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

  1. #11
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    Quote Originally Posted by Electric-Light View Post
    What does the machine do and is this something you are integrating or just testing for a client?
    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)
    Last edited by emiller233; 09-11-17 at 08:09 AM.

  2. #12
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    Quote Originally Posted by GoldDigger View Post
    Note that to use a three phase autotransformer it pretty much has to be a wye configuration.
    A "delta autotransformer" is a strange eccentric beast that "ungrounds" a corner grounded delta. Avoid it.

    Sent from my XT1585 using Tapatalk
    is the delta-wye autotranformer acceptable?

  3. #13
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    Quote Originally Posted by mike_kilroy View Post
    1) "just a single core thng" is a pretty bad description. Most transformers have a "single core" for each phase so that is no unique description for autoxfmr... multiple taps is good sttatement though. Yes, each phase is wound around single core just like an isolation 9iso) xfmr. And just like a typical iso xfmr primary winding, it has "multiple taps." The auto xfmr just stops there: it does not have a secondary winding. Finished. Done. That's all folks. Just a primary winding. So yes, a single winding [per phase] with taps. In your case at 480v and at 600v. Looks just like an iso xfmr. Reason it is cheaper it is just the pri winding, no cost for a secondary winding, and its physical size is reduce to (1-480/600)*75= 15kva physical size; hence you are paying for basically a 15kva xfmr instead of a 75kva.

    2) pros and cons? sure some potential ones already mentioned by other replies. But none of these re likely to effect you at all. Consider: your 75kva xfmr probably has Z (impedance) of about 5%. An auto xfmr has much lower Z than an equi iso, so you may be adding 2% more with it in series. Unless your machine uses some unique requirement servos such as Siemens, that require <3% Z input, this added 2% certainly won't bother it. Especially for just a single test. Sure it is a Y configuration, but like an induction motor, whether it is Y or D config, it has no meaning to you - it is simply going to be used as a voltage change device. Either will do the job as well and as transparently to you and your machine.

    3) No ground required or used; sure you can ground the metal "core" - there is likely a ground terminal on it for you.

    4) Suggest you ask them what they have in stock that can do your job; often they have something. As xfmr supplier, we often can get something required if needed quick so you should be able to - if you ask.

    5) Both places I posted ship worldwide. Many many others do too.

    1) this is the one i am currently looking at. Hammond Power # Y075QTC https://www.hammondpowersolutions.co...otransformers/

    2) i looked quickly thru the spec sheet that this Transformer will be powering, didn't see anything specifying this http://www.signaltestinc.com/v/vspfi..._Datasheet.pdf

    4) so far this morning, I've reached out to Eaton (they wont talk about expediting until they have a P.O.) and waiting to hear back from Hammond Power, hopefully they have something available

    5) I am going to look into these and get quotes from them as well!

  4. #14
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    Your system under test has an input delta-wye transformer. This will pretty much isolate it from whatever the supply grounding is. In other words you input transformer would probably work just fine with a wye supply (600/346V), a 'high leg' , a 'corner grounded' system, or something else.

    Your test specifications may limit the allowed supply, for example requiring a wye system balanced around ground potential or some other limiting factor.

    The most blog standard approach would be a delta-wye isolating transformer, with the neutral of the wye grounded.

    Autotransformer approaches will let you use smaller and off the shelf transformers, but this really needs to be engineered by a transformer supplier, not a web forum.

    I suggested one possibility which gives an output balanced around neutral; topgone suggested one that is more efficient.

    You won't find a 'delta-wye' autotransformer; since you don't have separate primary and secondary coils you have either delta or wye, not both at the same time.

    -Jon

  5. #15
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    Quote Originally Posted by winnie View Post
    An 'autotranformer' is one where there is a single coil (note: single for a phase) with multiple taps for your input and output voltages, rather than separate primary and secondary coils.

    A single phase transformer with separate primary and secondary coils can be connected as an autotransfomer; this is the common practice with so called buck-boost transformers.

    The huge benefit of using an autotransformer configuration is that only part of the power goes through the transformer, so you don't need the full kVA rating.

