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Pros/Cons/Practicality of Single Phase to 3 Phase Converters

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  • 29-07-2010 5:37pm
    #1
    Closed Accounts Posts: 2,389 ✭✭✭


    Am looking at some 3 phase wood working machinery that will be in an auction on Saturday and the auctioneer has suggested I buy a Single Phase to 3 Phase Converter.

    The single phase equivalent machines are 2.5/3 horsepower so I just wonder is it a practical option.

    The woodworking attraction is that the 3 phase machines are all cast iron whereas the single phase are just pressed metal.

    Is the converter a practical option in this case?

    Thanks.


Comments

  • Closed Accounts Posts: 4,431 ✭✭✭M cebee


    there'll be the 'capital cost' and the installation of convertor

    you'll need the equivalent capacity on the SP supply for the 3-phase machines installed

    VD could be a factor depending on supply quality/capacity

    i'm not sure how the 'starting KVA' on 3-phase machines transfers onto the supply side with these converters?:confused:


  • Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,591 Mod ✭✭✭✭2011


    Is the converter a practical option in this case?
    If this is the only 3 phase machine that you require, yes. They are over 95% efficient now. I don't know what they cost, but installation of a 3 phase supply will cost much more.
    you'll need the equivalent capacity on the SP supply for the 3-phase machines installed
    Exactly what I thought. The good news is 3 hp is about 2.2 kW so you do not require much capacity.
    VD could be a factor depending on supply quality/capacity
    No more so than any other single or 3 phase circuit.


  • Closed Accounts Posts: 2,389 ✭✭✭Carlow52


    Thanks guys, just see a 10 hp one for sale at 1500 euro so dont know if the math will work out


  • Closed Accounts Posts: 4,431 ✭✭✭M cebee


    10hp will alllow you to run a few 3hp machines simultaneously ie:no 'diversity' applied

    the 'maximum demand' could be as low as 3hp if you're only using 1 machine at a time

    i would do the costings of 3-phase v converter

    and check existing SP capacity for suitability

    dunno if DSO have to be informed when connecting 'disturbing loads' on existing supply?


  • Closed Accounts Posts: 4,431 ✭✭✭M cebee


    2011 wrote: »
    If this is the only 3 phase machine that you require, yes. They are over 95% efficient now. I don't know what they cost, but installation of a 3 phase supply will cost much more.


    Exactly what I thought. The good news is 3 hp is about 2.2 kW so you do not require much capacity.


    No more so than any other single or 3 phase circuit.

    installation VD for cables supplying motors can generally be calculated using FLA

    motor 'terminal voltage' during startup at 6-10*FLA can be affected by excessive DSO voltage drop

    i think i'm right in saying that DSO voltage drop is the product of the current and the external fault loop-impedance(for tn-c-s)


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  • Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,591 Mod ✭✭✭✭2011


    installation VD for cables supplying motors can generally be calculated using FLA
    This would be normal practice, yes.
    motor 'terminal voltage' during startup at 6-10*FLA can be affected by excessive DSO voltage drop
    Sorry, what do you mean by DSO?

    Volt drop is calculated by mV/A/m. Therefore it would follow that while starting the volt drop would be greatest. So yes, I agree with you. It would not be normal to size the cable for the larger start up current as it only lasts for a fraction of a second, as you say it would be sized for the full load current of the motor. The instant it starts to turn this current starts to drop off.

    Although VD is something that always needs to be looked at there is nothing here that suggests that it should be more of an issue than normal that is why I don't know what you mean by:
    VD could be a factor depending on supply quality/capacity
    check existing SP capacity for suitability
    You may have a point here. I am not too sure how large a motor is permitted by the ESB on a single phase supply. A quick phone call to ESB Networks may be a good idea. I am sure RoundyMoney would know this. You could send him a PM. A soft start may be possible through the inverter or a star delta starter would be the way to go (your motor control circuit may already have this).

    I have one of these:
    http://www.makitauk.com/index.php?page=36&catid=53&open=53

    It has a built in soft start and the motor is smaller than the OPs.


  • Closed Accounts Posts: 4,431 ✭✭✭M cebee


    http://www.ichpa.com/CHP_Online_Tool/DSO.php

    DSO -distribution system operator

    'starting kva' can be 6-10 times rated kva

    excessive voltage drop on the supply lines may affect the motor startup-
    it may be an issue on LV lines in rural areas


  • Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,591 Mod ✭✭✭✭2011


    DSO -distribution system operator
    Oh, you mean the ESB! Thanks

    I was talking to someone about this. It would seem that the ESB will have an issue with a motor this size on a single phase supply. I would suggest that the OP gets his electrical contractor to investigate further before investing any money.


  • Closed Accounts Posts: 4,431 ✭✭✭M cebee


    without soft start

    other customers can be affected depending on the supply


  • Closed Accounts Posts: 2,389 ✭✭✭Carlow52


    Thanks for all the input: just found this document
    http://homepage.ntlworld.com/bob.minchin/Induction%20motors%20-%20Issue2.pdf

    Interesting read:)


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  • Closed Accounts Posts: 4,431 ✭✭✭M cebee


    ya looks good

    i forgot when i was estimating the external VD that other customers on the same lines will affect it

    i suppose if you're on a trafo of your own it can be estimated


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