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Thread: 30kva 3phase step up transformer

  1. #1
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    30kva 3phase step up transformer

    I am running power for a sasso k600 extreme Cnc saw and it comes with a 30kva 3phase step up transformer.the saw requires 400volts, the transformers primary side is 230 volts and secondary side is 400 volts. The normal running amps for saw is 80 and a max of 125.so my ? Is what size wire do I need to run to the primary side of transformer and what amp breaker. And then what size wire coming of the secondary side going to saw? I'd appreciate any help

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    Quote Originally Posted by Pratch View Post
    I am running power for a sasso k600 extreme Cnc saw and it comes with a 30kva 3phase step up transformer.the saw requires 400volts, the transformers primary side is 230 volts and secondary side is 400 volts. The normal running amps for saw is 80 and a max of 125.so my ? Is what size wire do I need to run to the primary side of transformer and what amp breaker. And then what size wire coming of the secondary side going to saw? I'd appreciate any help
    30kVA at 230V is about 75A.
    30kVA at 400V s about 43A.

    Is the 80A for an intermittent duty rather than the NRL?
    Si hoc legere scis nimium eruditionis habes.

  3. #3
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    Welcome to the forum. Looked up that saw; it's a beast!

    https://www.youtube.com/watch?v=F7z-q2AG38A

    Anyway, look to article 430 for sizing your conductors for the motor. This article may be of some help:

    http://www.ecmweb.com/design/motor-c...uit-conductors

    For the transformer primary and overcurrent protection, see these two articles:

    http://www.ecmweb.com/code-basics/tr...ary-conductors

    https://www.ecmag.com/section/codes-...tors-part-xxvi

    It's too late and I dont do motor/xfmr calcs enough to give you hard numbers.
    Electricians do it until it Hertz!

  4. #4
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    This appears to be a duplicate thread. I posted a response to same question already.

    New member (welcome) your first few posts need to be approved by a moderator before they will show up so be patient, they just want to make sure you are legitimate member and not a robot.

  5. #5
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    I closed the duplicate thread.

    Where did the transformer requirement come from? In that video, I see an AC induction saw arbor motor. 400V implies that motor is designed for 400V 50Hz. If you give it 400V 60Hz here, you may damage the motor and the blade because of the change in speed and V/Hz ratio. We don't know how the entire machine is built however, i.e. Maybe there is a VFD on that arbor motor. So if the saw mfr is who told you to use a 30kVA transformer, they likely know more about how it needs to be powered. But if this is coming from someone else as an assumption, I would be very suspicious of it.
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  6. #6
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    400 vac at 80-125 A (avg ~100 A)
    I'ld size for 125

    primary 400/230 x 125 = 220 A, CB 250

    the xfmr is likely an auto xfmr (400 - 230) x 100 x sqrt3 ~ 30 kva

    seems like alot ~ 75 hp
    Last edited by Ingenieur; 01-12-18 at 03:23 PM.
    The difference between genius and stupidity is that genius has its limits.

  7. #7
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    Quote Originally Posted by Ingenieur View Post
    the xfmr is likely an auto xfmr (400 - 230) x 100 x sqrt3 ~ 30 kva
    We are told that the transformer has a primary and a secondary which would mean double wound.
    Si hoc legere scis nimium eruditionis habes.

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    Quote Originally Posted by Besoeker View Post
    We are told that the transformer has a primary and a secondary which would mean double wound.
    We didn't get solid confirmation of what kind of transformer it is, just that it has 230 in and 400 out.

    An autotransformer may explain why only 30 kVA rating when it appears the machine driven has even higher rating.

  9. #9
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    Quote Originally Posted by Besoeker View Post
    We are told that the transformer has a primary and a secondary which would mean double wound.
    an AT has a primary and secondary
    that does mean it has seperate windings

    https://goo.gl/images/WqUjGB
    The difference between genius and stupidity is that genius has its limits.

  10. #10
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    Quote Originally Posted by Ingenieur View Post
    an AT has a primary and secondary
    that does mean it has seperate windings

    https://goo.gl/images/WqUjGB
    How many separate windings are shown?
    Which one is the primary winding and which the secondary?
    Your diagram shows input and output voltages derived from the same winding.
    Si hoc legere scis nimium eruditionis habes.

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