    For 3 phase use, you could use 2 or 3 single phase transformers, connected as autotransformers.

    For your application, I think you could use a set of 3 480V to 120V 10 kVA transformers to boost 480V to 600V with a net capacity in excess of 75 kVA (you only need 5kVA 277 to 70V transformers, but 480 to 120 is a standard rating and likely cheaper). You would need to have an engineer or the transformer supplier do a detailed design.

    -Jon
    i am going to look into this. i am not familiar with buck-boost transformers either. this sounds like a good solution as well.

    wouldn't a 480V to 120V be a different ratio than 600V to 480V?

  6. #16
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    Quote Originally Posted by emiller233 View Post
    1) this is the one i am currently looking at. Hammond Power # Y075QTC https://www.hammondpowersolutions.co...otransformers/
    That looks like a good autotransformer solution, all packaged up. The Y075PKC...is also plausible, but the QTC has more taps and is more flexible.

    -Jon

  7. #17
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    Quote Originally Posted by topgone View Post
    3 X 10kVA transformers to be connected into 480/600V autotransformer? 480V single-phase transformers connected in wye will be underfluxed when supplied with 480V line-to-line voltage!(supply voltage will be 277V).

    You could use 480/120V single-phase transformers if you wired it open-delta. You only need two-10kVA, 480/120V transformers! Max amps = 83A @ 600V (86.6 kVA)
    i've never wired on in open delta, so i did a quick google search and was reading about it here http://myelectrical.com/notes/entryi...ta-transformer
    i am still confused how to do the calculation to get these numbers

  8. #18
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    Quote Originally Posted by emiller233 View Post
    i am going to look into this. i am not familiar with buck-boost transformers either. this sounds like a good solution as well.

    wouldn't a 480V to 120V be a different ratio than 600V to 480V?
    Look at the wiring diagram for the hammond autotransformer you are considering.

    Like most 3 phase transformers it can be considered as a set of 3 single phase transformers connected together.

    Each of the transformer legs is a 277V to (277+69)V autotransformer leg. You don't have a separate primary and secondary circuit; the secondary voltage gets derived magnetically but then _added_ to the primary voltage. The transformer is only supplying the 'boost' not the full kVA.

    277 to 277+69 is the same ratio as a 480V to (480+120)V. As topgone noted using a 480V transformer with a 277V supply is under-utilizing the full capability of the transformer. However this is perfectly safe to do, and 480V to 120V transformers are common and off the shelf.

    In theory, 3 of these banked together would give you what you need: http://www.gordonelectricsupply.com/...t~text~5914314

    However this would need to be confirmed by ACME or a suitably licensed engineer.

    -Jon

  9. #19
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    Quote Originally Posted by winnie View Post
    That looks like a good autotransformer solution, all packaged up. The Y075PKC...is also plausible, but the QTC has more taps and is more flexible.

    -Jon
    i agree, i didn't see that one (even tho it was right below it in the catalog). thanks for the recommendation!

  10. #20
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    Quote Originally Posted by winnie View Post
    Your system under test has an input delta-wye transformer. This will pretty much isolate it from whatever the supply grounding is. In other words you input transformer would probably work just fine with a wye supply (600/346V), a 'high leg' , a 'corner grounded' system, or something else.

    Your test specifications may limit the allowed supply, for example requiring a wye system balanced around ground potential or some other limiting factor.

    The most blog standard approach would be a delta-wye isolating transformer, with the neutral of the wye grounded.

    Autotransformer approaches will let you use smaller and off the shelf transformers, but this really needs to be engineered by a transformer supplier, not a web forum.

    I suggested one possibility which gives an output balanced around neutral; topgone suggested one that is more efficient.

    You won't find a 'delta-wye' autotransformer; since you don't have separate primary and secondary coils you have either delta or wye, not both at the same time.

    -Jon
    I have been trying to get in touch with the transformer folks, just haven't had any luck with them getting back to me yet. in the meantime, I'm trying to give myself a crash course in transformers ( as it is probably long over due for me to do this)

    I'm looking at this now, I'm still trying to catch up up all of the suggestions from you guys over the weekend. i was out of town and didn't get a chanc...

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