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  1. #121
    smithdoor's Avatar
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    You did not post any thing
    PC error

    Dave

    Quote Originally Posted by nhengineer View Post

  2. #122
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    Quote Originally Posted by smithdoor View Post
    You did not post any thing
    PC error

    Dave

    This is becoming a real challenge Mr. Smithdoor.

    Are you out there Rob?

    What planet am I on now?

  3. #123

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    DSLee,

    Yeh, I'm out here (there)
    I'm not sure, but I think it must be a different one to most other people. Maybe that's why I didn't post anything.

    Regards,
    Rob.

  4. #124

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    After some interesting reading I just have to get in on this discussion. I fail to see the difference between a 208-230 volt three phase US motor and a 3 phase motor used in Australia except the nominal RMS operating voltage and the frequency. A 208-230 volt single phase motor used in the US expects to see between 208 volts and 230 volts between it's two input terminals to operate around motor nameplate HP, current, and RPM (these are a function of motor load). Does this single phase motor know it has two separate phases as referenced to the neutral (AKA the midpoint of the transformer). Let's let one of the input phases (say L1) be the 0 volt reference point for L2. So now L2 referenced to L1 is a 208 to 230 volt sine wave at 60 Hz in the US. In my opinion that is why this is a single phase motor and not a two phase motor. Is the single phase motor in Australia any different? If we can rotate an unloaded 3 phase motor with single phase power in the US why can't they rotate an unloaded one in Australia with single phase power? Is anyone following my reasoning here?

    Just wondering

    Junker2
    AKA Terry

  5. #125
    smithdoor's Avatar
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    The 208 is used for offices for 120 volt with 3 leg save on cost of wire
    The 240 is for shop use
    This why some shop have to use 208

    Dave

  6. #126
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    Quote Originally Posted by Junker2 View Post
    If we can rotate an unloaded 3 phase motor with single phase power in the US why can't they rotate an unloaded one in Australia with single phase power? Is anyone following my reasoning here?

    Just wondering

    Junker2
    AKA Terry
    A three phase motor will NOT rotate on single phase. At least no three phase motor I've ever used would. None would even rotate on two phases without a pony motor to start it up. Where are you getting that from Terry?

    By the way, 208 is a product of a 3-phase "Y" generator.

    Rotary Phase Converter (Create 3-phase power from a single phase source)-208v-yschematic.jpg

    If you have 208V, it is unlikely that you have 240V too and the converse it also true. It has nothing to do with the location being home, office or shop. It is what your local electric company is producing.
    Last edited by nhengineer; 02-27-2017 at 09:11 AM.

  7. #127
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    Junker,

    In my opinion we are saddled with some unfortunate choices of terminology in the field of electricity. And there are those who will fiercely defend those definitions of terms, no matter what the evidence to the contrary may be. I am a citizen of the US and have never visited Australia, but it is my understanding that 220 or 230 Volts at 50 Hertz is the standard there while here in the US we have a 115/230 Volt standard that is commonly referred to as "split phase". But from some reading it would appear that in some installations the Australian 230 Volts can also be split to two 115 Volt "phases" by the addition of a neutral wire, just as is done in the US. Also, in the US the neutral wire is often not used for a 230 Volt outlet, making it more like the Australian. Things like an air conditioner or dryer outlet will not have a neutral connection in the socket. None of the 230 Volt outlets in my home and shop have a neutral connection: they are strictly 230 Volts, period. So, it would seem that the difference between the US and the Australian systems is more one of emphasis than strictly that of form. Both systems allow and encourage the use of a safety ground connection for many, if not all, service outlets. But this safety ground is just that, a safety ground and it is not to be used for powering any circuit. That would be the job of the neutral conductor if it is present.

    At the risk of being drown with abuse I would like to say a little more about the terminology. In the US we have a feed from the power poles that commonly is 115V - 0V - 115V which gives us the 230 Volt connection between the two 115V wires. These two 115V feeds are essentially 180 degrees out of phase with each other so, by vector addition, they add up to 230 Volts. Notice that I brought the word "phase" into the previous sentence. They "are out of phase" with each other. Now, from the viewpoint of vector math, that is the very definition of being different. They are DIFFERENT PHASES. But they are derived from a single phase of the three phases that are used to distribute power over the long lines around the country and around the city or local area. A single transformer with it's primary winding connected to a single one of the original three phases from the generator station is used to drop that higher Voltage down the the 230 Volt level. But the secondary winding of that single transformer has a center tap that is grounded with a ground wire that runs down the local power pole to a ground rod in my neighborhood. In my view it is this grounded, center tap that converts that single phase power on one side of the transformer to a split phase or TWO phase power feed on the secondary side of that same transformer. It is physics, not magic. AND, there is absolutely no reason why the same exact thing can not be done with Australia's 230 Volt, single phase power. And it can be done inside your house or shop just as it can be done on a power pole. Now, I know nothing about Australia's electrical code or regulations so whatever is done must be in accordance to those limitations.

