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Thread: 480 to 600 Transformer help - for testing a system

  1. #21
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    Quote Originally Posted by emiller233 View Post
    is the delta-wye autotranformer acceptable?
    AFAIK there is no such beast. You cannot have one end of the coil connected to two places at once!

    Sent from my XT1585 using Tapatalk

  2. #22
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    Quote Originally Posted by GoldDigger View Post
    AFAIK there is no such beast. You cannot have one end of the coil connected to two places at once!

    Sent from my XT1585 using Tapatalk
    sorry, that was a typo! I meant a delta-wye transformer (I had autotransformer on my mind)

  3. #23
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    Quote Originally Posted by emiller233 View Post
    this machine is fairly basic, it is a 'Test Bench' for testing an Air Compressor off of a train.
    this transformer will power up a 480V 3-phase air conditioner (3.4FLA) and a large 330VDC Power supply (30KW) http://www.signaltestinc.com/product-p/sga%20330-91.htm. Off the top of my head, this thing takes around 41A (I'd have to double check that #). so i need about 50A total

    the control circuits are thru a separate 120VAC feed...

    we looked into a mobile generator, and are willing to do this (that was priced into the job). the only thing is we may need to keep it much longer than we thought so the price would be quite a bit higher. that's why we are looking into using a transformer (that we could also use in the future if needed)
    The power supply alone takes around 78A at rated load.

    The AC is likely around 30A with locked rotor which is what is relevant when you're comparing line sag during start up.

    Transformers look plentiful if you can source from Canada. There's a 112.5 kVA 2% z available now. If you can sort out freight and getting it through customs.

    https://www.kijiji.ca/b-ontario/600-...former/k0l9004

  4. #24
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    Quote Originally Posted by Electric-Light View Post
    The power supply alone takes around 78A at rated load.

    The AC is likely around 30A with locked rotor which is what is relevant when you're comparing line sag during start up.

    Transformers look plentiful if you can source from Canada. There's a 112.5 kVA 2% z available now. If you can sort out freight and getting it through customs.

    https://www.kijiji.ca/b-ontario/600-...former/k0l9004
    Here is the response i got from Ametek, and the calculations i did are below that.
    If they do not look accurate, please advise!


    Manufacturer's response:
    almost there with the calculation but not quite. The formula is correct. The numbers are depended on worse case scenario which is full load at low line condition. So instead of nominal 480V we will would be looking at 396V as low line condition. Applying the formula gets us to 56A which is exactly what we already have stated on page 29 of the manual under the PFC section for Maximum AC current rating for this 30KW unit with the 480V nominal input. Please see Table 2-1 for reference in the manual.

    Sizing the breaker at 125% of 56A gets us to around 70A breaker to use.


    my calculations:
    Efficiency = 0.87
    Power factor = 0.9
    AC amps = (30,000W)/(Vac x 1.732 x PF x Efficiency)
    AC amps = (330VDC x 91Amp)/(Vac x 1.732 x PF x Efficiency)

    Amps = 30,000/(1.732 x 480 x 0.9 x 0.87) = 46.086 Amp (at 480VAC supply)

    ----------------------------------------------------

    this unit is then being powered thru a transformer.
    Power source is 600VAC (Canada)
    75KVA transformer is a 600V to 480V delta-WYE


    this big power supply should never be maxed out either (customer couldn't provide accurate data for the VFD that it powers direct to the DC bus)
    the customer also wouldn't accept the calculations using 396VAC input voltage to that power supply since it will actually be powered by 480VAC
    Last edited by emiller233; 09-11-17 at 05:39 PM.

  5. #25
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    Power factor:
    >0.69 typical for 440/480 VAC input (40V, 60V - 800V models, 0.9 available with modification “PF”)

    I used 0.69. The value you use depends on if your rig was ordered with the modification they mentioned

    For the AC, 30A is around the appropriate value to use for voltage drop. The voltage available with 30A added is what's available for motor while starting which isn't a big deal.

    Initially you didn't give much details so my comments didn't exclude the possibility about something like a 40 hp motor that must start across the line under full load where the transformer impedance becomes a big deal.

  6. #26
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    Quote Originally Posted by Electric-Light View Post
    Power factor:
    >0.69 typical for 440/480 VAC input (40V, 60V - 800V models, 0.9 available with modification “PF”)

    I used 0.69. The value you use depends on if your rig was ordered with the modification they mentioned

    For the AC, 30A is around the appropriate value to use for voltage drop. The voltage available with 30A added is what's available for motor while starting which isn't a big deal.

    Initially you didn't give much details so my comments didn't exclude the possibility about something like a 40 hp motor that must start across the line under full load where the transformer impedance becomes a big deal.
    it was ordered with the PF mod.

    do we need to be concerned with voltage drop, the transformer is like 10 feet away from this power supply

    sorry about that, i didn't know it was relevant or i would have! I'm still getting my feet wet with details such as these involving transformers.

  7. #27
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    is there a difference between a autotransformer, and a wye-wye autotransformer? or is it the same thing (which i believe it is)

  8. #28
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    Quote Originally Posted by emiller233 View Post
    is there a difference between a autotransformer, and a wye-wye autotransformer? or is it the same thing (which i believe it is)
    An autotransformer has a _single_ tapped coil circuit, an 'isolating' transformer has two separate coil circuits, primary and secondary.

    wye-wye would imply two circuits.
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  9. #29
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    Quote Originally Posted by winnie View Post
    An autotransformer has a _single_ tapped coil circuit, an 'isolating' transformer has two separate coil circuits, primary and secondary.

    wye-wye would imply two circuits.
    makes sense now that i see it!
    The Hammond Power rep said they only have Wye-Wye Autotransformers, is he just using the wrong wording?

  10. #30
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    Quote Originally Posted by emiller233 View Post
    makes sense now that i see it!
    The Hammond Power rep said they only have Wye-Wye Autotransformers, is he just using the wrong wording?
    IMHO slightly wrong...but as long as they show a proper diagram it isn't significant.

    -Jon

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