Two phase to three phase conversion in New Zealand - Page 3
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  1. #41
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    The reason you usually don't want to connect the star point to neutral on a motor is the motor will inherently act somewhat like a zig-zag transformer, and try to bring the neutral to the centre of the three phases. But if you have a little three-phase motor trying to correct an imbalance caused by tens of kilowatts of single-phase heating, you're going to get significant overcurrent.

    When using it to generate a third phase, that is the intention (well, not the overcurrent bit).

    And yeah, it's looking like simply adding the two present phases in reverse polarity should get you the third phase at the right phase angle and amplitude. And 230:230 isolating transformers are not too hard to find - there may even be some at the factory you're demolishing. They're probably not more than 1-2kVA, though.

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    I have looked into the transformer option over the last few days after it was suggested, I cannot find any transformers available locally that fit my needs or allow enough power through to run a 7.5hp motor without importing them so I am looking at the rpc more seriously as I have motors available.

    All 3phase motors above 4 or 5hp in New Zealand have 415v windings and are connected in Delta. Below is a sample of the motors available.

    rief.jpg

    baldor.jpg

    abb.jpg

    abb-tag.jpg

    baldor-2.jpg

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    Delta isn't gonna help much, so if that is what you have available, then just pretending you have single phase (no neutral), and going the normal RPC route, (just at 415V) may be what you have to do.

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    Quote Originally Posted by JST View Post
    Delta isn't gonna help much, so if that is what you have available, then just pretending you have single phase (no neutral), and going the normal RPC route, (just at 415V) may be what you have to do.

    Back to page 1 ;-)

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    We have a lot of american machinery at our site so there is a high possibility there are wye motors also, it more just if buying a replacement motor off the shelf locally Delta is more common.

    I found this motor which is american made and takes many different input voltages, suitable?

    baldor-gm.jpg

    baldor-gm1.jpg

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    Quote Originally Posted by Brian Campbell View Post
    We have a lot of american machinery at our site so there is a high possibility there are wye motors also, it more just if buying a replacement motor off the shelf locally Delta is more common.

    I found this motor which is american made and takes many different input voltages, suitable?

    baldor-gm1.jpg
    Could be just right.

    10 HP is about as large as is easy to cap-start without a high pucker-factor.

    The Voltages shout "Wye", but it isn't REALLY a big deal, either way. Just ignore the Neutral.

    Bog-standard "gummy bread" as to quality.
    Clean the rocks, birdshit, and insect nests out of 'er. Toss in a set of NEW sealed bearings.

    Should run 20 years in "idler" service?

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    The pictures you posted are of an ABB of 86 HP, a baldor of 55 HP and another that looks equally large- or larger.

    There are advantages to having an oversize idler- but for a 7.5 HP load you are well past that point..

    What do you have available in the 10 to 25 HP range?

    Do you have access to 4 or 5 motors of 4HP to 5HP and of wye windings? If all run together that would give you the equivalent of a motor the size of the HP added together. Because they would self start, all you need to do is turn them on before starting your machines. They will each be acting as an RPC to generate the 3rd phase you do not have coming from the power pole.

    If you are able to come up with one or two wye motors of 4 or 5 HP you may be able to use them to start a larger delta motor.

    Option 1: Start the wye motor as an idler supplying 230 volts to L1/neutral and L2/neutral. It generates 230 volts between L3/neutral- and the 415 volts between L2 and L3, and L1 and L3. After it is running connect your delta idler to the mains L1 and L2, and the generated L3 from the wye motor. The generated L3 gives the delta idler a start and direction in rotation. similar to what a capacitor start does. I would expect significant inrush current with this method.

    Option 2 Connect the wye motor with a direct drive to spin the delta idler. Start the wye motor and use it as a pony motor to spin up the delta idler. After the delta motor is up to speed, use a contactor to connect it to the mains L1 and L2. It will then start generating L3. This method will have much less of a current inrush due to using a pony motor.

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  9. #48
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    ThatS interesting about using smaller wye motors together, I could put together enough of these motors but they would not all be the same and I don't know if my ocd could handle four different sized and colored motors all together.

    I have found a motor as seen below that I think meets the criteria, it doesn't say specifically about wye and delta but from the voltages it uses and the terminal diagram Im hoping someone can tell me?

    Is it worth putting the two phases I have into this motor or is there no real benefit, should I just put one phase in?

    baldor-1.jpg

    baldor-2.jpg

    baldor-3.jpg

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    Transformer converter options work,...but only over a relatively small variation of loads

    Great for pumps. fans, etc

    Not so much for machine tools.

