power as a dc current at same voltages (avg.)
    2 phase is 66% eff.
    3 phase is 98% eff.
    ...
    6 phase is only 98.9% eff.
    as u can see, 3 phase is by far the best way of making and distributing (50HZ) power.
     
  20. Symon

    Symon Castigat ridendo mores

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    Single phase motors have to create a phase shift between the run and start windings in order to start turning. Once they are up and running there isn't a constant transfer of torque to the rotor (since there is a zero crossing twice every cycle). So they run rough and aren't very efficient.

    Three phase motors don't have to create a phase shift since there is a 120 deg shift already between any two phases. Due to the phases overlaping each other there is a constant transfer of torque to the rotor, so they run smoother and much more efficient.

    Interesting fact - Nikola Tesla calculated that the most efficient frequency was 60Hz, which is what most of America uses. However Australia chose 50Hz because it slots nicely into the metric system of measurement.
     

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