    But notice that in doing this, NEITHER of the split phases, of the two 115V phases is grounded. The ground is at a point that is exactly half way between them and this is the important point here. You should never attempt to connect either of the Lines of the 230 Volt feed, either in the US or in Australia, to ground or to neutral, which is also connected to ground. This would instantly blow a fuse or breaker.

    A single phase motor will not "know" any of the details of the lines that are feeding it. A 230 Volt motor could operate quite happily with two lines at 100 Volts and 330 Volts respectively. It will only "see" the difference between them or 230 Volts. And it certainly does not know or care about what terminology that we arbitrarily apply to these power feed wires. The only concern here would be for the Voltage rating of the insulation inside the motor that prevents the line Voltages from being shorted to the frame of the motor which would probably be grounded one way or another.

    An unloaded three phase motor, AKA a phase converter, CAN be powered from a single phase in both the US and in Australia. There will be some capacitors involved that will generate a third phase for the third input wire on the motor. In a capacitor the current will be out of phase with the Voltage and this capacitor(s) will be sized so that the third phase that is generated is 120 degrees out of phase with the original two phases of the power line. Notice that here I am forced to refer to the two power lines as a two phase feed. Otherwise, there would only be two phases on the three terminals of the three phase motor. And here is the real magic: if the capacitor(s) are properly sized for the rotary phase converter system, then the terminals of that idler motor and of the motor being powered by it will actually see three phases that ARE 120 degrees out of phase with respect to each other. This magic has been accomplished with vector math that effectively creates a virtual "ground" point that is at yet another phase angle and it's own Voltage value with respect to earth ground and the original, single phase power on the pole before the pole transformer. Not really magic, but vector math is involved and, as far as I can see, is the only way to properly explain and predict it.

    The only complicating factor that I can see here is with the difference between the actual, earth ground/neutral point that physically exists in both countries systems and the different, virtual neutral point that is created in any conversion from single phase (split phase or what I call two phase) to the three phase needed by three phase motors. Some methods of creating the third phase do not have any connections to the earth ground/neutral and these methods should work just fine in both countries' systems. But other methods will have connections to that earth ground/neutral point and then care must be taken to insure that the point actually used is indeed the half way point between the two sides of the 230 Volt power feed. This distinction should be possible from a careful examination of the actual circuits involved. But in some cases, like a VFD device, that may not be easily possible and you will need to consult the manufacturer.



    Quote Originally Posted by Junker2 View Post
    After some interesting reading I just have to get in on this discussion. I fail to see the difference between a 208-230 volt three phase US motor and a 3 phase motor used in Australia except the nominal RMS operating voltage and the frequency. A 208-230 volt single phase motor used in the US expects to see between 208 volts and 230 volts between it's two input terminals to operate around motor nameplate HP, current, and RPM (these are a function of motor load). Does this single phase motor know it has two separate phases as referenced to the neutral (AKA the midpoint of the transformer). Let's let one of the input phases (say L1) be the 0 volt reference point for L2. So now L2 referenced to L1 is a 208 to 230 volt sine wave at 60 Hz in the US. In my opinion that is why this is a single phase motor and not a two phase motor. Is the single phase motor in Australia any different? If we can rotate an unloaded 3 phase motor with single phase power in the US why can't they rotate an unloaded one in Australia with single phase power? Is anyone following my reasoning here?

    Just wondering

    Junker2
    AKA Terry
    Paul A.

  8. #128

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    junker2,

    "is the single phase motor in Australia any different?"

    The motor, no; but the power supply IS.
    Since this thread is about single to three phase conversion, single phase motors are really not under discussion. So, one more time, I don't know your location, but I would guess that you're in the USA. I the states you have the capability to split 220 volts into two single phases of 110 volts thereby enabling you to maintain the speed of a 3 phase motor with 2 phases, IN AUSTRALIA WE CANNOT DO THAT single phase is one hot line (L1) and ground (no L2).

    Rob.

  9. #129

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    paul,

    It was not until I had answered junker2 that I read your post. Whilst I have not read all of your post, the misconception is contained within the first paragraph.

    "it would appear that in some installations the Australian 230 Volts can also be split to two 115 Volt "phases" by the addition of a neutral wire"

    Not so under ANY circumstances. Single phase here is ONE hot line and ONE neutral bonded to ground, and cannot be split except with a 1:2 center tapped transformer where you will get the high end of the transformer putting out 220volts, and the low end of the transformer putting out 220 volts 180 degrees apart.

    Incidentally, 3 phase here is three separate phases of 220 volts 120 degrees apart.

    Rob

  10. #130
    nhengineer's Avatar
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    Quote Originally Posted by Paul Alciatore View Post
    Junker,

    In my opinion we are saddled....
    Paul, the first incorrect assumption you made is that electric service in the USA is 115/230V. Wrong. If you want 115V (I cannot imagine why you would) you would need a buck transformer. 125/250V is pretty much standard from generating stations in most metropolitan USA locations. By the time it gets to your house or shop, losses could have taken away as much as 10% giving you 112.5/225V but that is highly unlikely unless you live way way out in the boon-docks.

    Intending no disrespect but the rest of your manifesto is equally inaccurate. I only mention this, not to embarrass you, because there are some folks out there the may believe it and that could be dangerous for them.

    Thank you.

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