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    Quote Originally Posted by Brian Campbell View Post
    ThatS interesting about using smaller wye motors together, I could put together enough of these motors but they would not all be the same and I don't know if my ocd could handle four different sized and colored motors all together.

    I have found a motor as seen below that I think meets the criteria, it doesn't say specifically about wye and delta but from the voltages it uses and the terminal diagram Im hoping someone can tell me?

    Is it worth putting the two phases I have into this motor or is there no real benefit, should I just put one phase in?

    baldor-1.jpg

    baldor-2.jpg

    baldor-3.jpg
    I think that looks like it's wired for parallel-star. Use that in medium voltage (380V) mode and connect the neutral to both upper groups. Should be great.

    You definitely want to use both phases to spread the load.

    Where in NZ are you, out of curiosity?

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    Cheers for the reply and info.

    Im in Hawkes Bay, what about yourself?

    Would this motor (post 48) wired correctly self start on two phases or would I still need a pony motor to get it going?

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    While I was working on the below SomeoneSomewhere was posting his response.

    Here is a link to a Baldor document about voltage systems, motor design and the effects of high and low voltage on motor characteristics. https://www.powertransmission.com/is...dor-basics.pdf

    The thumbnail is of a Baldor document showing the wiring of that motor. It shows Low voltage as two delta , medium voltage as two wye, and high voltage as a single delta.

    While it does have a wye winding connection, that is rated for 380 volts. Wondering what would occur if it was supplied with 240 volts lead me to the Baldor document linked above. That document indicates that as the voltage supplied drops, the current required to meet a given load goes up by the same percent- and that this is not a problem until the amps reach the maximum amps the motor is rated for. If we feed the motor 240 volts instead of 380 we are at 63% or 37% low. Thus the amperage goes up by about 37%. But-- 37% of what. Because the motor is being run as an idler it is unloaded and the common figure is that this will be about 20% of the FLA.

    This looks promising- but for two things:

    The torque of the motor is also decreased. This is by the % voltage supplied multiplied by itself. so the 63% low voltage yields 39.7 % of the torque. Lower torque means longer to reach full RPM and thus a longer duration if higher starting current

    An RPC is acting as a motor generator. When a motor is connected to the RPC the current generated in L3 is a load on the motor. Will this load bring the amps up to the FLA? I do not know.

    Lots to think about.

    If you decide to go with the multiple smaller wye motors- paint them all the same color, put each on its own switch, and make a chart. Say you have 3 HP, 3.5 hp, 4 hp and 5 hp. That totals up to the equivalent of 15.5 HP. If you are going to run the lathe with a heavy load, start all of them. Light cuts, might be OK with the 4 and the 5 HP idlers. Going to start the bandsaw you did not know you were going to get- it may only need the 3.5 hp idler. By their not being the same you can match your supply to your load.
    Attached Thumbnails Attached Thumbnails screenshot-2022-01-14-00-04-09-cd0044.jpg  

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    Quick correction: it would be supplied 400/415V (depending on tap settings, voltage drop etc.). 230V line to neutral, 400V line to line. So the parallel star connection would be appropriate.

    It should work fine.

    Starting in series star to reduce inrush could be an interesting option, though requires more contactors.

    Unfortunately I'm in Wellington so a little way away...

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    I replied to a similar post a few years ago and it was equally disregarded.

    OP has 2 of the 3 phases and he has a neutral. therefore he has three phase, or any number of phases actually.

    two transformers of proper ratios can be devised to generate 3 phase, without the losses or impedance of a shitty RPC. the ratio you need is 230v:138. yes, you can get it. you need two 240v:120v transformers, and two 240v:16v transformers. conveniently, both are available as buck boost transformers.



    you can also find the neutral of any standard 230v/400v 3 phase motor and connect the neutral to your neutral, and 2 phases to your two phases, the motor will self start, and the third leg will generate the third leg.


    if you don't connect the neutral of the motor to the neutral and instead use it as if its an American bastard RPC,you will need both start caps and run caps and the motor has to work exactly 50% harder to generate the third leg. i actually did the math a year or so ago.

    img_20220113_232609877.jpg



    img_20220113_232835723.jpg

    two, 240v to 120v transformers plus a 208:32v transformer will get you 240v 3 phase from two phase 240v/400 plus neutral.

    if you have two 240v 120v transformers and two 240v 12 or 16v transformers you can add them in series in an attempt to get two 240v:138v transformers, and when you connect them you will get your 400v 3 phase again.

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    Thanks everyone for the detailed responses and thought you have put in to my situation, I really appreciate it.


    To do you all justice I will have to really do my homework and become familiar with more of the terminology and theory, just when I think Im getting my head around it something else pops up.

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    Quote Originally Posted by Brian Campbell View Post
    Hi Guys

    Thanks for the input.

    Just to clarify any confusion I am 100% certain I have two phases 120 degrees apart and a neutral coming in. That was never meant to be the topic of this post but can understand some people may want to clarify this. I was there when a technician installed a smart meter and he showed me it on his scope conclusively.

    In New Zealand most domestic houses have one leg of three phase power coming in with a neutral, this gives them 230v between the phase and neutral. On rural properties it is common to have one transformer on a power pole outside two rural properties. One phase and neutral will be sent to the smaller house (demanding less power) and two phases and neutral will be sent to the larger property.

    To be clear the house with two phases going in still has single phase at every outlet and appliance, one phase is simply hooked up to half the fuses on the switchboard and the other phase is hooked up to the other fuses on the switch board.

    All of my outlets and appliances have 230v between phase and neutral, however measuring between the two phases coming in to the switchboard has 415v between them as they are offset 120 degrees.

    I am simply trying to determine how to turn this into 3 legs 120 degrees apart.

    This may be uncommon or unheard of in America but for better or worse it is the system we have here in New Zealand.
    Here in the UK I have seemingly the same run into my place. Two of 3phases (only one connected atm) and neutral, the Power Network guy who lives round the corner confirmed this, ive the same voltages between legs and to neutral. Currently have a 30hp Transwave Rpc (way bigger than I need) so keen to see how you make out.

    Cheers
    D

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    johansen

    For those of us who do not know all the electrical symbols and conventions: can you draw out a diagram using the terms you would use to look for a transformer, draw out how they would connect, and describe how it works. In short- dumb it down for us.

    When I look for information on transformers what I fund is so basic it is not helpful- or is too advanced and has calculations I do not understand.

    I believe the rotary capacitor start RPC is popular because there are more instructions on how to build and size one- and it is easy to find, transport, and afford capacitors. Go to a HVAC supply store and you will find capacitors. I do not ever recall going to a store and finding a transformer of any capacity useful for an RPC. I can find used 3 phase motors on craigslist- but very few transformers.

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    That motor is absolutely wired correctly for the use. The 220/380 combination is delta at 220, and star (wye) at 380. Double sets, so two winding sets, and double star for the 380/400.

    The star points are the sets of three studs "barred together". That would go to neutral.

    With two sets of windings, there is always the question of connecting the star points together, and whether there is anything against doing that. The argument against is that the windings are probably not identical, and so the star point voltages may not be the same. That would cause extra current to flow.

    You really do not need to connect the two of them together. My reasoning here is that with an idler, the max power requirement is only 1/3 of full shaft power, as it supplies only the power for one of the three lines.

    One set of windings will adequately handle the draw for that, and the 3 phase will work at full current because the 3 wires are connected to both windings. So I would connect one wye point to neutral, and let the other one "float". All three line wires connect as usual. (the winding for the unconnected star point will still work just as they would in an RPC with no neutral)

    The OP says he found no transformers readily available of a size to do the trick here. So, while that would work, it's not his first choice, nor is it likely to be the cheapest method.

    It IS nice due to no moving parts, no noise, and good reliability. Just not an option here at the moment.

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    " It IS nice due to no moving parts, no noise, and good reliability. Just not an option here at the moment. "

    When I read this it seems to apply to several things. While written about using transformers, I found myself thinking about how simple the RPC can be for Brian with his 2 legs of 3 phase. All he needs is a magnetic switch and a contactor to switch on the RPC. No pony motor, no capacitors, no timers or potental relays. And if you forget to turn it on- the lathe should still run- just at 2/3 power.

    "Just not an option here at the moment"

    Not where I live, though it might be available someplace in the US. I have 3 phase power lines running up the road I live on. The electrical coop says that to run it up to the house means they have to not just run more wires, they also need to add transformers- and all the above means replacing the poles that hold it all up. I am sure I would get the same answer if I asked for just one more line and off a different leg. That and they would think I was an idiot...

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    Thanks guys

    Thiele do you have a larger version of the Baldor terminal image you posteD? it looks very useful but is to small for me to make out. I read all the attached info on Baldor motors and there voltage ratings, it was very helpful thankyou.

    JST Thanks for the confirmation about the use of the motor above. Do I lose out on any available power due to the fact there are two sets of wye windings and I will most likely not connect the star points together? I have just purchased a book by Graham Astbury called "three phase conversion", he mentions using a motor twice the size of the largest motor you wish to power on your machines.

    I agree about the transfomers, it looks like a neat solution, I have have no doubt it would work as you describe, however with budget in mind im largely driven by what I can get my hands on for minimal outlay.


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